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:
Autumn air has taken hold of New England and will remain in place through the end of the week, while returning warmth spreads showers toward New England over the course of the weekend.
In the meantime, though our Thursday morning began cool, it will be considerably milder than I'm expecting Friday to dawn as. Nonetheless, cool air has moved in both at the surface and aloft, and this autumn airmass will hold temperatures in the 60s in Central and Southern New England, and only in the 50s across the North and higher terrain! With such cold air just a few thousand feet off of ground level - below freezing at that altitude - cold puffy cumulus clouds will develop across New England Thursday afternoon, and a few of these clouds will grow tall enough to drop a few rain showers over the hills and mountains of New England Thursday afternoon in conjunction with an upper level jet stream disturbance moving over Northern New England during the day. Otherwise, expect dry but brisk conditions with an active northwest wind.
The active wind comes ahead of the center of cool Canadian air - a high pressure center that turns air clockwise around its center, keeping a northwest wind direction to continue the feed of cool air into New England right into Thursday night. These winds will ease through the overnight, however, as the center of the fair weather center slides from the Eastern Great Lakes to a position south of New England, and the decreasing winds will combine with clear skies and dry air to send temperatures tumbling...low enough for a hard freeze in deeper valleys of the north, a frost in most of Northern New England and in the valleys of Central New England (all the way into the Route 2 corridor of Northern MA), and scattered frost in only the deepest valleys of Southern New England. This will yield a chilly start for nearly all of us on Friday morning!
Once again, dry air will allow for sunshine and temperatures will respond to the combination of this sun and a shifting wind, blowing from the southwest as the center of fair weather begins to move east across the waters south of New England. The displacement of this dry and cool high pressure cell will allow for warmth and moisture to return to New England, and as is often the case with invading warmth and moisture, the new air will ride overhead first, and the result will be increasing clouds later in the afternoon and evening. In the lower several thousand feet of the atmosphere, though, enough dry air will remain in place to preclude any shower development.
The returning warmth and moisture streaming into New England will be guided in our direction by southwest winds cranking up around a couple of strong storm systems pulling from the Rocky Mountains to the Great Lakes, and the attendant counter-clockwise flow of air around them. As moisture continues to increase in the atmosphere, plenty of clouds will remain over New England on Saturday, though I expect the sun to shine through these clouds, which will begin several thousand feet above the ground Saturday morning. Increasing moisture will mean lowering clouds, however, and a few showers are likely to crop up, especially Saturday afternoon. At this point, I still don't see the showers as being numerous enough or long enough lasting to ruin the day, as most place should stay mostly dry through most of the day. The showers that begin scattered in nature will gain some organization Saturday evening and night across Northern New England, and eventually will morph into a band of rain for the north on Sunday. Farther south, scattered showers are likely on Sunday before the aforementioned band of rain settles southward into Central and Southern New England...likely later in the day and evening. Rain will fall heavily at times Sunday night, leaving lingering showers to give way to gradual clearing and a brief shot of cool air on Monday.
In the tropics, the same cold front that moved through New England a couple of days ago and brought in our fall airmass is now moving past Bermuda, and will pick up Hurricane Helene, likely sending her sailing back out to sea.
Finally, take a moment to remember the Great Hurricane of 1938 - which blew through 68 years ago today! For a link to what the Hurricane of '38 left in its wake, check out this great page from the National Weather Service in Taunton, MA!
Matt
Matt's Technical Meteorological Discussion: Updated Thursday, September 21 at 1:55 PM
Winds will abate as pressure gradient weakens with high pressure cell ready to pass S of NewEng. Sfc ridge axis will allow winds to become near calm under clear skies overnight and temps will tumble. NMM is too moist in the boundary layer - progging mid 40s dewpoints in its statistical guidance which is verifying across Upstate NY but not here in NewEng, and the combo of this drier air with decoupling will mean min temps settle much closer to the GFS min temps in the 30s for most of Nrn and Central NewEng, 40s South but 30s in deepest Southern valleys which is why I'm keeping forecast of frost in deepest valleys south and more widespread central and north. Hard freeze again in deeper northern valleys.
Fri will begin with good mixing and that will allow for quick temp rebound in conjuction with SW boundary layer wind, tho RH progged to soar at and above 500 mb during the afternoon and Ci deck should be rather thick after 16Z west and 19-20Z east, which will limit mixing for at least Central and Western areas from reaching max potential, thus have kept temps below what increasingly mild thermal profile could support.
