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SCATTERED SHOWERS TO SWEEP IN WEEKEND SHOT OF FALL AIR

A brief discussion today as I've been running behind...

Drier air is moving into New England and will take hold for the weekend but it's by no means an instant surge of drying.  Instead, new fall air is coming in installments, one chunk at a time - the first of which moved from west to east across New England Friday morning and the next sparked thunderstorms over Upstate NY that will move east and northeast, maintaining the most integrity across Western and Northern New England with the potential for a few damaging wind bursts and large hailstones in the stronger storms.  These storms will have a tendency to weaken as they move farther east in Southern New England, farther away from the upper level energetic disturbance that's resulting in their development.

Overnight Friday night we should see at least some clouds given the passage of the upper level disturbance overhead, though precipitation will diminish and a general clearing trend will take hold.  The new airmass is cool and dry, and temperatures will fall into the 40s even with an active wind.

The drying trend will bring fantastic, cool, but dry fall air into New England for the weekend, locking sunshine in for a great weekend of fall festivals and fairs! Saturday's high temperatures will rise to either side of 70 degrees - warmest south - and an area of high altitude clouds will filter the sunshine on Sunday but weather should continue to be pleasantly perfect by autumn standards for the American Liver Foundation's Football Walk in Boston that I'll be hosting (click here to find out more about it, and to find out how you can join the walk!).  Temperatures are likely to be cooler on Sunday, however, thanks to one final installment of fall chill and a northeast wind off the ocean.
 

Next week is likely to bring yet another stretch of fair weather and moderating temperatures at the beginning of the week as high pressure builds over New England and then off our coastline, though there are two features to pay attention to.  The first will be the potential for a southeast wind to bring low clouds or fog when the dry and pleasant air lets go and starts moving east, though that is contingent upon a number of factors and not at all certain, but something worth watching along the South Coast by late Tuesday.  What seems more likely is the northward expansion of a tropical feed of moisture up the coastline that would leave the East Coast vulnerable to tropical systems and tropical moisture once high pressure lets go...allowing rain to move in by later Tuesday and Wednesday, though the axis of deepest tropical moisture will still need to be determined.

Have a great weekend!

Technical Discussion:  None today.

Matt

MATT'S TECHNICAL DISCUSSION - Updated Wednesday, September 26 at 1:45 PM

Severe weather threat shaping up as discussed yesterday.  Dewpoints have risen into the middle 60s, temps are 90-95 and this is rapidly increasing instability.  Vort max already resulting in multiple cumulus lines across Nrn NewEng/Upstate NY as of this writing and that trend will continue as the cyclonic vorticity advection encounters instability with LIs to -4 and CAPE values of either side of 2000 J/kg.  Mid-lvl speed max discussed yesterday is present and plenty of mid and upper level dry air is available to further increase downburst potential.  Damaging downburst wind and frequent cloud to ground lightning to be biggest threat and I expect afternoon storms in Nrn/Wrn NewEng to initiate in orographically favored areas but then increase in cov'g and intensity in response to dynamic forcing.  Organizing line in Upstate NY looks ready to evolve into broken squall line and bowing segments are likely along the line given intense unidirectional flow and sufficient speed shear.  There will be some backing of the surface wind in north/south oriented valleys, but at this point it appears the lifted condensation level would remain high enough to avoid rotational problems in cells.  Convection should weaken overnight and leave a quiet cold front to stall in Central NewEng.

Guidance is touting a quick return as warm front to the Canadian border on Thu - that seems unlikely given magnitude of surface cool air behind the front and I think we'll be surprised by the surface cold and resultant clouds in North Country, tho farther S - esp from RUT-CON-PWM southward - sun should break thru and temps will respond by coming either side of 80 with warmest temps south.  Great agreement on dry air at multiple levels in Central/Srn NewEng on Thu and really don't think it looks like that bad of a day for most communities in these areas! Thunderstorms likely to refire either side of front in Central/Nrn NewEng later Thu and shortwave passage Thu night will expand coverage in these areas.  Still a very difficult call on what to do with the tropical wave that will parallel the coastline Thu Ngt into Fri. Yesterday I felt pretty good about the NMM being an outlier and the 00Z NMM was farther east, making me feel better.  Unfortunately, 12Z run is farther west than them all!  GFS is progging a sfc low to move over Cape Cod like the NMM, but analysis of the 850 mb vorticity shows it moves east of the Cape, as does the 850 mb vorticity on the GGEM.  For now, I continue to believe the NMM is too far west in error, and therefore continue to believe the shield of steady rain may move over SE MA and then perhaps into Ern ME Thu Ngt and Fri AM respectively, but I'm not excited about filling the rain in between the frontal precip and the tropical wave.  Nonetheless, both areas should produce heavy precip rates with over an inch of QPF with locally over 2" in the northwest frontal band, but I'm not ready to jump on the 2-3" NMM amounts farther east yet.

Fri AM rain to give way to sun with drier air advecting in on west wind behind occlusion, but reinforcing cold front and assoc wind shift comes later Fri afternoon - swinging from Berks to Boston between 18Z and 00Z, for example - and likely to bring one final round of late Friday scattered convection before dry and cold advection sets in on an active northwest wind Fri Ngt.

Matt

Tuesday's Discussion:

Increasing gradient flow to advect warmth and moisture into NewEng boundary layer with Tds on the rise and the first uncomfortably sticky night in awhile for Srn and Wrn NewEng.  Positive theta-e advection continues as SW wind continues on Wed, increasing instability regionwide as LIs drop to -2 Nrn and Wrn NewEng where dynamic lift moves in first assoc with vorticity lobe stretching across NY State and toward NewEng Wed afternoon.  Dynamic lift to shift SE into Central NewEng by Wed eve when LIs in Srn VT/Wrn MA/Srn NH drop to as low as -4 to -5 and CAPE values rise to in excess of 2000 J/kg!  Seems like it's been forever since we've seen this kind of instability given our recent stretch of fair weather, so let's be sure to take a good look at the potential for severe weather: 250 mb jet streak puts Central NewEng in particular into right rear quadrant of jet streak favoring large scale ascent.  500 mb winds are strongest across Nrn NewEng at 55-65 kts Wed afternoon but this is the core of the mid-lvl winds and speeds closer to 35-45 kts over Central NewEng, but that's plenty good for downburst creation and so are 700 mb winds on the order of 50+ kts north and 35-40 kts central.  At 850 mb jet streak is also centered across Nrn NewEng where confluent flow into Ern ME trof will keep winds fast and, alas, confluent, and this directional confluence will be supplemented by increasing speed confluence over Central NewEng later Wed with 25-35 kt llvl jet.  Dry air is available aloft and this should further enhance potential for damaging downbursts, which become increasingly likely as dynamic lift shifts south and east from RUT to MPV to IZG points southward into Wrn/Nrn MA.  Lift is deep and frequent cloud to ground lightning also likely.

