Philadelphia Weather Outlook

THIS WEEK’S WEATHER

Fair and Dry

The rest of the week as well as the weekend continues to look good. There’s little spread among the models for this forecast—

GEFS sea level pressure forecast with amount statistical spread (shading) for Sunday at 8 PM. Colors show only 0-2 mb of spread in the GFS ensemble pressure forecast, indicating high confidence, low uncertainty. Bermuda high with additional high pressure in the Virginias will provide fair skies. (Click on image for a larger view.)

Long Period of Warm and Dry Weather

Update Tue 09/13 @ 8:21 PM —An extended period of dry and increasingly warm weather will be with us through the weekend and well into next week.

GEFS forecast for Sunday at 8 AM Surface high pressure (1) and a building upper level high, with fixed low pressure (2) in the North West. (Click on image for a larger view.)

A building upper level ridge in the center of the country and a large area of high pressure at the surface will become somewhat stationary. No rain expected and high temperatures will be moving into the low 80s by the weekend and into the upper 80s by next Wednesday. Great weather to be in the outdoors; not much action for weather enthusiasts. Enjoy!

Updated Mon 9/12 9:54 PM —Tonight’s early models continue to show an expanding area of showers and some embedded storms developing. The area expands westward from NJ back into the Philadelphia area and moves northward.  Timing is between now and 1 AM.

Radar 10 PM

Updated Mon 9/12 8:53 PM —So with all the models I access daily indicating rain with some strong embedded storms this evening, I just saw the forecast from this morning’s LAMDAX experimental model.

It has exactly what we’re seeing now: weak rain here with most of the stronger storms moving through Baltimore and Washington.  A second line of storms will shear off to our northwest, according to the LAMDAX

Heavy Rain, Storms Monday Evening

Update Mon 09/12 @ 4:14 PM — Rain and thunderstorms are already developing to our southwest and will move into the area as early as 5:30 PM in western suburbs and the immediate Philadelphia area between 7 PM and 10 PM. Some activity may linger as late as 1 AM.

The latest HRRR seems to show the rain and storms intensifying as it moves into NJ with peak intensity there between 9:30 and 1 AM.

Today’s 18z HRRR shows high thunderstorm cloud tops as it enters New Jersey at 10 PM (cloud tops 32,000-35,000 feet) (Click on image for a larger view.)

Previously Posted Mon 9:46 AM —

A deep upper low is over the Great Lakes area and will move east. A cold front will move through this evening at a time of moderately high instability and strong upper air dynamics. Some heavy rain and thunderstorms are forecast as the result of high CAPE and high PWAT.

Only low to moderate vertical shear and helicity, so strong storms possible, but severe storms not as likely.

Current situation as shown on water vapor image—

Water Vapor image Monday morning shows deep upper low (L) and cold front drawn. (Click on image for a larger view.)

Weather Map corresponding to above image —

NAEFS current forecast map corresponding to above water vapor image. (Click on image for a larger view.)

Current forecast shows some very widely scattered showers/storms this afternoon, but the main event will likely be between 7 PM and 11 PM this evening.

I’ll update later this afternoon about 4:30 PM with the latest HRRR and NAM-NEST model data.