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
Wednesday Podcast: Issued
General Weather Summary:
After reaching over 50 degrees in some of far Southern New England on Tuesday, and holding at a high temperature of 10 degrees in Northern Maine - a remarkable spread of 40 degrees that was most evident in the spread of temperatures between Southern New Hampshire and Northern Massachusetts. Wednesday's temperatures won't feature such a dramatic spread, but still will vary considerably from south to north.
This variation in temperature comes coutesy of a stalled front - a stationary front - that's draped from the Northern Plains through the Upper Great Lakes and all the way into New England. This front is dividing arctic air to the north from milder air to the south, and also is co-located with the jet stream winds aloft. As explained in my discussions often, the jet stream is a fast corridor of wind aloft that steers our storm systems and acts as a thermostat for the atmosphere, separating cold and warm air. Riding these jet stream winds across the Northern Tier of the U.S. on Wednesday morning is a very energetic disturbance and its associated surface storm over North Dakota. Though this system is racing east, it will not arrive to New England until Thursday afternoon through Thursday night. In the meantime, Wednesday brings quiet weather with a light north wind only very gradually carrying colder air southward. This drain of cooler air will mean temperatures don't quite make it to the 50 degree mark they hit in far Southern New England yesterday, but more breaks in the clouds across the Northern reaches of New England will actually help to mix the atmosphere a bit, and thereby warm temperatures more than Tuesday's values in the north. Though sunshine will be abundant south, there will be enough moisture in the lowest few thousand feet of the atmosphere for numerous clouds in Northern and Western New England, especially with heating of the land Wednesday afternoon.
A quiet night Wednesday night will yield some early morning sunshine on Thursday, followed quickly by advancing and thickening clouds. These clouds come quickly in advance of the same disturbance moving across the Northern Plains as of this writing, trekking east so fast it will already be located in Southern Ontario, by Georgian Bay, early Thursday morning. Snow showers and flurries will likely precede this disturbance by mid morning for northwestern New England, while the remainder of the area finds temperatures warming slowly into the middle and even a few upper 30s before precipitation spreads southeast across New England thanks to a combination of weak early sunshine with a milder flow ahead of the incoming storm. Though mild enough to begin as a mix of rain and snow, or even mostly rain for some parts of Southern New England, on Thursday afternoon, the airmass should be dry enough to cool as precipitation falls into it, allowing a transition to mostly snow in many locales by Thursday evening and Thursday night. The question is: just how much snow we can anticipate? While this disturbance is going to be quite strong, and carries a great deal of energy, it will accelerate rapidly from the Upper Great Lakes to a position near Cape Cod from early Thursday to Thursday evening. This rate of forward speed is very quick, and favors what's called a "center jump" at the surface - that is, because the surface low pressure center can't move at the same pace as the upper level energy, the first is left behind as another forms ahead of the energy, in this case near Cape Cod. This usuallly results in a precipitation minimum under the area where the "jump" occurs, and in this case that looks to be right here in New England. Still, the combination of available moisture and energy aloft will yield at least a period of precipitation from Thursday afternoon into Thursday night, and there will be enough energy to crank out bands of fairly intense precipitation at times - snow for many but rain in much of Southern New England to start, then switching to snow that may fall at a healthy rate for a time. Nonetheless, the shear speed of the system is what's likely to limit accumulations to a few inches in even the hardest hit areas as a result of the fast forward speed. A few factors that could still change this would be a slower speed, which looks unlikely, and certainly mountains and hilly terrain can result in locally higher snowfall totals. The final characteristic to watch will be the possibility of a lingering "trough" behind the storm that would keep snow lingering on Cape Cod later through Thursday night, but that, too, looks rather unlikely at this point.
