Sunday, December 04, 2011

Prelude To Late Week Cold

Today's mild weather and the warmth we're expecting through Tuesday will be a distant memory by week's end. A slow moving frontal boundary will take until Thursday to fully leave the region, with the potential for a few rounds or precipitation between Monday night and Thursday. The first couple of rounds will be mild and showery -- with temperatures generally in the 50's at night on Monday night and most of Tuesday night before a cold front slides through towards dawn on Wednesday.

 The third shot of precipitation develops along the front and slides northeast in the form of weak low pressure on Thursday.  Modeling consensus keeps the low far enough to our southeast and weak enough that precipitation will be confined to south/east of I-95, generally in the form of rain. An outlier, the GFS computer model, has been waffling and incredibly inconsistent in showing different solutions as it brings this low in much stronger and not as sheared out as the Euro computer model does. As a result, the stronger GFS solution brings more precipitation...and perhaps snow...to the Delaware and Lehigh Valleys. Keep in mind that the GFS has varied in solution and forecast for each of its last several forecasts whereas the Euro so far has held a much more consistent course and has generally shown a weaker system that brings little in the way of precipitation and even less in the way of snow.   The consistency in the Euro may not ultimately verify but it lends a lot of confidence to less or no snow as opposed to a rain/snow event on Thursday.
Assuming the weak solution holds...any significant precipitation (generally rain) stays away from Philly and to the Shore and Delmarva.   What is more consistent among computer models is coming for this weekend in the form of a stronger shot of Canadian chill -- a cold front crosses the region on Friday night, with temperatures struggling to reach 40 on Saturday and perhaps holding in the mid 40's on Sunday...if not colder.   Winter's slow march is about to hit...it might not really seem that way with the mild weather we're getting but by week's end it's going to feel much more like December than it is today.