MIDWEEK BREAK TO BE FOLLOWED BY INTENSE BUT SHORT-LIVED BAND OF RAIN AND WIND TO END MILD STREAK
AFTER LONG STRETCH OF MILD WEATHER, TEMPERATURES TO RETURN BELOW NORMAL

FLOODING RAINS, DAMAGING WINDS AND THUNDERSTORMS ALL POSSIBILITIES ACROSS NEW ENGLAND

Welcome to the weather blog - a regular Monday through Friday discussion of the weather!  While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants.  I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible.  You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is [email protected].  This blog is for you, so I hope you enjoy it!  -Matt Noyes

General Weather Summary:

A very late post today due to lots going on behind the scenes here at NECN.

An intense round of heavy, locally flooding rain, gusty and potentially damaging wind, and embedded thunderstorms will sweep across New England late Thursday night through early Friday.  A potent storm system moving slowly across Kentucky has established a deep feed of tropical moisture out of the Gulf of Mexico and the Tropical Atlantic, and this is feeding a combination of severe weather and tornadoes from the Carolinas through the Mid-Atlantic coastline, to heavy rainfall up the spine of the Appalachians.

For New England, the surge of tropical warmth and moisture brought dense morning fog early Thursday for many areas, and this fog was quite stubborn to lift in Central New England, in the battlezone of incoming tropical air and the relatively cooler, drier air that was in place.  This boundary is draped across Southern New England Thursday afternoon and is evident as a wind shift and the back edge to low altitude clouds.  The front will serve as the focus for heavy rainfall later Thursday night into Friday, and already has been responsible for scattered heavy downpours.

What were expected to be simply scattered showers along this leading edge of tropical warmth instead have blossomed into scattered downpours for some Thursday afternoon.  This trend will continue into Thursday evening, as the flow of increasingly warm and humid air continues.  In fact, in areas squarely into this warmth through Connecticut, Rhode Island and Southeastern Massachusetts, breaks of sun have emerged and pushed temperatures well into the 60s and to near 70 degrees!

The well-defined swirling storm system to our southwest is gradually nosing toward New England, and it's the very fast corridor of wind ahead of the low pressure center that has tapped such deep tropical moisture.  Of course, just because this air is moisture loaded doesn't mean its speed slows any in that fast corridor of wind, and winds just a few thousand feet off of ground level are blowing at over 60 mph.  This corridor of wind, and the moisture it carries, will progress northeast ahead of the storm center and the energetic upper level disturbance that's driving it.  The result will be twofold: 1) Winds will increase across Vermont and will likely gust over 60 mph Thursday night with scattered power outages and downed trees, and 2) steadier and heavier rain develops late Thursday night, and a band of narrow but intense rainfall marches into New England from late Thursday night through Friday morning.

This band of rain will be so intense, that between one and three inches of rain is likely to fall in a very short period of time, with locally higher amounts possible!  This would result in nearly-certain street flooding and hydroplaning concerns for the morning drive on Friday, especially in Central and Eastern New England where the band of rain would move through at peak commute times, and also is likely to push at least some streams out of their banks for flash flooding, especially where 3" amounts of rain are observed.  In these locales, small rivers also may briefly spill their banks.  Given the amount of warmth and moisture in the lower few thousand feet of the sky, and the energy aloft, thunderstorms are likely to be embedded in this line of downpours, and any thunderstorms would have the capability of pulling down the strong winds aloft, producing damaging wind gusts in excess of 60 mph in at least a few communities that see thunderstorms Friday morning, and this would produce isolated power outages.

This corridor of wind and water will be focused along and ahead of a cold front sweeping east, and the drier and cooler air behind the front will ensure the rain band keeps moving, as well as providing an effort to break some sunshine out later Friday.  With cool and dry air spilling into New England, expect gradual clearing Friday night to bring a blend of clouds and sun on Saturday with high temperatures still near or perhaps slightly above normal, but noticeably cooler than they've been.  This will be the beginning of a new jet stream pattern that will feature a trough - or dip - in the jet stream winds over New England, returning the six-state region to a near or below normal temperature pattern for at least a few days after two weeks of above to much above normal temperatures.  Though this will not be a bona fide, long-lasting and well-defined cool pattern - lasting only until Wednesday of next week - it's enough so that ski areas should plan on making hay while the sun shines, so to speak, as snowmaking conditions should be good for this window of time.  In fact, while most of New England sees a brisk blend of clouds and sun on Saturday, northern mountains may be graced with snow showers from time to time.

The complication to the weekend forecast is that the jet stream winds aloft - the fast river of air high in the sky that steers our storms - will still flow over New England.  This means a disturbance aloft will be subject to riding overhead on Sunday with increased clouds Saturday night into Sunday, and the chance of early Sunday rain showers south and snow showers north.  Thereafter, Sunday afternoon would likely bring plenty of lingering clouds among breaks of sun.  Monday looks to be a break in the action here in New England for at least part of the day, but another upper level disturbance will spawn a coastal storm off the Mid-Atlantic, and this storm may pass close enough to deliver rain and snow to some of New England late Monday into Tuesday, though that is highly uncertain at this point.

