1:05 PM | *Light snow and ice threat continues for Saturday/Saturday night with highest precipitation amounts in DC...major ice storm to unfold from Central Plains to Midwest*

12Z GFS forecast map for early Saturday afternoon (snow in blue, sleet in purple, freezing rain in pink); map courtesy tropicaltidbits.com, NOAA/EMC

Overview
A major ice storm will unfold over the next few days for much of the country from northern Texas to Ohio and by Saturday, some icing can take place right here in the Mid-Atlantic region though not nearly on the same scale as to our west.  The main culprit will be building Arctic high pressure to our north and this will produce shallow, but very cold, low-level air in the DC, Philly and NYC metro regions following on the heels of a cold frontal passage early tomorrow. This frontal system will stall out in the southern Mid-Atlantic region by the weekend and an upper-level disturbance will ride along its boundary zone bringing us the potential for some light snow and ice.  The greatest potential for any problems this weekend in the Mid-Atlantic's I-95 corridor could very well turn out to be across the DC metro region as higher precipitation amounts are likely there as compared with places farther to the northeast.

Details
Today’s unusual warmth will be only temporary as a cold front will slip through the region on Friday.  As a result, temperatures tomorrow afternoon are likely to be around 15 degrees colder than today and they will tend to drop as evening approaches.  Temperatures later tomorrow night are quite likely to drop well down into the 20’s in Philly and NYC and to below freezing in DC and this will set the stage for potential problems on Saturday in those areas that receive some precipitation.

24-hour precipitation totals from early Saturday to early Sunday using 12Z GFS with highest amounts in I-95 corridor across the DC metro region and the lowest amounts in and around NYC; map courtesy tropicaltidbits.com, NOAA

By early Saturday morning, moisture will already be working its way into the Mid-Atlantic region riding along the stalled out frontal boundary zone and the DC metro region may actually see some snow, ice and/or freezing rain just before dawn. The precipitation is likely to make into into SE PA later Saturday morning in the form of snow or a mix of snow and ice, but that is not a 100% guarantee, and odds for precipitation to reach NYC are looking quite small at this time.  The upper-level waves of energy that are headed our way are going to get squeezed into “convergent” flow aloft; consequently, they will tend to weaken as they move to the north and east.  As a result, the highest precipitation amounts on Saturday and Saturday night in the DC-to-Philly-to-NYC corridor are likely to occur in the DC metro region with less in Philly and little, if any, making it to the NYC metro region.  

In addition to the likelihood of higher precipitation amounts from this Saturday system across the DC metro region, the temperatures there may actually be more favorable for icing compared to areas northeast of the PA/MD border where what actually falls may be more in the way of snow and less in the way of ice (which is a good thing). Nonetheless, there can be some (light) icing in SE PA on Saturday and Saturday night. Anything that actually makes it into the NYC metro region – and I don’t expect much at all up there – would likely be all snow. Any snow and/or ice accumulations on Saturday in DC and Philly will be on the light side, but it doesn’t take much to cause problems on untreated surfaces.  

To our west, a major ice storm will unfold on Friday from the Texas Panhandle to southern Illinois and Indiana and then expand northward and eastward at night.  The thickness of the ice will become substantial enough to weigh down trees and power lines in portions Texas, Oklahoma, Kansas, Missouri and Illinois with the worst hit region likely to be from Kansas into Missouri.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com