2:15 PM | ***Dynamic weather pattern continues…snow tomorrow in parts of the Mid-Atlantic…active early weekend frontal passage with pre-frontal rain/strong storms…post-frontal extreme winds, snow***

Heavier bands of precipitation can form on Wednesday morning and mid-day due to expected strong mid-level “frontogenesis” and this can result in a quick changeover from rain-to-snow with dynamical cooling in the atmosphere. Map courtesy NOAA, tropicaltidbits.com

Overview

The wild weather pattern continues in the Mid-Atlantic region…

First, we’ll have to deal with some snow on Wednesday in parts of the Mid-Atlantic region which can even result in small accumulations; primarily, on grassy surfaces to the north of the PA/MD border. Low pressure will push from the Tennessee Valley early tomorrow to southeastern Virginia and then to a position out over the open waters of the western Atlantic Ocean by later in the afternoon.

Looking ahead, a bigger concern than tomorrow’s system will be a very active Arctic cold frontal passage early this weekend that will be accompanied by some vigorous support in the upper part of the atmosphere and a rapidly intensifying surface low pressure system. That next strong cold front will come with pre-frontal rains and possible strong thunderstorms and post-frontal extreme winds are likely as is a changeover to accumulating snow across interior sections of the Mid-Atlantic/NE US.  In fact, there is the possibility for some post-frontal accumulating snow all the way down into coastal sections of the northeastern quadrant of the nation. Very cold air for this time of year will envelope the entire region for the Saturday night/Sunday time period and then a big time warm up will take place in the first half of next week as the wild temperature swings continue. 

Snow threat on Wednesday for parts of the Mid-Atlantic region

Temperatures yesterday soared into the mid and upper 70’s in many spots along the DC-to-Philly-to-NYC corridor and record highs were set in numerous locations.  A strong cold front blasted through the region last night with brief, but heavy downpours and powerful wind gusts that knocked down tree limbs in many areas.  Following the frontal passage, winds today have remained brisk from a northwesterly direction and temperatures are much more seasonable compared to yesterday’s unusual warmth.  High pressure will quickly move overhead later today from the Upper Midwest and then clouds will lower and thicken early tonight as moisture begins to head this way from our southwest.

Snow on Wednesday is more likely to fall in areas to the north of the PA/MD border and small accumulations are possible; primarily, on grassy surfaces and in suburban locations. Map courtesy NOAA, tropicaltidbits.com

Precipitation is likely to break out in much of the Mid-Atlantic region just before daybreak on Wednesday and it can be cold enough for snow; primarily, in areas to the north of the PA/MD border.  During the day, rain will be the primary precipitation type in and around the DC metro region, but a snow/rain mix is likely from southeastern PA to the NYC metro region.  One of the things to watch for on Wednesday morning and mid-day will be the possibility of heavier bands of precipitation to develop given the expected quite strong “frontogenesis” that will form at mid-levels of the atmosphere. In any burst of heavier precipitation to the north of the PA/MD border, “dynamic cooling” in the atmosphere associated with the “frontogenesis” can cause a quick changeover from rain-to-snow.

Temperatures over the next five days will average below-normal across a good chunk of the nation and this includes much of the the cold air outbreak that arrives in the eastern states on Saturday. Map courtesy NOAA, Weather Bell Analytics (Meteorologist Joe Bastardi, Twitter)

As is often the case with daytime snow this time of year, the greatest chance for accumulations on Wednesday will be on grassy surfaces to the north and west of the Philly and New York City and especially in any higher elevation location (e.g., western Chester, Upper Bucks, western Montgomery in SE PA; interior NW NJ).  In terms of estimates on snow accumulations, while there is an outside chance for a coating of snow in some of the far northern and western suburbs of DC, this is primarily a rain event south of the PA/MD border. A coating to a couple of inches of snow is likely on grassy surfaces in areas to the north and west of Philly and New York City with even a bit higher amounts possible in those higher elevation suburban locations mentioned earlier. The precipitation winds down by tomorrow evening from southwest-to-northeast. One final note, freezing rain is not likely with this mid-week system as atmospheric temperatures are not likely to be conducive (i.e., surface temperatures should be above freezing for the most part), but sleet can mix in at times; especially, across southeastern PA during the mid-day hours on Wednesday.

A powerful jet streak aloft on Saturday, March 12th, will contribute to very strong low-level winds that are likely to develop in the Mid-Atlantic/NE US from later Saturday into Saturday night. Map courtesy NOAA, tropicaltidbits.com

Very active early weekend Arctic frontal passage with extreme winds, accumulating snow on the table

After a couple of fairly tranquil days on Thursday and Friday, the weather turns more active at week’s end and going into the early part of the weekend…and it likely becomes very active.  Another strong Arctic cold front will sweep eastward at week’s end and its passage on Saturday in the Mid-Atlantic/NE US will become quite a weather-maker. The Arctic cold front will be supported by some vigorous upper-air energy and a rapidly intensifying surface low pressure system will form along the boundary zone. There will be some pre-frontal rains from Friday night into early Saturday in the Mid-Atlantic/NE US and perhaps even some strong-to-severe thunderstorm activity.  Behind the front, temperatures will likely drop sharply later Saturday and the rain can very well change to accumulating snow across interior sections of the Mid-Atlantic and Northeast US.  In fact, there is a chance for a changeover to accumulating snow all the way into the I-95 corridor later Saturday and even to all coastal sections.

The vast difference in pressure later Saturday between the departing, very strong and still intensifying low pressure system over northern New England and a building high pressure in the southern US will likely result in extreme winds for the Mid-Atlantic/NE US. Map courtesy NOAA, tropicaltidbits.com

In addition to the threat for accumulating snow on Saturday, a big concern is the chance for extreme winds following the passage of the strong Arctic cold front.  A tremendous pressure gradient will develop between the departing, strong and still intensifying low pressure system over northern New England by later Saturday and a strong high pressure system building over the southern states.  The result could be wind gusts in the 50-60 mph range from later Saturday into Saturday night and this kind of intensity can certainly raise the possibility of some downed tree limbs and power outages. The atmosphere calms down some by later Sunday, but temperatures will remain well below-normal for this time of year as we close out the upcoming weekend. There is a big warm up likely coming to the eastern states by later next week.

12Z Euro features a very vigorous wave energy aloft by Saturday evening which will support a strong and still intensifying surface low pressure system over the Northeast US. Map courtesy NOAA, Pivotal Weather

Stay tuned on this early weekend event…still a few days away and a very energetic pattern is setting up that will require close attention.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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