Dirty warm sector on Saturday trending toward simply more squarely into the warm sector, though the antecedent sfc airmass will be cool and will hold onto plenty of clouds to mix with sun. Guidance has trended in the direction I've been waiting for, which is to delay significant rain until the energy driving it moves east, but will hold onto a few showers on Sat and not bite on keeping precip out entirely. Isentropic lift over old cool boundary layer dome will be the main factor, and while it's tempting to bite on a gorgeous and warm Sat, we're advecting 850 mb air some +8.5 C over the course of the day - Central NewEng, for example, warms at 850 from +7 to +15.5 C - and I don't see it possible to warm and moisten the airmass this significantly without clouds around. As for showers, scattered in Southern areas seems best given lack of dynamical focus, then most will focus on Nrn NewEng where greatest lift owing to advection will be taking place during the afternoon - as NewEng continues to transition into the warm sector.
Biggest question for Sun revolves around temp, which will depend on amount of insolation and how quickly rain expands southward across NewEng as cool frontal boundary drops south. I have trouble buying a solution along the lines of the NMM, which puts NewEng into a clean warm sector - at least Central and Srn NewEng - on Sunday with a well defined line of convection dropping SE with the sagging cold front ahead of barrelling vort max. With deep SW flow, I do believe we transition into a warm sector in these areas on Sun, I just question how much sun will be present given moist source of airmass both in lower and upper levels, so for now have kept temps and amount of insolation tempered. That said, I also think new 12Z GFS is much too dry with the passage of this disturbance, which will have narrow but effective moisture tap from the Gulf and will wring that moisture out with strong vorticity advection. Given slow southward movement of front, showers/clouds into early Mon are a possibility I'm believing in before cool and dry advection takes hold.
The next shot of cool air for early next week will be short-lived, as the parade of bowling ball upper lows continues from the active and energetic northern stream. The next disturbance en route for midweek next week is woefully under-represented by the operational GFS, as this storm should be quite impressive, carrying a chunk of impressive warmth northward ahead of it that will once again move into NewEng Tue/Wed, then an impressive chunk of cold behind it. In fact, given how strong our parade of northern stream shortwaves have been - maximizing over the Rockies this week, but shifting east with the longwave trough next week - this storm should grow strong enough to bring strong winds and dare I say wrap-around snow to its backside across the Upper Great Lakes and/or Northern Plains! The important part for NewEng also revolves around something it seems the operational GFS is missing, and that's how much moisture becomes available. An area of tropical moisture will be available over and north of the Bahamas, and most Ensemble members agree on pulling this northward up the East Coast in addition to Gulf moisture that's tapped for quite a rain event here in NewEng, and I certainly am inclined to believe this given that the trend is for slower and stronger with the longwave trof axis, and more ridge pulsing ahead of the wave, so heavy rains appear to return sometime around next Thu to NewEng.
Looking farther out, Ensemble members are also hinting at tropical development on the south side of that front by the following Mon/Tue, then possible entrainment of a westward moving tropical wave or system thereafter. Let's keep an eye on the first week of October, but more important is to not lose sight of the shorter range, which will bring plenty of action.
Matt
Wednesday's Discussions:
2:30 PM: A very quick update today as everything appears on track from yesterday. That is, rainfall has moved thru, and here were some highlights from NECN spotters:
Yarmouth, MA: 1.80", Portsmouth, NH: 1.64", Windham, ME: 1.75"
Thanks to all who contributed with amounts to weather@necn.com
As for what's to come - instability Cu continue popping with showers Nrn and Wrn NewEng and showers less likely in downslope areas tho sprinkles still possible with healthy Cu development. Diurnal effects allow Cu to die tonight but winds stay active enuf to preclude frost. No changes to my thinking for Thu, including orographically induced convection on S side of strong but channelled vort max over Nrn NewEng. Have dropped shower threat for Fri given dry boundary layer air, and have stuck to my synoptic guns for the weekend - a dirty warm sector of clouds, some sun, a few showers but a mainly dry Sat, then more widespread showers and areas of rain Sat Ngt thru Sun.
See you here tomorrow.
Matt
Tuesday's Discussions:
1:50 PM: Weak band of showers assoc with strong cold front will gain new life as it encounters increased low level moisture. A few evidences of this moisture today - from the low altitude clouds widespread early, to the lingering low level clouds that show warm and moist advection along the coast of Maine, and this increasing moisture will help to contribute to an already moist prefrontal environment for an efficient rain-producing system tonight. Will still watch potential for an isolated strong wind gust with any convection that develops in Wrn NewEng today tho convective coverage will be limited. Good to see the guidance has come in line with the synoptic setup we looked at in this discussion together yesterday, and that is to put out the most precip where synoptics and moisture intersect, and that is in Eastern NewEng. Now good agreement on 1-2" of rain in Central and Ern NewEng, with a sharp dropoff in amounts west. Interesting that this sharp precip gradient lines up nearly perfectly with the Cu lined up from Nrn ME to Central CT at midday evident on VIS imagery, which may indeed be related to the tropical envelope above ground level that is spreading north from the circulation off the Eastern Seaboard we looked at here yesterday.