Of course, the fun won't stop here as frontal boundary slows/stalls with lack of strong height falls aloft and ridge holding strong over Western Atlantic.  This persistent ridge will be problematic from two levels - first, it will hold the front over Central NewEng to focus occasionally heavy rainfall again on Thu, which may not be so impressive in its areal coverage as it will be for the locally intense nature of it, which should be situated over Central NewEng and governed largely by convective processes that will remain healthy given either side of this front will be an amazing temp difference as cool, dry air settling southward into the North Country will have moisture added and therefore cool substantially to support temps in the upper 50s to lower 60s for highs, while Srn NewEng remains on the warm side of the front and finds temps around 80 - perhaps higher in any areas that can find sunshine.  Rain and thunder vicinity of the front are likely to be heaviest during the afternoon and evening not only because of diurnal contributions but also given passage of weak vort max.

Meanwhile, an important feature will be rounding the western periphery of the Western Atlantic ridge.  This feature has been rather subtle in previous guidance cycles, but has been present throughout and will undoubtedly garner more attention given the 12Z NMM attempt to spin up a tropical cyclone along the Eastern Seaboard and bring a glancing blow to Cape Cod late Thursday night and early Friday morning.  I should start by noting that this is a concern I've been keeping an eye on for several days, as this tropical wave has been very well modeled, but more than that it's the combination of an Ohio Valley trough trying to dig while the Western Atlantic ridge holds firm, and this potential was laid out in Tuesday, September 18's technical discussion, so it's something that's begged for attention for a long time.  Now the question is much more finely tuned - how close does the tropical wave come to NewEng and how quickly does it intensify.  Though the NMM paints the solution I've been most concerned about, this is a western and strong outlier of scenarios.  I'm willing to entertain the potential for quicker strengthening given relatively warm waters sitting in the path of the wave and the dynamic interactions that will occur as it nears the height falls and quickening jet, but it's that fast jet that gives me pause on buying into a western solution, as confluent flow is very well pronounced through early Thu.  It does relax as the wave rides northward and the strong shortwaves dig across the Great Lakes, but it appears as though the backing of the mid-level flow comes literally just about 12 hours too late to get the wave up over Cape Cod, and the speed of the wave very well may leave it as a transient open wave that carries a load of tropical moisture east of NewEng that becomes a bigger player upon merger with the northern stream energy in Nrn Canada, instead contributing to our Friday and Friday night wind.  This definitely is still something to watch carefully, but my estimate right now is that the NMM western outlier solution is probably not going to verify.

Shortwaves combine to drive longwave trof thru NewEng Fri Ngt after occlusion carries drier air but not cold air into Northeast Fri afternoon after Fri AM rain, and though drying occurs behind this front there very well could be one more round of convective showers with the passage of the trough Fri eve or early Fri Ngt, after which the winds become northwest and quite active overnight as drier air moves in ahead of next high pressure bubble.  Fair weather cell in charge this weekend as it follows in the footsteps of its predecessors, slowly shifting east and ready to settle in a position offshore Mid-Atlantic coast. This difference this time is the indication that there will be a bit more moisture return ready to come back at NewEng, and with the combination of cool and dry air relinquishing control while winds become southeast, low clouds and fog are a possibility on Mon before nicer wx settles in next week with only very gradually moderating temps unlike the current stretch of warmth, largely because the high center doesn't shift as far south and therefore there will be more ocean input to our air, though average NewEng temps will still be above normal after Monday.

In the longer range, it's waaaayyyy too early to try and speculate on whether newly formed Karen or the tropical wave by the Lesser Antilles will be contenders in NewEng weather, but one way to at least get a general idea is to examine the long wave pattern in the extended range.  Any attempt by the wave near the Lesser Antilles, should it attempt a move toward NewEng, would come after the upcoming push of high pressure and cool air (which incidentally may help to fuel development of a system near the FL east coast, but that shouldn't have an opportunity to move toward Neweng and will be dealt with on the Tropical Meteorology Page) which means the Lesser Antilles wave, or future cyclone if it develops, would come at a time when an inverted trough *would* be near the Eastern Seaboard with lingering very weak troughing after departure of this weekend's Ern US trough, but it also looks as though the SE US ridge holds enough to keep this inverted trough offshore, thereby indicating a northward jog by any wave would stay east of Neweng.  The situation with Karen, however, who is over the Central Atlantic is more interesting for the East Coast, if not determinable from this far out for NewEng or not.  That is, the storm is currently forecasted to curve northwest and then most guidance takes the storm northward thereafter, which would result in a nearly certain recurve given the strengthening jet that far north.  I believe this widely agreed upon solution is probably in error, though, given the strength of the Atlantic ridge and the hesitancy for this ridge to break down.  This should keep Karen on a WNW course longer than anticipated, and once we reach the middle of next week the jet stream actually lifts north and by 10 days (end of next week) ridging tries to rebuild from the Western Atlantic to the Eastern Seaboard, indicating Karen would have very little opportunity for recurvature and given East Coast residents something to at least pay attention to.  Again, too early to even guess, but not to early to guess on the longwave pattern which indicates Karen may pop up in a few more discussions!

Have a great Tuesday.
Matt

FRIDAY PODCAST: SCATTERED SHOWERS TO SWEEP IN WEEKEND SHOT OF FALL AIR

The Quick Weather Synopsis is now a Podcast!  You can either click on the audio controls above the forecast on the Quick Forecast Page, or to subscribe to the Monday-Friday podcast (updated on all days I'm working):

Easiest way is to subscribe by clicking here!

You can also use the "Subscribe to Podcast" link in the upper left corner of the main page.

The daily file you will receive is Daily_Weather_Synopsis.mp3

SCATTERED SHOWERS AND STRONG THUNDER FOR SOME...ANOTHER SUMMER DAY FOR OTHERS...FALL AIR ON THE WAY FOR US ALL

Records, records, everywhere!  For the second day in a row, record high temperatures were set across New England.  A sampling of these records include Caribou, Bangor, Augusta and Portland, Maine; Concord and Manchester, NH; Windsor Locks, CT; Blue Hill Observatory in Milton, MA, and Montpelier, VT, just to name a few!  One notable exception to the record high temperatures is the City of Boston - why would the city be exempt from a record after a 93 degree afternoon high, while other records fell across New England?  The answer is that Boston has a long record of weather data, back into the 1800s, while many other cities across New England don't have such a long period of time on record.  So, while Wednesday was the hottest day in recorded history for some locales - beating records that have been standing since the 1920s for some New England cities - cities like Boston with a long historical record have 1881 as being the hottest September 26 on record, when Boston's thermometer recorded a temperature of 97 degrees.  Regardless, I think we can all agree...it was hot!

Severe thunderstorms rumbled across Central and Northern New England Wednesday evening as a cold front dropped south and southeast into New England, running into the wealth of warm air centered off the Mid-Atlantic coast and extending into New England, causing the cold front to stall over Central New England Wednesday night, while to our west the jet stream winds buckled across the Great Lakes.  Keep in mind that the jet stream is the fast river of air aloft that steers our storm systems and acts as a thermostat, separating cold air to the north from warm to the south.  As the trough, or dip in the jet stream, has carved across the Great Lakes, strong and cold energetic disturbances are pounding the ridge of warm high pressure slowly southward.  With such slow changes at the jet stream level, and such well established mild air, the stalled cold front over Central New England has actually turned around and is attempting a return north Thursday, ahead of a stronger upper level disturbance that will be approaching New England.  On the cool northern side of this front across the extreme North Country, temperatures will hover in the 60s Thursday afternoon and clouds with showers should be stubborn most of the day.  Near the front - through Central New England - some sun is likely between lots of clouds and temperatures will respond by jumping into the lower 80s with mild and sticky summer air still in place and repeated rounds of scattered showers and thunderstorms developing in the still-humid air near the front from the Berkshires to Southern New Hampshire points north, including most of Maine, and some of these thunderstorms will reach severe limits with strong wind and large hailstones.  Farther south still, we may see a shower or thunderstorm dropping into far Northern Massachusetts by Thursday evening, though most of the day will stay dry, and Boston to Providence to Hartford should remain dry through the day.  On Cape Cod and the Islands, winds blowing from the southeast will carry warmer and more humid air across cooling ocean waters and the result will be stubborn fog and persistent low altitude clouds.

