2:00 PM (Wednesday) | **Much colder air arrives tomorrow in the Mid-Atlantic region riding in on strong NW winds…snow-to-ice-to-rain on Saturday with some front end accumulations**
Paul Dorian
A cold, dry air mass will be in place on Saturday morning when precipitation arrives and this dense air will be reluctant to give up its ground. Temperatures will likely still be below freezing in the DC-to-Philly-to-NYC corridor during the early afternoon hours according to this forecast by the 12Z GFS. Map courtesy NOAA, tropicaltidbits.com
Overview
Temperatures are climbing into the 50’s today in the I-95 corridor which is well above-normal for this time of year, but a strong frontal passage early tomorrow will usher in a much colder air mass for the end of the work week. The much colder air will ride into the region on strong NW winds that can gust to 50 mph at times. Strong high pressure will build into southeastern Canada on Friday and high temperatures in the I-95 corridor will be some 20 degrees lower compared to this afternoon’s readings. On Saturday, low pressure will move from the Upper Midwest to the central Great Lakes and precipitation will move east into our area. Given the cold, dry air mass in place on Saturday, there is likely to be a period of frozen precipitation at the onset in the DC-to-Philly-to-NYC corridor with some accumulations likely.
Temperatures will be hard pressed to ride above freezing on Saturday in much of the I-95 corridor and this will result in an extended period of frozen precipitation (snow shown in blue, sleet/freezing rain shown in purple/pink). Map courtesy NOAA, tropicaltidbits.com
Details
An amplifying upper-level trough will push a fast-moving surface low pressure system east of New England on Thursday and this will drag a strong cold front through the Mid-Atlantic region early in the day. Arctic air will pour into the region later tomorrow and tomorrow night riding in on strong NW winds that can gust to 50 mph and importantly, dew points will drop noticeably in what is a very dry incoming air mass. Strong high pressure will build across southeastern Canada on Friday and this system will be a key player in the likelihood of frozen precipitation on Saturday.
Snowfall map by the 12Z GEFS for the weekend event; map courtesy Weather Bell Analytics, NOAA
Another intensifying upper-level trough will cross the central Plains later Friday into Saturday and this will generate low pressure over the Upper Midwest that will take a track towards the central Great Lakes. A warm front extending well to the east of this low pressure system will generate west-to-east moving precipitation and given the cold, dry air mass in place, it is very likely to arrive as something frozen in the I-95 corridor. Snow is likely at the onset in areas north of the PA/MD border such as in the Philly and NYC metro regions and either snow or ice in DC or a combination of the two. Eventually, the warming aloft looks like it will result in a transition from frozen precipitation to rain, but it may take awhile; especially, in areas north of the PA/MD border as the low-level cold, dense air mass will be reluctant to give up its ground. An early estimate for snow accumulations at the onset of the weekend event in the Philly and NYC metro regions is 1-3 inches and a coating to an inch or so of snow and ice could accumulate in the DC metro region. Another shot of cold air will follow on Sunday with strong NW winds and temperatures could drop into the teens for lows on Sunday night and again on Monday night.
Stay tuned…a small shift in storm track or a change in the arrival time of the west-to-east moving precipitation shield can have a big impact.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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