Northeast Weather Blog

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Forecast Discussion - Issued 11/20 @3:00am


Despite being without sleep for the last 24 hours I feel compelled to write tonight given the upcoming lake effect event expected to develop Friday and last into Saturday evening and, perhaps, Sunday morning. In the pipeline for Thanksgiving week is the potential for a major winter storm to affect the interior, but coastal locations may get in on the act too. More on that later but first thing first.


A weak clipper system is currently diving towards the Niagara Frontier at the time of this writing producing an area of light snow and flurries in the above-mentioned area and in a band extending east across south-central New York and north-central Pennsylvania. Outside of this area of light snowfall mid and high level clouds have helped to prevent another freefall in temperatures, as is occurring where the skies are mostly clear across much of central and western Maine and New Hampshire. Temperatures to begin the day will be in the teens across areas that remain clear, 20’s elsewhere.

As the clipper low continues southeastwards during the day on Thursday it will weaken markedly. The mid-level shortwave nearly loses its identity amongst the vorticity rope within the trough, the surface reflection of the low becomes absorbed within the pressure field of the larger low to the northeast over Labrador, a dry atmosphere and a weakening thermal gradient all spell a quick collapse to this clipper. However, lingering snow showers and flurries will still be present, mainly across the higher terrain of the Poconos and Catskills and extending back towards the Great Lakes. There will be a slight bit of lake enhancement that may deliver an inch or two to favored snow belt locations but accumulations elsewhere should range from a dusting to a very localized inch. Slightly milder airmass will be over the region with the –10°C isotherm @850mb retreating to central New York and New England but persistent clouds will play their role in keeping temperatures down across the southwestern two thirds of the region and should assert themselves once convective temperatures are reached across Maine. Along the coastal plain temperatures should have no trouble climbing into the 30’s (low 40’s urban centers). However, across the interior seeing temperatures exceed the freezing mark will be hard to come by, more so over northern New York and New England. Winds will be variable during the day, mainly from a southerly direction during the morning around 5mph, then shifting more westerly by afternoon as the clipper falls apart around 5-10mph.

Clouds, snow showers and flurries remain in place during the evening and into the overnight. Once again, most activity will be concentrated adjacent to the lakes thanks to their moisture/heat flux, though a veering flow ahead of an approaching arctic front will keep any snowbands on the move, limiting accumulations to a couple inches at most. Skies will be partly cloudy over the remainder of the region with a chilly light breeze. Lows will bottom out in the teens where skies manage to remain mostly clear. Elsewhere it’ll be in the 20’s once again, although along the immediate coast 30’s will do.



Friday will feature an arctic frontal passage that should deliver the coldest airmass of the season across the Northeast (yes, it’s gonna get even colder!) and set the stage for a widespread significant, in some cases substantial, lake effect event that’ll take us straight into Sunday. The arctic front will enter the Northeast after midnight and ooze over the region throughout the day on Friday. There’s no real sharp boundary with this arctic front and given the dry atmosphere in place any **snow squall activity looks to be isolated, but present none-the-less**. If one should encounter any of these squalls there will be rapid reductions in visibility and quickly accumulating snow. Behind the boundary lake effect snow will attempt to organize but will likely remain in broken line/cellular activity until later Friday afternoon as diurnal influences wane. With the passage of the arctic front temperatures are not likely to climb far from their morning lows and should begin to fall back down the ladder by mid-afternoon. A biting wind will increase out of the northwest at 10-15mph and be gusty at times.

**These are usually the most hazardous of all winter weather scenarios to encounter while driving, especially if it’s a locations first snowfall. Road will usually be salt-free and first flakes will tend to melt upon landing only to quickly refreeze as the heavier snow moves in, leaving a thin black ice coating. Also, the sudden shock of coming upon a squall may cause a loss of focus. I feel like hitting this hard because snow squalls are sort of the unmentionables of winter. Winter’s dirty laundry. There’s no specific advisory or warning for these events despite them being just as dangerous in terms of lives put at risk as a severe thunderstorm or flash flood. If conditions become bad enough, pull over and wait for the squall to clear; they usually do so in 10-15 minutes. After visibilities rise proceed slowly.**


The show is on Friday night as the coldest airmass of the season advects over comparatively blistering waters of Lake Erie and Ontario. DeltaT’s approach 25°C as the flow becomes increasingly aligned along a 305-310° heading. Inversion levels are nearly through the roof, over 10,000’ with tremendous lift intersecting through the snow dendrite growth region. Only limiting factor will be paltry synoptic moisture but given this airmass is straight down from the arctic, it’s not surprising. Georgian Bay connection will have to be watched and the implications downstream over Lake Ontario. The 305-310° flow is the tipping point in whether we see a multi-band event over central New York or a dominant band setting up. Sometimes what happens over Georgain Bay determines the dynamics of the band development over Lake Ontario. Regardless, the above mentioned favorable factors should lead to a 18-30 hour period of significant lake effect snowfall downwind of Lake Ontario and Lake Erie. By the time all is set and done accumulations of over a foot will be common across a good chunk of real estate downwind of both lakes. Should a more significant band develop at any time during this event even higher amounts may be realized in some of the more favored locations. Accumulating snow will extend pretty far from the lake as well, This event may require snowmap to be posted in an updated version of this blog tomorrow. Additional upslope snow showers will be found across the higher terrain of northern New York and New England in deep cyclonic flow. Skies should remain partly to mostly cloudy along the coastal plain, although a few snow showers or flurries might survive the trip over the mountains. Temperatures are expected to run 10-20 degrees below seasonal averages.


High pressure will be building in on Sunday but as seen earlier, the lake effect is sometimes hard to shut off, especially across central New York but the strong ~1035mb surface high building into the region will have a say in that. Across the remainder of the region it should remain partly to mostly sunny. There will be a slight recovery in temperatures too, although they will still run well below seasonal norms for mid/late November.


The next system of concern begins to move into the region Sunday night into Monday. Warm advection/isentropic lift precipitation may break out across northern New York and New England late Sunday night but most of the region will see just an increase in clouds. As the trough approaches during the day on Monday an expanding area of precipitation will enter western New York and Pennsylvania. Precipitation type is likely to be elevation dependent, with snow levels around 1,000’ south of the New York/Pennsylvania border. The trough continues marching east but slows its progression as it approaches the coast. Here’s where models continue to show disagreement. The Euro model insists that the 500mb trough will cut-off south of Long Island and back up over New York State while the Canadian and American models lift the trough out much quicker. Bottom line is that a significant synoptic snowfall is becoming increasingly likely across the interior. Thus far models have not had this storm becoming an inside runner and all take the system close to the 40-70 benchmark Tuesday. Deep vertically stacked low remains in the vicinity straight trough the Thanksgiving Holiday keeping the weather cold and unsettled. The big shopping weekend also looks to be in jeopardy as the longwave trough over the Northeast buckles once again as another potent northern stream disturbance is progged to drop down the backside of the trough as the relentless wintry weather pattern continues on.

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Radar: Northeast Region Loop




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2008-09 Winter Forecast