Overnight Thursday night, the upper level disturbance driving our unsettled weather will move over Northern New England, prompting expansion an increasing intensity of the area of rain in Central and Northern New England, helping to fuel a localized band of rain close to the once again stalled front where one to two inches of rain are possible in the heaviest band across the Champlain Valley.  Meanwhile, as the jet stream trough over the Great Lakes moves east, winds will blow out of the south along the Eastern Seaboard, carrying a tropical disturbance northward parallel but just east of the U.S. East Coast.  This tropical disturbance is evident on both satellite and radar imagery today, and is loaded with moisture, attempting to develop a surface low pressure center near the middle of the moisture plume.  Though the jet stream will be oriented to carry this tropical wave northward, it appears as though there will be just enough of a southwest wind aloft to nudge the deepest moisure east as it approaches New England, dropping Thursday night heavy rain after midnight on Cape Cod with an inch of rain possible on the Outer Cape, but only spreading showers west even to places like Boston.  Fog, on the other hand, should be widespread with increasing warmth and moisture streaming inland on a southeast wind before winds shift late at night, though fog is still likely to remain in place, along with low altitude clouds, into Friday morning.

Any lingering Friday morning rain should yield a westerly wind and enough dry air to allow sunshine to break out sometime either side of midday.  Though sunshine may boost temperatures into the 70s south and central and 60s north in this drier air, a batch of much cooler air will be moving east across Ontario and toward New England.  Later Friday afternoon, the passage of yet another energetic disturbance and its attendant surface front will swing winds to blow from the northwest, carrying both windy and cooler conditions into New England Friday evening behind a possible final scattered shower or thunderstorm.

The drying trend will bring fantastic, cool, but dry fall air into New England for the weekend, locking sunshine in for a great weekend of fall festivals and fairs! Saturday's high temperatures will rise to either side of 70 degrees - warmest south - and an area of high altitude clouds will filter the sunshine on Sunday but weather should continue to be pleasantly perfect by autumn standards for the American Liver Foundation's Football Walk in Boston that I'll be hosting (click here to find out more about it, and to find out how you can join the walk!). 

Next week is likely to bring yet another stretch of fair weather and moderating temperatures as high pressure builds over New England and then off our coastline, though there are two features to pay attention to.  The first will be the potential for a southeast wind to bring low clouds or fog when the dry and pleasant air lets go and starts moving east, though that is contingent upon a number of factors and not at all certain.  What seems more likely is the northward expansion of a tropical feed of moisture up the coastline that would leave the East Coast vulnerable to tropical systems and tropical moisture once high pressure lets go...but it's still somewhat uncertain the timeframe for that to happen.

Enjoy a great Thursday!

Technical Discussion:  None today.

Matt

MATT'S TECHNICAL DISCUSSION - Updated Wednesday, September 26 at 1:45 PM

Severe weather threat shaping up as discussed yesterday.  Dewpoints have risen into the middle 60s, temps are 90-95 and this is rapidly increasing instability.  Vort max already resulting in multiple cumulus lines across Nrn NewEng/Upstate NY as of this writing and that trend will continue as the cyclonic vorticity advection encounters instability with LIs to -4 and CAPE values of either side of 2000 J/kg.  Mid-lvl speed max discussed yesterday is present and plenty of mid and upper level dry air is available to further increase downburst potential.  Damaging downburst wind and frequent cloud to ground lightning to be biggest threat and I expect afternoon storms in Nrn/Wrn NewEng to initiate in orographically favored areas but then increase in cov'g and intensity in response to dynamic forcing.  Organizing line in Upstate NY looks ready to evolve into broken squall line and bowing segments are likely along the line given intense unidirectional flow and sufficient speed shear.  There will be some backing of the surface wind in north/south oriented valleys, but at this point it appears the lifted condensation level would remain high enough to avoid rotational problems in cells.  Convection should weaken overnight and leave a quiet cold front to stall in Central NewEng.

Guidance is touting a quick return as warm front to the Canadian border on Thu - that seems unlikely given magnitude of surface cool air behind the front and I think we'll be surprised by the surface cold and resultant clouds in North Country, tho farther S - esp from RUT-CON-PWM southward - sun should break thru and temps will respond by coming either side of 80 with warmest temps south.  Great agreement on dry air at multiple levels in Central/Srn NewEng on Thu and really don't think it looks like that bad of a day for most communities in these areas! Thunderstorms likely to refire either side of front in Central/Nrn NewEng later Thu and shortwave passage Thu night will expand coverage in these areas.  Still a very difficult call on what to do with the tropical wave that will parallel the coastline Thu Ngt into Fri. Yesterday I felt pretty good about the NMM being an outlier and the 00Z NMM was farther east, making me feel better.  Unfortunately, 12Z run is farther west than them all!  GFS is progging a sfc low to move over Cape Cod like the NMM, but analysis of the 850 mb vorticity shows it moves east of the Cape, as does the 850 mb vorticity on the GGEM.  For now, I continue to believe the NMM is too far west in error, and therefore continue to believe the shield of steady rain may move over SE MA and then perhaps into Ern ME Thu Ngt and Fri AM respectively, but I'm not excited about filling the rain in between the frontal precip and the tropical wave.  Nonetheless, both areas should produce heavy precip rates with over an inch of QPF with locally over 2" in the northwest frontal band, but I'm not ready to jump on the 2-3" NMM amounts farther east yet.

Fri AM rain to give way to sun with drier air advecting in on west wind behind occlusion, but reinforcing cold front and assoc wind shift comes later Fri afternoon - swinging from Berks to Boston between 18Z and 00Z, for example - and likely to bring one final round of late Friday scattered convection before dry and cold advection sets in on an active northwest wind Fri Ngt.

