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12:30 PM | *Snow, ice to rain on Wednesday with snow accumulations likely at the onset; especially, to the north of the PA/MD border*

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Weather forecasting and analysis, space and historic events, climate information

12:30 PM | *Snow, ice to rain on Wednesday with snow accumulations likely at the onset; especially, to the north of the PA/MD border*

Paul Dorian

 12Z NAM snow depth change for the upcoming event; courtesy NOAA/EMC, tropicaltidbits.com

12Z NAM snow depth change for the upcoming event; courtesy NOAA/EMC, tropicaltidbits.com

Overview
The overall weather pattern is not too different from what we saw on Sunday and a combination of snow, ice and rain is headed to the I-95 corridor for Wednesday.  Low pressure will slide from southwest-to-northeast on Wednesday just to the northwest of the I-95 corridor and given that track, milder air should push in off the ocean to change any AM frozen precipitation to plain rain for the PM hours.  There will likely be some snow accumulation early tomorrow throughout the Philly and NYC metro regions and perhaps a coating in the northern and western suburbs of DC.  Black ice is a threat for late tomorrow night/early Thursday as temperatures will drop well below freezing in the overnight hours following the PM rainfall.  

 Leading edge of the ice (pink, purple) and snow (blue) near the DC, Philly metro regions at 6 AM as depicted by the 12Z NAM (12-km) model; courtesy NOAA/EMC, tropicaltidbits.com

Leading edge of the ice (pink, purple) and snow (blue) near the DC, Philly metro regions at 6 AM as depicted by the 12Z NAM (12-km) model; courtesy NOAA/EMC, tropicaltidbits.com

Details
The air mass leading into this mid-week event is quite cold in the I-95 corridor – perhaps even a bit colder than that which preceded the mess on Sunday.  Precipitation is likely to begin as snow north of the Mason-Dixon line early tomorrow and an inch or two can accumulate in the Philly and NYC metro regions before a changeover to a wintry mix and then ultimately to plain rain.  While a coating of snow cannot be ruled out at the onset in the DC metro region, a period of freezing rain and sleet is more likely there at the onset before the eventual changeover to plain rain.  In all three metro regions, the timing of the precipitation is not too good as it could result in slippery spots for the morning commute.  All three metro regions, however, should have plain rain with above freezing temperatures in time for the late afternoon commute.

 A change to plain rain (green) is likely in the DC, Philly, NYC metro regions for tomorrow afternoon, but snow and ice will continue in areas to the northwest of the the big cities; courtesy NOAA/EMC, tropicaltidbits.com

A change to plain rain (green) is likely in the DC, Philly, NYC metro regions for tomorrow afternoon, but snow and ice will continue in areas to the northwest of the the big cities; courtesy NOAA/EMC, tropicaltidbits.com

The rain will wind down tomorrow night and there is the chance that it ends as a brief period of freezing rain with temperatures dropping back towards the freezing mark.  Whether or not the freezing rain actually materializes before midnight, black ice will be a threat late tomorrow night into early Thursday morning as temperatures will drop way down into the 20’s in the wee hours and wet surfaces could become slick on untreated surfaces.  Thursday promises to be a cold, breezy and dry day in the I-95 corridor with much better conditions for a parade in Philly compared to the originally planned Wednesday event.

The potential for more substantial snow and ice on Wednesday increases rather quickly the farther northwest one travels with, for example, central and northeastern PA in line for several inches of snow.  Also, there can be quite a dramatic difference tomorrow across New Jersey with most, if not all, ordinary rain at the South Jersey coastline, but several inches of snow are possible in the higher elevations of interior NW NJ.   

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com 

AM video discussion: