11:20 AM (Thursday) | ***50 mph wind gusts possible today in the Mid-Atlantic region as cold and very dry Arctic air arrives…sets the stage for a frozen precipitation event on Saturday***

Temperatures will hang near or below freezing on Saturday into at least the early afternoon hours according to this high-resolution forecast map of the NAM (3-km version); map courtesy NOAA, tropicaltidbits.com

Overview

Watch the dew points over the next 24 hours or so as they will plummet as a cold and very dry Arctic air mass pours into the Mid-Atlantic region on strong NW winds that can gust to 50 mph.  This incoming air mass will be anchored by strong high pressure centered over the southeastern part of Canada from Friday into Saturday and it will set the stage for an extended period of frozen precipitation on Saturday in the Mid-Atlantic.  Temperatures will only be able to reach the low-to-mid 30’s for highs on Friday afternoon in the DC-to-Philly-to-NYC corridor…some 20 degrees lower than yesterday.  On Saturday, low pressure will move from the Upper Midwest to the central Great Lakes and precipitation will slide eastward from the Ohio Valley into the Mid-Atlantic region.  Given the cold and very dry air mass in place on Saturday morning, there is likely to be an extended period of frozen precipitation in the Mid-Atlantic region with accumulations of snow and ice likely at the onset of this event.  

The influx of Arctic air today into the Mid-Atlantic region has its origins in the Northern Plains and southern Canada where temperatures were generally well below normal this morning; map courtesy coolwx.com, NOAA

Details

A strong cold front pushed through the I-95 corridor earlier today and winds have increased dramatically in the wake of the frontal passage as the pressure gradient tightens between departing and intensifying low pressure east of New England and incoming strong high pressure over the Northern Plains where temperatures were generally well below zero this morning. The winds can gust to 50 mph in the DC-to-Philly-to-NYC corridor from mid-day into the early evening as the Arctic air mass floods the region and there can be some snow shower activity as well; especially, to the north of the PA/MD border.  Heavier snow squalls are possible later today across higher elevation locations of upstate Pennsylvania and New York State.

On Friday, strong high pressure will be building over southeastern Canada and temperatures will struggle in the I-95 corridor to rise above the freezing mark.  Winds will continue to be quite noticeable on Friday gusting up to 30 mph or so, but they won’t be quite as severe as what we’ll experience later today.  Not only will this incoming air mass be quite cold, it’ll be very dry as well which is quite characteristic of Arctic air.  If you have an indoor weather station, you may want to take a look at the dew point reading as it’ll plummet over the next 24 hours – possibly to the single digits.  Temperatures tomorrow night will drop to near 20 degrees for lows as clouds increase and some suburban locations to the north and west of the metro regions could actually make it all the down into the upper teens by the time we start the day on Saturday.

Even as late as 7PM on Saturday, temperatures will hover near the freezing mark in much of the DC-to-Philly-to-NYC corridor as the cold, very dry, dense Arctic air will be reluctant to give up its ground; map courtesy NOAA, tropicaltidbits.com

On Saturday, precipitation will be heading in a general west-to-east fashion across the Ohio Valley and right towards the Mid-Atlantic region.  Given the cold and very dry air mass in place on Saturday morning, the initial batch of precipitation is quite likely to be frozen and begin as snow north of the PA/MD border and snow or ice or some combination of the two in the DC metro region.  The extremely dry nature of the air mass will lead to “evaporative cooling” at the onset which will enhance the chances for frozen precipitation.  In addition, the dry air will likely may it difficult for the snow to actually reach the ground as it’ll evaporate for awhile until the lower atmosphere moistens up a bit.

This cold, dry air mass will be quite dense and reluctant to retreat to the north on Saturday; consequently, temperatures at the ground level will struggle to climb above the freezing mark in much of the DC-to-Philly-to-NYC corridor. Warmer air will move into the upper atmosphere more easily by later Saturday changing the frozen precipitation to liquid in parts of the I-95 corridor, but ground level temperatures will be hard-pressed to rise above freezing for awhile leading to the potential of icing. 

The precipitation is likely to arrive in the DC metro region as snow or sleet or a combination of the two during the early-to-mid morning hours with possible accumulations at the onset of a coating to an inch or two.  The snow is likely to start in the Philly area during the late morning or early afternoon hours – delayed somewhat by the very dry air mass – and accumulations at the front end can end up in the 1-3 inch range before a changeover to ice/rain.  In NYC, the snow will likely hold off until the afternoon hours and there can be 1-3 inches of accumulation up there before a changeover to ice/rain.  With temperatures struggling to climb above freezing in the DC-to-Philly-to-NYC corridor, slick spots will likely become a concern on Saturday and Saturday night.  The precipitation ends by early Sunday possibly changing back to snow in some spots and another shot of cold air will push into the region on strong NW winds.  Temperatures could drop into the teens for lows on Sunday night and again on Monday night as some of the coldest air so far begins the new week.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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