Nor’easter, Clipper Threaten Weekend Snow For East Coast

23 Jan 2015 | Author: | No comments yet »

Brace Yourself: A Big Storm Is Coming to the East Coast.

A nor’easter could wreak havoc all along the East Coast over the next 24 hours, with a mix of rain and snow that will likely cause airline and traffic delays along the I-81 and I-95 corridors.The first round of snow is expected to begin falling along the Interstate 95 corridor sometime between 9 p.m. and midnight, according to the National Weather Service. That’s what the models are forecasting and, like many of the other clippers preceding it, there are important questions about if and where accumulating snow will fall and how cold it will be. Temperatures for the first storm — to occur on Saturday — will place the D.C. area right on the rain-snow line and will need an almost perfect storm track to produce significant snowfall.

The NAM model, just in, indicates a period of moderate to heavy snow and/or mixed precipitation for much of the metro region – focused on the period between about 7 p.m. and 1 a.m. The winter weather advisory for the state takes effect at midnight for the five northeastern counties and at 9 p.m. this evening for the rest of New Jersey.

But the temperatures and intensity of the precipitation, which will make the difference between a nuisance storm and one that disrupts travel, are highly dependent on the track of this weather system. The various simulations of last night’s European model, known as ensemble members, show there is still considerable spread in exactly where the clipper’s low pressure center will end up. The precipitation event slated for late Friday night into Saturday still lacks a high pressure system to the north to help feed cold air southward, so temperatures will be marginal to support snow, especially along and east of I-95. They forecast surface temperatures above freezing since we end up on the warm side of the clipper and would offer little potential for accumulating snow.

We must stress that this is just one run of one model, which tends to be inconsistent and sometimes overdoes the intensity of precipitation and amount of available cold air. On the other hand, if the track shifted west (or left on the above map) across eastern North Carolina to the Delmarva Peninsula rather than just offshore, as simulated by several of the ensemble members, it would primarily result in rain across the area. However, well west of the city, the temperatures aloft are cooler, suggesting the precipitation out toward Winchester and points west still could end up as wet snow if the GFS scenario panned out. A mix or mostly rain scenario looks more likely than an all-snow event except possibly for the far western and northern areas, especially those with elevation. The GFS would give us snow in this case as the upper level temperatures are quite cold (even though surface temperatures would probably be a little above freezing, taking the model literally).

Both the GFS and European model solutions have pretty strong upper level troughs (pools of cold air at high altitudes) associated with the system, making it an interesting one. It’s still way too early to say much more than there will be a clipper tracking toward the Mid-Atlantic region on Monday and someone is likely to see snow from it.

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