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 contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes
General Weather Summary:
It's all about timing for the next several days here in New England - timing of periods of showers and rain that will slide across the region. The jet stream winds aloft - the fast river of air high in the sky that steers our storms and acts as a thermostat for the atmosphere, separating warm air to the south from cooler and drier air to the north - continue to race across Southern Canada and dip across New England. This will lock the Northeast into a progressive weather pattern that swings new disturbances through frequently, placing New England on a battlezone between deep summer warmth and humidity brewing to our south, and shots of cooler and dry Canadian air that continue to penetrate south into the Northeastern United States.
A reinforcing shot of cool and dry Canadian air pushed through Northern New England yesterday afternoon and evening, producing scattered showers and thunderstorms - even a severe thunderstorm in Eastern Maine - as the cold front leading the charge moved through. Wednesday finds that same front only very slowly trudging through Southern New England, ushering in relatively dry and cool air for the North, while bringing a few showers and thunderstorms to parts of Southern New England later Wednesday afternoon. Greatest focus will be on Southeast New Hampshire through Eastern Massachusetts, though even those areas that see a shower or thunderstorm will find them to be quick moving and short-lived, so most of us enjoy a very nice summer day.
Behind this front, a reinforcing shot of cool and dry air is settling southward through Quebec and Ontario, where overnight low temperatures dropped into the 40s and 30s. This air will produce similar numbers across the North Country Wednesday night, while the remainder of New England also finds a cool night that begins clear, but ends with increasing clouds late. Those clouds will be the leading edge of an approaching jet stream disturbance...one in what will be a parade of disturbances to move through New England over the coming days.
The situation is complicated by a few factors, one of which is the dome of dry and cool Canadian air - defined on the weather map by an area of high pressure - settling just east of New England on Thursday. The clockwise flow of air around this fair weather center will favor an "onshore" flow - that is, air blowing in off of the Atlantic, combining with the cool nature of the airmass to keep temperatures from climbing too high on Thursday afternoon. Another factor in our cool Thursday will be clouds, which should be plentiful given that I'm expecting the next disturbance to usher warmth and moisture northward over this cool dome, and the clash will mean increasing and thickening clouds Thursday. Finally, by Thursday afternoon the clash of airmasses between surface cool and elevated warmth will cause showers to break out from west to east, and a steadier shield of rain is probable Thursday evening into night.
Such begins the story of the next several days - a battle of Canadian air and tropical air taking place right over New England, wringing out rainfall when the collide, allowing comfortable sunshine at times, and giving way to a burst of warmth and humidity perhaps before the weekend is over. With the jet stream winds steering each of these systems along very quickly, the key as a meteorologist is to try and nail down the timing of each disturbance, as this will be so important to planning our weekend. It still appears to me as though Thursday night's rain should give way to a break in the action on Friday, when some breaks of sunshine would be possible as we await the next disturbance, slated to bring returning rain showers Friday night.
By Saturday, warmer and more humid air will make a more formidable push into the Northeastern U.S. as a storm center wraps up over the Great Lakes and the counter-clockwise flow of air around it helps to propel this warmth northward. The result will be plenty of clouds, a slightly warmer feel in Southern New England, and afternoon showers and thunderstorms across most of New England as cool Canadian air will still hold strong over Northern New England. By Sunday, I'm expecting the warmer air to be in place for most of the day in Central and Southern New England, though Northern areas will see continued clouds and periodic showers. In fact, those areas that do break into warmer and more humid air on Sunday could squeeze out a nice but sticky summer day before rain and thunder moves east out of the Great Lakes Sunday night.
This next disturbance Sunday night through Monday will be the strongest of the bunch, likely to deliver a shot of heavy rain to New England.
Meanwhile, in the tropics, Tropical Depression #4 has been named Tropical Storm Debby by the National Hurricane Center. This storm will continue moving west-northwest over the Central Atlantic, perhaps strengthening to a hurricane as it does so, and will continue to be watched for several days, though is nearly two weeks from any possible threat to the United States, if it should survive the trip. A new cluster of thunderstorms bears watching approaching the Windward Islands, and will be entering an area more favorable for storm development over the next 24 hours as it crosses the Windward and Leeward Islands. Finally, the cluster of thunderstorms northeast of the coast of Nicaragua, located in the Western Caribbean Sea between Cuba and Nicaragua still has not organized yet, and conditions still remain somwhat unfavorable for development.
Have a great Wednesday!
Matt
Matt's Technical Meteorological Discussion: Updated Wednesday, August 23 at 1:55 PM
Hello techies - going to make a change in the way these are posted. Will leave the entire week's up each week and start clean on Mondays...this way you don't have to read thru them in the archives to access them. Also, this will allow me to issue short updates during the day if time doesn't allow for one lengthy post. Note the update times I'll include with each one...with the latest update time always in the text above. Most recent will always appear on top.
