Northeast Weather Blog

Current watches, warnings and advisories.




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Forecast Discussion


Synopsis - Issued 12/03 @3:30pm


A sharp cold front with anafront characteristics will move through the Northeast Thursday, delivering an icy blast of arctic air that will remain entrenched over the region until early next week. Lake effect snow will follow in its wake, which could be quite a significant event in the snowbelts. High pressure builds in to begin the weekend but will quickly give way to a clipper to close out the weekend that may undergo coastal redevelopment, bringing an accumulating snowfall to Maine.


Short-term - Issued 12/03 @3:30pm


Mainly clear skies will begin the night but clouds will increase as the night wears on as warm air advection ensues behind the departing high in southerly flow. However, enough clear skies and a decoupling of the winds after dusk should make for ideal radiational cooling conditions for a couple hours, especially across the eastern portion of the region. The cold front will punch into western New York and Pennsylvania after midnight, accompanied by rain showers that will quickly change to snow as colder air filters in aloft. A coating to an inch or two of snow may fall behind the front, which is a nuisance snowfall for Northeasterners, but what lies beneath is where there will be trouble. The initial liquid precip followed by a rapid cooling may result in a flash freeze of road surfaces. Anyone traveling across the western half of the region will have to keep this in mind. Temperatures tonight will drop sharply after sundown before leveling off, or even rising a couple degrees, once the cloud deck moves in. Across western sections, temperatures will drop once again after the frontal passage, so a rather atypical temperature profile across the region tonight. Lows will fall into the 20’s across the interior with 30’s along the coastal plain and across the far western sections of the region where clouds will move in quickly after sunset. Winds will be light and variable but increase to around 10mph out of the south just ahead of the front and turn towards the west after its passage.

The cold front continues to march across the Northeast during the day on Thursday, with much of the associated precipitation falling behind it. QPF with this feature will be light, mainly a tenth to a quarter inch. Ahead of the front, temperatures in the boundary layer should warm sufficiently to allow for rain showers to fall initially, but rapidly cooling air thanks to strong cold air advection behind the front and dynamic cooling of the column will make for a quick transition to snow across the interior. Along the coastal plain this changeover will likely take much longer to occur, if at all. Elevations above 1,000’ could see a fast inch or two of snow accumulation while at lower elevations any accumulations will likely be confined to colder surfaces, such as grassy areas or car tops. Lake effect activity will also develop by afternoon as increasing deltaT’s create enough lake induced instability for snow showers. Once again, temperatures will follow an atypical diurnal trend. Across the western half of the region, where the frontal passage will occur during the overnight/early morning hours, temperatures will slowly fall during the day from the 30’s into the 20’s by mid afternoon. Meanwhile, areas that see the frontal passage occur during the late morning/early afternoon will see a fast rise in temperatures into the upper 30’s to low 40’s, then after the frontal passage a slow fall back into the low to mid 30’s. Along the immediate coastal plain temperatures should easily climb into the upper 40’s as the front won’t reach these areas until late in the afternoon. Southerly winds of 10-15mph ahead of the front will quickly turn to the west behind it and become quite gusty in strong cold air advection.

The cold front will be off the coast by this evening will any lingering precipitation along the coastal plain transitioning over the snow showers. Lake effect snows will increase as 850mb temperatures drop to nearly –15°C in/around the Great Lakes region, increasing deltaT’s to ~20-22°C. Despite the extreme lake induced instabilities and rather high inversion levels, there will be some deterring factors to seeing a substantial event. For one, the flow won’t be well aligned and will likely oscillate between 270-290°, which won’t keep the bands over any one particular area for any significant length of time. There’s also likely to be about 20-30° of directional shear in the 1000-700mb flow that should spread the band out and synoptic moisture will be lacking. Regardless of these deterrents, snowfall across the Tug Hill Plateau, western Adirondacks and across some of the higher terrain of Northwest Pennsylvania to the region surrounding Jamestown, NY could easily see 6-12” of lake effect snow overnight. Lighter amounts will fall in the immediate surrounding regions. Lows will fall back into the teens across the interior with 20’s along the coastal plain. Winds will be out of the west around 10-15mph.


Mid-term - Issued 12/03 @3:30pm


Cold air continues to bleed into the Northeast on Friday, keeping temperatures well below normal while lake effect snows continue across upstate New York. The flow will turn to more of a west-southwesterly direction as the day progresses as high pressure slides by to the south over the Mid-Atlantic. Inversion levels will also lower, making for lighter lake snows as the bands progress to the north, reaching the Buffalo/Watertown areas. Elsewhere skies will be partly to mostly sunny as temperatures remain in the 20’s across the interior, with 30’s along the coastal plain.

The next system of concern will be a potent clipper system dropping into the deep trough carved out over the eastern half of the nation this weekend. Being from the northern branch, this system will be moisture-starved, but will carry with it some rather impressive dynamics that should be able to squeeze out whatever available moisture presented to it. Hence, a widespread snow shower event is expected to spread over the entire region. As the trough reaches the coast it should begin to take on a negative tilt with a secondary surface low pressure developing offshore. Models are currently hinting at the possibility of a norlun trough developing between the offshore low and the parent low hanging back over the US/Canadian border region. A surface trough axis in the pressure field is apparent, as well as a thermal ridge axis. As Atlantic moisture is tapped an accumulating snowfall may develop across coastal New England, especially Downeast Maine. Lots of time to sort out the details here but the weekend may be a snowy one from Cape Cod to Eastport, Maine, including the greater Boston area. The lake effect machine will also fire up behind the departing clipper in a strong northwest flow. Temperatures will continue to average well below normal for early December.


Long-term - Issued 12/03 @3:30pm


High pressure quickly builds in on Monday, ending the lake effect snowfall. It will remain cold, however, with 850mb temperatures progged to range from –7°C to –15°C from south to north. Complications arise by midweek as an attempt of northern/southern stream phasing occurs in/around the Ohio Valley region of the country. Earlier model prognostications had a much more phased/amplified pattern developing across the eastern half of the country, which allowed warm air to flood up the coast bringing a rain event to much of the Northeast with a mix or snow confined to the far northwestern sections of the region. Ensuing model runs now show the possibility of the northern stream system outrunning the southern stream disturbance, for a time, before they catch up to one another. This would bring a sharp cold front into the Northeast where it will become hung up as both branches of the jet phase at a further east longitude. The result would be a much more wintry scenario to the region and a much more complicated forecast. Skipping on the details and focusing on the generalities, it appears as a significant QPF event is likely during the middle of next week with a very tight baroclinic zone setting up north-south across the region. The warm side of the storm could see flooding rainfall while the cold side of the system could see substantial snow/ice accumulations. More on this in the days to follow but be prepared to the possibility of a high impact weather event developing next week that could have widespread effects.


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Radar: Northeast Region Loop



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2008-09 Winter Forecast