Welcome to the weather blog - a regular Monday through Friday discussion of the weather! You'll find a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow. If no technical discussion is available when you check in during the morning, check back later as it often comes after the Weather Summary - I try to indicate at the end of the general weather summary when/if a technical discussion is coming. My email is contact@mattnoyes.net. While the discussions usually will only come on days I'm working, I'll occasionally issue special updates when the weather warrants. This blog is for you, so I hope you enjoy it! -Matt Noyes
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Matt's Weather Summary: Tuesday dawned with a blend of mountain clouds, sunshine and widespread black ice, though with the help of sun and a light southwest wind, temperatures will rise above freezing in most communities during the afternoon. While the day will be quiet, the atmosphere is in a state of flux. A strong disturbance dropping through South-Central Canada is racing east-southeast toward New England, and is strengthening as it makes the trip. This upper level storm - a strong bundle of energy driven by the jet stream winds aloft that steer our storms - will bring with it plenty of cold air thousands of feet above our heads. At ground level, however, cold air will be lacking, and by later Tuesday, this difference between warm ground and cold sky will begin to manifest itself as a developing area of low pressure at the surface over the Eastern Great Lakes, poised to drag an attendant front across New England Tuesday night.
Expect clouds to build later Tuesday afternoon ahead of the storm, and as the cold air associated with this system high in the sky moves overhead, snow showers and heavier snow squalls will develop from west to east across New England Tuesday evening and night. Some of these squalls will drop a quick couple of inches of snow, and will create some snow-covered and slippery spots for Wednesday morning's commute. Though there's not a lot of moisture forecasted to fall with this disturbance, the cold air aloft combined with warmer air in the lower levels of the atmosphere will be the perfect setup for big, quickly accumulating snowflakes, which will allow fluffy snow to pile up quickly. Please see accumulation maps at the bottom of this discussion for forecasted amounts by Wednesday 8 AM - NOT including Wednesday snowfall (read on...).
Wednesday's forecast is a tricky and intriguing one - as it features an attempt to match an upper level pattern and surface pattern that just don't seem to go well together. By that, I mean the upper level pattern is a cold and wintry looking one, while the surface pattern will remain rather mild and allow temperatures to rise into the middle and upper 30's. When we see a mismatched atmosphere like this, the result is always that air has to move - either horizontally (wind) or vertically (clouds and precipitation). In this case, while localized breezes may be gusty, a large amount of the atmosphere's energy will likely go into creating scattered snow showers and heavier snow squalls. In addition, the front that will have swung through New England Tuesday night will be stalling on top of us and beginning to fade - but still helping to focus precipitation as it extends from the White Mountains to a developing area of low pressure in the Gulf of Maine. With relatively mild air at the surface and cold air aloft, plenty of "instability" - favorable conditions for clouds and precipitation - will be in place across New England, and this dying front will act as an infrequently seen "Norlun Trough" - a disturbance that can create localized bands of persistent accumulating snow along them - specifically from South Coastal Maine to South Coastal New Hampshire on Wednesday. In these locales - and, of course, we'll need to monitor this closely for Northeastern MA - we'll find additional accumulations of snow through the day Wednesday and total storm accumulations of Tuesday night and this extra snow Wednesday may exceed half a foot anywhere between Portland and Salisbury - wherever this localized band of snow sets up. Elsewhere, snow showers will continue to bring scattered fresh coatings through the day, which may keep some roads slippery even after recovering from the early morning snows.
With a persistent flow of northwest winds Wednesday night - and a steady stream of disturbances caught in the jet stream winds aloft, diving from Canada and settling into the slow and energetic disturbance that will be prodding east of New England - cold air situated in Central Canada will finally be tapped, and begin to charge southeast. By Thursday morning, expect the cold air to be moving into place here at ground level, as it catches up with the precursor wintry cold pattern aloft. Most of Thursday will bring lots of clouds, some sunshine, and scattered snow showers with an active northwest wind.
The workweek rounds out with a blend of sun and clouds for the daylight hours as New England finds ourselves sandwiched between the large and energetic storm departing slowly to our east, and a new bundle of energy the jet stream winds will be driving in our direction from the Central Plains. This new disturbance will spread clouds and precipitation over New England Friday evening and night, as a slug of warmth and moisture riding northward in the counterclockwise airflow around this approaching disturbance clashes with the cool air that will already be in place in New England, resulting in a period of Friday night snow and rain.
