Wednesday, April 10, 2013

April -- The Cruelest Month

In the wake of today's run for record...or near record warmth, tomorrow is offering my hair a chance to turn gray given the potential for a backdoor front sliding on south through the region.  Modeling has varied with the front and we have a pretty wide spread in the guidance regarding how tomorrow plays out....but the GFS and NAM are in pretty solid agreement that the backdoor front slides through later tonight in the wake of any thunderstorms that fire up and move through.

Temperatures tomorrow could be significantly (and that's an understatement) cooler than what has been predicted by many until recently...and potentially that may even be a bit warm.  With an east breeze off of 45 degree (or so) water, temperatures are going to struggle to warm...and with low clouds likely to push in from New England and off of the Atlantic, plus additional clouds pushing in from the west with another storm system, it's going to be a rather "fun" forecast day.

The first graphic below shows the temperature spread according to the NAM on Thursday around 11 AM -- with mid and upper 70's to our south, around 60 in the city, and 40's and 50's across the northern and eastern burbs.  Temperatures don't warm from here through the balance of the day and in fact drop into the 40's by dinner north and east of the city.

...and even into the upper 30's in the Poconos and Lehigh Valley according to the NAM by late Thursday night as the storm system that brings us Friday's rains push on in.  These graphics are in pretty stark contrast to what we talked about last night, when it appeared we might be able to coax a milder day out of tomorrow.  One of the factors in this is the increased threat for thunder this evening with a disturbance pushing east along the front that's to our north.  This disturbance will help pull the backdoor front down to our south a bit more and could very well send the front through Philadelphia late tonight.


Two modeling exceptions to the GFS and NAM are the Euro and the UK models -- both of which keep the front north of the city for most of Thursday and both support upper 70's to near 80 for highs on Thursday.

We'll keep a close eye on this since Thursday's forecast could vary quite a bit by location -- and could result in quite a bit of a temperature bust over a short geographic spread. It wouldn't be April without a backdoor front!