Monthly Archives: September 2024

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Uncertain Forecast for Francine Remnants

Posted Thursday 09/12/24 @ 8:13 PM — Despite this morning’s forecast for coastal redevelopment of Francine, today’s models are all different with no clear forecast. Perhaps the most consistent forecast is for a poorly defined area of rain to try to move northward as part of an inverted trough. The heavy rain may not make it into Philadelphia. (Wow, what’s new.)

The artificial intelligence ECMWF model has a storm off our coast next Tuesday, but it’s an outlier right now. So no clear forecast.

12z ECMWF AIFS forecast for next Tuesday.
Hurricane Francine Re-forms?

Posted Thursday 09/12/24 @ 8:15 AM —Recent model runs now show the secondary low remnants of Francine off the North Carolina coast re-forming back to a possible hurricane next Tuesday and moving northward, affecting our area next Wednesday or Thursday.

06z GFS forecast for next Tuesday afternoon. (Click on image for larger view.)


An interesting potential development. Stay tuned.

Blocking High Pressure

Posted Wednesday 09/11/24 @ 5:18 PM — The models have been in remarkably good agreement regarding the path and fate of hurricane Francine’s energy over the next several days. Blocking high pressure will prevent northward movement of the moisture remnants and been a forecast for secondary low pressure to develop off of the southeast coast. This, too, will be blocked from reaching our area.

ECMWF AI model forecast for Saturday night. (Click on image for larger view.)

Some moisture will attempt to move northward aloft on Thursday and Friday in the form of high cirrus clouds, but even that moisture will be pushed southward by Saturday.

Posted Monday 09/09/24 @ 5:02 PM — A mid and upper level high pressure system, part of a strong upper ridge, will keep us in sunny skies and gradually warmer temperatures. The upper air configuration shows the current blocked setup—

NAEFS Jet stream level winds (200 mb) Forecast for Friday. (Click on image for a larger view.)

While hurricane Francine is likely to make landfall in Louisiana late Wednesday, the upper ridge over our area will block the storm from affecting us directly.

ECMWF forecast for Hurricane Francine (Click on image for a larger view.)

Some high clouds may move into South Jersey and Delaware of Friday, but they’re forecast to dissipate by Saturday.

Tropical System Enters the Picture this Week

Originally Posted Sun @ 10:44 AM — —Most of our week will be dominated by large, sprawling high pressure that warms up to above seasonable levels, into the low 80s, by Wednesday. Another beautiful weather week ahead for us.

A likely tropical system or hurricane is expected to develop in the western Gulf of Mexico and move towards Louisiana this week. Most models show this developing into a tropical storm or hurricane, likely directly impacting Louisiana with rain with the system extending into western Tennessee The path of the tropical moisture associated with this storm beyond this that point is uncertain.

Here’s the current water vapor image—

Sunday morning 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. The tropical system looks to develop into a tropical storm or a hurricane and make landfall

Here’s the latest ECMWF AI (machine learning- artificial intelligence) model forecast for Wednesday—

06z ECMWF-AI model forecast for Wednesday at 2 PM EST (Click on image for a larger view.)

The moisture from this storm may never make it into our area, being blocked by high pressure (GFS forecast) or may move up from the south to give us rain sometime next weekend (ECMWF).

Stay tuned.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Posted Saturday 09/07/24 @ 3:51 PM — Radar shows an additional area of light rain behind this anafront that may move in between 4 PM and 7 PM. This additional area is showing in today’s models that became available late this morning.

Sat 3:39 PM —Forecast Review — The showers moved in on schedule and many areas received minimal rainfall while some received a decent amount, but hardly a drought buster.

Here’s the MRMS rainfall summary—

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.)

The model forecast below did pretty good at capturing the area around Philadelphia that got minimal rainfall.

Saturday Update

Posted Saturday 09/07/24 @ 9:45 AM — The approaching cold front (classified asa frontal type “anafront” due to the precipitation lagging the actual surface front) will pass through here between 1 PM (western Montco/Bucks/Chester) and 2-3 PM (Philadelphia) and 4-5 PM (NJ).

Here’s the Water vapor/radar image—

“Anafront” type cold front with the precipitation lagging the surface front (blue cold front) (Click on image for a larger view.)

Expected total rainfall continues to lessen for our immediate area, with areas receiving 0.00″ to 0.15″—

00z REFS experimental total rainfall forecast. (Click on image for a larger view.)

Originally Posted Fri 5:34 PM —A cold front will move through our area between noon and 3PM Saturday. What had looked earlier this week to be a decent rain-maker has diminished to a chance of a few showers with precipitation totals of about 0.20″ or less. Our dry pattern continues and appears to be worsening.

Those of you who followed the discussion this past week about rain “skipping over” Philadelphia will recognize the rainfall pattern of the 06z experimental REFS forecast for Saturday—

06z REFS total rainfall The NBM model forecast is below. (Click on image for a larger view.)

The high pressure system that follows for Sunday will further suppress any possibility of rainfall far south of our area for much of the upcoming week.

Current satellite water vapor shows the current setup—

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. Cold front will bring light showers on Saturday. The moisture and rain is suppressed to the southern US. (Click on image for a larger view.)

Originally Posted Fri @ 5:34 PM —

Saturday Forecast

Cloudy. Showers move in to western Montco/Bucks/Chester counties about noon and through the city by 2 PM into NJ. Strong wind gusts with the frontal passage.

Total Rainfall (Model Blend)

NBM high temperatures: Blue Bell, PA 76º Philadelphia, PA 78º
High Uncertainty (based on standard deviation): ± 2.3º

Sunday Forecast

Sunny and breezy.

NBM high temperatures: Blue Bell, PA 71º Philadelphia, PA 73º
Low Uncertainty (based on standard deviation): ± 0.7º