The upcoming weekend is likely to begin rather benign on Saturday, but will feature a stronger storm developing to our west, and likely moving into New England by late Sunday and into Monday. This one may be a moisture-loaded system, and there are still large questions looming on how quickly a cold front situated north of New England plows through - if it comes through soon enough and before the storm, we'll be talking about an accumulating snow event, which is a real possibility, so it's one I'll likely focus on more as the week progresses.
Make it a great Tuesday.
Matt
Matt's Technical Meteorological Discussion: Updated Tuesday, January 24 at 1:25 PM
Inversion well established Tue AM across NewEng will have an uphill battle to mix out with very little wind as sfc ridge moves overhead. Diurnal heating will create thermals and help to create some mixing, though fresh snowpack will limit these effects as well, and have gone close to NAM MOS for today's temps...well below GFS MOS numbers.
SW wind picks up a bit later in the day ahead of extremely impressive vortex dropping across the Great Lakes. Satellite presentation is excellent with this upper level disturbance and spokes of abundant energy have been interacting with low level moisture - some lake enhancement, too - to create bands of convective snow across the Great Lakes. As this upper level low pinwheels east, a tremendous amount of vorticity and associated upper level cold pool will migrate over NewEng tonight thru Thu, and this will bring truly intriguing weather across all six states. The best way to think about just how crazy this weather is going to be is to realize that the upper and lower levels of the atmosphere simply aren't going to match up beginning tonight - that is, 500 mb temps to -37 C (truly winter air) moves in aloft, while 850 mb temps closer to -8 C and boundary layer temps in the +0's C are going to make for a tremendously steep lapse rate in the lower and middle levels. As an example, 850 to 500 mb temp diff described above brings widespread lapse rates of 7.7 C/km beginning Tue ngt and lasting thru Wed. As far as the atmosphere goes, this is a powderkeg of instability.
Surface reflection of upper level storm moves east into Tue Ngt and thrusts associated occluded front east thru NY state Tue eve and into NewEng mainly after midnight Tue Ngt from W to E. Normally in a situation like this, one would expect to see an arctic front driven in association with a disturbance of this magnitude, but the abnormal warmth of Central and Western Canada has prohibited a strong release of cold air, and instead the deep cold that was in place over the Upper Midwest on Monday has been thrust northeast into Eastern Canada, and while it will be available to pull down by the end of the week, that will only come after persistent NW and Nly flow tugs at it long enough. In the meantime, it's a rare and meteorologically active combination of cold air aloft and energy normally associated with the leading edge to an arctic outbreak, but we're going to sit it on top of an airmass that's still abnormally warm and moist. There are two basic parameters that govern meteorology that we learn about early in meteorological coursework - one is airmasses, and the other is energy. In this case, we have a vertical clash of airmasses, AND we have plenty of energy. Not just cyclonic vorticity advecting in, but also the energy present through the warmth and moisture in the lower levels. This will create a tongue of CAPE (convective available potential energy) in Eastern New England, and eventually that will be an important ingredient in what may wind up being a localized snowstorm for Southern Maine, Coastal NH and perhaps extreme NE MA...more on that below.
But first we need to tackle the cyclonic vorticity advection and attendant occluded front for the overnight. QPF amounts that were varying between guidance have come closer in line with a general .10-.25" of QPF expected for overnight Tue Ngt, and this looks reasonable given: a) upstream activity, b) amount of energy involved, c) warm and moist Theta-E tongue and positive theta-e advection that occurs ahead of trough axis. But caution must be exercised here by meteorologists and weather enthusiasts alike. Greatest upward vertical motion coincides nearly perfectly with a thermal profile favoring dendritic crystal growth in the midlevels, followed by subfreezing but sufficiently warmer temperatures in the lower levels for aggregates to develop as dendritic crystals will develop sticky ends and form large, quickly and nearly ideally accumulating snowflakes. The ratio, therefore, is likely to be closer to 18 and even in some spots greater than 20:1 with this event - excepting Southern CT, Providence, RI to Duxbury, MA, points south where profile warm enough for mix or even all rain event. Elsewhere, fluff factor to be an issue, but equally important and not to be overlooked with this event is the intensity at which snow will fall. The rate of snow will be for these 2, 3 and 4" amounts to fall after midnight Tuesday night - and in most areas during the predawn hours. This will be too fast for road crews to keep up in many areas, and it will take awhile to catch up.