I still favor a relatively slow progression, and certainly this is supported by current data. The result will be to hold onto rain in Ern areas into early Wed, then to hold lots of clouds thru the day as advertised previously. I'm aware that both operational and statistical guidance supports warmer temps than what I'm going with for Wed, but given the drop in temps with the front, the time of day fropa occurs, and the dry nature of the incoming air with little insolation expected, I'm sticking with cooler temps.
No big changes for Thu when we may see an instability shower in the hilly terrain and across the North. Model RH progs are plenty dry but midlvl temps are quite cold, esp near the Canadian border and most certainly in Nrn ME where 500 mb temps fall to -24 C on Thu! This instability, combined with orographic forcing, should favor at least some convective activity from the Greens all the way into Central and Nrn ME, on the Srn edge of an amplifying vort max. No big changes for Fri, either, when I think plenty of clouds will crop up especially later in the day as a result of increasing warm and moist advection, tho I don't see the low levels moistening enuf for precip until later in the day across the North Country.
The weekend holds plenty of uncertainty with regard to both timing and intensity of precip. The synoptic thinking laid down yesterday still holds, which is that another powerful upper low will move east out of the Rockies and across the Midwest - two, actually, as the first deamplifies while merging back into the Northern stream flow over the Upper Great Lakes, and the second is a deeper upper low that migrates from Montana to the Central/Northern Plains before heading ENE across the Great Lakes. Most of the guidance is cranking out precip - heavy at that - for Sat, but right now I think this is premature. The mechanism driving this precip in the models is clearly the warm and moist advection occurring ahead of the strong shortwave, and the longwave trof it's pulling east. While this warm and moist advection is moderate to strong, it comes thru Fri thru Fri Ngt and I could certainly support the band of showers later Fri turning into something a bit more formidable as it moves toward the Canadian border into Fri Ngt. Thereafter, however, we quickly make the transition to warmer air at 850 mb - some 4 C above normal by Sat afternoon - and it would seem with the upper energy still slow to move east that this may support a solution more along the lines of a "dirty" warm sector for Sat, with lots of clouds, only a few breaks of sun, but scattered showers as opposed to a rain, with areas farther south perhaps staying mostly dry for the day. Again, this is hard to support right now with even the 00Z ECMWF - which usually handles situations like this well - blasting high RH and precip thru here Sat and actually leaving a break on Sunday. I just have trouble lining this up with the synoptics and favor a solution simply determined by the 500 mb forecast and available moisture rather than the QPF forecast. Nearly every time, this is the way to go, so will follow that dirty warm sector forecast for Sat right now, delaying steadier rain until Sat Ngt or Sun. Cool air to follow for Mon.
In the tropics, all of the ideas shared here yesterday for Helene's potential should she break west still hold, but all guidance is now unanimous on a recurvature, so the point seems moot. The following image is a terrific look at track model guidance - track guidance plot provided courtesy of courtesy of Jonathan Vigh, Colorado State University. For more information about the graphic, click here.
Matt
Monday's Discussions:
1:40 PM: Summer eve in store followed by summer night that will bring return of fog to valleys, tho likely not as widespread as last night with slightly less ideal cooling conditions (few more clouds, slightly more wind). Nonetheless, valley fog that does develop will be thick and some patches of low altitude clouds will be present in the AM on Tue.
