Daily Archives: Friday, May 8, 2026 7:05 pm

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Sunday Forecast Updates

Posted Sunday 05/10/26 @ 9:37 AM — This morning’s models show showers (and some thunderstorms) developing in western sections as early as 3 PM but won’t likely move into the city until 6-8 PM. The thunderstorms will likely not be severe and will occur mostly in southern Chester and Delaware counties.

As the front stalls a wave of low pressure will bring additional showers around midnight. The latest Model Blend (NBM) has the showers exiting early Monday morning, except in S. Jersey.

Dry and clouds gradually clearing on Monday.

12z Model Blend showing clouds (dark) and showers at 12 noon Monday. Our area will be dry and gradually clearing. (Click on image for a larger view.)

Updated Saturday 05/09/26 @ 9:42 PM — Much of our area had very little rain today. As for Sunday, the models are increasingly forecasting a line of showers to pass through with a cold front during the mid to late afternoon into the early evening. This front is expected to stall as a wave of low pressure rides up with showers into Monday.

Unlike Saturday’s weather which was driven by upper air disturbances and “forcing”, Sunday’s weather will be more surface frontal-based and should be forecast better by the models.

Saturday Forecast Update

Posted Saturday 05/09/26 @ 11:00 AM — This morning’s high resolution models have become available. The NAM-NEST model seems to be most aligned with what is happening on radar and satellite imagery, although its rain shield still lags about 1-2 hours.

Rain is already falling in western sections and will likely continue. The trigger for increased rainfall is shown in the image below and it will cause rain mostly west of our area to start.

Theta level thermodynamic upper air trigger identified. Path of this trigger identified with white arrows. (Click on image for a larger view.)

The NAM-NEST has rain moving in about 1 PM to the immediate PHL area, if not sooner. But where this system will cause heavier rain varies and is uncertain.

One thing this morning’s models have in common- rainfall about 7-8 PM in Philadelphia, possibly affecting the Phillies game. None of the models have particularly heavy rain in-store for us, except a few locations in NJ. The doughnut (or donut) hole of little precipitation still shows for parts of the immediate PHL area with this system. No matter how you cut it, today’s forecast remains low confidence.

Saturday Known Unknowns

Posted Saturday 05/09/26 @ 9:10 AM — With this upper air driven system, the models are having difficulty with the forecast today— none of the models from last night remotely match the current MRMS radar—

MRMS radar image at 8:30 AM. None of the models match this precipitation pattern at all. (Click on image for a larger view.)

I’ve even run the 11z RAP and RRFS, models from just 7 AM this morning; again neither captured the forward advance of the rain into Lancaster/Berks counties.

Additionally, surface pressure change, another parameter I like to match to determine the model best capturing ‘reality’ all come up short. As a result, the forecast for today is extremely uncertain. Rain will move in…actual timing may become clearer with the 12z models (which take direct upper air measurements with weather balloons.)

For now, expect showers. Will we get higher amounts in NJ as forecast last night? Will there really be some moderate level thunderstorms about 4 PM? It’s unclear.

Sometimes the best forecast information is knowing that we just don’t know.

Previously Posted Fri @ 7:05 PM — —Our weather on Saturday will be influenced by strong upper air disturbances with an assist from the position of the jet stream.

Water Vapor image at 5 PM with superimposed RAP model MSL pressure (black contours), GFS/NAM potential vorticity contours (yellow & violet fine contours) with MRMS Radar and surface wind barbs, The stream of radar echos from the upper air disturbance in Oklahoma/Missouri will move and induce precipitation in our area on Saturday. Click on image for a larger view.)

Because this weather is being forced by upper air disturbances and jet stream induced lift, placement of the rainfall maxima will be difficult to predict accurately. I’ve reviewed the HRRR, HRDPS, ECMWF-AI, GFS, NBM, REFS and RRFS to get a handle on the rainfall for Saturday.

The model blend (NBM) is the best bet here for accumulated rainfall—

18z NBM total rainfall forecast by Sunday morning. (Click on image for a larger view.)
Saturday

Low clouds will predominate on Saturday. While some light showers are possible in the morning, most areas may not see any precipitation. The action starts about 2-4 PM as rain and moderate level embedded thunderstorms develop. Some models have an abrupt end around 6 PM; others keep showers around until at least 8 PM. Highs: Blue Bell- 67º Philadelphia 69º ±3.5º (Large standard deviation!)

Sunday

Clouds early, the mostly sunny for much of the day. A very widely scattered shower or thunderstorm is possible late afternoon; most areas will not have any showers. Most likely areas are Delaware and northern Bucks County. Highs: Blue Bell- 79º Philadelphia 81º ± 2.5º (Average standard deviation!)