3:40 PM | ***Howling Arctic winds relax on Friday...trouble begins tomorrow night***
Paul Dorian
12Z GFS forecast map of 850 mb temperature anomalies for Friday morning - Arctic air still in control: map courtesy tropicaltidbits.com, NOAA
Overview
Strong Arctic high pressure will move right on top of the Mid-Atlantic region on Friday and this will result in a relaxation of the pressure gradient which, in turn, will result in diminishing winds so the cold will be easier to take. The Arctic air mass will begin to retreat to the north tomorrow evening, but moisture will push in before it has a chance to fully retreat. As a result, snow is likely to break out around or shortly after midnight in the I-95 corridor region from DC-to-Philly-to-NYC. As the Arctic air retreats, there will be a transition of snow to ice and ultimately to plain rain up and down the I-95 corridor, but accumulations will occur before the changeover and slippery conditions can be expected on the roadways.
12Z GFS forecast map of 850 mb temperature anomalies for Saturday morning - Arctic air retreats; map courtesy tropicaltidbits.com, NOAA
The breakdown by region as it currently stands:
DC metro region:
Snow breaks out around midnight or shortly thereafter and likely mixes with sleet during the wee hours of the morning. There can be a snow and ice accumulation of a coating to an inch or so by daybreak on Saturday. Early Saturday morning, there is likely to be a mix of freezing rain and sleet and then just freezing rain during the mid-morning hours and finally, plain rain by around mid-day. Before the changeover to all (plain) rain, there can be a layer of ice that accumulates on top of any overnight snow causing slippery road conditions; especially, in the northern sections of the DC metro region. During the afternoon hours, temperatures can climb to 50 degrees with some more (plain) rain likely. Occasional showers on Saturday night will give way to steadier rain on Sunday and that can change briefly to snow and/or sleet by Sunday night as another Arctic air mass moves in with the best chance for the changeover in the northern and western suburbs.
Philly and NYC metro regions:
Snow breaks out around midnight or shortly thereafter and continues in the overnight hours. There can be a snow accumulation of 1-2 inches by daybreak on Saturday. On Saturday, the snow is likely to transition to a period of sleet and freezing rain around mid-morning and then finally to plain rain by mid-day or early afternoon. Before the changeover to all (plain) rain, there can be an additional 1-3 inches of snow resulting in a total snowfall estimate of 2-5 inches during this event with the highest amounts in that range in the northern and western suburbs. A layer of ice on top of the snow will contribute to slippery road conditions for awhile late Friday night and Saturday morning. During the afternoon hours, temperatures can climb to 50 degrees with some more (plain) rain likely. Occasional showers on Saturday night will give way to steadier rain on Sunday and that can change briefly to snow and/or sleet by Sunday night as another Arctic air mass moves in with the best chance for the changeover in the northern and western suburbs.
Stay tuned…complicated forecast.
Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com