Matt

Tuesday's Discussion:

Increasing gradient flow to advect warmth and moisture into NewEng boundary layer with Tds on the rise and the first uncomfortably sticky night in awhile for Srn and Wrn NewEng.  Positive theta-e advection continues as SW wind continues on Wed, increasing instability regionwide as LIs drop to -2 Nrn and Wrn NewEng where dynamic lift moves in first assoc with vorticity lobe stretching across NY State and toward NewEng Wed afternoon.  Dynamic lift to shift SE into Central NewEng by Wed eve when LIs in Srn VT/Wrn MA/Srn NH drop to as low as -4 to -5 and CAPE values rise to in excess of 2000 J/kg!  Seems like it's been forever since we've seen this kind of instability given our recent stretch of fair weather, so let's be sure to take a good look at the potential for severe weather: 250 mb jet streak puts Central NewEng in particular into right rear quadrant of jet streak favoring large scale ascent.  500 mb winds are strongest across Nrn NewEng at 55-65 kts Wed afternoon but this is the core of the mid-lvl winds and speeds closer to 35-45 kts over Central NewEng, but that's plenty good for downburst creation and so are 700 mb winds on the order of 50+ kts north and 35-40 kts central.  At 850 mb jet streak is also centered across Nrn NewEng where confluent flow into Ern ME trof will keep winds fast and, alas, confluent, and this directional confluence will be supplemented by increasing speed confluence over Central NewEng later Wed with 25-35 kt llvl jet.  Dry air is available aloft and this should further enhance potential for damaging downbursts, which become increasingly likely as dynamic lift shifts south and east from RUT to MPV to IZG points southward into Wrn/Nrn MA.  Lift is deep and frequent cloud to ground lightning also likely.

Of course, the fun won't stop here as frontal boundary slows/stalls with lack of strong height falls aloft and ridge holding strong over Western Atlantic.  This persistent ridge will be problematic from two levels - first, it will hold the front over Central NewEng to focus occasionally heavy rainfall again on Thu, which may not be so impressive in its areal coverage as it will be for the locally intense nature of it, which should be situated over Central NewEng and governed largely by convective processes that will remain healthy given either side of this front will be an amazing temp difference as cool, dry air settling southward into the North Country will have moisture added and therefore cool substantially to support temps in the upper 50s to lower 60s for highs, while Srn NewEng remains on the warm side of the front and finds temps around 80 - perhaps higher in any areas that can find sunshine.  Rain and thunder vicinity of the front are likely to be heaviest during the afternoon and evening not only because of diurnal contributions but also given passage of weak vort max.

Meanwhile, an important feature will be rounding the western periphery of the Western Atlantic ridge.  This feature has been rather subtle in previous guidance cycles, but has been present throughout and will undoubtedly garner more attention given the 12Z NMM attempt to spin up a tropical cyclone along the Eastern Seaboard and bring a glancing blow to Cape Cod late Thursday night and early Friday morning.  I should start by noting that this is a concern I've been keeping an eye on for several days, as this tropical wave has been very well modeled, but more than that it's the combination of an Ohio Valley trough trying to dig while the Western Atlantic ridge holds firm, and this potential was laid out in Tuesday, September 18's technical discussion, so it's something that's begged for attention for a long time.  Now the question is much more finely tuned - how close does the tropical wave come to NewEng and how quickly does it intensify.  Though the NMM paints the solution I've been most concerned about, this is a western and strong outlier of scenarios.  I'm willing to entertain the potential for quicker strengthening given relatively warm waters sitting in the path of the wave and the dynamic interactions that will occur as it nears the height falls and quickening jet, but it's that fast jet that gives me pause on buying into a western solution, as confluent flow is very well pronounced through early Thu.  It does relax as the wave rides northward and the strong shortwaves dig across the Great Lakes, but it appears as though the backing of the mid-level flow comes literally just about 12 hours too late to get the wave up over Cape Cod, and the speed of the wave very well may leave it as a transient open wave that carries a load of tropical moisture east of NewEng that becomes a bigger player upon merger with the northern stream energy in Nrn Canada, instead contributing to our Friday and Friday night wind.  This definitely is still something to watch carefully, but my estimate right now is that the NMM western outlier solution is probably not going to verify.

Shortwaves combine to drive longwave trof thru NewEng Fri Ngt after occlusion carries drier air but not cold air into Northeast Fri afternoon after Fri AM rain, and though drying occurs behind this front there very well could be one more round of convective showers with the passage of the trough Fri eve or early Fri Ngt, after which the winds become northwest and quite active overnight as drier air moves in ahead of next high pressure bubble.  Fair weather cell in charge this weekend as it follows in the footsteps of its predecessors, slowly shifting east and ready to settle in a position offshore Mid-Atlantic coast. This difference this time is the indication that there will be a bit more moisture return ready to come back at NewEng, and with the combination of cool and dry air relinquishing control while winds become southeast, low clouds and fog are a possibility on Mon before nicer wx settles in next week with only very gradually moderating temps unlike the current stretch of warmth, largely because the high center doesn't shift as far south and therefore there will be more ocean input to our air, though average NewEng temps will still be above normal after Monday.

In the longer range, it's waaaayyyy too early to try and speculate on whether newly formed Karen or the tropical wave by the Lesser Antilles will be contenders in NewEng weather, but one way to at least get a general idea is to examine the long wave pattern in the extended range.  Any attempt by the wave near the Lesser Antilles, should it attempt a move toward NewEng, would come after the upcoming push of high pressure and cool air (which incidentally may help to fuel development of a system near the FL east coast, but that shouldn't have an opportunity to move toward Neweng and will be dealt with on the Tropical Meteorology Page) which means the Lesser Antilles wave, or future cyclone if it develops, would come at a time when an inverted trough *would* be near the Eastern Seaboard with lingering very weak troughing after departure of this weekend's Ern US trough, but it also looks as though the SE US ridge holds enough to keep this inverted trough offshore, thereby indicating a northward jog by any wave would stay east of Neweng.  The situation with Karen, however, who is over the Central Atlantic is more interesting for the East Coast, if not determinable from this far out for NewEng or not.  That is, the storm is currently forecasted to curve northwest and then most guidance takes the storm northward thereafter, which would result in a nearly certain recurve given the strengthening jet that far north.  I believe this widely agreed upon solution is probably in error, though, given the strength of the Atlantic ridge and the hesitancy for this ridge to break down.  This should keep Karen on a WNW course longer than anticipated, and once we reach the middle of next week the jet stream actually lifts north and by 10 days (end of next week) ridging tries to rebuild from the Western Atlantic to the Eastern Seaboard, indicating Karen would have very little opportunity for recurvature and given East Coast residents something to at least pay attention to.  Again, too early to even guess, but not to early to guess on the longwave pattern which indicates Karen may pop up in a few more discussions!

Have a great Tuesday.
Matt

HARVEST MOON PUTS ON A SHOW FOR NEW ENGLANDERS

The Harvest Moon was a beauty for New Englanders, and managed to come on a summer night clear enough for viewing in many locales.  The Harvest Moon got its name thanks to its historical significance - that is, before electricity was harnessed to light the evening landscape, farmers relied on moonlight to help them harvest the fall crops into the overnight.  This picture was snapped by Cassandra, Gabrielle and Jeremy Neary-Orne from the Susan B. Anthony Middle School in Revere, MA - way to go kids, and thanks for sharing this with the rest of us New Englanders!

Have a thought on this blog item?  Feel free to write it in the comments section of this post!

HARVEST MOON PUTS ON A SHOW FOR NEW ENGLANDERS

The Harvest Moon was a beauty for New Englanders, and managed to come on a summer night clear enough for viewing in many locales.  The Harvest Moon got its name thanks to its historical significance - that is, before electricity was harnessed to light the evening landscape, farmers relied on moonlight to help them harvest the fall crops into the overnight.  This picture was snapped by Cassandra, Gabrielle and Jeremy Neary-Orne from the Susan B. Anthony Middle School in Revere, MA - way to go kids, and thanks for sharing this with the rest of us New Englanders!