Behind this disturbance, another shot of chill will pour south for Friday - much less intense than it's Monday counterpart. Thereafter, a stronger storm will develop over the Central United States in response to a digging jet stream "trough" coming east from the Western U.S. Remember from past discussions that these troughs represent dips in the jet stream where cold air penetrates southward, and often can breed storms along the battlezones of protruding cold air with antecedent warmth. This will be the case over the Mississippi River Valley next weekend, and with a storm track to our west and counter-clockwise flow of air around the storm, warm air will surge northward along with Gulf moisture, meaning snow changing to rain is the most likely precipitation type for many of us by late Sunday, though perhaps not for all. Regardless, that would come after a gorgeous winter Saturday, perfectly designed for winter sports under sunshine and slightly below normal temperatures. By Sunday, expect sunshine early, then increasing clouds with a wintry mix likely to develop late in the day. In Southern New England, any snow or mix would likely change to rain given the aforementioned storm track. One caveat that makes it less cut and dry (or cut and rainy, in this case) is the likely development of a secondary coastal storm south of New England. As this storm develops Sunday night into Monday, its counter-clockwise flow would help to turn winds from the north across Northern and perhaps Central New England, and this would raise the chances for snow rather than rain. So, snow lovers in Northern and Central New England get a couple of inches with this Thursday's event, then should keep fingers crossed for Sunday night and Monday!
Technical Discussion: None today.
Matt
Matt's Technical Meteorological Discussion: Updated Tuesday, February 20 at 1:55 PM
Amazing sfc temp contrast across NewEng today as boundary layer thermal gradient encourages isentropic lift to perpetuate clouds in lowest few thousand feet across Central/Nrn NewEng while sunshine has broken out for a time in warm sector across Srn NewEng. Used low level thickness fcst combined with early AM temps that were already near 40 to put fcst into the 40s for Srn NewEng. The tight baroclinic zone comes as cold dense air remains locked in place across Nrn and esp NE NewEng, preventing mixing and promoting lift. Shortwave heading for NewEng tonight is producing active CG lightning strikes over IL this afternoon and will produce convective elements over NewEng overnight Tue night. Doubt we'll be looking at any lightning, but healthy convective downpours that will quickly incorporate big, fat flakes esp as the shortwave axis swings thru and we capitalize on cold enuf air thru all levels but the boundary layer, which will cool evaporatively, dynamically and thru advection late tonight. The result will be a setup for some black ice in Srn VT/NH/Nrn MA, tho the strip affected by this will probably be rather narrow because farther north it's been cold today and farther south it'll still be above freezing Wed AM.
The remainder of Wed looks relatively quiet tho high RH progged in the lowest 100-150 mb has me on guard for widespread cold advective stratocu in esp Nrn/Central NewEng, broken up by downsloping flow and less intense CAA farther south. Our next shortwave will be compact and very impressive as it moves across or just north of the Upper Great Lakes. The problem for NewEng snowlovers is what it does thereafter. If this thing simply turned southeast and held its integrity, we could try to wring something decent out of it. Instead, it's going to become caught in very fast northwest flow over NewEng - confluent flow between the upper low north of Nova Scotia and the ridge axis over the Southern and Central Plains. This very fast motion will not only degrade the compact nature of the vort by stretching it out, but also will increase the speed of the compromised vort. The former means that vorticity advection will be channeled, and not coming tangential to the geostrophic flow, thereby creating a limited duration and areal scope of dynamic lift. The latter means an even more limited duration of CVA/PVA, thereby favoring a center jump scenario where the Srn Ontario low dies as the energy prompts new low development over Cape Cod, but in between we get a relative precip min. There are two factors to watch: 1) Confluent flow is less intense, meaning the vort maintains more consistency and a more favorable speed - this would increase the intensity and duration of squally bands and clusters, and 2) When the vort prepares to gather itself and surface cyclogenesis results, it does so a bit farther west or a bit earlier in the game, or slows a bit earlier before moving east, this would give more time for an easterly flow to develop in the lower and middle levels, thereby allowing enhanced snowfall earlier in the game. Though this doesn't appear highly likely, it is one thing to watch.
Cold air streams south on Friday with active wind and good mixing but enuf cold air aloft for instability Cu and snow showers in the mountains. Though the weekend starts quiet, Sunday brings warm and moist advection and good agreement on a spike in 850 mb temp anomalies that should mean snow changing to rain for most areas unless we can find a way to get lingering confluent flow aloft to hold in low level cold for some Northern locales. Doesn't look great right now, but there is plenty of antecedent cold, which means all we'll need is a weak bubble sfc high to hold it in for snow in the North Country - so enjoy this stretch while it's here, but don't give up all hope on pulling some snow out of Sunday/Monday system.
Have a great Tuesday.
Matt
