12/25/10: Final Storm Forecast

Today was a mainly cloudy day across the area as the leftovers of a snowstorm in the Ohio Valley brought scattered snow showers to parts of the area today. Looking at the latest radar, light to moderate snow is currently falling in southern Virginia with more snow headed towards these areas. We are currently tracking a low pressure moving through Florida right now, which tonight into tomorrow will start to turn northeast and then north to bring a blizzard to parts of the area into southern New England that may rival some of the blizzards of last winter.

Storm Development And Track:

Up until today, the storm’s development was the most uncertain part of the forecast, and put the range of possibilities from a major snowstorm to no snow with barely a small shift. Several days ago, it was mentioned that the two possible tracks would either take this storm up the coast or out to sea, but the models trended to a consensus that was out to sea once the storm’s energy entered the United States. While usually, the models would then become more consistent with this solution as this was in the short range, the GFS model started an unusual last minute trend yesterday that was big enough to bring heavy snow well into the NYC area, and now it appears that the storm will take the western path up the coast.

Up until tomorrow morning, the radar appearance of the storm may make it seem as if it is going out to sea, when it will not do so. Tonight, as precipitation continues to affect Virginia and the Carolinas, the low pressure will move towards the coast of the Carolinas, with a NE movement making it seem as if the storm is going out to sea, however the storm will start to take more of a neutral tilt, meaning that it will start to move NNE and then north. Yesterday’s model runs had the storm with a positive tilt when off the coast of the Carolinas, meaning it would continue to move northeast and out to sea, though now all of the models show a neutral to slightly negative tilt by that time.

By the early afternoon hours, as the storm starts to move more north while rapidly intensifying, the precipitation will start to move more north, extending slightly west the further north the storm gets. It is then expected to peak between 970 and 975 mb tomorrow night while briefly stalling off the coast of Long Island. Afterwards, the storm will start to move northeast and away from the area while producing windy conditions.

Forecast For The NYC Area:

Until at least tomorrow afternoon, cloudy skies with an isolated flurry are expected for the area as the storm develops to the south of the area. Starting around 12-2 PM, snow will move into the area from south to north, steadily intensifying and becoming heavy by the late afternoon hours. Temperatures will be stuck in the mid to upper 20s across most of the area, with upper 20s to lower 30s further east. By the late afternoon hours, as the storm slows down southeast of NYC, widespread heavy snow will start to cover the area, with increasing winds and dropping temperatures, leading to a high liquid to snow ratio snowfall across most of the area as snow will fall with temperatures in the lower to mid 20s away from the coast.

The heaviest snow will fall between the late afternoon and overnight hours, with the heaviest snowfall in the immediate NYC area and western/central Long Island and southern Connecticut. Due to the proximity of the storm, the snow may mix with rain at times in eastern Long Island, which will lead to slightly lower snow accumulations there. At the peak of the storm, snowfall rates as high as 2-3 inches per hour are possible where heavier snow bands develop, wind gusts potentially over 40 mph will lead to blizzard conditions at times for the central and eastern parts of the area, and even thundersnow cannot be ruled out. By the morning hours on Monday, the snow should start to come to an end as the storm exits the area.

Forecast For The Northeast Region And Snow Map:

By the time that the storm is over, between 8 and 16 inches of snow are possible inland, 12 to 18 inches for the immediate NYC area, and 10 to 18 inches for Long Island and southern Connecticut as potential mixing will lead to slightly lower amounts in eastern Long Island. Depending on where the heavier snow bands set up, amounts locally as high as 20-24 inches are possible in the central and eastern parts of the area, and while it is also possible that some places could see slightly lower snow totals than expected, snow totals will still be very high, over 10 inches in the immediate NYC area and western/central Long Island/S CT.

Due to the NNE/north motion of the storm at first, most of the heavy precipitation will stay offshore tomorrow afternoon, keeping snow totals lower in the Washington DC area, with up to 6 inches of snow possible there, but this will need to be watched as it is possible that the storm could end slightly west, bringing even more snow to DC. The storm’s precipitation shield will then expand northwest, with heavy snow developing in the NYC area and moving northeast through much of southern New England into southern Maine.

It appears that there should be a tight snow gradient to the west and northwest of the storm, and there is some uncertainty on where this gradient sets up, which could be slightly west or east of the snow map above. Regardless of changes with this gradient, it will stay to the west of NYC, meaning that heavy snow is still expected in the central and eastern parts of the area, with the westernmost parts of the area having the potential for slightly lower snowfall amounts if this gradient is further east and the eastern parts of the area having the potential for rain mixing with the snow if this gradient is further west.

Even though the general storm scenario has been figured out, there can still be some slight changes while the storm is ongoing, including potentially shifting the heavy snow axis slightly west or east. Storm updates will be posted throughout the day tomorrow covering the short term forecasts and and any potential changes if needed.

This is a dangerous storm and has the capability of producing well over a foot of snow, blizzard conditions with near zero visibility at times, and very hazardous traveling conditions. Stay tuned for updates tomorrow on this storm.

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