Have a thought on this blog item?  Feel free to write it in the comments section of this post!

THURSDAY PODCAST: SCATTERED SHOWERS AND STRONG THUNDER FOR SOME...ANOTHER SUMMER DAY FOR OTHERS...FALL AIR ON THE WAY FOR US ALL

The Quick Weather Synopsis is now a Podcast!  You can either click on the audio controls above the forecast on the Quick Forecast Page, or to subscribe to the Monday-Friday podcast (updated on all days I'm working):

Easiest way is to subscribe by clicking here!

You can also use the "Subscribe to Podcast" link in the upper left corner of the main page.

The daily file you will receive is Daily_Weather_Synopsis.mp3

AS TEMPERATURES RISE, RECORDS FALL AGAIN TODAY - STRONG THUNDERSTORMS POSSIBLE FOR SOME

Another day of record heat is expected across New England today, after setting records in Windsor Locks, CT (90 - old record 88 from 1970), Caribou, ME (83 - old record 73 from 2004), Montpelier, VT (85 - old record 82 from 1984), and Mounts Washington and Mansfield (72 and 70, respectively - old records 58 in 1937 and 68 in 1984).  The continuation of a southwest wind and ample sunshine will boost temperatures into the 90-95 degree range for many spots, absolutely shattering some records, like in Bangor, ME, where the old record for Wednesday is a mere 80 degrees!

The warmth surging across New England is thrust northeast between a large and well-established area of high pressure off the Mid-Atlantic coastline, and a storm system wrapping into Canada, dragging an attendant cold front across the Great Lakes and toward New England.  Between these two systems a southwest wind increases, steady at 15-25 mph in some spots Wednesday afternoon and gusting as high as 30 mph on hilltops and near coastlines.  These winds are important in the thunderstorm forecast for later in the day, and may contribute to the development of damaging downburst winds in some storms.  The setup is as follows: The approaching cold front moving east from the Great Lakes and Ohio Valley is the focus for moisture that stems from the Gulf of Mexico, where a steady feed of moisture a couple of days ago reached all the way through the Central United States.  Though that supply of moisture has been significantly diminished, there is still plenty available that's being transported on a southwest wind ahead of the approaching front.  Meanwhile, a series of upper level energetic disturbances are riding in the deep southwest atmospheric wind flow, as well, and these disturbances will ride east in advance of the front.  One already was responsible for morning showers in extreme northern New England Wednesday morning, and a stronger energetic disturbance strung out across Upstate New York will approach Wednesday afternoon.  This will keep clouds popping in the Green Mountains and the mountainous terrain of the north, while surface temperatures and dewpoint temperatures - the measure of the amount of moisture in the air - will continue to climb.  Increasing heat and humidity will not only bring a sticky feeling, but also serve as fuel for these clouds to continue growing, eventually growing tall enough not only for scattered North Country showers late Wednesday morning, but the development of thunderstorms in Northern and extreme Western New England Wednesday afternoon.  The approach of the incoming cold front will continue to focus the moisture ahead of it, and thunderstorms will continue to blossom ahead of it, moving southeast Wednesday late afternoon and evening, and perhaps making it as far south as the Northern Massachusetts border towns Wednesday evening.  With strong wind not only here at the surface but also through several thousand feet of the atmosphere, thunderstorms will be able to tap these winds and therefore create localized damaging downburst winds while towering cumulonimbus clouds will bring frequent cloud to ground lightning in any storms that develop.

The cold front is expected to settle south Wednesday night and will encounter the wealth of warm air, and a ridge of high pressure off the Mid-Atlantic coast that will not be eager or willing to quickly break down.  The result will be a front that stalls over Central New England, while to our west the jet stream winds buckle across the Great Lakes.  Keep in mind that the jet stream is the fast river of air aloft that steers our storm systems and acts as a thermostat, separating cold air to the north from warm to the south.  As the trough, or dip in the jet stream, is carved across the Great Lakes Wednesday night, strong and cold energetic disturbances will pound the ridge of warm high pressure slowly southward, meaning cold air will advance south across the far North Country Wednesday night.  With such slow changes at the jet stream level, and such well established mild air, the stalled cold front over Central New England may actually turn around and return north for a time ahead of a stronger upper level disturbance that will be approaching New England.  On the cool northern side of this front, temperatures will hover in the 60s Thursday afternoon and clouds with showers should be stubborn most of the day.  South of the front - through Central and Southern New England - some sun is likely and temperatures will respond by jumping into the upper 70s and lower 80s with mild and sticky summer air still in place.  The approach of the strong upper level disturbance later Thursday will mean bands of rain and thunder will be rejuvenated Thursday afternoon and evening, and a few of these heavy rain bands may even cause a few smaller streams to come above bankfull by Thursday night.

Overnight Thursday night, the upper level disturbance driving our unsettled weather will move overhead, prompting expansion of the areas of rain across Central and Northern New England.  Meanwhile, as the jet stream trough over the Great Lakes moves east, winds will blow out of the south along the Eastern Seaboard, carrying a tropical disturbance northward parallel but just east of the U.S. East Coast.  This tropical disturbance will be loaded with moisture, but largely will miss New England, delivering a glancing blow of rain to Southeastern Massachusetts very late Thursday night into Friday morning, with perhaps a narrow stripe of less rain between this tropical batch and the recurrent thunder across Central and Northern New England.

Believe it or not, this upper level disturbance will be only the first of a few to cross New England through Friday night, but it also will be the one to nudge deepest moisture eastward, meaning any lingering Friday morning rain should yield a westerly wind and enough dry air to allow sunshine to break out.  Though sunshine may boost temperatures into the 70s south and central and 60s north in this drier air, a batch of much cooler air will be moving east across Ontario and toward New England.  Later Friday afternoon, the passage of yet another energetic disturbance and its attendant surface front will swing winds to blow from the northwest, carrying both windy and cooler conditions into New England Friday evening behind a possible final scattered shower or thunderstorm.

The drying trend will bring fantastic, cool, but dry fall air into New England for the weekend, locking sunshine in for a great weekend of fall festivals and fairs!  Saturday's high temperatures will rise to either side of 70 degrees - warmest south - and an area of high altitude clouds will filter the sunshine on Sunday but weather should continue to be pleasantly perfect by autumn standards for the American Liver Foundation's Football Walk in Boston that I'll be hosting (click here to find out more about it, and to find out how you can join the walk!). 

Next week is likely to bring yet another stretch of fair weather and moderating temperatures as high pressure builds off the Mid-Atlantic coastline, though the transition to that new pattern may come with an onshore, southeast wind on Monday, capable of producing plenty of clouds and areas of fog before the new stretch of fantastic weather settles in.

Here's to a wonderful Wednesday.

