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A very different rain storm than had been forecast two days ago.

Update Sun 11/26 @ 3:58 PM — The latest HRRR and NAM-NEST have rainfall amounts during tonight’s Eagles game significantly higher than had been forecast—

Here’s the total rainfall forecast through midnight—

Sunday Forecast Update

Update Sun 11/26 @ 9:24 AM — No change from the forecast update last night. An earlier start of the rain, and much heavier than previous model guidance had forecast. A faster system that will leave around or before midnight, but not after almost 0.75″ of rain falling!

Current Radar/Water Vapor at 9:15 AM—

Here’s my original forecast from Friday evening:

Cloudy early, the some sun towards noon, becoming cloudy again during the afternoon. Light rain moves in about 6-8 PM. Breezy.

High temperature 49º ( NBM model— location Blue Bell, PA)
High temperature 51º ( NBM model— location Philadelphia, PA)
uncertainty is about average with a ± 2.0º sd

Here’s my latest forecast for today:

Cloudy early, then some sun towards late morning, becoming cloudy again just around noon. Light rain moves in between 3-4 PM and becomes heavier during the second half of the Eagles game. Rain departs about 11 PM to midnight.

High temperature 49º ( NBM model— location Blue Bell, PA)
High temperature 52º ( NBM model— location Philadelphia, PA)
uncertainty is about average with a ± 1.8º sd

Winds breezy and gusty up to 25 mph around 7 PM

Here’s the latest, NBM 12z forecast total rainfall by midnight—

Sunday Forecast Update

Update Sat 11/25 11:18 PM — As mentioned this morning, there was a shift in the forecast towards an earlier start of the rain but the GFS became what was possibly an outlier. Well, this afternoon, and this evening, the models converged on an earlier start with some light rain as early as 3-4 PM. The HRDPS has been the most consistent and it’s forecasting some significant rain by the Eagles second half.

Rain likely after the Eagles Game Sunday

Update Sat 11/25 @ 11:12 AM — A quick update. Our high resolution models have joined the Canadian and European ECMWF with an earlier onset of the rain, 5 PM to 7 PM Sunday, and somewhat heavier. This morning’s GFS, just available, has moved in the opposite direction: a more eastward track of the storm, a later start to the rain, and less overall rainfall for Philadelphia. So high uncertainty.

Update Sat 11/25 @ 09:17 AM —

There remains timing issues with the onset of the light rain late Sunday afternoon/evening. The ECMWF and Canadian HRDPS continue with an earlier onset of the light rain, about 4-7 PM. Our NOAA models (GFS, HRRR, HREF) show a later start, after 8 PM. I’m leaning towards a later start, but this forecast is lower than average confidence.

Either way, any rainfall during the game should be light, on the order of 0.01″ – 0.03″ inches or so.

The HRDPS has the most rain during the game 0.03″ at 7 PM—

Our NOAA HREF shows 0.00″ at 7 PM —

I’ll provide further updates later.

Previously Posted Fri 8:02 PM —

Following a weak cold front that moved through today, colder weather is expected. High pressure directly over us will provide mostly sunny skies on Saturday—

Low pressure will approach from the south on Sunday and very light rain with this system will move in about 6-8 PM Sunday. The rain will become somewhat heavier after midnight, but only about 0.25 inches of rain are expected, somewhat heavier north and east into NJ —

Colder weather expected next week.

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Friday Update

Update Thu 11/23 9:38 PM — A weak cold front will move through mid day Friday with a few hours of mid and high level cloudiness.

Details for the weekend tomorrow. Currently, it appears that the showers will arrive Sunday evening between 6 and 8 PM. Initially, they’ll be quite light.

Possible Weekend Forecast Change

Updated Wed 11/22 @ 7:58 PM — The next few days are expected to be mostly sunny, but there’s been a shift in the forecast for Sunday.

Some background first:
Earlier this week, a coastal storm was expected to form in the Friday to Saturday time frame. Model runs by Tuesday had the storm moving out to sea, well to our south, not affecting our weather.

