Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Rainfall

Posted Friday 11/15/24 @ 8:34 AM — Yesterday’s high resolution model forecast was pretty good in forecasting the very light precip areas to our west received.

Here’s the MRMS rainfall summary—

MRMS estimated actual total rainfall for Thursday night (Click on image for a larger view.)

We could really use some rain, but it looks like we’ll need to wait until next Wednesday -Thursday (if we’re lucky) to receive any.

Thursday Precipitation Update

Posted Thursday 11/14/24 @ 3:00 PM — Several of the latest high resolution models (HRRR, RRFS) have moved the light precipitation this evening slightly eastward, perhaps giving more of the western suburbs of Philadelphia a bit of much-needed light rain.

Here’s the latest HRRR—

11-14-24 18z HRRR total rainfall Thursday evening/night. (Click on image for a larger view.)
No Rain Today But Possible Pattern Change

Posted Thursday 11/14/24 @ 10:07 AM — All models, including those late to this forecast (ICON, HRDPS), have come together for a cloudy but dry forecast for the immediate Philadelphia area today and tonight.

Another front moving in late Monday may also meet the same fate of a mostly dry frontal passage. This is all due to an upper anti-cyclonic flow over us that has persisted—

ECMWF-AIFS forecast for late Tuesday Note the curvature of the orange arrows, depicting a flow that has an anticyclonic curvature, causing downward vertical motion and works against rainfall. However note the plunge of colder air in the Midwest which should result in at least a temporary change in the position of the jet flow and set up a cyclonic flow over us late next week. (Click on image for a larger view.)

Note the plunge of colder air in the above graphic which should result in at least a temporary change in the position of the jet flow and set up a cyclonic flow over us next Thursday or Friday. Additionally, high pressure in the western Atlantic is setting up further southward. This system has been blocking rainfall in our area, but may finally lose its grip if it sets up further southward. Much of this change is simply seasonal, as colder air builds in the polar areas.

Unfortunately, I’m not sure that any new pattern setting up will be persistent, so any change to colder (and possibly stormier weather) may not last more than a week or two.

No Rain for Thursday Evening. Another Tropical System?

Posted Wednesday 11/13/24 @ 10:45 AM — Last night’s models have continued a trend set by the ECMWF, where any rain Thursday will stay west and south of our area.

Here’s the latest model blend (NBM)—

11-13-24 12z NBM accumulated Precipitation Thursday night (Click on image for a larger view.)

The National Hurricane Center is keeping its eye on the Caribbean for a likely hurricane to develop and hit the Yucatan, then likely dissipate with its moisture eventually brought up along the US southeast and east coast early next week.

Here’s the latest AIFS —

ECMWF-AIFS forecast for next Tuesday night. (Click on image for a larger view.)

This is just one of many possible scenarios with this developing tropical system.

Any Rain Thursday?

Posted Tuesday 11/12/24 @ 10:03 AM — Low pressure is expected to develop later Thursday off of the North Carolina coast.

Depending on the model, the Philadelphia area will be in the periphery of the precipitation shield, with the latest ECMWF keeping us totally dry while the GFS, Canadian and NAM-Nest have us receiving anywhere from 0.05″ to 0.20″ of rain Thursday night.

If the ECMWF is correct, the Eagles game will be rain-free. Otherwise, light rain possible during the game. I’m leaning towards the very light rain forecast.

Here’s the latest model blend (NBM) which shows the periphery of the rain shield—

11-12-24 12z NBM total precipitation forecast for Thurday night (Click on image for a larger view.)
Our Drought Continues

Posted Monday 11/11/24 @ 4:04 PM — For the past several days, it looked like we might get some rain on Thursday. Over the past day, the chance of any significant rain on Thursday is now looking unlikely. Any rain here late Thursday will be light.

An expected low pressure system now looks to develop too far to our south and east—

NAEFS model statistical “average” version with overlayed GEFS model “bias-corrected” precipitation forecast for Thursday. Orange arrows depict the mid-level ridge expected to move in. (Click on image for a larger view.)