Matt

MATT'S TECHNICAL DISCUSSION - Updated Wednesday, September 26 at 1:45 PM

Severe weather threat shaping up as discussed yesterday.  Dewpoints have risen into the middle 60s, temps are 90-95 and this is rapidly increasing instability.  Vort max already resulting in multiple cumulus lines across Nrn NewEng/Upstate NY as of this writing and that trend will continue as the cyclonic vorticity advection encounters instability with LIs to -4 and CAPE values of either side of 2000 J/kg.  Mid-lvl speed max discussed yesterday is present and plenty of mid and upper level dry air is available to further increase downburst potential.  Damaging downburst wind and frequent cloud to ground lightning to be biggest threat and I expect afternoon storms in Nrn/Wrn NewEng to initiate in orographically favored areas but then increase in cov'g and intensity in response to dynamic forcing.  Organizing line in Upstate NY looks ready to evolve into broken squall line and bowing segments are likely along the line given intense unidirectional flow and sufficient speed shear.  There will be some backing of the surface wind in north/south oriented valleys, but at this point it appears the lifted condensation level would remain high enough to avoid rotational problems in cells.  Convection should weaken overnight and leave a quiet cold front to stall in Central NewEng.

Guidance is touting a quick return as warm front to the Canadian border on Thu - that seems unlikely given magnitude of surface cool air behind the front and I think we'll be surprised by the surface cold and resultant clouds in North Country, tho farther S - esp from RUT-CON-PWM southward - sun should break thru and temps will respond by coming either side of 80 with warmest temps south.  Great agreement on dry air at multiple levels in Central/Srn NewEng on Thu and really don't think it looks like that bad of a day for most communities in these areas!  Thunderstorms likely to refire either side of front in Central/Nrn NewEng later Thu and shortwave passage Thu night will expand coverage in these areas.  Still a very difficult call on what to do with the tropical wave that will parallel the coastline Thu Ngt into Fri.  Yesterday I felt pretty good about the NMM being an outlier and the 00Z NMM was farther east, making me feel better.  Unfortunately, 12Z run is farther west than them all!  GFS is progging a sfc low to move over Cape Cod like the NMM, but analysis of the 850 mb vorticity shows it moves east of the Cape, as does the 850 mb vorticity on the GGEM.  For now, I continue to believe the NMM is too far west in error, and therefore continue to believe the shield of steady rain may move over SE MA and then perhaps into Ern ME Thu Ngt and Fri AM respectively, but I'm not excited about filling the rain in between the frontal precip and the tropical wave.  Nonetheless, both areas should produce heavy precip rates with over an inch of QPF with locally over 2" in the northwest frontal band, but I'm not ready to jump on the 2-3" NMM amounts farther east yet.

Fri AM rain to give way to sun with drier air advecting in on west wind behind occlusion, but reinforcing cold front and assoc wind shift comes later Fri afternoon - swinging from Berks to Boston between 18Z and 00Z, for example - and likely to bring one final round of late Friday scattered convection before dry and cold advection sets in on an active northwest wind Fri Ngt.

Matt

Tuesday's Discussion:

Increasing gradient flow to advect warmth and moisture into NewEng boundary layer with Tds on the rise and the first uncomfortably sticky night in awhile for Srn and Wrn NewEng.  Positive theta-e advection continues as SW wind continues on Wed, increasing instability regionwide as LIs drop to -2 Nrn and Wrn NewEng where dynamic lift moves in first assoc with vorticity lobe stretching across NY State and toward NewEng Wed afternoon.  Dynamic lift to shift SE into Central NewEng by Wed eve when LIs in Srn VT/Wrn MA/Srn NH drop to as low as -4 to -5 and CAPE values rise to in excess of 2000 J/kg!  Seems like it's been forever since we've seen this kind of instability given our recent stretch of fair weather, so let's be sure to take a good look at the potential for severe weather: 250 mb jet streak puts Central NewEng in particular into right rear quadrant of jet streak favoring large scale ascent.  500 mb winds are strongest across Nrn NewEng at 55-65 kts Wed afternoon but this is the core of the mid-lvl winds and speeds closer to 35-45 kts over Central NewEng, but that's plenty good for downburst creation and so are 700 mb winds on the order of 50+ kts north and 35-40 kts central.  At 850 mb jet streak is also centered across Nrn NewEng where confluent flow into Ern ME trof will keep winds fast and, alas, confluent, and this directional confluence will be supplemented by increasing speed confluence over Central NewEng later Wed with 25-35 kt llvl jet.  Dry air is available aloft and this should further enhance potential for damaging downbursts, which become increasingly likely as dynamic lift shifts south and east from RUT to MPV to IZG points southward into Wrn/Nrn MA.  Lift is deep and frequent cloud to ground lightning also likely.

Of course, the fun won't stop here as frontal boundary slows/stalls with lack of strong height falls aloft and ridge holding strong over Western Atlantic.  This persistent ridge will be problematic from two levels - first, it will hold the front over Central NewEng to focus occasionally heavy rainfall again on Thu, which may not be so impressive in its areal coverage as it will be for the locally intense nature of it, which should be situated over Central NewEng and governed largely by convective processes that will remain healthy given either side of this front will be an amazing temp difference as cool, dry air settling southward into the North Country will have moisture added and therefore cool substantially to support temps in the upper 50s to lower 60s for highs, while Srn NewEng remains on the warm side of the front and finds temps around 80 - perhaps higher in any areas that can find sunshine.  Rain and thunder vicinity of the front are likely to be heaviest during the afternoon and evening not only because of diurnal contributions but also given passage of weak vort max.

Meanwhile, an important feature will be rounding the western periphery of the Western Atlantic ridge.  This feature has been rather subtle in previous guidance cycles, but has been present throughout and will undoubtedly garner more attention given the 12Z NMM attempt to spin up a tropical cyclone along the Eastern Seaboard and bring a glancing blow to Cape Cod late Thursday night and early Friday morning.  I should start by noting that this is a concern I've been keeping an eye on for several days, as this tropical wave has been very well modeled, but more than that it's the combination of an Ohio Valley trough trying to dig while the Western Atlantic ridge holds firm, and this potential was laid out in Tuesday, September 18's technical discussion, so it's something that's begged for attention for a long time.  Now the question is much more finely tuned - how close does the tropical wave come to NewEng and how quickly does it intensify.  Though the NMM paints the solution I've been most concerned about, this is a western and strong outlier of scenarios.  I'm willing to entertain the potential for quicker strengthening given relatively warm waters sitting in the path of the wave and the dynamic interactions that will occur as it nears the height falls and quickening jet, but it's that fast jet that gives me pause on buying into a western solution, as confluent flow is very well pronounced through early Thu.  It does relax as the wave rides northward and the strong shortwaves dig across the Great Lakes, but it appears as though the backing of the mid-level flow comes literally just about 12 hours too late to get the wave up over Cape Cod, and the speed of the wave very well may leave it as a transient open wave that carries a load of tropical moisture east of NewEng that becomes a bigger player upon merger with the northern stream energy in Nrn Canada, instead contributing to our Friday and Friday night wind.  This definitely is still something to watch carefully, but my estimate right now is that the NMM western outlier solution is probably not going to verify.