Tropics: See yesterday's discussion (below) of why I'm not really hip on Debby. Satellite imagery is showing the trend you and I were waiting for if you read the discussion already, and that is, SW shear limiting outflow on the southern semi-circle, blowing the tops of a storm that has shifted to west motion. It's a long uphill battle for Debby and one that will be tough for her to win...especially regarding any chance of her continuing a jaunt westward. Still plenty to watch with the wave approaching the Windward Islands, though...you can see below for thoughts on that, too, and let's plan on examining that a bit closer tomorrow.
1:35 PM Update: Instability and low level convergent frontal zone doing their dirty work this afternoon with healthy blossoming Cu field that will continue to produce showers and embedded thunder this afternoon. Given dry atmosphere aloft, expecting pulse-type convection to be the rule. Winds are marginal for damaging bursts and would only be strongest of the pulses that could produce strong enuf downbursts, so have left mention out of the public forecast given limited coverage of convection in the first place, and downright isolated threat of anything strong.
Convective clouds will diminish after sunset and give way to a clear start to the night and this will allow for quick radiational cooling. Clouds associated with weakening shower/thunderstorm complex ejecting E out of Great Lakes will move in late Wed Ngt/Early Thu AM, however, and will halt or reverse downward temp trend. Some dim sun possible thru these clouds Thu AM before more substantial warm and moist advection aloft overruns cool dome of Canadian high pressure and differential advection (which later becomes warm advection over neutral low level advection) will thicken clouds. Only prohibition to precip production will be the dry low levels and this will be enuf to preclude precip for first half of day in most areas, tho late morning thru afternoon will bring advancement of showers from W to E as low levels begin to moisten and mid-level isentropic lift increases. Parade of shortwaves to move across Canadian border with vort lobes running parallel to these thru NY/PA and across NJ. This combo allows falling heights to combine with available moisture along with moderate dynamic lift, and this will mean rain should continue thru Thu Ngt with heavy rain esp first half of night. Showers should continue until PVA shuts down, which won't be until Fri AM according to guidance...tho fast flow may push these thru a bit faster to allow heavy Thu Ngt rains to taper by dawn Fri, tho clouds will linger.
A tremendously challenging forecast continues right thru the weekend as so much depends upon shortwave timing. My take on the timing of all of this has changed little over the past few days, largely thanks to an accurate forecast of the longwave pattern by the Ensemble means, and the ability to apply operational timing to these means. Of course, that doesn't mean the forecast is going to be right...only consistent in timing. That also doesn't mean that the forecast has been equally consistent in temperatures, which I've had to bring down in the short term...delaying the brief Southern NewEng warmup until later in the weekend as the placement of the baroclinic zone has come farther south in the next few days, owing primarily to strong confluent flow staying just slightly farther west than originally progged.
With NVA and low level Canadian air spilling in thru Nrn NewEng and inching into Srn NewEng, enuf drying shud take place to significantly erode low level cloud deck on Fri with warm advection at 700 mb and up still producing at least a BKN mid-level deck, but the bottom line is that some sunshine is likely, which will help to warm a cool boundary layer somewhat. Next shortwave is in for Fri Ngt, and again, showers will result largely thanks to mid-level isentropic lift, tho once again NVA and drying low level air will assist in bringing sunshine out for a time. With expanding sfc anticyclone on Sat extending from extreme Ern Canada to waters S of NewEng, frontal boundary will be pushed SW of NewEng for most of the day which is a big reason why I mention that while shortwave timing may be similar, placement of low level baroclinic zone has resulted in fcst chage, as obviously we're not going to get the chunk of warmth and humidity in here for Sat afternoon. Instead, warm thrust returns in two installments with the first coming back into NewEng later Sat. With strong amplified shortwave riding overhead on Sat, at least some shower development will have to occur Sat, tho unlikely to be as formidable as I thought yesterday given that less instability will be present in Srn NewEng. Northern NewEng will transition back to mid-level WAA and PVA Sat Ngt, when a renewed stripe of precip is possible in the North Country. Now, return flow looks to establish on Sun and have pushed warmth for Srn NewEng to this day ahead of approaching bowling-ball upper low and attendant strong sfc low pulling NE across Great Lakes. Sandwiched between 1028 high SE of Nova Scotia and 1000 mb low on Ontario/Quebec line, gradient is going to tighten enough for a windy day of warm transport into most of Central/Southern NewEng, tho Nrn New Eng may be harder pressed to erode low level deck.
Though 12Z GFS is trending even slower with the incoming shortwave for Sun Ngt/Mon and keeping some of NewEng dry and prefrontal until Mon eve, Ensemble means and most other operational guidance still brings rains in Sun Ngt into Mon as incoming trof will eventually slow and go negatively tilted in response to stronger vortex over Hudson Bay, though that interaction shouldn't take place until later Mon...after it has passed us...at which point those two shortwaves will help to pull the longwave trof east of New Eng.
