Daily Archives: Monday, April 20, 2026 9:30 am

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Weekend Rain Update

Posted Friday 04/24/26 @ 9:08 AM — As mentioned last night, the RRFS was predicting more sun than clouds today (Friday) and was somewhat an outlier compared to the GFS and others. But it appears so far to be correct.

For the weekend, the latest RRFS is also somewhat of an outlier, with a band of heavy rain through our region.

Latest RRFS (06z) shows very heavy rain through our region. It’s somewhat of an outlier. The fact that its cloud forecast for today, Friday, seems more accurate, I’m still going with the RRFS for Saturday. This could change. (Click on image for a larger view.)

Most of the other models (GFS, HGEFS, GEFS, ECMWF-AI) have this band of heavier rain through NYC, not Philadelphia. We only get 0.60″ of rain around here, less to our south. I’m staying with the RRFS for now.

Scattered rain moves in during the morning, then becomes widespread and heavier during the afternoon and evening on Saturday. Windy and cool!

Slow clearing on Sunday; some scattered showers in NJ during the afternoon. Gradual break in clouds western suburbs early afternoon.

Friday & The Weekend Outlook

Posted Thursday 04/23/26 @ 8:03 PM — For Friday, we’ll see a mix of sun and clouds. Some models (GFS HRDPS) are forecasting significant cloudiness especially just north of Philadelphia. The RRFS shows much more sun than clouds and I’m leaning towards the RRFS.

Interestingly, the GFS, NAM-NEST, NBM and the HRDP show a brief sprinkle in Chester county as well as in the northwest suburbs Friday afternoon but I think it will rain free in most areas on Friday.

A strong system in the upper Midwest moves in for Saturday and perhaps part of Sunday—

Water Vapor image at 8 PM Friday with superimposed RAP model MSL pressure (black contours), GFS/NAM potential vorticity contours (yellow & violet fine contours) with MRMS Radar and surface wind barbs, (Click on image for a larger view.)

Showers become more widespread Friday night into Saturday morning. By Saturday afternoon, some widespread, banded heavy rain will be falling. It will be quite windy and chilly with the winds coming from the east.

Rain is forecast to become quite heavy. Some models are cranking out 1.5+ inches of rain by noon on Sunday. There are some very strong dynamics favoring rain on Saturday. Here’s one measure of the dynamic called “frontogenic forcing” right into Philadelphia and especially north—

RRFS strong frontogenic couplet from Philadelphia northward Saturday afternoon. Heavy banded rain. (Click on image for a larger view.)

There’s model disagreement regarding how soon the rain exits on Sunday. The GFS has the rain continuing on Sunday while the latest ECMWF-AI has the rain ending by mid morning. The RRFS also has the rain ending. This uncertainty has existed for several days. It should hopefully clarify by tomorrow.

Check back for my regular Weekend Weather Forecast later Friday afternoon.

Wednesday Forecast Update

Posted Wednesday 04/22/26 @ 7:40 AM — Some very light showers moved through before daybreak. Some additional showers are poised to move through later this morning.

Water Vapor image at 7:30AM with superimposed RAP model MSL pressure (black contours), GFS/NAM potential vorticity contours (violet fine contours) with MRMS Radar and surface wind barbs, (Click on image for a larger view.)

Following this next round of showers around 10-12 PM, there will be clearing and sun breaking out.

In the above WV image, the violet box surrounds violet contours of “potential vorticity”. These are forecast to trigger additional showers in our area this evening, about 8 PM according to the latest RRFS—

06z RRFS simulated radar forecast for 8 PM tonight. (Click on image for a larger view.)

As has been the ongoing pattern, the heavier rain will move mostly to our south missing much of the immediate PHL area.

Today, the persistent ‘anticyclonic bulge’ in the yellow thickness contours captures the fact that the disturbance is moving into Philadelphia are encountering an unfavorable environment for rain.

Anticyclonic curvature (bulge) in the thickness contours right over our area results in an unfavorable environment of rain. Showers may reduce in intensity as they move towards Philadelphia. (Click on image for a larger view.)

Thursday looks sunny and warm!

Wednesday Forecast Update

Posted Tuesday 04/21/26 @ 6:08 PM — This morning’s forecast of light rain for Wednesday morning is still intact, with some minor changes:

The disturbance is moving through faster and will arrive about 2 AM-3 AM Wednesday morning with showers. It will also exit earlier; expect sun to break out by 12-1 PM, earlier to our west. Temperatures reach 60 by late afternoon.

RRFS Forecast Rainfall—

Tuesday-Wednesday

Posted Tuesday 04/21/26 @ 9:32 AM — We’ll have a sunny day today with a gradual warmup. A small, weak upper air disturbance will drop down from the Great Lakes area tonight—

WV image Tuesday morning with superimposed RAP and GFS model data. Fine violet contours indicate an area of “potential vorticity” (red boxed area) that will drop down over us following the jet flow. The same weak contours are anticyclonic over our area. Light scattered showers will result. (Click on image for a larger view.)

This disturbance will result in light showers over our region Wednesday morning—

ECMWF-AI forecast 6 hour precipitation by 2 PM. Light showers over our area Wednesday morning from this disturbance, as it mimics a warm front. Warmer weather by late Wednesday into Thursday! (The ECMWF-AI is a low resolution both temporally and spatially; rainfall looks more impressive than it is.) (Click on image for a larger view.)
Mon 8:20 PM —Rainfall— With all the clouds and showers, you might think we’re starting to get some much-needed rainfall. Unfortunately, we remain fairly dry.

Here’s the rainfall total (MRMS) over the past 3 days—

MRMS 72 hour rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

We may see some rain Wednesday morning. Forecast amounts are on the light side.

Originally Posted Mon 9:30 AM —A current large dip in the jet with cold high pressure will move off by later Tuesday. Cold air aloft along with some upper air disturbances may cause some light scattered sprinkles early this afternoon near Philadelphia and especially in S. Jersey.

06z ECMWF-AI forecast for Monday showing deep dip in the jet as indicated by the red/magenta thickness lines. (Click on image for a larger view.)

Freezing temperatures have been well-advertised for Monday night into early Tuesday morning.

Today’s 12z NBM minimum Temperatures by 7 AM Tuesday. All ± 1.5º (Click on image for a larger view.)

By Wednesday the high pressure system and jet dip moves off and we see a warm front bring some light scattered showers mid day.

06z ECMWF-AI forecast for Wednesday at 2 PM. Rain coverage likely not as great as shown here. (low resolution model) (Click on image for a larger view.)

A warm up is expected for Thursday and Friday