Daily Archives: Sunday, November 12, 2023 6:52 pm

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Week’s Weather Update- Philadelphia Marathon Outlook

Updated Thu 11/16 @ 5:22 PM — The approaching cold front Friday will bring clouds and should be considerably cloudy (high level cloudiness- cirrus) between 1 and 3 PM from the city westward.

High temperatures on Friday will be 65º (Blue Bell) and 67º (Philadelphia) with a higher than usual uncertainty of ± 2.4º due to differences in cloud cover forecasts.

As has been the forecast trend, our immediate area will receive little to no rain from this system. Here’s the latest NBM rain totals—

Today’s 18z NBM accumulated rainfall (Click on image for a larger view.)

The forecast for the Philadelphia Marathon on Sunday is mostly unchanged.

Sunday Philadelphia Marathon Outlook — Mostly sunny early. Temperatures somewhat colder at the start- 37º early, rising to 46º in the city between 8 AM and 11 AM. Highs low to mid 50s. Winds 11 mph gusting to 20+ mph by late morning from the W.

The longer range forecast shows a good chance of rain on Tuesday.

Something that I’ve mentioned over the past year: NOAA has been developing a new model, the RRFS (“Rapid Refresh Forecast System“) which is going to be beginning of a major advance in high resolution weather forecasting. The model will run hourly, will have a 3 km resolution, and its forecasts will extend out to 60 hours. It will also have an statistical ensemble component.

The RRFS takes much of its physics from the HRRR and will use the FV3 core used in the recently updated GFS.

This RRFS is going through a series of testing and fine tuning and the groundwork is being laid for it to be operational around September 2024.

Of great relevance, about 6 months after it is released, many of the models I look at regularly (NAM, NAM-NEST, RAP, SREF, all three flavors of the HIRESW) will cease operation.

My mantra “Never Ignore the NAM” will become a thing of the past.

I’ve always felt there are “too many models” and it appears that the RRFS is incorporating all the best approaches to numerical weather modeling that have been distilled out from these earlier models.

NOAA/NWS has been making the development version and their testbed variants available on a NOAA- Amazon Web Services site (AWS) for some time.

In recent weeks, I’ve been experimenting with downloading these RRFS runs. AWS has certain restraints that the main NOAA NOMADS site doesn’t have, along with different directory structures (buckets). Nonetheless, I hope to be downloading and using the RRFS model in some winter forecasts soon.

The RRFS version 1 release will truly be a big deal. I’ll be posting more information in coming weeks.

Week’s Weather Update- Philadelphia Marathon Outlook

Updated Wed 11/15 @ 8:56 PM — We had a bit more cloudiness than forecast today.

Thursday should be quite nice, with sunny skies and warm temperatures, 63º in Blue Bell and 65º in Philadelphia.

Friday will be mostly cloudy by noon but still mild.

As discussed previously at length in previous updates, it does appear that there will be little rainfall in Philadelphia with the passage of a cold front Friday night. At most, the models, including the ensembles, crank out 0.10 inches and many show even less rain.

Saturday clears in the morning. Very windy conditions expected.

NAEFS forecast for 7 AM Saturday with previous 6 hour accumulated rainfall. (Click on image for a larger view.)
Sunday Philadelphia Marathon Outlook — Mostly sunny early. Temperatures somewhat colder at the start- 37º early, rising to 46º in the city between 8 AM and 11 AM. Highs low to mid 50s. Winds 13 mph gusting to 20+ mph by late morning from the W.
Week’s Weather Update- Philadelphia Marathon Outlook

Updated Tue 11/14 @ 5:57 PM — No change in the forecast since this morning. Thursday and Friday now look dry. The “ensemble” models (GEFS, NAEFS, GEPS) still crank out about 0.20″-0.40″ of rain Friday night into Saturday morning. The “deterministic” models (ECMWF, GFS) have the energy transferring to the low pressure system east of us, with little or no rain here. The forecast of the Philadelphia Marathon on Sunday remains unchanged.

Updated Tue 11/14 @ 9:12 AM — As has been the case many times over the past several months, the dip in the jet stream forecast for this weekend is now expected to be less amplified and the coastal system (and its associated rain) may totally miss us as the energy from the approaching cold front skips over us to our northeast. The latest ECMWF and ICON models support this scenario—

00z ECMWF shows the storm to our east with later secondary development to our northeast. The rain misses us! (Click on image for a larger view.)

We could really use the rain. If this keeps up, could we have another almost snowless winter?