The extended pattern, however, brings southern stream ridging westward, and this ridge bubbles northward over the Rockies by the start of September, and the downstream response is for longwave retrogression of the trof to a position back over the Western Great Lakes and Western Ohio Valley...leaving the Eastern Seaboard open to the tropics. By the second week of September, additional energy dumps out of the polar vortex into the trough developing off the Pacific coast, resulting in a downstream amplification of the ridge-trough couplet from the Rockies into the Ohio Valley, thereby continuing the open feed of the tropics to the East Coast. The bottom line of all this is that I'm quite certain from all indications that we will have half of the first month of September - a peak time for hurricane development - in which the longwave pattern leaves the entire Eastern Seaboard quite vulnerable, and as meteorologically inclined folks, we should be very much aware and on-guard. I'll, of course, continue to share my thoughts as we go along.
Enjoy your day.
Matt
Tuesday's Discussion:
2:20 PM: Tuesday afternoon/eve shortwave is driving cold front southward thru Quebec en route to North Country where well developed Cu line ahead of front has been migrating east out of Nrn NY. Diurnal instabililty will help to expand activity east with CAPE over 1000 J/kg and LIs to -4. Even with this sfc based instability, there is plenty of dry air aloft and that will fight development of more widespread convection, tho line segments certainly are a possibility along the low level convergence zone. Though the mid level forcing does push south into Srn NewEng Tue eve, and this may carry a few quickly weakening showers with it, instability will be waning by that point and dry air is abundant below and above max lift at 700 mb and this won't favor survival of the convection.
Result should be a quiet night with clouds gradually shrinking and front with weak wind shift settling slowly southward. This should create a decent difference in overnight min temps from widespread 50s and some 40s north to 60s south.
With such dry ambient atmosphere, sunshine will quickly work on lingering warm air in Srn NewEng Wed AM to boost temps to around 80 while low level cold advection will hold temps down across the North. We've seen no post-frontal precip with this front in Canada and I don't see much reason to expect any tomorrow, so key to landing area of precip threat is landing where front stops, and the trend has been farther north on especially the E side. 12Z cycle of NAM tries to develop wave along frontal boundary in Ern MA, and given superior handling of low level airmasses with high resolution, it makes sense to keep at least chc shra/tsra in for most of Srn NewEng Wed afternoon, tho not expecting action in Western MA, Ern areas will exceed 1500 J/kg CAPE.
Passage of Wed shortwave shunts front southward and Thu bubble high will not only bring cool Canadian air but also will turn winds onshore many locales which will contribute to cool afternoon for all. One shortwave will bring warm advection overhead late Thu and Thu Ngt which should produce precip as isentropic lift occurs over cool dome, especially Thu eve and night. With the general pattern of synoptic warm advection and a parade of shortwaves, timing of rainfall will be dependent upon timing of shortwaves, which always becomes clearer the closer we draw to the forecast period in a fast flow, and that timing looks like a break to start Friday but another shield of precip later and into the night. Still, of course, subject to adjustment dependent on how the timing shakes out.
Overall, though, keep in mind that this is part of a transition to warmer air and the process allowing for the repetitive rains is in fact the advancement of the deep summer warmth and humidity from the southwest. Eventually, this warm and moist assault will erode the southern edge of the cool and dry Canadian airmass and Southern NewEng should be back into soupy air on Sat, tho given confluent flow over Nova Scotia at 500 mb thanks to the broad trof over the Canadian maritimes, I have trouble believing we can blast this warmth into Northern NewEng, where overrunning showers are likely to continue periodically with plenty of clouds and resultantly cool temps. Another in the parade of shortwaves should touch off thunder in Southern NewEng later Sat. By Sun into Mon, extremely strong bowling-ball upper low moves E from Upper Great Lakes and thru NewEng, and this sets the stage for a heavy rainfall event in that time frame. Ensemble means have remained in excellent agreement on heavy amounts with this event, tho timing has trended slightly slower, largely owing to strength and amplification of the incoming system.
