Tuesday, March 06, 2012

How Warm Can Thursday Go

For those who love warm weather in March, this year may be one of those occasions when you're smiling frequently. After the cool chill of the past three days, high pressure will reward everyone with a two day taste of Spring starting tomorrow afternoon.  As the high nudges off the coast, milder southwest breezes will take over across the Mid Atlantic, helping boost temperatures quickly tomorrow to the lower 60's in many locations.  This high is almost in an optimal position for big time warming -- southeast (or east-southeast) of us, with a nice southwest trajectory of wind at the surface and also aloft.  Those two factors will combine to give us another Spring Fling in the Delaware Valley in a cold season that has featured plenty.

This setup is a bit different than the one we had in early February...the one where we had temperatures get to 67 in Philadelphia and nudged close to 70 in some parts of the region.  In that warm surge, the factor at play was a west wind post-frontal boundary passage and a lack of a cold air push with the front when it moved through.  This time, the front is farther west...over the Great Lakes.   In this type of setup, under sunny conditions, we would have a really good shot at hitting 70 on Thursday afternoon in the city and someone south of the city could easily end up in the middle 70's.  The one fly in the ointment will be low level moisture in that broad southwesterly flow -- you can see it in the Carolinas on the GFS depiction up above for Thursday afternoon in the light green shading.  Some of that may sneak up into the region, increasing clouds on Wednesday night and early Thursday morning before sunshine is able to bust through those lower clouds and clear things up in the mid/late morning.

If the cloud cover issue does rear its head Wednesday night and Thursday morning, temperatures probably don't get to 70 in Philadelphia but instead "only" get into the mid and upper 60's, which is where computer guidance has us for Thursday (they do account for some lower clouds developing).   Still rather nice -- still significantly above average for this time of the year -- just not that seventy degree reading some of the warm mongers are drooling for.  We'll need a bit of a goldilocks outcome to get there -- near full sunshine and a minimum of cloud cover.  If we can get those, 70 may just happen.