Updated Sat 10:01 PM —Tonight’s models are showing light showers and clouds lingering early morning Sunday before clearing develops from Philadelphia and westward by noon. Mostly sunny skies develop in the afternoon.

Clouds and showers linger several hours longer in NJ. 

Update Sat @ 9:00 PM —

Updated Sat 7:08 PM —So far today, the showers and thunderstorms developed south and east of Philadelphia with an upper air disturbance moving east.  This feature was first visible on water vapor imagery at 12 PM.

So the storms stayed to our south. Incredibly, the models are still showing showers and storms developing later this evening that will affect more of the Philadelphia area, but most activity south and in NJ. I’m not convinced

Mobile Update Sat 1:43 PM — Looking at water vapor imaging (while riding my bike!), it looks like the front boundary is right at Phladelphia at 1 PM. Any storms will develop from Philadephia south and east about 4-6 PM. Latest HRRR downplays storms.

Update Sat @ 9:36 AM — Latest 12z models just becoming available. Partly to mostly sunny for much of the day. Showers and thunderstorms move in between 4 and 6 PM.

Latest NBM at 4 PM—

Latest 12z HRRR at 6 PM—

Updated Fri 10:53 PM — Tonight’s early models continue with the moving target forecast for Saturday. Of interest is the NAM-NEST which has significant sunshine for most of the day, with a line of thunderstorms moving through between 7 and 8 PM Saturday evening. The NAM-NEST has been relatively consistent over the past day.  

Tonight’s HIRESW is similar to the NAM-NEST, but the line of showers comes through 4-6 PM 

The new NAM-NEST is similar to today’s Canadian High resolution model (HRDPS), so  I’m leaning towards this forecast, but with low confidence.

Tonight’s HRRR has a forecast similar to that posted earlier this evening, with showers and storms beginning early afternoon. The latest ECMWF has showers throughout the day. So an uncertain forecast. 

Previously Posted Fri 7:54 PM —

Over the past few days, I’ve watched the weekend forecast change with each model run. There hasn’t been any one model that has done any better than any other. Each model run has been different with little continuity. I expect the same with the specifics of Saturday’s forecast.

Even the current weather (Friday afternoon) was not accurately depicted by the morning models; storms developed Friday afternoon in Lancaster and Chester counties, but not in Lehigh or Carbon counties as forecast. The storms fell apart as they tried to move eastward; to some extent, this had been hinted at last night.

One thing that HAS been consistent: the weekend weather forecast for the immediate PHL area has continued to improve. Most models now show Sunday and Monday rain-free!

So, the unknown now is the specifics of Saturday’s forecast. The models differ: some have showers and storms early to mid afternoon. Some have showers and thunderstorms developing after 4 PM. Some keep most of the activity just south of the Philadelphia area into Delaware, Maryland and South Jersey.

Example: Several models (all different resolutions) showing precip at 4 PM Saturday—

As different as these model forecast appear, this is actually as close as they’ve been. We can pretty much count on some rain at 4 PM somewhere. (or can we?)

Saturday

Sunny in the morning, some clouds. Increasing clouds in the afternoon. Showers/thunderstorms break out between 2-4 PM. (see NBM below for likely location) Showers and thunderstorms continue and taper after 8-10 PM. High temp 87.2º± 2.7º, NBM Model for Blue Bell PA.

Sunday

Some clouds in the morning, breaking for sunshine by late morning. (Clouds linger later further east into NJ) High temp 85.6º± 2.6º, NBM Model for Blue Bell PA.