Daily Archives: Friday, September 4, 2026 8:05 pm

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sunday Forecast Update

Posted Saturday 09/05/26 @ 5:26 PM — Today there was considerable cloudiness in Delaware and Chester counties as thunderstorm activity in Maryland and Delaware sent outflow moisture as cirrus clouds over our southern counties.

Combined with mid level moisture, these high cirrus clouds cast a shadow, cooling the moist air below to allow for a “Lifting Condensation Level” (LCL) to establish itself, thus allowing rather threatening, dark, billowy cumulus clouds to form. Despite the threatening appearance, no rain fell from these clouds near us.

On Sunday we’re confronted with a forecast that involves a closed upper low near Nova Scotia, and an easterly flow off the Atlantic. The AI models (ECMWF-AI and AIGFS) show light scattered rainfall along the coast and in NJ. The HRRR keeps this activity off shore while the RRFS has almost no cloudiness to speak of. The NAM-NEST is most like the AI models—

18z NAM-NEST forecast for varying clouds and scattered showers at the shore at 2 PM. This is most compatible with the AI models. (Click on image for a larger view.)

Usually the NAM-NEST does not lean towards cloudy as a rule, so its similarity with the AI models suggests we should lean towards its forecast rather than the very sunny and dry RRFS/HRRR.

Originally Posted Fri 8:05 PM —The edge of the heat dome is expected to sink south of our area over the weekend. Some moisture and some disturbances may result in some isolated showers tonight and again on Sunday afternoon.

Current water vapor image shows the 576 heat dome edge just to our south tonight as disturbances bring showers from Baltimore and southward.

Water Vapor image at 7:30 PM with superimposed RAP model Mean Seal Level pressure (black contours), 500-1000mb Thickness (yellow contours), RAP potential vorticity contours (violet fine contours) with MRMS Radar with surface wind barbs, (Click on image for a larger view.)

By Sunday, the GFS has some disturbance rotating around an upper low pressure system near Nova Scotia. A few isolated showers are possible on Sunday, especially at the shore.

GFS forecast for Sunday at noon. Some showers develop from an easterly flow and triggers that rotate around the upper closed low. (Click on image for a larger view.)

Monday looks to be the best day of the Labor Day Weekend with plenty of sunshine and low humidity.

Saturday– Some clouds in the morning then partly to mostly sunny.

Sunday– Sunny in the morning, some cloudiness in the afternoon with isolated to scattered showers possible, most likely at the shore.

Monday– Sunny and pleasant.