Updated Sat 11:35 PM — No change in Sunday’s forecast.

Update Sat @ 10:45 AM — The latest models show more showers developing early afternoon than previous forecasts. I’ve been waiting to decide on a bike ride today; not sure if I want to get rained on. Today’s forecast has been a moving target and a challenge all of this past week.

Updated Sat 8:48 AM — Last night’s 06z models keep the showers for the most part, far northern areas today, even a little further north than last night’s NAM-NEST update graphic immediately below. The original forecast still holds.

Update Fri @ 11:09 PM — The second batch of storms has entered our area tonight as forecast. The several rounds of storms may move through before 5 AM.

For Saturday —Tonight’s models have the upper low closing off around mid-day Saturday. As a result, more showers are expected, especially north and northwest of Philadelphia during the mid day and early afternoon Saturday.

Tonight’s NAM-NEST captures it —

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Previously Posted Fri 5:53 PM —

Those of you who regularly read this site have known there has been uncertainty with this weekend’s forecast, specifically Saturday’s forecast; a closed upper air low correctly predicted by the GFS as early as last weekend has undergone every conceivable forecast permutation. The ECMWF and the GFS have traded places over the week with forecasts of a closed low and open low.

As of 4 PM Friday, the closed low is clearly visible on radar image—

The GFS model forecast pretty much lines up with the current situation (as does the ECMWF) —

This closed low was expected to “open” as it moved over Pennsylvania Friday night.

Unfortunately, the GFS (but not the ECMWF) closes it off again Saturday afternoon!—

Since the GFS has been the [relatively] consistent about the closed low forecast and because it is supported by the latest GEFS, I’m inclined to lean towards its forecast for Saturday. However, the latest NAM opens the low and has a more optimistic forecast.

A closed low would mean more unsettled weather for Saturday throughout our area. The open low means that mainly areas north and northwest of the city would have showers. So Saturday’s forecast still has a lower than usual confidence.

Saturday

A mix of clouds and sunshine. Showers likely during the day north and northwest of the Philadelphia area. Some showers may sneak into Philadelphia. (Southern NJ looks much better- probably no rain.) High temp 77.4º ± 2.0º NBM model, Blue Bell

Sunday

Mostly sunny and warmer High 81.3º ± 1.3º NBM model, Blue Bell