Today’s GEFS, NAEFS, ECMWF, ICON and GFS now have this coastal system moving up the coast late on Sunday and interacting with an approaching cold front late Sunday afternoon into evening, possibly during the Eagles game.

The timing varies, with the ECMWF having some rain moving in during the mid afternoon Sunday, while the GFS has the rain developing after 8 PM or so.

Here’s this morning’s ECMWF forecast for 7 PM—

There are currently timing differences, with the GFS slower and later with the rain here. This system has been tough to nail down and I would expect further changes in the forecast.

Wed 9:49 AM Forecast Review — We had the heavy rain as forecast, although totals were somewhat overdone by the HRRR (but more accurate with the development version of the RRFS). The banding of heavier rain set up close to the forecast with a strip of 2″ rains right through the immediate Philadelphia area.

Here’s the MRMS total rainfall for the past 24 hours—

Here’s yesterday’s 12z RRFS—

As for Wednesday, several models continue with the idea of mostly cloudy, but a few breaks of sunshine can’t be ruled out. It will be mild. There’s the possibility of a few widely scattered sprinkles about 8 PM this evening.

Sunny for Thanksgiving Day and into the weekend. The trend is for lower temperatures here into the next week or so.

Wednesday Outlook

Updated Tue 11/21 @ 8:36 PM — The rain moved in on schedule and the heaviest rain is expected between 11 PM and 2 AM tonight. Winds are also expected to peak in the same time frame.

Here’s the current situation at 8:30 PM—

The rain ends about 4-5 AM Wednesday and skies will be cloudy early morning. There will likely be some brief periods of sunshine early to mid morning, but instability cloudiness will be with us for most of the day Wednesday. There’s even a slight chance of a widely scattered sprinkle.

It will be very mild! High 59º-61º, but somewhat windy.

Thanksgiving Day will be sunny, but cooler. high 51º-53º

Tuesday Rain Update

Updated Mon 11/20 @ 5:30 PM — We’re back to an earlier start of the rain on Tuesday, with the GFS, HRRR and NBM all shows rain moving in from the southwest, as early as 12:30 PM in Chester County and moving into the rest of our area after 1-2 PM.

1 PM HRRR simulated radar forecast—

The latest HRRR cranks out some impressive rainfall and wind gusts later Tuesday approaching 40 mph —

It looks like the rain will end about daybreak Wednesday. We may see sunshine as early as 9-10 AM. but instability cloudiness will quickly move in with considerable cloudiness by afternoon.

Tuesday Rain Update

Updated Mon 11/20 @ 10:02 AM — There has been some uncertainty with the onset of the rain in Philadelphia on Tuesday. This morning’s trend is towards a somewhat later start, about 3-4 PM, earlier in southern Chester county. The latest 12z NBM (which tends to lag when showing changes) is still showing a 1-2 PM start.

The total rainfall forecast based on this morning’s 12z HRRR—

I’ve been playing with the still experimental RRFS and it shows similar totals, although placement is different—

The big story will be the WIND around midnight Tuesday into early Wednesday morning. Gusts are being forecast to 40 mph! Combined, with heavy rain, it will be an interesting 12 hours.

Previously Posted Sun 8:38 PM —

Low pressure is developing to our southwest and will move into our area Tuesday afternoon with rain. The rain may be heavy Tuesday night.

There has been some spread in the timing onset of the rain on Tuesday. Earlier forecasts were going with 4 PM. Recent models have some light rain as early as noon. Others delay the rain until 1-2 PM. The 1-2 PM start looks best at this time.

Rainfall totals are expected to be moderate to heavy with totals 1.6 +”. Here’s the latest NBM total accumulated rainfall forecast—

The heavy rainfall forecast has been consistently high. (We really need the rain!)

The speed of the system is still somewhat uncertain. The general consensus is that the rain ends Wednesday morning but clouds linger for much of the day. It will be quite windy.

Thursday, Thanksgiving Day, looks sunny but chilly. Highs upper 40s to low 50s.

There’s another chance of rain in the Friday through late Saturday time frame due to a coastal storm. Much uncertainty with the details right now.