With the exit of this low on Friday, a strong mid level ridge with warmer temperatures will move in for next weekend. And more dry weather.

Low End of the Forecast Range

Originally Posted Mon 9:40 AM — Last night’s rainfall was in the low end of the forecast range, closer to the Canadian models and somewhat disappointing compared to the HRRR, RRFS and GFS forecasts.

Here’s the MRMS precipitation totals from last night—

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.)

Following several additional days (today through much of Thursday) of nice weather, we’ll see another chance for rain late Thursday evening.

11-11-24 06z GFS forecast for Friday at 1 AM (Click on image for a larger view.)

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sunday Evening Rain Update

Posted Sunday 11/10/24 @ 10:10 AM — Things still look good for an end to the dry period we’ve been in here (although, tonight will not be a drought-buster). The models have trended upwards in the rainfall amounts and many areas may see 0.5″ –0.6″ or more this evening and tonight. Rain expected to move in between 6 PM and 8 PM.

Here’s the latest Water Vapor/Radar image—

Current satellite water vapor image 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.)

The latest HRRR is below—

11-10-24 12z HRRR total rainfall tonight. (Click on image for a larger view.)

Not posted is the latest RRFS which had many areas receiving in excess of one inch of rain here. (Probably not correct, but we’ll see if they corrected the excessive rainfall bias for this still experimental model.)

Additional rainfall expected here Thursday!

Sunday Evening Rain Update

Posted Saturday 11/09/24 @ 3:25 PM — It’s been an awfully long time since I posted a rainfall forecast, but it looks very likely that we’ll get some rain in the Philadelphia area Sunday evening and night.

As always, the models show a range of rainfall totals and distributions, but most models are between 0.25″ and 0.60″ with 0.30″– 0.40″ being solid bet. Today’s models are showing light rain to start in western areas around 6 PM and it moves into Philadelphia and then NJ about 8 PM or so.

Before then, a mostly cloudy to cloudy day. (Can’t remember the last time we had a cloudy day!)

Here’s the latest HRRR rainfall forecast which is running a bit higher than the NBM and RRFS totals—

11-09-24 18z HRRR total accumulated rainfall Sunday night. White contours are 0.1″ increments The rain ends around daybreak Monday. (Click on image for a larger view.)

We have another chance of rain Thursday.

Originally Posted Fri 10:23 AM —High pressure will continue to provide beautiful weather through Saturday, although it appears that it might become quite windy at times, especially Friday night.

An approaching low pressure system will pass to our north and a warm front followed by a cold front will move through Sunday night.

Friday morning Water Vapor/Composite Radar with superimposed RAP model thickness (500-1000mb- yellow contours) and potential vorticity (violet lines) (Click on image for a larger view.)

Following a sunny day Saturday, Sunday will be mostly cloudy. Rain should hold off until 4-7 PM

It had appeared that moisture from Rafael might enhance the rainfall here, but that is appearing less likely as the hurricane is forecast to to remain in the Gulf and gradually dissipate.

Total rainfall looks to be in the 0.3″ to 0.5″ range by Monday morning with the larger amounts west of the city. Hardly a drought-buster but better than nothing. There’s another chance of rain next Thursday.

Saturday Forecast

Sunny and somewhat breezy.

NBM high temperatures: Blue Bell, PA 56º Philadelphia, PA 58º
Uncertainty (based on standard deviation): ± 1.3º average to low uncertainty. Average seasonal high temp is 56º

Sunday Forecast

Cloudy and increasingly windy. There may be some breaks of sun through high clouds mid-day. Light rain develops west to east from about 5 PM through 7 PM and continues into early Monday morning. Windy and gusty at night.

NBM high temperatures: Blue Bell, PA 61º Philadelphia, PA 62º
Uncertainty (based on standard deviation): Low to average uncertainty ±1.2º

Weather… and Other Things 'Up in the Air'