1:00 PM | **"Winter" to go out with a bang this weekend; especially, north of the PA/MD border**

12Z GFS total snowfall map for weekend system (Note - 10:1 snow ratio is used for this map and that is probably overdone); map courtesy tropicaltidbits.com, NOAA

Overview
This could very well be the end game of the 2015-2016 winter season in the Mid-Atlantic region (FINALLY!) and it is looking more and more like it will be quite a remarkable finish; especially, in areas north of the PA/MD border.  Another Arctic air mass will move into the Mid-Atlantic region this weekend and this one will be accompanied by accumulating snow in areas north of the PA/MD border with several inches possible in some of the higher elevation locations (e.g., Poconos).  In addition to the cold and accumulating snow, winds will become a factor on Saturday and pick up dramatically as the day progresses.  An increasing concern has to be the potential for power outages north of the PA/MD border given the possible combination of strong winds, heavy wet snow, and trees now with budding leaves.  After this storm departs, temperatures will drop sharply - perhaps to record levels for so late in the season - with lows by early Sunday morning in the 20’s in most areas (map below).  

12Z NAM forecast map for Sunday morning low temperatures; map courtesy Weather Bell Analytics, NOAA

“Clipper” system
A strong upper-level wave of energy will spin off a “clipper” type of low pressure system in the Ohio Valley by early tonight.  This low pressure system will travel in a general west-to-east on Saturday across southern Pennsylvania.  Precipitation amounts will tend to be considerably higher for this upcoming system along and to the north of this expected west-to-east storm track (see 12Z GFS total precipitation forecast map below); consequently, the greatest threat for snow accumulations on Saturday will be in areas north of the PA/MD border.  As the storm strengthens on Saturday, the winds will pick up noticeably and gusts to 40+ mph will be possible by late in the day and those strong wind gusts will continue tomorrow night. 

12Z GFS total precipitation amounts for weekend system with highest amounts north of the Pennsylvania/Maryland border; map courtesy NOAA

North of the PA/MD border 
In this region, there will be cold, accumulating snow, and strong winds to deal with this weekend.  First a word about snow accumulations in April… they can be quite variable across a given metro region and are especially dependent on the following factors: time of day (i.e., sun angle), elevation, and ground-level temperatures.  Any snow that falls during the day on Saturday is likely to stick much more readily on grass and other “non-paved” surfaces. However, don’t be too complacent - if snow comes down hard enough and it probably will - it can stick to roadways even in the daytime in April as was proven just last weekend across much of southern New England. In general, elevations in the Philly-to-NYC corridor tend to pick up to the north and west of the cities.   The greatest snowfall amounts on Saturday and Saturday night are likely to occur in the highest elevation locations to the north and west of Philly and NYC (e.g., interior northern NJ, east-central PA and the Poconos Mountains in NE PA).  

Precipitation is likely to break out early tomorrow morning across eastern PA, NJ and the NYC metro region and continue intermittently for awhile as a mixture of rain and snow  By later in the morning, precipitation should become all snow in all areas as colder air wraps around the system and winds will pick up noticeably during the afternoon. Snow is likely to continue tomorrow evening and winds could gust past 40 mph. After midnight, skies will gradually clear and temperatures will generally drop to the low-to-mid 20’s by the time Sunday morning rolls around - watch for "black ice". Accumulations in the Philly and NYC metro regions will likely vary quite a bit from a “coating" to as much as “4 or 5 inches” depending on such factors as elevation and surface type.     

South of the PA/MD border
In this region, the cold and strong winds will be more important factors to deal with this weekend than the snow.  Snow showers are likely to break out after midnight in the DC metro region – likely mixed with rain at times and perhaps even some thunder.  Snow and/or rain showers will likely continue through Saturday morning and then taper off during the late afternoon hours or early evening hours. Winds will pick up noticeably by tomorrow afternoon and gusts to 40+ mph are possible later tomorrow afternoon and early evening.  As far as snowfall is concerned, a “coating to an inch or so” is possible to the north and west of the District; especially, in higher elevation locations. 

Temperatures will drop into the middle 20’s for lows by the time Sunday morning rolls around. According to the Washington Post/Capital Weather Gang, if the temperature falls to 32 degrees or lower in Washington, D.C. early Sunday morning, it will be the first time that has happened this late since 1997 when the record low temperature for April 10 was set (28 degrees). If Reagan National Airport (DCA) hits 29 degrees or lower, it will tie for the 10th-coldest temperature observed so late in the season. Any temperature below 28 degrees on Sunday morning at DCA would rank in the top-5 coldest late-season temperatures on record. The coldest/latest on record was 22 degrees on April 19, 1875. The coldest April temperature on record for the city was 15 degrees on April 1, 1923 (info courtesy Washington Post/Capital Weather Gang).
 

Phillies/Mets
One final note, the Phils are scheduled to play the Mets tomorrow evening in New York – weather permitting (and also this afternoon).  Odds favor a postponement for tomorrow’s game given the expectation of the chill, strong winds and possible snow; however, if they manage to play it could be quite an interesting scene.

Meteorologist Paul Dorian
Vencore, Inc.