Category Archives: Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

Sat 7:50 PM —Forecast Review —There was quite a range in rainfall totals for Saturday. As is almost always the case, the models rarely forecast the heavier banding of rainfall in a way that way that closely resembles reality.

Here’s what the MRMS rainfall summary shows—

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.)

Rainfall totals today did little to reduce the current deficit. A hot, dry summer remains a strong possibility.

Saturday Forecast Update

Posted Saturday 04/26/25 @ 9:34 AM — As forecast, “some bright spots and even some sunshine” has already developed. (The models often don’t show this following a warm front passage.) That said, it will still be difficult to forecast a specific time period today where we’ll definitely be rain-free, since the models shows scattered showers and storms in different locations at different times throughout the day.

The most likely time for somewhat organized rainfall will be with the cold front, still forecast to occur between 3 PM and 7 PM. Here’s the latest REFS (experimental) forecast for 6 PM—

06z REFS combined rain (plus statistical spread) at 7 PM. The experimental REFS is a statistical model that uses the experimental RRFS and combines it with time-lagged HRRR model forecasts to create a group of models, allowing a statistical analysis. The group of models is called an ensemble. Standard deviation (statiscal spread) can be calculated from this group of models. (Click on image for a larger view.)
06z REFS total rainfall forecast. Hardly a drought buster. (Click on image for a larger view.)

Not much rainfall expected with this system and certainly less than the 1.4″ the much-touted regular ECMWF was forecasting two days ago. (The ECMWF-AI did much better with a forecast of 0.52″ or less.)

Any prolonged sunshine this afternoon (still a possibility) may result in heavier thunderstorms and more localized rainfall.


Saturday Forecast Update

Posted Friday 04/25/25 @ 5:10 PM — There’s greater agreement among the models regarding the total rainfall. Most have between 0.5″ and 1.0″ of rain with the majority of the immediate PHL area seeing only the 0.5″ amount. Not really the soaking that was talked about.

Many models are showing scattered showers with possibly some thunder tonight, as early as 11 PM with the warm front. Rain tapers off about 8 AM Saturday morning, but there’s an increasing chance of more showers and possibly some thunderstorms again from noon to 8 PM.

It would not surprise me if we see some bright spots and even some sunshine at times during the day. But, it’s difficult to pinpoint any definite lull in the action. There will be lulls several times during the day.

The ECMWF and ECMWF-AI have showers lasting until 8-10 PM, while the NAM-NEST and experimental RRFS/REFS have the precipitation ending earlier with the final line of storms moving through between 3 PM and 7 PM. Some of the thunderstorms may be strong (but not severe.)

12z RRFS (experimental) rain/radar at 6 PM (Click on image for a larger view.)

Early Edition

Posted Friday 04/25/25 @ 8:51 AM —The forecast for today, Friday as well as Saturday, has a bit more uncertainty from yesterday’s posting regarding the timing of the rain and thunderstorms, as well as the amount of rainfall in our immediate area.

An associated warm front and cold front of a low pressure system will pass through our area later tonight and through Saturday.

Current satellite water vapor image (8 AM Friday) with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. (Click on image for a larger view.)

It appears that more cloudiness this afternoon is likely, compared to yesterday’s forecast. Light rain is possible this evening, according to the latest ECMWF-AI model and the experimental REFS. So the system is approaching faster than previous forecasts.

Showers persist Saturday morning, but it’s likely we’ll see some bright spots or even some sun before the cold front moves through with more showers and thunderstorms.

Yesterday’s forecast had the cold front moving through about 2-3 PM Saturday with rapid clearing by evening.

Today’s forecast has Saturday‘s rain/thunderstorms somewhat later, between 3 PM and 7 PM, (although the ECMWF shows showers with the cold front as early as 1-2 PM) and lingering into the evening hours as the cold front sharpens and intensifies as it moves through. So we may still have some showers as late as 8-9 PM. Saturday will also be quite windy! So the timing of the heavier rain/thunder on Saturday is “up in the air”.

Regular ECMWF model prior 3 hour rain forecast at 2 PM Saturday. (Click on image for a larger view.)

Sunday looks partly to mostly sunny and fairly windy. (The experimental RRFS-A shows periods of instability cloudiness with less sunshine. Sunday’s highs low to mid 60s


WEEKEND WEATHER FORECAST

Posted Friday 04/11/25 @ 1:49 PM —An upper closed low pressure system will bring rain and chilly conditions, as it keeps the surface low developing off the coast from exiting.

Rain Friday night into much of Saturday. Here’s the ECMWF-AI forecast for 2 PM Saturday—

ECMWF-AI forecast for 2 PM Saturday. The Blue L is the upper low which will sit directly over our area. Rain much of the day, tapering later in the day. (Click on image for a larger view.)

By Sunday, the upper low has moved off the coast but a cold pocket of air aloft (red thickness contours) will keep cloudy skies. A shower can’t be ruled out. An inch to two inches of rain is currently forecast.

ECMWF-AI forecast for 2 PM Sunday. Rain has for the most part stopped, but the red thickness lines indicate cold air aloft that will keep things fairly cloudy. (Click on image for a larger view.)

The ridge developing in the Central US will bring milder temperatures and better weather next week.