Monthly Archives: March 2024

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Friday and Interesting Saturday

Posted Friday 03/08/24 @ 9:36 AM — Sunshine through a thin layer of clouds this morning will give way to sunshine for much of the afternoon Friday. High cirrus clouds move in mid afternoon and cloudiness thickens by 5 PM from the southwest. Light winds today with highs 55º-57º.

An interesting setup for Saturday as two jet streams interact over us—

GFS jet stream wind forecast for 9 PM Saturday. Highly cyclonic northern jet with strong southern jet. Faster areas in the jet stream are called “jet streaks”. The red box is an area called the ‘left exit region’ of the jet streak , an area of maximal upward motion. Heavy rain is most likely in this area, which will be just northwest of the Philadelphia region. Small changes in the position of the jet streak can result in major changes in forecast rainfall. (Click on image for a larger view.)

There’s a wide range of model forecast rainfall amounts for Saturday, depending on each model’s forecast position of the jet. As little as 0.7″ to 2″ is forecast. Hopefully, we’ll have some clarification later.

Today’s NAM-NEST has joined yesterday’s ECMWF in forecasting light drizzle or rain as early as 11 AM Saturday. Likely time is 11 AM to 2 PM.

The above jet stream configuration will spawn strong low pressure that will pass right near us. Colder air behind the low will be give us a windy and cold day on Sunday.

Stay tuned for the Weekend Weather Forecast late this afternoon.

Friday Sunshine

Updated Thursday 03/07/24 @9:26 PM — Sunshine will make its appearance on Friday. There may be a period of cloudiness moving through in the morning hours. Some high cirrus clouds come in from the west around sunset. Somewhat breezy. Highs near 58º in the city, 56º in Blue Bell.

Saturday starts quite cloudy. Light drizzle or rain moves in from the southwest as early as 11 AM (ECMWF) but more likely around 12-2 PM. Heavier rain moves in by evening. Another 0.8″- 1.1″ expected. An easterly wind will keep it temperatures a bit cooler, in the low 50s.

03-07-24 18z [experimental] RRFS 1 hour rain accumulation by 1 PM Saturday. (Click on image for a larger view.)

Colder and windy on Sunday.

Thursday Update

Posted Thursday 03/07/24 @ 9:07 AM — We had a few bright spots and even some blue skies for a brief period west of the city this morning. However, an upper trough will swing through today and a mix of clouds is expected to return with even some drizzle in eastern NJ.

Last night’s HREF model most closely predicted this early brief clearing and here’s its forecast for 1 PM that includes the slight possibility of some drizzle or sprinkles —

03-07-24 06z HREF cloud and simulated radar at 1 PM today. (Click on image for a larger view.)

Sunshine for Friday

Forecasting Sun instead of Rain

Posted Wednesday 03/06/24 @ 4:50 PM — Over the years, I’ve hoped this web site would be come a destination for storm forecasts. After this week, I may need to rethink this and become the destination for when we’ll see the sun again.

The rain moved in pretty much on schedule Wednesday. A generalized 1.1″ to over 2 inches in NJ.

Today’s REFS (experimental RRFS ensemble) total rainfall. (Click on image for a larger view.)

There has been some question about whether the rain would linger well into Thursday.

It now appears that the rain will end during the early morning Thursday. No sun, but maybe some bright spots as varying amounts of low clouds appear to be the current model forecast.

Skies clear for Friday and we’ll see the sun return, but some cloudiness works its way back in Friday afternoon.

Saturday looks cloudy. Rain moves in early afternoon (1-2 PM, earlier western sections)

Wednesday Forecast Update

Posted Tuesday 03/05/24 @ 5:48 PM —The next system to bring rain will arrive as early as 11 AM Wednesday (earlier in S Jersey) . The system now appears to be somewhat elongated and is expected to bring heavy rain through at least Thursday morning. The heaviest rain will be along the NJ shore.

Current satellite water vapor (5:30 PM) mage 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 next system arriving Wednesday morning has become somewhat elongated and rain will linger into Thursday late morning. Some of the models suggest light drizzle and slow clearing, so the ‘rain free’ period for Thursday afternoon mentioned in the earlier update may not occur. Friday still looks good. (Click on image for a larger view.)
Yet Another Update- Looking for Sunshine

Posted Tuesday 03/05/24 @ 11:50 AM — Looking for a break in the rain, the latest GFS suggests that the rain ends late Thursday morning and we may be rain free from that point through Friday.

It looks like we’ll have sunshine on Friday. Cloudy on Saturday with rain mainly far western areas early. Rain moves into the immediate Philadelphia during the mid afternoon Saturday.

Tuesday Rain Update

Posted Tuesday 03/05/24 @ 10:56 AM — Over the weekend, it appeared that we might have some significant breaks between the low pressure systems expected this week. That’s looking less likely through Thursday.

We’ve had the rain since last night (total amounts less than forecast except in NJ) , but currently we have the low pressure center just approaching our area—

Current (~10:30 AM) 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. Additional light rain and drizzle is expected until about 5 PM or so.

