Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Fri 9:24 AM —Forecast Review — Last evening’s rain arrived within the time range given, but really about an hour or so later than I had expected. Total rainfall was somewhat on target, with much heavier rain than forecast eastern areas and in New Jersey.

Here’s the MRMS QPE (quantity of precipitation estimate)

MRMS 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.)

Thursday Forecast Update

Posted Thursday 03/20/25 @ 11:04 AM — It looks like the breaks of sun will be in the morning. Increasingly cloudy in the afternoon.

Visible Satellite and Radar with HRRR 3 hour surface pressure delta. Notice the area of negative pressure delta just east of Philadelphia. Low pressure will form in this area. (Click on image for a larger view.)

Posted Thursday 03/20/25 @ 8:42 AM —Today’s forecast mostly on-track. Low clouds this morning will give way to mid level cloudiness this afternoon. Some areas may see some sun for a period this afternoon, but most will remain cloudy. Showers and rain moves in from the west between 5:30 PM and 8 PM. Total rainfall this evening between 0.45″ and 0.70″ (western suburbs may receive the higher amount). Windy conditions later this afternoon and then again later tonight. The actual frontal passage may not have much in the way of winds.

Posted Wednesday 03/19/25 @ 5:57 PM — The AI ‘experiment’ showed no winners, with the spatial and temporal resolution differences between the models over-shadowing any small differences in forecast high temperatures. That said, except for Center City, the NBM high temps were overall too low. Here’s the RTMA temps at 3:45 PM. the likely high temps for the day—

RTMA temperatures at 3:45 PM The RTMA records preliminary observed and interpolated temperatures at 15 minute intervals. (Click on image for a larger view.)

As for Thursday, a cold front (technically an ‘anafront’ type cold front, due to the rain following the frontal passage) will move across about 6 PM with showers and possible thunderstorms.

GFS forecast showing the ‘anafront’ type cold front. (Click on image for a larger view.)

Low clouds in the morning with mid-level cloudiness in the afternoon. Some breaks in the overcast possible just before the front moves across about 6 PM. Low pressure expected to form along the anafront, bringing more windy conditions. About 0.4-0.6″ of rain expected during the evening Thursday.

Yet Another AI Model ‘Experiment’

Posted Wednesday 03/19/25 @ 9:34 AM — There are differences today between the high resolution NBM model (our best model for temperatures) and the lower resolution ECMWF-AI-Single model regarding high temperatures for today.

The AI model has an easterly wind keeping temperatures from the city eastward below 70º, while large areas just west of the city are above 70º

ECMWF-AI-Single high temperatures at 2 PM. It should be noted that the AI model only forecasts on 6 hour increments, The high temperature will likely be reached at 3:00 PM or so, not 2 PM, so these temperatures may be a bit low. (Click on image for a larger view.)

Here’s the latest 12z NBM model high temperature forecast for today—

The latest NBM shows most of the area just under 70º as a high. (Click on image for a larger view.)

An interesting and significant difference in the forecast. Either way, a very nice day, with some high thing cirrus clouds moving in about 3 PM.

Thursday will likely have rain moving in between 3PM and 6 PM ahead of a cold front. Some ‘interesting’ weather possible.

Wednesday through Thursday Outlook

Posted Tuesday 03/18/25 @ 5:34 PM — Wednesday promises to be a spectacular day, with mild temperatures just short of 70º. Sunshine in the afternoon will be through some thin cirrus clouds as moisture and milder air move in aloft ahead of a cold front expected late Thursday.

ECMWF-AI Single forecast high temperatures at 2 PM. Lately, this AI model has been more accurate than the NBM regarding high temperatures. (Click on image for a larger view.)

A strong cold front approaches on Thursday with some rain/showers moving in by mid to late afternoon—

ECMWF-AI-Single forecast for 8 PM Thursday. Advancing cold front with low pressure forming on the front. Much convective activity (yellow green color) (Click on image for a larger view.)

About 0.5″ of rain is expected with this system.

Originally Posted Mon 8:04 AM —Some rain is still falling at the Jersey Shore and there’s a chance of a light shower this morning, especially east into NJ.

RADAR 8 AM Monday morning. (Click on image for a larger view.)

Clouds should break for some sun around noon or early afternoon.

The rain occurred later than forecast, the strong wind gusts preceded the rain. Many areas did eventually receive the 1+ inch forecast —

MRMS (Pass 2) 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.)

Our next chance for rain is late Thursday into Thursday night with a system somewhat similar to Sunday’s cold front passage.