Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Past 72 Hour Rainfall Totals

Posted Sunday 09/29/24 @ 10:31 AM — Through 9 AM Sunday, the MRMS rainfall totals for the previous 72 hours—

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.)

Not much additional rain expected through Tuesday, except in areas shown below.

Sunday Update – Week Forecast Outlook

Posted Sunday 09/29/24 @ 9:55 AM — Humid tropical air in our area overrunning high pressure to our northeast will continue to bring low level clouds, mist and the chance of light drizzle or light rain today, Sunday. Total rainfall looks to be less than Saturday. Northeast wind flow will keep us near 70º.

A break in the action with even some sun possible during the afternoon Monday, especially areas Philadelphia and northeastward, as high pressure builds down.

Low pressure developing along the Virginia coastline had been expected to bring us a decent rainfall Tuesday, but there’s been a consistent trend towards this low being too far to our south, suppressed by blocking high pressure. So very little rain now expected for Tuesday—

09-29-24 06z GFS Total rainfall by Wednesday morning. (Click on image for a larger view.)

A cold front moves through Wednesday. Little additional rainfall here.

Incredibly, the extended range models are strongly hinting at another tropical storm or hurricane in the Gulf next weekend, with a track similar to Helene. The machine learning/AI model ECMWF-AIFS has also been consistently showing a storm forming by next Saturday—

09-29-24 06z ECMWF-AIFS forecast for next Saturday at 8 PM. (Click on image for a larger view.)
Continued Cloudy with Varying Light Showers

Posted Saturday 09/28/24 @ 10:12 AM — Last nights 06z models and this morning’s 12z models continue to forecast low clouds and intermittent light showers through Saturday. Some models show some thinning of clouds in southern Delaware and Chester counties towards evening, but that reverses itself overnight.

There isn’t much change for Sunday according to the RRFS and REFS experimental models.

Here’s the current setup Saturday morning with light showers from very moist southeasterly flow—

Composite Radar at 10 AM with boundary level winds (low level) from the SE (blue contours) and1000-500 mb thickness (yellow contours) (Click on image for a larger view.)

While some models continue with a more substantial rainfall for Tuesday, the GFS is suggesting a further southeasterly development of low pressure which would have the heavier rain miss us. Too soon to tell.

Total Rainfall So Far

Posted Friday 09/27/24 @ 5:44 PM — We need the rain. How much rain have we gotten over the recent days? Here’s the MRMS totals through 4 PM today.

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.)

Quite a range of values over our region!

Originally Posted Fri @ 5:01 PM — —The remnants of Hurricane Helene continue to rotate into and merge with an upper air low over Tennessee.

Considerable moisture is being flung up towards Philadelphia from the south and southeast around this combined system and as it hits a high pressure ridge just northeast of us, the moisture is riding up over it and condensing out as rain.

Friday afternoon 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. Low pressure at the surface will rotate and merge with upper level low (blue L) Moisture on east side will rotate into our area . (Click on image for a larger view.)

By Sunday afternoon, the upper low will have remained almost stationary, but will begin to move eastward and perhaps induce a surface low off the coast for Tuesday—

09-27-24 12z GFS forecast for Sunday at 2 PM. Secondary coastal low possible by Tuesday. (Click on image for a larger view.)

Saturday Forecast

Low clouds. areas of fog possible early, with showers likely throughout the day, widespread in the morning, more scattered and light in the afternoon.

NBM high temperatures: Blue Bell 73º Philadelphia 76º
Above Average Uncertainty (based on standard deviation): ± 2.4º

Sunday Forecast

Low clouds, fog, some sprinkles early, then cloudy in the afternoon but little in the way of additional showers.

NBM high temperatures: Blue Bell, 69º Philadelphia 71 º
Above Average Uncertainty (based on standard deviation): ± 2.7º

A break in the rain on Monday, widespread rain likely on Tuesday.

3 thoughts on “WEEKEND WEATHER FORECAST”

  1. Thanks as always.

    What are you thinking in terms of total rainfall between now and Monday (i.e., up to just before any potential coastal low Tuesday)?

    NWS seems to be saying about .25 inches, which is welcome but certainly no drought-buster.

    1. Yes, we need the rain. The NBM (model blend) is showing .35″ through Sunday midnight. I think that’s a reasonable expectation and in line with many models. It will be spotty and localized so your mileage may vary. I’m planning on posting the total rainfall we’ve received over the past 72 hours tomorrow morning. Regionally, it’s been quite a range of values so far.
      The rain on Tuesday looks widespread and perhaps an inch or so. But let’s not count our chickens until they’ve hatched.

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