Shortwaves combine to drive longwave trof thru NewEng Fri Ngt after occlusion carries drier air but not cold air into Northeast Fri afternoon after Fri AM rain, and though drying occurs behind this front there very well could be one more round of convective showers with the passage of the trough Fri eve or early Fri Ngt, after which the winds become northwest and quite active overnight as drier air moves in ahead of next high pressure bubble.  Fair weather cell in charge this weekend as it follows in the footsteps of its predecessors, slowly shifting east and ready to settle in a position offshore Mid-Atlantic coast. This difference this time is the indication that there will be a bit more moisture return ready to come back at NewEng, and with the combination of cool and dry air relinquishing control while winds become southeast, low clouds and fog are a possibility on Mon before nicer wx settles in next week with only very gradually moderating temps unlike the current stretch of warmth, largely because the high center doesn't shift as far south and therefore there will be more ocean input to our air, though average NewEng temps will still be above normal after Monday.

In the longer range, it's waaaayyyy too early to try and speculate on whether newly formed Karen or the tropical wave by the Lesser Antilles will be contenders in NewEng weather, but one way to at least get a general idea is to examine the long wave pattern in the extended range.  Any attempt by the wave near the Lesser Antilles, should it attempt a move toward NewEng, would come after the upcoming push of high pressure and cool air (which incidentally may help to fuel development of a system near the FL east coast, but that shouldn't have an opportunity to move toward Neweng and will be dealt with on the Tropical Meteorology Page) which means the Lesser Antilles wave, or future cyclone if it develops, would come at a time when an inverted trough *would* be near the Eastern Seaboard with lingering very weak troughing after departure of this weekend's Ern US trough, but it also looks as though the SE US ridge holds enough to keep this inverted trough offshore, thereby indicating a northward jog by any wave would stay east of Neweng.  The situation with Karen, however, who is over the Central Atlantic is more interesting for the East Coast, if not determinable from this far out for NewEng or not.  That is, the storm is currently forecasted to curve northwest and then most guidance takes the storm northward thereafter, which would result in a nearly certain recurve given the strengthening jet that far north.  I believe this widely agreed upon solution is probably in error, though, given the strength of the Atlantic ridge and the hesitancy for this ridge to break down.  This should keep Karen on a WNW course longer than anticipated, and once we reach the middle of next week the jet stream actually lifts north and by 10 days (end of next week) ridging tries to rebuild from the Western Atlantic to the Eastern Seaboard, indicating Karen would have very little opportunity for recurvature and given East Coast residents something to at least pay attention to.  Again, too early to even guess, but not to early to guess on the longwave pattern which indicates Karen may pop up in a few more discussions!

Have a great Tuesday.
Matt

WEDNESDAY PODCAST: AS TEMPERATURES RISE, RECORDS FALL AGAIN TODAY - STRONG THUNDERSTORMS POSSIBLE FOR SOME

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RECORD BREAKING HEAT TODAY AND WEDNESDAY...TRANSITION TO FALL FEEL THIS WEEKEND

Records will be challenged across New England Tuesday and Wednesday as summer heat builds across the Northeast behind a departing area of high pressure, and ahead of a storm and its frontal boundary, approaching from the west.  The result will be a transition from summer weather to start the week, to an unsettled change in airmasses, leaving behind a dry but crisp fall air for the upcoming weekend.

The anticipated temperature rise Tuesday afternoon comes after a clear morning in most locales, with a warm front developing across far Northern Maine where a few clouds and even a brief shower resulted.  For most, however, the warmth is already in place and Tuesday will remain dry as a large ridge - a bump in the jet stream - crests overhead.  Because the jet stream both steers storms and acts as a thermostat for the atmosphere, separating cold to the north from warm to the south, a ridge over New England implies both that storms and energetic disturbances will be ushered to our west and north along these jet stream winds, and that warmth has bubbled across New England not only at ground level, but also aloft - actually warm enough several thousand feet above our heads to prohibit any deep clouds from growing, thereby ensuring dry conditions Tuesday.  At the surface, New England is sandwiched between the same area of high pressure that moved overhead this weekend with fair weather - now moving south of us and over the waters east of the Mid-Atlantic - and the energetic storm marching across the Midwest and Great Lakes.  Around the high pressure cell, a clockwise flow of air keeps a southwest wind flowing into New England while the counter-clockwise flow around the storm to our west enhances this southwest wind, creating breezy conditions Tuesday afternoon that are ushering in warmth, teamed with sunshine for some record breaking temperatures.  In fact, in cities like Burlington, Vermont, the record of 85 degrees has been standing since 1891!  All the while, for parts of Central and Eastern New England the same phenomenon will help to further warm the air - a process known as downsloping flow.  As described yesterday, this is wind sloping down off the hills and mountains and as it descends, the pressure around it increases (the lower one is in altitude, the greater the atmospheric pressure).  By the properties of physics, as pressure increases on air, so does temperature, and the result is a warming and drying of the air as it moves into lower elevations.

Of course, while the downsloping process may be drying the air a bit, having a greater impact is the southwest wind that's ushering in more humid air gradually across the Northeast.  In fact, as dewpoint temperatures - the measure of the amount of moisture in the air - rise into the 50s, some may notice a a slightly stickier feeling Tuesday afternoon that will surely become more noticeable overnight Tuesday night beneath clear skies south and partly cloudy skies north, as a humid feeling returns for the first overnight in quite awhile.  This humid feeling will continue on Wednesday, and while some increase in moisture is likely to result in patches of middle altitude clouds, plenty of sunshine is expected again which will quickly warm an already mild airmass into the 80s for most spots again - perhaps even pushing 90 in a few communities - challenging record high temperatures for the second day in a row.  With the return of warmth and humidity, coupled with the approaching energetic disturbance and associated cold front, will come an increasing chance of thunderstorms Wednesday afternoon in Northern and Western New England, and across Central New England by Wednesday evening.

As the cold front pressing into New England encounters the warm air, and a jet stream ridge that will not be eager or willing to quickly break down, the front will slow.  As the jet stream winds buckle across the Great Lakes on Wednesday night - and especially on Thursday - strong and cold energetic disturbances will pound the ridge slowly southward, meaning cold air will advance south and east into New England slowly but surely on Thursday, both aloft and at the surface, where the stalled surface cold front will not only serve to focus bands of locally heavy rain as atmospheric energy moves overhead on Thursday, but also will define a tremendous difference in air.  North of the front, high temperatures will not make it out of the 50s in some North Country locales, while straddling the front will mean the difference between highs in the 60s and those in the 70s across Central New England, while farther south we'll find Southern New England highs reaching well into the 70s and perhaps even into the 80s for a few communities.

The approach of additional energetic disturbances will team with a residual flow of tropical moisture - ushered northward ahead of this storm as it moved through the Central United States but still a part of the system as it moves east - will wring out periodic showers and bands of locally heavy rainfall Thursday night into the first part of Friday.  As the energy and moisture consolidates into a strong storm pulling out of New England, high pressure to our west will prepare to take its place from Central Canada, kicking winds up out of the west Friday afternoon and nosing drier air into New England for breaks of sun that will push temperatures into the 70s south, 60s north.  Not long after this, though, a chunk of cool air pulled southward out of Canada will move in Friday night and take hold for the weekend, locking drier air in place for fall festivals and fairs across New England for a windy and crisp Friday night, a sunny and dry but cool Saturday, and some moderation in temperatures by Sunday beneath continued sun in an early fall air.

Next week is likely to bring yet another stretch of fair weather and moderating temperatures as high pressure builds off the Mid-Atlantic coastline, though the transition to that new pattern may come with an onshore, southeast wind on Monday, capable of producing plenty of clouds and areas of fog before the new stretch of fantastic weather settles in.

