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:
Tuesday will bring our final day in this stint of summer weather, and though cooler autumn weather is on the way, we'll have to get through a somewhat wet and bumpy transition that will persist from late Tuesday through Wednesday.
The stark contrast in weather from the beginning of the week to week's end comes with the very same disturbance at the jet stream level that brought snow this weekend to Alberta, Canada, and held maximum temperatures at only 50 degrees in parts of Michigan on Monday. As this disturbance moves east - driving an attendant cold front at the surface - warm air in place across New England will be overturned, and rainfall will be the result.
Before these changes begin in earnest, though, most of New England will enjoy another fine summer day on Tuesday. Though many areas begin the day with clouds and areas of fog, the clouds in most places have only been a few hundred feet off the ground and only a few hundred feet thick. With drier air aloft, these clouds continue breaking up and another mild day of sun and clouds is expected, with an exception found in parts of Central and Downeast coastal Maine, where clouds will linger for quite some time today. The combination of sunshine and a southerly wind will push temperatures back near and above 80 degrees for many communities, however, with showers and rainfall only gradually moving east out of New York State. The first areas to see rain will be northwestern Vermont, but by mid-afternoon, most of Vermont will find showers and a few embedded thunderstorms around, and this should spread into Western MA and Western CT, approaching Springfield and Hartford, by 5 PM. Farther east, a dry day is expected in advance of the approaching cold front.
Rain and thunder will arrive in Eastern New England by 9 or 10 PM, and in Central and Eastern Maine after midnight. Yesterday I mentioned that satellite imagery the last few days has shown an area of low pressure twirling east of the Carolinas by a few hundred miles, not completely tropical in nature but certainly infused with at least some tropical moisture. This moisture will slide northward and a chunk of it will help to feed rainfall with the passage of the cold front, and rain will fall heavily at times overnight Tuesday night, with an inch or more of rain likely in most of the heart of New England. Heaviest rainfall amounts will likely be recorded in Eastern New England during this period of rain, which will linger into at least part of the day Wednesday.
Though steady morning rains in eastern areas will taper to scattered showers found primarily in the hills and mountains, and across Eastern Maine, clouds will stick around and winds will increase during the day Wednesday as cooler air pours in behind the cold front. This autumn air will be especially evident by later Wednesday afternoon, and temperatures will only rise into the upper 60s in most areas - some 10-15 degrees cooler than Tuesday.
Chilly air will be in place for a brisk Thursday, when higher terrain of Northern New England will hold in the lower and middle 50s, while some Southern New England locales struggle to break 60! Nonetheless, sunshine will be with most of New England Thursday, though a few puffy cumulus clouds may build tall enough for a few showers in the hills and mountains of Northern New England. Friday brings continued cool temperatures, though the gradual return of warmth aloft will come with a gradual increase in clouds and a chance of a late day shower in Northern and Western New England later in the day, though I'm not expecting these to amount to much.
The upcoming weekend isn't looking all that fantastic right now, largely because another strong upper level disturbance will eject east out of the Rocky Mountains and across the Ohio Valley. The counterclockwise flow of air around this system will once again tap tropical moisture from the Gulf of Mexico, leaving an efficient rain-maker headed for New England. There are questions about the timing of this system...with a surge of warm and moist air taking aim on New England for Saturday, but the energy driving this system lingering well to our west, this would appear to favor more clouds than sun, perhaps a few showers, but heavier rain holding off until the main chunk of energy could swing through Saturday night and Sunday. Behind this disturbance, another shot of cool air will settle in for the beginning of next week.
In the tropics, Hurricane Gordon continues moving east across the North Atlantic directly toward the Azores, and is no threat to America. Hurricane Helene, however, is over the Tropical Atlantic and is the second major hurricane of the 2006 season. She is moving west-northwest at present, and will be watched for a time to come, though the trend is certainly to recurve her out to sea, east of Bermuda.
Matt
Matt's Technical Meteorological Discussion: Updated Tuesday, September 19 at 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
