March 21st, 2011 Forecast

 Cool air will slowly retreat as a storm system works into the Mid Atlantic tonight and tomorrow.   As the cool air retreats and precipitation moves in, rain will fall for most but the farther north one is the better your chances for some snow and sleet overnight.  As of now, the best chances for frozen precipitation reside north of I-78 but some sleet pellets can't be ruled out into the northern suburbs overnight tonight.    Precipitation will gradually change to rain up north during the morning hours on Monday.   There could be an inch or two of snow/slop north of I-78 late tonight and tomorrow morning and winter weather advisories are out for the Poconos due to the potential for accumulating slop overnight.

Temperatures tonight will drop into the mid and upper 30's south of I-78, near or just below freezing to the north.  Precipitation should move in after 4 AM west of Philly and after 5 AM in the city and points east.   Rain will transition into showers during the midday hours north of the city, while warmer air nudges in from the south during the day.  Skies will brighten a touch although there will not be much sunshine during the day for many of us as the warm push is not strong at the surface.  It should be, however, strong enough to nudge temperatures into the 50's during the afternoon hours for locations south of the Poconos, with low 60's possible in Delaware.   If there is some decent sun, temperatures could spike higher to the south.

A cool front will slide on southeast during the afternoon a line of thundershowers could pop along the front, especially south of Philadelphia, during the afternoon and early evening hours.  

Week Ahead:   With the aforementioned cool front slipping south on Monday night, Tuesday shapes up as a variably cloudy day.  The cool push before the front isn't that strong so temperatures should generally hang out in the 50's on Tuesday.   A second low pressure system works east on Wednesday and will bring us a chilly rain that could have some sleet or snow mixed in closer to Philadelphia.  Right now, I think the odds for frozen remain confined again to north of I-78 but this is not etched in stone by any stretch.   Temperatures on Wednesday will be rather cool -- low and mid 40's for highs in Philly.  This second storm organizes and intensifies into a blocking storm off of Newfoundland, setting up a cool regime for the end of the week with high temperatures staying in the 40's through next weekend.