Enjoy your Tuesday!

Matt

MATT'S TECHNICAL DISCUSSION - Updated Tuesday, September 25 at 1:45 PM

Increasing gradient flow to advect warmth and moisture into NewEng boundary layer with Tds on the rise and the first uncomfortably sticky night in awhile for Srn and Wrn NewEng.  Positive theta-e advection continues as SW wind continues on Wed, increasing instability regionwide as LIs drop to -2 Nrn and Wrn NewEng where dynamic lift moves in first assoc with vorticity lobe stretching across NY State and toward NewEng Wed afternoon.  Dynamic lift to shift SE into Central NewEng by Wed eve when LIs in Srn VT/Wrn MA/Srn NH drop to as low as -4 to -5 and CAPE values rise to in excess of 2000 J/kg!  Seems like it's been forever since we've seen this kind of instability given our recent stretch of fair weather, so let's be sure to take a good look at the potential for severe weather: 250 mb jet streak puts Central NewEng in particular into right rear quadrant of jet streak favoring large scale ascent.  500 mb winds are strongest across Nrn NewEng at 55-65 kts Wed afternoon but this is the core of the mid-lvl winds and speeds closer to 35-45 kts over Central NewEng, but that's plenty good for downburst creation and so are 700 mb winds on the order of 50+ kts north and 35-40 kts central.  At 850 mb jet streak is also centered across Nrn NewEng where confluent flow into Ern ME trof will keep winds fast and, alas, confluent, and this directional confluence will be supplemented by increasing speed confluence over Central NewEng later Wed with 25-35 kt llvl jet.  Dry air is available aloft and this should further enhance potential for damaging downbursts, which become increasingly likely as dynamic lift shifts south and east from RUT to MPV to IZG points southward into Wrn/Nrn MA.  Lift is deep and frequent cloud to ground lightning also likely.

Of course, the fun won't stop here as frontal boundary slows/stalls with lack of strong height falls aloft and ridge holding strong over Western Atlantic.  This persistent ridge will be problematic from two levels - first, it will hold the front over Central NewEng to focus occasionally heavy rainfall again on Thu, which may not be so impressive in its areal coverage as it will be for the locally intense nature of it, which should be situated over Central NewEng and governed largely by convective processes that will remain healthy given either side of this front will be an amazing temp difference as cool, dry air settling southward into the North Country will have moisture added and therefore cool substantially to support temps in the upper 50s to lower 60s for highs, while Srn NewEng remains on the warm side of the front and finds temps around 80 - perhaps higher in any areas that can find sunshine.  Rain and thunder vicinity of the front are likely to be heaviest during the afternoon and evening not only because of diurnal contributions but also given passage of weak vort max.

Meanwhile, an important feature will be rounding the western periphery of the Western Atlantic ridge.  This feature has been rather subtle in previous guidance cycles, but has been present throughout and will undoubtedly garner more attention given the 12Z NMM attempt to spin up a tropical cyclone along the Eastern Seaboard and bring a glancing blow to Cape Cod late Thursday night and early Friday morning.  I should start by noting that this is a concern I've been keeping an eye on for several days, as this tropical wave has been very well modeled, but more than that it's the combination of an Ohio Valley trough trying to dig while the Western Atlantic ridge holds firm, and this potential was laid out in Tuesday, September 18's technical discussion, so it's something that's begged for attention for a long time.  Now the question is much more finely tuned - how close does the tropical wave come to NewEng and how quickly does it intensify.  Though the NMM paints the solution I've been most concerned about, this is a western and strong outlier of scenarios.  I'm willing to entertain the potential for quicker strengthening given relatively warm waters sitting in the path of the wave and the dynamic interactions that will occur as it nears the height falls and quickening jet, but it's that fast jet that gives me pause on buying into a western solution, as confluent flow is very well pronounced through early Thu.  It does relax as the wave rides northward and the strong shortwaves dig across the Great Lakes, but it appears as though the backing of the mid-level flow comes literally just about 12 hours too late to get the wave up over Cape Cod, and the speed of the wave very well may leave it as a transient open wave that carries a load of tropical moisture east of NewEng that becomes a bigger player upon merger with the northern stream energy in Nrn Canada, instead contributing to our Friday and Friday night wind.  This definitely is still something to watch carefully, but my estimate right now is that the NMM western outlier solution is probably not going to verify.

Shortwaves combine to drive longwave trof thru NewEng Fri Ngt after occlusion carries drier air but not cold air into Northeast Fri afternoon after Fri AM rain, and though drying occurs behind this front there very well could be one more round of convective showers with the passage of the trough Fri eve or early Fri Ngt, after which the winds become northwest and quite active overnight as drier air moves in ahead of next high pressure bubble.  Fair weather cell in charge this weekend as it follows in the footsteps of its predecessors, slowly shifting east and ready to settle in a position offshore Mid-Atlantic coast.  This difference this time is the indication that there will be a bit more moisture return ready to come back at NewEng, and with the combination of cool and dry air relinquishing control while winds become southeast, low clouds and fog are a possibility on Mon before nicer wx settles in next week with only very gradually moderating temps unlike the current stretch of warmth, largely because the high center doesn't shift as far south and therefore there will be more ocean input to our air, though average NewEng temps will still be above normal after Monday.

In the longer range, it's waaaayyyy too early to try and speculate on whether newly formed Karen or the tropical wave by the Lesser Antilles will be contenders in NewEng weather, but one way to at least get a general idea is to examine the long wave pattern in the extended range.  Any attempt by the wave near the Lesser Antilles, should it attempt a move toward NewEng, would come after the upcoming push of high pressure and cool air (which incidentally may help to fuel development of a system near the FL east coast, but that shouldn't have an opportunity to move toward Neweng and will be dealt with on the Tropical Meteorology Page) which means the Lesser Antilles wave, or future cyclone if it develops, would come at a time when an inverted trough *would* be near the Eastern Seaboard with lingering very weak troughing after departure of this weekend's Ern US trough, but it also looks as though the SE US ridge holds enough to keep this inverted trough offshore, thereby indicating a northward jog by any wave would stay east of Neweng.  The situation with Karen, however, who is over the Central Atlantic is more interesting for the East Coast, if not determinable from this far out for NewEng or not.  That is, the storm is currently forecasted to curve northwest and then most guidance takes the storm northward thereafter, which would result in a nearly certain recurve given the strengthening jet that far north.  I believe this widely agreed upon solution is probably in error, though, given the strength of the Atlantic ridge and the hesitancy for this ridge to break down.  This should keep Karen on a WNW course longer than anticipated, and once we reach the middle of next week the jet stream actually lifts north and by 10 days (end of next week) ridging tries to rebuild from the Western Atlantic to the Eastern Seaboard, indicating Karen would have very little opportunity for recurvature and given East Coast residents something to at least pay attention to.  Again, too early to even guess, but not to early to guess on the longwave pattern which indicates Karen may pop up in a few more discussions!

Have a great Tuesday.
Matt

TUESDAY PODCAST: RECORD BREAKING HEAT TODAY AND WEDNESDAY...TRANSITION TO FALL FEEL THIS WEEKEND

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