Plain-language summary:
A rapidly-strengthening Nor'easter will bring the heaviest snow south of region, but at least moderate amounts are still likely from southern Vermont to central Maine through Monday, while it stays dry and even mostly sunny to the northwest. It then stays modestly cold with light snow likely on Wednesday and a potential though likely not big storm Friday. A brief thaw Saturday will likely be followed by a short period of rain and snow Saturday night before turning very cold for at least a few days. It could turn milder in early March, but it could also just turn more volatile with big temperature swings and potential for storminess and even snowstorms if the cold arctic air from the north meet up with the strengthening warm and moist air masses from the south at the right time. The first chances of bigger storms are around March 2 and March 5.
Meteorological discussion:
Rapidly strengthening Nor'easter brings heaviest snow south of our region through Monday but still at least moderate amounts likely from southern Vermont to central Maine, while it stays dry to the northwest
It has been a messy weather pattern, but rather surprisingly, a seemingly relatively weak and broad upper-level low currently over the eastern Great Lakes will explode into a rapidly strengthening Nor'easter just off the U.S. East Coast tonight into Monday. With relatively weak flow aloft due to a blocking high-pressure to the north, the Nor'easter will move relatively slowly, delivering feet of snow to southern New England. It is the kind of storm that has not happened in years. However, the ever present suppressive Atlantic Canada upper-level low that is so prevalent this year will suppress the storm mainly to the south and prevent a quick turn north. It will move slowly northeastward and will likely bring at least moderate snow to southern Vermont to central Maine. However, this area will be near the northwestern edge of the snow area, so even small shifts will cause big differences in snowfall totals, and Nor'easters that explode like this just off the coast are notoriously tricky to forecast, and models were until yesterday still disagreeing on the details. In fact, a few days ago, almost all models had the storm weaker and farther offshore, bringing little impact to land areas, except the GFS which has consistently shown a stronger storm closer to the coast and has actually done relatively well over the past several days in contrast to the rest of the winter. Nonetheless, due to the suppressive nature of the weather pattern, the Champlain Valley northwestward will stay dry and even mostly sunny, except for a few light snow showers in eastern Ontario today from the predecessor weak disturbance which will disappear tonight as the Nor'easter consolidates all of the energy and moisture. With such a strong low-pressure system, areas in the snow zone will see strong winds, making for possible blizzard conditions, with winds becoming weaker heading northwest. There will also be a sharp cut-off between heavy snow under one of the frontogenetic bands and little or nothing with sinking air just to the northwest.
 |
| Source: TropicalTidbits |
This explosive, slow-moving, and somewhat blocked setup is a bit surprising given the -PNA and +NAO, but the high-latitude blocking appears to be directly north of our region in northern Quebec as opposed to over Greenland. This is also allowing storms to tunnel underneath the block despite the -PNA normally allowing storms from the Rockies to track northeastward easily, especially with a +NAO. Also, a strong blocking upper-level ridge in the Gulf of Alaska is displacing the main jet stream much farther south than usual over all of North America. This is one caveat to simple teleconnection indices like the PNA and NAO. However, that pattern will be breaking down over the next week.