Technical Discussion:  None today.

Matt

Matt's Technical Meteorological Discussion:  Updated Wednesday, November 15 at 2:25 PM

Short term fcst to carry pulsing showers fed by low level tropical inflow northward from SCoast of NewEng thru remainder of area overnight Wed Ngt.  Combo of mostly cloudy skies and active S wind at sfc and moreover a few thousand feet off the ground will inhibit cooling and overnight low temps will be remarkably mild, with 50s in many Srn NewEng cities - evidence provided by mid 50s Tds as of this writing.  Tho KBOS is unlikely to stay above 59 degrees overnight Wed Ngt, KCON record warm min temp is 51 from 1960 and a new warm min may be set tonight.  KCAR is within one degree of record high of 56 as of this writing.

Expect any light showers early Thu caused by combo of low level WAA and PVA with vort moving from S to N to wane as NVA sets in for most of the day and brings drier air to the midlvls, and breaks of sun shud result for a time.  Wind will strengthen along SCoast first, then across most of NewEng by later Thu as pressure gradient tightens between 1024-1026 mb high S of Nova Scotia and 988 mb low over OH.  Intense llvl jet at 850 mb will be to our W across PA/NY and this is where heaviest flooding rains will fall on Thu.

Trend continues to be slower with the upper low but this shud not be too surprising, as it is truly a continuation of the pattern we've already been dealing with.  Two weeks ago we saw a similar scenario with our upper low originally looking as though it would deliver a solid chunk of cold but then backing farther and farther west until finally it was evident it would be unable to pull deep cold this far east.  With an Ensemble longwave pattern forecast of pulling the upper low to James Bay by Friday evening and a new strong shortwave coming thru the NW US at the same time, while amplified ridge axis peaks over Ern Canada and Maritimes, it's simply not possible to pull the upper low far enough east to deliver a formidable shot of deep cold to NewEng.

But that doesn't mean we're not looking at cold enough conditions for snow making in the mountains once again, and that also doesn't mean the above to much above normal pattern rolls on, as shallow cold is still cold nonetheless, even if there is no monster high to drive it south, and this will make for chilly nights and cool days.  That said, there may be more than one devil in the details with regard to the weekend forecast, as the longwave pattern indicates there should be little comfort for NewEng forecasters.  Tho Sat features a break between systems as the upper low recoils a bit into SCentral Canada, this recoiling will yank shortwaves down from the active Pacific flow and they will round the base of the trof - the first rounding the trof base in the OH Valley Sat ngt and ejecting NE.  This shortwave will move over NewEng late Sat Ngt or more likely on Sun.  Those of you who read regularly know that I find the upper level RH field to be a very telling sign of what may follow in surface trends, largely because it is devoid of low level baroclinicity, which can certainly be a driving factor, but in this instance will largely be determined by the upper level flow.  Not only is the 12Z NAM picking up on this upper level RH extending northward toward NewEng, but it would make sense that if we're banking on the upper level flow being sluggish we should also bank on the low level baroclinic zone not shifting as far east as forecasted by the guidance currently.  This raises concern for precip Sat Ngt into Sun, esp early Sun with the passage of the vort max overhead.  This introduces an event of low forecastabillity thanks to the variation between expected longwave pattern and forecasted results at the surface by the guidance, but instinct says be cautious and introduce a chance of precip for at least early Sun and have adjusted fcst accordingly as of this writing.

But this isn't the end of the story, as the Pacific NW shortwave mentioned earlier in this disc will traverse the Nrn Plains and then drop into the base of the trof in the OH valley, like its predecessor, and will force the longwave trof to tilt neutrally Mon, likely prompting low pressure development at the Mid-Atl coast.  Mon Ngt into Tue, this surface low will be captured by the upper level support, and the low will attempt to stack vertically.  This introduces tremendous uncertainty with regard to where and when this interaction of vertical circulations takes place, and this uncertainty is reflected in Ensemble spread, as well, though it's worth noting that some GFS Ensemble members and ECMWF Ensemble members paint moderate precip onto Ern NewEng while Canadian Members miss and keep precip offshore.  Of course, my thoughts on precip forecasts with such an uncertain pattern at such a long forecast period is that they should be taken with a grain of salt, and the message we're getting from the longwave pattern is far more important.

As for Sergio...strengthening off the western coast of Mexico...indications are that his moisture will filter rather than surge over the next several days, as it's tugged both northward by the intense Pacific disturbances, and eastward as these systems strengthen in the OH and TN valleys, so rather than a rapid integration, a slow feed of fuel from the system is more likely.

While colder air will undoubtedly bleed into NewEng under the belly of the large upper low by James Bay, and a more significant chunk of surface cold may wrap south behind any disturbances Sat Ngt/Sun and then again later Mon/Tue, without a mechanism to hold this cold into NewEng, average temp regime is likely to return to near or somewhat above normal by middle of next week, though not by nearly as much as the past two weeks, still bringing cool enuf nights for snowmaking and returning us to an oscillating pattern of warmth ahead of shortwaves and brief shots of shallow cool behind them.

Enjoy your Wednesday.

Matt