A few features of interest on the map that will affect NewEng on Tue - one is of course the powerful cold front driven by intense upper level energy, and the other is the circulation due south of NewEng as of this writing, off the Carolina coastline. This system will make its second pass at NewEng after bringing heavy rains to CT early in the weekend when it jogs northward on Tue, driven by increasing S wind ahead of the digging upper trough. Originally, the NMM and GFS were both trying to nudge moisture into Ern NewEng on Tue from the west side of this sys - now the timing is somewhat slower and the track a bit farther E. Nonetheless, there is certainly an envelope of tropical air that travels with this circulation, esp in the lower 15,000 feet of the atmosphere, and this high Theta-E air will allow for moderate midlvl theta-e advection on the W and NW side of the decaying circulation as it moves N later Tue. Of course, the approaching frontal boundary already comes with plenty of its own moisture as it taps broken remnants of Lane, along with both Pacific and Gulf moisture. The end result will be a very efficient rainmaker, esp as it interacts with the Atlantic tropical surge Tue Ngt into Wed. As for how the two interact, my guess is that the guidance isn't doing such a stellar job with the interaction, as the tropical envelope associated with the northward rising system is likely a bit more fluid than the models would like to make it out to be, and this may have a few implications. One result would be for a faster low level transport of the tropical air northward than is progged, which would bring low level clouds and even drizzle or showers into the mid and Downeast coasts of Maine during the day, so I'm hesitant about promising too much for Tue in these areas, tho the Srn coast of ME would likely be a different story. Another likely effect is to find more midlvl clouds than currently progged on the W side of the circulation where moderate Theta-E advection will be occurring, meaning up the Eastern MA/NH/ME Seacoast corridor. Finally, given the more fluid nature of the moisture associated with the disturbance, I'd be more inclined to expect a merger of the prefrontal atmosphere approaching from the west and the tropical atmosphere approaching from the south. This calls into doubt just how much the QPF fields can be trusted - while GFS/NMM/MM5 all agree on band of heaviest precip in Wrn NewEng, one can make a case for other heavier bands in Central/Eastern ME coast (guidance progs this in extreme E ME into Canada), and also in Ern MA/NH/Srn ME where current guidance agrees on virtually no precip, but this is where greatest precipitable water values assoc with prefrontal environment intersect with strong cyclonic vorticity advection. This goes hand in hand with the hunch that slower is better in this forecast situation, as digging trough and upper flow becoming less perpendicular to the surface front favors some slowing, and deep moisture with tropical connection favors waves along the front which would further slow it. To take this idea and put it together with the synoptic setup seems to actually favor increasing rainfall amounts east...or at least a secondary maximum east...so I'm not ready to buy into little or no precip in Eastern areas that synoptically should get a good soaking.
Also in line with a slower solution is to be cautious with Wednesday, when surface waves will still ripple, loaded with moisture, up a front that will be as sluggish to push east as the upper level trough driving it, which takes a good part of Wednesday to move thru. Am lingering rain for first half of Wed at this point, then only limited and slow clearing late for some areas. Autumn air en route for Wed Ngt and Thu means business. This is the followup to the clipper system we started watching in these technical discussions at the beginning of last week before I took off for the extended weekend (which was a great time on Cape Cod!) and together we knew this clipper would mean business. At the time, I mentioned I thought severe weather was a possibility, and while the timing of the frontal passage will cut back on diurnal instability, severe weather is still a possibility both Tue and Wed. On Tue, convection enters Wrn NewEng during the afternoon into the eve, and winds are 30-50 kts unidirectional SW up the Wrn corridor of NewEng, which will be sufficient for damaging straight line winds. Given the tropical nature of the airmass and the tropical connection in the prefrontal environment, embedded mesocyclones are a potential, as are a few bowing line segments. By Wed, one would expect a far lesser threat for svr wx given the morning rainfall, but winds are 35+ kts from 850 up along Eastern MA, where deep tropical envelope boosts even SBCAPE values to >250 J/kg. While this isn't much instability as convection goes, it's sufficient when it involves a tropical feed.
I seem to have taken a bit of a side-step from my original line of thinking on this shortwave, though, which was to emphasize the cool air behind it. This same system that brought accumulating snow to Alberta this weekend means business, and with -6 to -8 C standard deviation anomalies at 850 mb, this supports only upper 50s on average across NewEng. Adjusting for downslope flow and a super-dry adiabatic lapse rate, I've gone into the lower 60s on avg but higher elevations will certainly stay in the 50s Thu afternoon. Warm advection on Fri will be quite slow to occur, and mostly occurs late in the day into the night. This will mean another cool day of increasing clouds with enough isentropic lift for showers late in Wrn and Nrn NewEng.
The questions beyond this time frame revolve around Helene and the system in the Rockies by the end of the week. Certainly, if Helene can manage to dodge the shortwave that will try to recurve her mid-week, she has the potential to be a problem here, largely because the synoptic pattern will feature a very strong, amplified and digging Rockies vort max shooting east, but unable to make quick progress east thanks to confluent flow over the Canadian waters south of Newfoundland around the base of another sluggish longwave trough. Under this confluent upper flow will be a strong high shifting east over the waters, which - if Helene has not already made the turn - will stop her from a recurvature and force her west where she would be subject to the increasing south flow around the mega upper low coming out of the Rockies and would be a big headache for the Eastern Seaboard. Cooler heads must prevail - and are - at this stage of the game when the majority of guidance shows a recurvature with the first opportunity at midweek, but at least some members including the NOGAPS (and depending on the cycle, the GFS) are leaning toward a westward solution, having Helene miss the shortwave. For now, it's a possibility to acknowledge and one to watch carefully.
Barring this scenario from playing out, however, the Rockies upper low will trudge east for next weekend, likely amplified enough that it will slow a bit more than currently progged (hence the concern if Helene makes it thru) and bring another shot of rain - probably more formidable than the one in the short-range - as it taps the Gulf of Mexico and provides a bit more tangential cyclonic vorticity advection.
Enjoy your day.
Matt