 |
| Source: Climate Prediction Center |
 |
| Source: TropicalTidbits |
Weakening clipper brings light snow Wednesday, possible storm Friday though could be suppressed south and weak again, with previously expected thaw to fail to occur
After the Nor'easter moves out Monday night, slightly colder air will filter in from the north, but the true arctic air will stay to the north. Still, with the direct northerly flow, frozen lakes, and widespread deep snow cover, temperatures will be modestly below average. Surface high pressure will bring mostly sunny weather on Tuesday before an Alberta clipper moves into the region later Wednesday and brings light snow, though it appears to be weakening and moisture-starved given its track to the east-southeast, like most of the systems this winter. With southerly flow, the southern Adirondacks and Laurentians will see upslope enhancement, making for moderate snow amounts, possibly >4" (10 cm) locally. Another disturbance could follow behind the clipper, pick up some Gulf of Mexico moisture, and move into our region for Friday, though most models show it being relatively weak and suppressed to the south. This is quite a shift from just a few days ago, when most models showed it possibly warming up enough for it to rain, but typical of this winter, especially the past month, the weather pattern keeps shifting to more of a upper-level ridge in western North America and trough in eastern North America than first modeled. However, it is a rather difficult forecast as pieces of energy will eject out of a slow-moving upper-level low in the eastern Pacific underneath a strong blocking upper-level ridge in the Gulf of Alaska through early next week. Such upper-level lows are always very tricky to forecast, and given that this one will be over the ocean where there is less data for a few more days, it will be even trickier to forecast. Even model initializations are considerably different. Friday's system will highly depend on the exact nature of the energy coming out of the upper-level low (straighter and strung out would mean weaker and farther south storm, whereas a more curved, consolidated piece would mean a stronger and farther north storm). Nonetheless, a more suppressed pattern with much less precipitation than originally expected would fit the theme of most of this winter.
 |
| Source: TropicalTidbits |
Brief thaw Saturday with a little rain and snow Saturday night, then arctic air returns
With the rising EPO and positive NAO, the blocking pattern will fade away next week, and there will actually be a stronger than average temperature gradient and jet stream strength by next weekend. A clipper will likely track well north of our region on Saturday, bringing a brief one-day mostly dry warmup powered by the stronger late February sun and southwesterly flow. The clipper's cold front may bring a short period of rain and snow Saturday night (rain more likely at lower elevations and snow more likely at higher elevations). Given the cold, dry air mass shortly preceding the clipper and the clipper's northern track, there is unlikely to be any appreciable Gulf of Mexico moisture involved, making total precipitation amounts light, unless there is a secondary wave that forms on the tail end of the clipper's cold front, which is somewhat possible but not likely. Despite it being a week away, models are actually in rather good agreement on this general scenario, perhaps due to the fast upper-level flow and only one main system (being the clipper). If next week's storms are weak, moisture-starved, and/or suppressed as most models currently show, parts of the region, especially northwestern Maine into the Laurentians, could have one of the driest Februarys on record. Despite it being the start of meteorological spring, the arctic air
mass behind the clipper appears to be quite impressive and coming directly out of the
north with no modification, with an ideal surface high-pressure placement just to our north over Quebec. It could reach -4F or -20C in many areas if
current projections are correct and the coldest air mass is timed well with a clear, calm night.
 |
| Source: TropicalTidbits |
Strong temperature contrasts raise potential for wild temperature swings and storminess while Arctic air nearby keeps snow potential alive in early March
For the following week, models mostly agree on an impressive amount of arctic air building across Canada fighting with a strengthening southern U.S. ridge. This normally is a favorable setup for storminess for our region, but given how this winter has gone, I have to be a bit skeptical. Still, given the strengthening warm and humid air masses in March to our south and the climatologically less stable air masses combined with the arctic air masses still within reach, it would not take much to spawn a storm that has strong dynamics and at least some Gulf of Mexico moisture that could bring a more substantial widespread storm to our region, as rare as that has been lately. Arctic air means that snowstorms are still possible, and if a system can ram warm and moist Gulf of Mexico air straight into the fresh cold air masses, a widespread heavy snow will result. The first chances are around March 2 and March 5. March can be a wild month with wild temperature swings, and given the stronger than average temperature contrasts expected, that could be even more so this year. Some models are also showing just high-pressure dominating both at the surface and aloft, leading to mostly dry weather as the March sun angle quickly moderates arctic air masses. Still, I wonder if the models will back off on any real upper-level ridge in the southeast U.S., shifting it to our west instead, leading to a more suppressive pattern that has dominated most of this winter. The frozen Great Lakes and widespread deep snow cover will act as negative feedbacks or roadblocks to any big thaws. Small changes in the upper-level flow will make a big difference in sensible weather in our region with temperature gradients this strong.
 |
| Source: TropicalTidbits |
 |
| Source: TropicalTidbits |
No comments:
Post a Comment