This occluded front begins to lose its frontal characteristics during the day Wednesday as it encounters easterly flow ahead of it around a developing low pressure center over the Eastern Gulf of Maine. But what this occluded front does not lose is its ability to enhance low level convergence. Feeding off the available CAPE, and interacting with the very steep lapse rates, this setup will favor the development of a Norlun Instability Trough. These events are notorious for providing an outlet for available CAPE by creating a path of surface and low level convergence, and with moist east and northeast flow ahead of the trough, most often the heavy precip will occur along and east of the trough axis. As mentioned above, profiles will favor quickly accumulating snowflakes with high ratio, and given the amount of deep instability in the atmosphere, I wouldn't be surprised if model QPF is too low - at least in the case of the NAM...the GFS with .75 to 1.0" under the center of this band is probably closer. Coupled with high ratios, I don't need to tell you the amounts this could result in. Now is when the difficult part comes into play - placing the band. I've seen these events work out wonderfully, and I've seen these events end up verifying beautifully just 20 miles offshore where the fish get a great snowstorm. The trick here is from a scientific perspective is to key in on where the synoptic scenario would favor placement of the trough, and from a broadcasting/public dissemination perspective the key is to leave the door open for surrounding areas and afford the public the opportunity to know there's going to be some high intensity snow that will persist through most of the day, but uncertainty is present and this MUST be conveyed to the public given the high stakes to the forecast. The best position estimate is to line the trough up under the upper level low as the surface weakness will be driven by the upper level cold pool resulting in enhanced vertical motion, and this should lay across the NH seacoast, placing the persistent band of snow from the north shore of MA through the South Coast of ME. Heaviest amounts under the band should total over 6", and if all plays out right it would be much higher than that, but there is a great risk to the forecast with the public if this thing goes offshore, so the best bet seems to be to hit that over 6" mark and convey the point that it will be a significant event without going overboard.
Elsewhere, scattered snow showers and heavier squalls are just about a given thanks to the lapse rates, upper low and available surface moisture and warmth. Icy road conditions will recur during the day as a result. Some mountain locales will continue to pile up signficant amounts, but this will be largely orographically and convectively driven and are nearly impossible to pinpoint.
Cold air will finally be on the move at the surface Wed Ngt, though now even slower in the progs and just ready to move into Northern NewEng Thu AM. I haven't raised temps yet as cold advection does begin in earnest Thu AM and falling temps thru the day not impossible, tho I'll likely have to bump temps up just slightly tomorrow.
Cold stays with us on Fri as ridge prepares to crest overhead, then behind ridge axis I'm still carrying clouds and chance light precip Fri Ngt as warmth returns aloft along with weak vort embedded in the flow. Behind this, it makes sense to bring warmth back in on Sat - there is an impending arctic front pushing toward NewEng but agreement almost across the board favors bringing this front thru later Sat or Sat Eve so will follow this solution appropriately and bring increasing SW wind Sat to help boost temps up ahead of frontal boundary, then cold air arrives Sun.
This sets up a quandry for Sunday/Monday, doesn't it, when next storm is set to move thru and question becomes to rain or to snow? My take on it is that we're dealing with a well defined shortwave trough that comes thru in NW flow Sat. Though the trough will naturally deamplify as it encounters confluent flow, the air behind it is cold to the tune of -15 to -18 C at 850 mb. I don't think we'll see a direct transfer of this air behind the shortwave, but an 850 mb ridge builds over Hudson Bay Sat Ngt into Sun AM behind this trof as it moves over NewEng, and this should serve to enhance northwest flow urging cold air to filter southeast toward NewEng. Therefore, right now I'm thinking the push of cold will be a bit deeper and colder than forecasted currently. Not A LOT deeper and colder, but enough so that the next storm for Sun eve into Mon is going to be a snowy problem at least to start for Southern NewEng before a changeover, and likely a mostly snow event for the mountains. The next few days will, of course, be crucial in determining just how cold that Central Canadian air will be, and whether my idea of carrying deeper cold will be fortified by successive model runs.
That's all for today. Good luck with your forecasts.
Matt