We’ll have a break in the rain tonight (still damp) but the models are showing rain moving back in as early as 11 AM to 1 PM on Wednesday—

03-05-24 06z REFS (experimental) 1 hour rain plus standard deviation at 1 PM Wednesday. (Click on image for a larger view.)

An additional system is forecast to move in on Thursday. There may be little to no break in the action .

Rainy Tuesday and Wednesday and Saturday!

Posted Monday 03/04/24 @ 5:51 PM — Low pressure is forming as expected and rain will move in after midnight tonight and likely continue on and off until about 4 PM Tuesday.

Another system seems to have accelerated and will be here on Wednesday. Another system arrives Saturday, possibly sooner.

The latest water vapor satellite image captures the setup—

Current satellite water vapor image (5:30 PM ) with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. Tuesday’s storm (1) is just to our south. Our next storm (2) has accelerated somewhat and will be here on Wednesday. It looks like another rainy Saturday as storm (3) will be ahead of a cold front. (Click on image for a larger view.)

Rainfall on Tuesday will be less uniform than last Saturday’s storm—

03-04-24 06z HREF accumulated rainfall forecast for Tuesday. (Click on image for a larger view.)

Previously Posted Sun 5:47 PM —

This Week’s Weather Overview

This week, we’ll see a continuation of the mild trend started this past weekend with a complex, split jet flow and an upper trough off of the southeastern US coast that will induce low pressure formation.

The latest ECMWF jet wind flow (300 mb level) shows the weak upper trough.

03-03-24 12z ECMWF 300mb wind speed and heights. Forecast is for Tuesday. I’ve drawn the trough axis in blue and accentuated the weak wind flow isopleths outlining the upper trough. Cold air remains above the 500 mb thickness line (dark red contour north ) and mild air southward. (Click on image for a larger view.)

Here’s the NAEFS forecast for Tuesday showing a near coastal low (very similar structured to the system that gave us the rainy day Saturday) —

03-03-24 12z NAEFS with GEFS bias-corrected precip overlay forecast for Tuesday. Low pressure over us on Tuesday. Another forming in near the Gulf will be here on Thursday. (Click on image for a larger view.)

It may get briefly colder next Sunday.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Sun 4:15 PM —Forecast Review — It’s a good thing I didn’t go whole hog into the HRRR cloud forecast— It couldn’t have been a nicer day! The HRRR, since its revision/update almost two years ago , tends to overstate low cloudiness.

I’m looking forward to the HRRR’s replacement, the RRFS, which seemed to do much better—

03-03-24 12z experimental RRFS cloud forecast for today. The grey shading is about 28% cloud cover, closer to reality than the HRRR. (Click on image for a larger view.)

Sunday Update

Posted Sunday 03/03/24 @ 9:06 AM —The models have for the most part turned to a forecast of mostly sunny, (with some occasional clouds) but more cloudiness in northern Bucks county and western Montgomery county.

The HRRR still maintains a fair amount of low level cloudiness developing here this afternoon—

03-03-24 12z Latest HRRR still has clouds developing this afternoon. (clouds are grey black) (Click on image for a larger view.)

Very warm. The NBM and ECMWF have us reaching 65-66º in Philadelphia and 65º in Blue Bell with an uncertainty of ± 2º. If the HRRR is correct, those numbers may be a bit high.

Clouds move in this evening and Monday will be mostly cloudy. A similar wet system to Saturday’s (inverted front becoming a coastal low) brings rain Tuesday.

Saturday Update

Posted Saturday 03/02/24 @ 7:38 AM — Last night’s models continue a trend towards heavier rainfall today (Saturday). The GFS and HRRR have rainfall totals over 1-1.3″.

The [experimental] RRFS has even higher totals—

03-02-24 06z RRFS. The RRFS continues to be improved and is now at beta 0.8 with recent changes in data assimilation. (Click on image for a larger view.)

Rainfall should be ending from south to north about 6-8 PM tonight.

Clouds break for a very nice, warm, sunny March day on Sunday. A few clouds possible in the afternoon Sunday. Highs 62º Blue Bell, 64º Philadelphia (± 2.2º)

Previously Posted Fri 9:36 PM —(Delayed post due to some model data download issues, now resolved.)

As posted yesterday and this morning, our weather will be affected Saturday by an inverted trough along the coast that will become a weak low pressure system moving very near us. Rain starts after midnight tonight and lasts through much of the day and possibly early evening on Saturday.

Saturday

Cloudy with rain until early evening. Mild

NBM high temperatures: Blue Bell, PA 51º Philadelphia, PA 54º
uncertainty (based on standard deviation): ± 2º

Rainfall amounts;

NBM rainfall totals through Saturday. (Click on image for a larger view.)

Sunday

There’s been uncertainty with the forecast for Sunday. As posted this morning, it appears now that we’ll have sunshine for much of the morning but with low clouds with breaks of sun developing in the afternoon. Very mild!

NBM high temperatures: Blue Bell, PA 62º Philadelphia, PA 63º
uncertainty (based on standard deviation): ± 1.8º