Sunday Philadelphia Marathon Outlook — With a less amplified trough, expect more sunshine and less wind than my previous forecast. Mostly sunny early. Partly cloudy in the afternoon. Temperatures 39º early, rising to 46º in the city between 8 AM and 11 AM. Winds 10mph gusting to 20mph by late morning from the WNW.
Week’s Weather Update- Philadelphia Marathon Outlook

Updated Mon 11/13 @ 7:33 PM — The latest models have slowed down the movement of the coastal system as it interacts with the trough and cold front. It now appears that clouds, originally expected to move in on Thursday will move in on Friday.

With less cloudiness, high temperatures for Thursday will be in the low 60s and probably mid 60s by Friday.

The amount of rainfall with the next system, Friday into Saturday, now appears to be less than previously thought, with some models having the rain skip past us. The Ensemble models are forecasting about 0.40 inches of much needed rain, but the GFS is less impressive and the Canadian even less so.

Here’s the latest NAEFS with GEFS precip, just available, for Friday night (1 AM Sat) —

Combined 18z NAEFS (mode version) forecast with Bias-Corrected GEFS model 6 hour precip for Friday night 1 AM Complex interaction of coastal system with approaching upper trough and cold front (blue line) (Click on image for a larger view.)

The interaction between the trough and coastal low appears to be be a challenge and it’s too early know how it will play out.

Sunday Philadelphia Marathon Outlook — Here’s the current outlook for Philadelphia, Sunday morning. Partly sunny early. Increasingly cloudy by late morning. Temperatures 39º early, rising to 46º in the city between 8 AM and 11 AM. Quite windy, especially by late morning. Chance of a sprinkle early afternoon.

Updated Mon 11/13 @ 9:09 AM — Nice weather continues through Thursday with a slow increase in high temperatures—

Today’s 12z NBM shows high temperatures somewhat steady until Thursday. (Click on image for a larger view.)

It looks like clouds move in Thursday afternoon ahead of the next system and cold front. There’s a range of model forecasts, depending upon how deep the plunge of cold air makes it southward—

Today’s 06z NAEFS forecast for Saturday morning shows a moderate plunge of cold air (red arrow and red 540 thickness contour) and the track of the coastal storm (white arrows) (Click on image for a larger view.)

The sharper the trough dip, the more westward the storm track and the longer it affects our weather on Saturday. It will also greatly affect whether we get a soaker or another light precipitation event.

Too early to see a trend with this storm, but the recent history over past months is for the storm to be eastward, therefore, less rainfall and some clearing on Saturday afternoon.

Previously Posted Sun 6:52 PM —

Large sprawling high pressure will dominate our weather through late Thursday. Nothing much is happening here, weather-wise. Continued fair with gradually moderating temperatures into the end of the week.

Commentary — As much as I enjoy nice weather and I enjoy following the weather, it’s periods like these where I’d hate to be a full time meteorologist, on-TV or otherwise. (Ok, they make good money.)

There’s simply nothing happening; the weather has been uneventful for several weeks and will remain that way this week.

How long can one harp on normal-range colder temperatures or want to be thanked for forecasting a warmup later in the week?

Now that I got that off my chest, our next weather event is Friday, as a cold front moves through. It may become interesting where a semi- tropical system affecting Florida this week moves up the coast, causing rain to linger into Saturday. Lately all of those scenarios have fizzled, with the storm staying east in the Atlantic.

We could really use some rain.

Here’s the latest NAEFS forecast for Friday—

Today’s 12z NAEFS forecast for Friday, shows low pressure off the Florida coast with a sharp dip in the jet flow and a cold front whose general position is the red 540-thickness line. Notice how the warm air is all the way up into Alberta Canada in this highly amplified jet flow. (Click on image for a larger view.)

So no rain until later on Friday and mostly sunny skies.

Winter Outlook Discussion —Which brings me to the winter forecast. Frankly, I think we’re going to see large swings in temperatures here with primarily mixed precipitation events here. Not necessarily large accumulation snow storms.

The jet pattern these past several months has been somewhat different than last year. With almost no accumulating snow last year, it’s unlikely to be similar, but it doesn’t mean we’re “due” for big snow storms.

Last winter, a persistent dip in the jet had the main axis of the trough directly over us, causing storm formation to occur in the Atlantic. This year, I ‘m seeing more favorable positioning of the axis of the jet dips (more to our west), but favoring warm air preceding any storm. The major storm developments over recent months have all been to our north and east, missing us. Will that continue?

Patterns change; what we have now could be different in January. But the trend towards warmer temperatures may be an increasingly large factor when it comes to getting large snow storms here.