Daily Archives: Monday, April 13, 2026 8:50 am

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday Forecast Update

Posted Friday 04/17/26 @ 11:03 AM — A weak upper air disturbance will combine with some moisture and instability CAPE to set off some showers about 3-5 PM. The showers will be scattered and not every area will receive some precip.

RRFS forecast for 4 PM Friday. Light scattered showers moving from the north towards the south-southeast. (Model precipitation forecasts rarely pinpoint the exact location for the scattered rainfall. Later (and earlier) model runs will likely show different areas receiving some light showers.) It’s just a general guide. (Click on image for a larger view.)

The latest ECMWF is forecasting showers for Sunday with likely greater areal coverage and amounts. Stay tuned for my regular “Weekend Weather Forecast” later today.

Friday

Posted Thursday 04/16/26 @ 9:43 PM — A weak cold front will move through after midnight. Showers and thunderstorms in central PA will fall apart as they move towards Philadelphia. The immediate Philadelphia area may see a few scattered drops before daybreak.

Friday will have periods of sunshine and periods of clouds. It will be considerably cooler, but still above average temperatures in the upper 70s.

For Friday, the RRFS remains the sole model predicting a weak low pressure circulation to form associated with an upper trough. A few scattered showers may develop late afternoon. (The latest HRRR and the GFS keep us dry.)

18z RRFS light rain accumulation by 9 PM. Rain moves off to the southeast. (Click on image for a larger view.)
Thursday-Friday

Posted Thursday 04/16/26 @ 12:35 PM — Temperatures today are expected to reach the low 90s.

13z NBM high temperatures at 4 PM Thursday. (Click on image for a larger view.)

A weak cold front and upper trough will pass through around or after midnight Thursday night. Once again, a line of storms will fall apart as they approach Philadelphia. Little or no rainfall expected.

The upper trough that moves through Friday may close off or spawn a surface low right over us. Some much needed rainfall is possible late Friday afternoon.

Several periods rain forecast earlier this past week have fallen apart. We’ll have to see if Friday’s forecast holds.

Wednesday Forecast Update

Posted Wednesday 04/15/26 @ 10:26 AM — The record breaking temperatures are on the way, according to the NBM—

Today’s 12z NBM v 5 High temperatures The sd is 1.8º. I wouldn’t be surprised if we hit 93º Fine Black Contours are near ground (2m) temperatures in 1º increments. (Click on image for a larger view.)

Despite the temperatures, Heat Indices (“Apparent Temperatures”) will be cooler (87º-90º) due to dew points in the low 60s. If you factor in the wind, it will feel even cooler than that.

As for thundershowers or any rainfall, the energy is available, but the track of the disturbance will be far north of Philadelphia today, mostly in NY State.

WV and RAP model potential vorticity. (yellow contours) The energy will end up along the NY State border with PA. (Click on image for a larger view.)
Showers Tuesday Night Update

Posted Tuesday 04/14/26 @ 8:16 PM — There are showers and thundershowers to our west. Looking at the track, you’d think this rain will move in here. See caption below.

Water Vapor Upper level with theta 305ºK tracks. Notice the red circled vertical motion (Omega). Negative is downward movement here. There is no support and slightly negative support for these storms as they move closer to Philadelphia. As posted earlier, we may get as much as 0.15 inches of rain close to the city. But they will then fall apart. Notice the curvature of the arrows…the curvature is anticyclonic, also causing the showers to fall apart. (Click on image for a larger view.)

As of tonight, this may be the only rain we get this week. Next chance is Sunday and the rainfall totals aren’t looking too heavy for Sunday.

This tendency for rain to fall apart as it reaches this area is a trend and a concern for this current season. We need some rain.

Showers Tuesday Night

Posted Tuesday 04/14/26 @ 5:25 PM — Despite the overall pattern that works against precipitation here, there’s enough energy moving over the ridge of high pressure to induce some showers tonight, mostly from 11 PM to 3 AM near the city. There’s increased confidence that we’ll see something with both the HRRR and RRFS cranking out a small accumulation.

