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Friday Updates

Posted Friday 05/16/25 @ 4:38 PM — The first short wave moved through around noon. It kept together better than I had forecast. A second short wave will bring showers and thunderstorms here, also a bit later than had been earlier forecast.

Here’s the current radar at 4:50 PM—

The HRRR and NAM-NEST have these storms dissipating before getting here between 8 and 9 PM. The RRFS and Canadian HRDPS have the storms moving into our area. I’m leaning towards the RRFS.

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Posted Friday 05/16/25 @ 11:45 AM — There’s strong upper level support for the storms currently in western sections, but lower level support is lacking as it moves eastward at 11:44 AM. Let’s see which will prevails.

The models are showing less distinction between the original two short waves, now predicting showers and thunderstorms through the afternoon and early evening hours.

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Posted Friday 05/16/25 @ 9:06 AM — A quick update. Latest radar shows a bow echo associated with the first of two short waves that will move across our area today.

The current area of fast moving heavy rain rain/ strong storms is expected to weaken as it moves into Philadelphia later this morning. Some rain still possible with this batch. Current RAP model shows moderate downward motion ahead of this impulse consistent with some weakening.

Another impulse expected later this afternoon (2-6 PM) will be fueled by higher CAPE values and higher vertical wind shear. Some stronger storms expected with this second short wave. I’ll update around noon with newer models.

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Revised Forecast Posted Thursday 05/15/25 @ 7:40 PM — After reviewing the afternoon (18z) models which became available after my previous posting, I have to revise my forecast.

It appears that there will be two waves of energy that pass through on Friday. The first, in the late morning, will be strong in far western areas, but several models have this rapidly diminishing in intensity as it encounters a weak mid-level ridge over Philadelphia.

A second impulse moves through between 2 and 5 PM, as noted below, which appears to have more mid-level support, causing some very strong storms as it moves into NJ. We’ll see how it all plays out. I’ll update tomorrow morning.

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Posted Thursday 05/15/25 @ 5:15 PM — A potent disturbance will move through during Friday afternoon. Previously expected around noon, the latest models have it moving through about 2-5 PM, earlier to our far west.

The upper air will support strengthening as it approaches, but it’s forecast to hit a weak mid-level ridge right over Philadelphia. Some models (HRRR) have it weakening and moving to our north and south over this ridge. The latest RRFS (experimental) maintains some of its strength and has it further intensify as it makes it across the river into NJ.

So this disturbance (called a “short wave”) is not looking as intense as it was yesterday, but some of the thunderheads may reach 50,000 feet according to the RRFS with fast onset heavy rains and winds.

The weather clears for Saturday, but a few widely scattered late day thunderstorms still possible.

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Thursday through Friday

Posted Wednesday 05/14/25 @ 5:28 PM —Following some scattered showers Thursday morning, many of us may finally see some sun Thursday by mid afternoon. Unfortunately the upper air will be cold and thermal instability will lead to scattered showers and thundershowers between 2 and 6 PM. A mix of clouds. sun and scattered storms sums it up for the afternoon.

Friday, a strong impulse rotating around the upper low near the Great Lakes will result in potentially some strong fast moving storms here around noon. Here’s the RRFS, which suggests a bow-echo formation around noon—

The potential for damaging winds Friday with this impulse needs to be watched.

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Posted Wednesday 05/14/25 @ 12:14 PM — Opted against going to the afternoon Phillies game. The morning models support a dry slot developing, and current radar/water vapor imagery shows dry slot advancing northward—

The hold-out for improving conditions is the experimental RRFS. It still shows some showers during the afternoon game. (Perhaps we’ll see why it’s still ‘experimental.)

What about the Phillies Games today?

Posted Wednesday 05/14/25 @ 9:10 AM —It does look like there will be a relative ‘dry slot’ develop beginning about 2-3 PM today in the city. The latest HRRR (11z) shows rain exiting to the northwest.

Here’s the simulated radar forecast for 1 PM. There may be some showers at the scheduled game start—

The latest HREF model, which is a statistical ‘ensemble’ of the HRRR, NAM-NEST and RAP models shows minimal rain for the hour preceding 2 PM —

Additional rain is expected during the evening, but the models are leaning towards it being somewhat west of the city.

As for total rainfall so far for this event, this has been the most significant widespread rainfall we’ve had in a long time. Here’s the latest 48 hour total estimate—

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Wednesday Forecast Update

Posted Tuesday 05/13/25 @ 5:19 PM — The weather is unfolding as forecast, with a stream of increasingly heavy showers moving up from the south southeast around a closed upper low to our west.

The latest ECMWF-AI model has rain continuing tonight and becoming quite heavy by early morning Wednesday. Some thunderstorms may be in the mix on Wednesday. A total of almost 2″ of much needed rain is forecast for our area through midnight Wednesday.

It looks like some rain/showers continue on Thursday as the upper trough axis moves over us. Thunderstorms also possible.

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Tuesday Forecast Update

Posted Monday 05/12/25 @ 5:56 PM — The forecast appears to be generally on-track with rain expected in the immediate Philadelphia area on or before 5 AM Tuesday morning.

Here’s the current satellite water vapor image—

Light showers to start, then bands of heavier rain move in later in the morning and continuing, with some breaks, through the afternoon and Tuesday night. Rain tapers off somewhat on Wednesday, but thundershowers will likely develop during the afternoon.

Total rainfall around 1 inch possible in and around Philadelphia, by Wednesday morning. more west of the city.

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Posted Monday 05/12/25 @ 7:40 AM — This week’s model forecasts continues to evolve, with a shift towards some heavier rain in the immediate Philadelphia area by Wednesday. (I’ll have to see it to believe it.)

For today, sunshine through high cirrus clouds, with clouds thickening between 4 PM and 7 PM from southwest to northeast. Rain begins here before daybreak Tuesday, but much of the rain will be showery in the morning.

The chance of more moderate to heavy rain waits until later on Tuesday and most likely Tuesday night into Wednesday morning.

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Originally Posted Sun 8:17 PM —Monday will have sun through high clouds, then increasing cloudiness by 4PM. High temps similar to Sunday, near or just above 80º. Rain begins after midnight early Tuesday morning.

An active weather week ahead, where another upper level closed low will bring good chances for rain from before daybreak Tuesday through Friday.

Despite this forecast, it’s not entirely clear whether the needed heavier rain will be in and around Philadelphia, or continue a long standing pattern for the heavier rain to remain to our far north and west. Some models are showing heavier banding right over Philadelphia, but others (Canadian and various runs of the German ICON model and the RRFS) show the heaviest rain to our far northwest.

The latest GFS shows this west-northwest trend—

Some models show just intermittent showers on Tuesday, while others are forecasting periods of moderate, continuous rainfall here. Too early to be sure.

There will also be the possibilities of thunderstorms during the week; the higher dew points, available moisture aloft and instability will set the stage for these storms, especially late afternoons and evenings.

Stay tuned.

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