Sunday, February 26, 2012

Raw Wednesday...Could Be Snowy Or Icy Nearby

Leap Day has never been particularly noteworthy meteorologically -- the most snow that has ever fallen on Leap Day since records were first kept was 1.0" in 1968.  I'll have more climate goodness later in the week on a once-in-four year plugged in calendar day but this Leap Day might end up being a bit raw and rotten here in Philadelphia, with snow possible not too far to our north.

A storm system is poised to organize across the Midwest and Great Plains on Tuesday, with the primary low pressure center tracking into Minnesota on Wednesday morning.  However, its northward advance will be halted thanks to the presence of high pressure over Quebec.  The high will force the storm energy east through the Great Lakes and into the Northeast, spreading rain for Philadelphia but a plethora of precipitation types to Poconos and higher elevations north of Philadelphia.

While the models agree in principle on the idea that energy will shoot east and that precipitation will fall.  However, as this precipitation shoots east along the southern periphery of the high pressure center, the models disagree in how strong the high pressure center is going to be.
The European computer model is the stronger modeled of the two -- its high pressure center is over 1032 millibars (pretty strong high), while the GFS' is below 1032.  This is critical because that Canadian high's influence on our weather is dependent on its strength.  A stronger high pressure center will be able to funnel colder air into our region and also hold the chill in place longer.  This would allow precipitation to start as snow closer to our region before the transition to a cold rain as milder air pushes in aloft.   One also has to look at the possibility of icy rain and sleet falling over the Poconos or perhaps even the Lehigh Valley if the lower level cold air holds or funnels in while above freezing air pushes in aloft.  Alas, the plethora of precipitation ahead of us.

As of now, Philadelphia and the immediate suburbs are in line for rain from this.  There could be some front end flakes or sleet in the northern parts of Chester/Montco/Bucks before a transition to rain, with a steadier burst of snow possible in the Lehigh Valley and Poconos, which is where the best chance of accumulations resides.   Some spots could pick up a few to even several inches of snow in the Poconos from this event before any transition to icy rain or sleet.   Lots of uncertainty resides about specific precipitation type up to the north of I-78 but it's looking more likely as we approach this storm system that they see at least some wintry precipitation from it...whether it be snow, sleet, or icy rain.

We'll keep an eye on it over the coming days.