Updating Sunday's Rainy Weather

A malaise of gray and mildness today ahead of Sunday's soggy storm system that will bring a period of rain through the region, with some of that rain becoming rather heavy and causing stream flooding or water ponding on roads.  Flood Watches have been issued for Pennsylvania, Northern New Jersey (effectively north/west of the Turnpike from Trenton on north), and points north as the potential for some flooding does exist due to soggy ground and the potential of some heavy rainfall.

Sunday's event is looking like it will bring a rather significant amount of rain, once again, to our west, with areas east and southeast of Philadelphia getting the lower rainfall totals -- a half inch of rain or less is certainly not out of the question in Southern Delaware while parts of the Poconos or Lehigh Valley could see a couple of inches of rain.   The rainfall disparity is due to the track of low pressure with this storm.   While the primary low responsible for the cold front will track into Canada, a secondary low will develop on the frontal boundary and track northeast starting later today and intensify on Sunday.  This low will effectively track along or just northwest of I-95 from Raleigh through New York City into New England.   Areas to the east of the low track will see lower rainfall totals -- but could get some thunderstorms on Sunday afternoon as the low lifts in -- whereas west of the low track could see some steady to heavy rainfall starting Sunday morning and continuing until just after the low lifts past.

An example of the rainfall disparity is shown above -- the Euro is really socking Pittsburgh, Erie, State College, and Scranton with lots of rainfall while there's a pretty sharp cutoff once one gets to Philadelphia and even less rain falls to the east and south.  This trend is reflected in the other guidance as well -- although the GFS and NAM are hinting at a rainfall "bullseye" in the Poconos of 2-3" of rain (which the Euro is not).

Timing-wise, expect some spotty drizzle today while rain spreads east overnight tonight, hitting the western burbs by sunrise and spreading into the Philadelphia area during the morning hours.  South Jersey will be the last to see rain move in.   Some patchy showers can't be ruled out before the steadier rains hit on Sunday.   Since we will end up on the "warm" side of the storm for the most part -- temperatures in Southeastern Pennsylvania and New Jersey will stay mild tonight and Sunday, possibly staying in the low 50's in Philly overnight tonight.