Thursday, April 19, 2012

Saturday Might Be Best Shot For Rain

The somewhat ballyhooed storm system for this weekend may, like many a storm system that looked good on paper a while back, end up not playing out close to model hype when reality sets in this weekend.  24 hours ago at this time, it looked like we would be faced with a relatively wet Sunday and Monday as low pressure was modeled to soak up the East Coast, bringing much needed rains to the region.  At this point, the low is still modeled to show up but the potential for a track farther offshore can't be discounted.

That leads us to Saturday...the potential for showers and storms is pretty high in the midday and afternoon hours as a cool front pushes in from the west.  The NAM and GFS are quicker (NAM below) than the Euro (bottom of the two maps) in timing the front through the region, with showers and storms possible into the area by midday in Philadelphia, in the afternoon at the Shore.   Severe, at this point, doesn't look likely but a few gusty rumbles of thunder along with a decent round of rainfall with the front are more probable.

Saturday, in general, doesn't shape up as a soaking event where the region would pick up an inch of rain or anything like that -- half inch totals can't be ruled out though as the front comes through the Delaware Valley in the afternoon and evening hours.   The frontal passage itself sets the stage for what happens with the southern low, which is poised to begin developing on Saturday afternoon and evening in the Gulf of Mexico. The relatively faster progression of the front in modeling is important as the front will set up a highway for the low to travel along.  The mid level trough that pushes in behind the surface front will be critical in determining how strong the surface low ultimately gets as well.  The GFS and Euro have two different views on the upcoming low as of this morning.

The Euro has a sharper trough in the mid levels (the 552 line is down into North Georgia), which helps develop a stronger surface storm.  The sharper trough helps keep the storm on a track closer to the coast.  The result would be some rain to parts of the region but heavier rains to North Jersey into New England, with us on the glancing blow side of the storm but where the Shore could pick up an inch or more of rain...not as much as prior runs, but a decent storm.   The GFS' trough placement is much less sharp -- the 552 line gets only to the Tidewater and is much more broad in base...the result is a weaker storm that generally impacts coastal sections of New England with some rain...but little in the way of moisture for us.  The "cold season" pattern this year has been dominated by faster moving, weaker systems...the odds would lean more in that direction and less in the wrapped up direction at this point...but getting some sort of impacts in terms of rain still can't be discounted completely.

We have seen the modeling on this storm shift from an inland track to out to sea over the past couple of days -- it would not surprise if there is another waffle as we approach the weekend...but which way the waffle ultimately goes will determine how much rain we get out of the second wave...if we even get rain at all.