18z HRRR total accumulated rain by 3 AM (Click on image for a larger view.)
18z RRFS total accumulated rainfall by 4 AM Wednesday. (Click on image for a larger view.)

The main energy dissipates after moving through Lancaster and Berks counties; the models are forecasting some rain here despite the collapse of the trigger.

Our high today was 88º KPHL (Philadelphia airport) and 85º (KLOM- Wings Field Blue Bell, PA). That was close to the mean + standard deviation of the NBM.

If we look at the mean + standard deviation for Wednesday, that brings us to 93ºF KPHL (airport) and 91º Wings Field KLOM. Dew points will be low and it will be breezy, so the ‘feels like’ will be about 2º less.

Tuesday Forecast Update

Posted Tuesday 04/14/26 @ 8:58 AM — The high temperatures forecast for today still look to be on-track according to the latest NBM version 5. (For reasons unclear to me, the RRFS and REFS forecast lower high temperatures by about 3-4ºF ).

As for any rainfall, we remain in an unfavorable upper air pattern for showers/thunderstorms in Philadelphia and especially S. Jersey. Looking at the upper water vapor image (channel 8) there are a few triggers that are in Ohio that may move in later today, between 6 PM and 8 PM—

Upper level water vapor (channel 8) with Omega at 305ºK. (yellow contours- Positive = triggers) The RRFS below shows these disturbances only make it into central and southern areas of PA/MD. (Click on image for a larger view.)

The RRFS shows these triggers to fall apart after 8 PM, only making into central PA and Maryland. A few ‘pieces of energy’ may make it into western suburbs of Philadelphia—

RRFS forecast at 8 PM. A strong wave (white circle) only makes into Central PA/northern MD at 8 PM. The maroon shading is RH at 700 mb. Purple/red – ‘pieces of energy’ Some activity may make it into western suburbs before falling apart by 9 PM. (Click on image for a larger view.)
Tuesday

Posted Monday 04/13/26 @ 8:30 PM — The warm air arrived late Monday afternoon with an increase in humidity. Mostly sunny through high clouds on Tuesday; occasional periods of cloudiness, especially northwest of the city and later in the afternoon. The NBM is forecasting some light scattered showers/thundershowers from 5 PM into the evening. (Can we believe it?)

RRFS forecast high temps at 4 PM Fine Black Contours are near ground (2m) temperatures in 1º increments. +(Click on image for a larger view.)

It will be windy. The winds will make it feel cooler than the actual temperatures.

Interesting Weather Monday
Mon 8:24 PM —Forecast Review — It looked threatening at 2 PM, but few areas saw any precipitation. The showers that had been forecast for this evening have materialized to our far north and west but are not here as had been forecast. The NAM-NEST, the HRDPS and the RRFS are still showing some light shower activity around midnight; most of the showers will move off to our north- Northern Bucks and northwestern Montco may see the most in the way of light showers.
Current RRFS (22z) forecast for midnight– light showers mostly north of the city. (Click on image for a larger view.)

Originally Posted Mon 8:50 AM — The forecast has changed from what I heard on TV last night. Signs of this change were showing on last night’s early models.

There are some areas of energy to our WEST this morning. These are forecast to move towards the Philadelphia area this afternoon and this evening.

Water Vapor image at XX with superimposed RAP model MSL pressure (black contours), GFS/NAM potential vorticity contours (yellow & violet fine contours) with and surface wind barbs, LIGHT BLUE AREAS WITH ORANGE ARROWS ARE FORECAST TO MOVE OVER PHILADELPHIA . (Click on image for a larger view.)

An area of moisture with some lift will move over our area between 2-4 PM this afternoon. Very widely isolated showers and thundershowers are possible at this time.

A more organized area of moisture and vertical motion (omega) will move down over our area about 7-10 PM, causing slightly more widespread showers and thundershowers—

RRFS forecast for 8 PM Monday evening. Short waves (wavy blue lines) along with moisture (dark magenta) and vertical motion (dz/dt) red/yellow areas. (Click on image for a larger view.)

While precipitation may be overall light and scattered, we need any rain we can get.

This set up looks interesting and some localized strong storms sometimes occur with these setups as a ‘surprise’. Stay tuned.