Tropics: The tropics have been heating up recently, as well, and while I've been less attendant to the tropics in this technical discussion this year contrasted to last, it's largely because there hasn't been a great deal to speak of that I felt was worth putting so much time into. Thinigs are changing quickly in the Tropical Atlantic, though, and I think the East Coast of the United States will be in a precarious position for the coming weeks - especially the Southeast and Mid-Atlantic coastlines, but NewEng is always just one good shortwave interaction away. Let's set the stage first, which is that we've seen very little action thus far in the Atlantic, owing to a combination of factors led by an over-abundance of dry air in the Western Atlantic and the Caribbean, leaving deep moisture confined to the intertropical convergence zone, where storm development is very difficult to achieve. There also has likely been at least a week feedback mechanism with the Eastern Equitorial Pacific, which, as mentioned in this discussion a few weeks ago was showing El Nino indications with a warm tongue of sea-surface temperatures extending west off the coast of South America and indicating a weakening in the Equatorial Pacific trade winds. This anomaly, though present, has weakened since that time. Additionally - and this is not a scientifically tried and tested fact - but the negative PNA (Pacific North America Pattern) of late has favored higher pressures over the Caribbean, Western Atlantic and Southeastern US, and this of course is not conducive to tropical development, but the PNA is forecasted to reverse in the coming week and last as positive into the beginning of September. Again, no statistical correlation here, just something worth keeping an eye on. Sea surface temps are doing well across most of the Atlantic with 1-3 Celsius anomalies except in the Eastern half of the Atlantic, where temps are slightly below normal. The overall pattern in the tropics feaures the semi-permanent Central Atlantic ridge though a few mid-level troughs are found on its periphery - one near 30N/60W, and the other near 18N/38W. Of course, given the location of TS4/Debby just southwest of the Cape Verde Islands, it is the latter that is important in the forecast of current tropical activity. This mid-level low is not reflected in the upper level wind structure, but is introducing a definite southwest shear ahead of TS4, and the models are unanimously keying in on this SW shear to push the cyclone on a northwest course consistently. I'm not sold on this for a few reasons, aside from simply the fact that the Atlantic ridge is located to the north. Part of my other problems with this is that the mean layer wind flow from the mid-levels to the surface...essential in steering a thus far shallow storm like this one...are from northeast to southwest, then virtually due west around the Atlantic ridge. This knowledge, combined with analysis of water vapor satellite imagery, makes it hard for me to bite into the guidance idea of carrying the storm blindly NW. Rather, it's entirely possible that the storm continues WNW for 24-36 hours, encountering the envelope of little shear that lay just to its west as of this writing and strengthening steadily until encountering the SW shear, which rather than alter course significantly would instead shear the top of the storm, disrupting outflow, weakening the storm, but not turning it far off of a WNW heading. What this means for the long-term future of the storm is questionable, especially since the mid-level trof is forecasted to only slowly decay while moving west - in other words, how long could the cyclone survive continued shear? Eventually, the upper low will interact and decay with the former trough currently to its west, but that will take days to occur and SW shear will remain ahead of the cyclone for several days, which is a long and hard battle for a cyclone to survive. So, my take on the cylone is that she has a long and unlikely battle to win, but if I've misjudged the motion of the low level center and indeed the SW shear pushes her more NW, she will ride north of the shear and therefore have a more fruitful existence for the time-being, though she'll be more subject to shortwave influence later down the line.
This isn't the end of fun in the tropics, however, as another wave moving across the Windward Islands also holds promise. This wave doesn't look tremendously well organized at present, but it's moving into an area of low shear and a general westerly steering flow. While TD4 takes the show for now and keeps the attention of many, this wave has the potential to make far bigger "waves" in the meteorological world if it can capitalize on the increasingly favorable atmospheric conditions. Ahead of this wave, convection has been limited due to negative 500 mb theta-e anomalies, but a lead tropical wave moving into the region should help to modify the airmass while shear continues to decrease and this all should prime the region for the wave currently approaching the Windwards. The big challenge should this thing develop will be to track...with the FSU MM5 moving the system due north as it interacts with the upper trofs mentioned earlier, the Canadian slams the Yucatan with a strong hurricane and the GFS lay in the middle with what is a more reasonable solution. I'm not sold on the northward MM5 track given that I think the separation will be sufficient from the decaying upper trof to avoid pulling the wave north, and the westerly steering flow is strong and forecasted to weaken but remain moderate. This would lead me to believe a more WNW track for at least the time-being.
Finally, a strong wave over Central Africa will emerge off the African coastline a la TD4 in a few days time, but this time there will be no upper trof awaiting it in its path, and the potential for growth - and especially sustained growth - will be better than it has been/looks to be for TD4.
All the while, the Ensembles are showing an eastward shift in the longwave trough over the next 10 days as the barrelling shortwave on Sunday/Monday that brings our heavy rain helps to nudge the trof east. This does create a weakness in the trough off the East Coast during that time period, but with the trof axis so far east it's unlikely we'd have much to worry about in the upcoming 10 day period here in NewEng. Thereafter, however, new shortwave energy begins digging into the midwest, which allows for longwave trough retrogression in the northern stream, while the Atlantic ridge expands westward and rebuilds toward the SE US coastline, forcing the ridge weakness closer to the coastline. The bottom line of this pattern evolution is that just as the tropics heat up, the East Coast is left in a precarious position for the start of September...
That's all for today.
Matt
