Monday, December 26, 2011

Flood Watch For Parts Of Region Tomorrow PM

Southeastern Pennsylvania (including the city) and New Castle County are under Flood Watches for tomorrow afternoon and evening for the potential of a couple of inches of rain in short order.  Rain will move in during the midday and afternoon hours from southwest to northeast, becoming heavy at times during the late afternoon and evening rush hour before tapering off after 7 PM from west to east as low pressure tracks up I-81 and sends a cold front through the region during the evening hours.  This system will be a rainmaker as it moves through the region -- the track (west of the city, generally Harrisburg-Scranton for the low center) and timing (daytime) preclude any shot of snow on the front end of the storm.  It's possible the Poconos could see the system end as a few snowflakes but the region should avoid any frozen precipitation from the storm as it moves through.

Rain will be steady in the afternoon, heavy during the evening rush as the low pushes the frontal boundary through.  Computer model estimates suggest at least an inch of rain for parts of the region (the green shaded areas on the map below), with the potential for some isolated 1.50" amounts in parts of Southeast Pennsylvania.  The NAM is suggesting the most rainfall, with the GFS and Euro both suggesting about an inch or less for many.   All of the models suggest that rainfall totals will be highest across Eastern and Southeastern Pennsylvania -- both with the recent heavier rainfall last week across the region and the potential that rains could fall at a rather heavy rate during the evening rush tomorrow a flood watch was issued by the National Weather Service.
Rainfall shouldn't extend too far into the evening on Tuesday...ending in the western burbs after 7 and ending at the Shore by 9 or 10 PM.  In the wake of this system, Wednesday night could bring our coldest night of the cold season so far as low temperatures in Philadelphia drop into the mid 20's, with teens possible in the outer burbs.