1:30 PM | ***Atmosphere turns colder leading to the first snow in many spots along the I-95 corridor...significant mountain snows in the Mid-Atlantic...cold pattern late November into December***
Paul Dorian
High-resolution forecast map (HRRR model) of radar reflectivities as of early Friday indicate snow will be quite widespread in the Mid-Atlantic region. Map courtesy NOAA
Overview
A strong cold front passed through in the overnight hours with a band of heavy rainfall and gusty winds and colder air has followed into the Mid-Atlantic region. Surface low pressure has formed along the northern Mid-Atlantic coastline, and instead of pushing to the north, it will be “forced” to rotate around as it becomes increasingly influenced by strong blocking high pressure to the north. As such, an area of moisture now over the northern Mid-Atlantic will loop back around and impact the entire region by later tonight and through the day on Friday.
As the atmosphere turns colder, the precipitation will mix with snow and/or ice pellets by later tonight in the DC-to-Philly-to-NYC corridor and then likely to all snow for awhile on Friday in much of the area. In fact, small accumulations are possible on Friday across many of the northern and western suburbs along the I-95 corridor. Significant snowfall of at least 6-12 inches is coming to much of the Appalachian Mountain chain including in the region from West Virginia to the Laurel Highlands of southwestern PA, and from the Poconos in northeastern PA to the Catskills and Adirondacks of upstate NY.
Looking ahead, there are signs for multiple cold air outbreaks to make their way from northern Canada into the central and eastern US as we push through the remainder of November and into the early part of December...quite a wintry look to the unfolding weather pattern that will include additional threats of snow for the Mid-Atlantic/Northeast US.
Significant snowfall is likely during this event in two higher elevation zones of the Mid-Atlantic region including “SW PA to West Virginia” and “northeastern PA to upstate NY”. Small accumulations are possible on Friday on grassy surfaces of the northern and western suburbs of DC, Philly and NYC. Map courtesy NOAA, tropicaltidbits.com
Significant storm system in the northeastern part of the country
A deepening upper-level trough of low pressure is sliding southeast today and will be positioned over the Mid-Atlantic region by later tonight. At the surface, a secondary low pressure system has formed over the northern Mid-Atlantic coastline and it will rotate around to the south and west during the next 24 hours as a result of intense blocking high pressure centered to the north over Canada.
Surface low pressure will rotate around during the 24-hour period from later tonight to later tomorrow night and this will prolong the precipitation in the I-95 corridor through tomorrow evening. Maps courtesy NOAA, tropicaltidbits.com
An area of precipitation now centered over the northern Mid-Atlantic will “wrap round” later today and end up encompassing the entire Mid-Atlantic region by early Friday. As the atmosphere turns colder, the precipitation is likely to mix with snow and/or ice pellets later tonight across the I-95 corridor and then likely to all snow for awhile on Friday. In fact, small snow accumulations are possible on Friday; especially, on grassy surfaces to the north and west of the big cities. Later in the day and early tomorrow night, if “all snow” actually does materialize, it can change back to rain as the overall upward motion in the atmosphere weakens.
In higher elevation locations of the Mid-Atlantic, significant snowfall is likely with 6-12 inches in many areas and some “bullseye” spots can receive more than a foot. The snow should be of the heavy, wet variety given the “borderline” temperatures expected during the duration of this slow-moving storm system. The higher elevation areas with the best chance of significant snowfall include northeastern Pennsylvania (e.g., Poconos), upstate NY (e.g., Catskills, Adirondacks), interior northwestern NJ, and also back to the southwest in the zone from the Laurel Highlands of southwestern PA to central/eastern West Virginia.
Widespread colder-than-normal conditions are likely from later next week through the first week of December. Map courtesy ECMWF, weathermodels.com
Cold pattern from late November into December
Looking ahead, an overall wintry weather pattern is shaping up for much of the central and eastern US with additional cold air outbreaks likely from late November into December. The upper air pattern will favor the transport of cold air masses from northern Canada into the northern US as we progress from later next week into the first week of December..
The upper atmosphere will feature high pressure ridging over northeastern Canada and near Alaska as we push through the latter part of November and into early December and a deep trough will exist over the eastern states. This combination will allow for the transport of cold air masses from northern Canada into the northern US and perhaps even some “cross polar” flow of air. Map courtesy ECMWF, weathermodels.com
This pattern aloft should include continued high-latitude blocking over northeastern Canada and Greenland, an upper-level trough over the central and eastern US, and a strong ridge over Alaska. This combination should allow for air masses way up in Canada – and perhaps even across the pole – to move southeastward into the northern states. This evolving cold weather pattern is quite likely to include additional snow threats for the Mid-Atlantic region and Northeast US...including perhaps something by late next week.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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