Tag Archives: Daylight Saving Time

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Posted Friday 03/14/25 @ 9:30 AM — This morning’s clouds weren’t accurately predicted by several models, most notably the GFS. Also missing this cloud forecast was the ECMWF-AI-Single. Higher resolution models — the HRRR and HRRR-dependent NBM along with the NAM-NEST did predict this cloudiness—

06z NBM model cloud cover forecast for now (9:29 AM). (Click on image for a larger view.)

All models have the clouds dissipating between 11 AM and 1PM. Saturday looks cloudy but mild. Light rain begins as early as mid-morning on Sunday. Details later today with my regular “Weekend Weather Forecast”.

I’m looking for signs that the experimental RRFS will return. Its model runs are currently on hiatus, being evaluated for operational release. Its current status is available in this .pdf from NOAA.

Thu 8:49 AM —Forecast Review — The ECMWF-AI-Single model continues to be impressive. Its forecast for some sunshine through a considerable high layer of clouds has so far verified, in stark contrast to the GFS and NAM-NEST forecasting a dark low cloud day, even with drizzle. After years of ‘doing the weather’, this AI model appears to be the most impressive advance in forecasting I’ve seen.

(Gee, I wonder whether the TV people providing the “exclusive” forecast will acknowledge the blown forecast for today? They often don’t, or they find some area within a 100 mile radius that actually had the dark low clouds forecast.)

Hey, it may be too soon to celebrate, and some low clouds might still roll in from the east. That said, the latest ECMWF-AI just available has clouds thinning and dissipating for even more sunshine this afternoon.

Latest ECMWF-AI-Single at 2 PM—

ECMWF-AI-SINGLE Cloud and Temperature Forecast for 2 PM Thursday. (Click on image for a larger view.)

If this new AI model continues to prove itself, I can reduce my data costs and eliminate many more models I download daily. (I’ve already eliminated downloading the HIRESW-FV3, the HIRESW-ARW, the HIRESW-ARW-MEM2, the RAP, and the SREF. )

Yet Another AI Model ‘Experiment’ Continued

Posted Wednesday 03/12/25 @ 10:52 PM —Tonight’s models are even more emphatic about low clouds Thursday morning into the afternoon. Tonight’s NAM-NEST even shows some drizzle. As I posted earlier, the AI model shows sun through thin high clouds. We’ll see what happens.

Posted Wednesday 03/12/25 @ 8:07 PM — We had a sunny day today (Wednesday), very close to the AI model forecast.

I’m still seeing many of today’s models forecasting low clouds for Thursday, but today’s ECMWF-AI-Single model runs have only high cloudiness for Thursday, albeit with a thicker high cloud layer than forecast yesterday.

The latest ECMWF-AI-Single model just became available and it keeps its sunshine through high clouds forecast intact—

ECMWF-AI-Single cloud forecast for noon Thursday. (Click on image for a larger view.)

Let’s see how it plays out tomorrow!

Yet Another AI Model ‘Experiment’

Posted Tuesday 03/11/25 @ 5:46 PM —The latest ECMWF-AI mode (single) and the latest GFS have very different forecasts for Wednesday and Thursday regarding cloud cover. An easterly flow behind a back door cold front may result in very cloud conditions.

Here’s the latest GFS cloud cover for Thursday noon—

18z GFS forecast for Thursday noon. Very cloudy and damp. (Click on image for a larger view.)

Here’s the ECMWF-AI-Single forecast for Thursday noon—

12z ECMWF-AI Single has little to no low clouds. Plenty of sun through high thin clouds. (Click on image for a larger view.)

The two forecasts couldn’t be more different regarding cloud cover. Ordinarily, with these forecasts, I would go with the GFS model. (The GFS relative humidity fields support a very dark cloudy mid-day. The NAM-NEST also is forecasting low clouds. )

The ECMWF-AI-Single model has really impressed me regarding temperature forecasts. It’s also done well with rainfall. Let’s see how Thursday’s cloud cover turns out. (Or whether the models come together.)

Posted Monday 03/10/25 @ 5:07 PM —A large ridge of high pressure in the central US with a split jet flow moving around this central high will continue to bring above average temperatures to our area.

Current (Monday 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. Warm upper air ridge in center of the US. Split jef flow. The disturbance to bring rain late Saturday isn’t visible yet in this image. (Click on image for a larger view.)

Dry weather is expected to continue until late Saturday afternoon or evening.

Previously Posted Sun @ 5:03 PM — —The big story (and actually the only story) for the weather this coming week will be the warmer temperatures expected. Additionally, winds and wind gusts will be considerably lower than recent days.

For Monday, here’s the latest model blend (NBM). What’s interesting is how close the the ECMWF-AI model is to the NBM model with less computational effort.

18z NBM forecast high temperatures for Monday (Click on image for a larger view.)

By Tuesday, warmer temperatures push in from the southwest. We’ll be in the 67º-69º —

ECMWF-AI Single model temperatures at 2 PM Tuesday. (Click on image for a larger view.)

It’s been well-advertised about the 70º temperatures for this coming Saturday. The latest AI model suggests we may not reach that.

The change to Daylight Saving Time always takes some adjustment. For me, the biggest adjustment is the one hour later availability of weather model data. One hour doesn’t sound like much, but it brings models out a bit too late in the morning to be as useful and too late in the evening to make the 11 PM TV weather. I’ve written about this many times over past years—

Little Known Facts about Daylight Saving Time and TV Weather Forecasts

Daylight Saving Time and Weather Models

“Check Back at 11” — TV Weather and Daylight Saving Time

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Posted Thursday 03/14/24 @ 9:50 PM — We did reach an official high of 77º in Philadelphia on Thursday with sunshine. Could not have been a nicer day.

Friday will be cloudy with very light and widely scattered showers in the morning and afternoon as a weak cold front passes through. The cold front really just means a slight reduction in temperatures and a wind shift. The upper air dynamics will pass to our north and the latest models actually show minimal precipitation for us. Indeed, the HRDPS shows no rain at all in the immediate PHL area on Friday and the HRRR isn’t far from that.

Saturday looks very nice!

Another cold front comes through on Sunday.

Posted Thursday 03/14/24 @ 10:07 AM — The forecast for Friday has clarified as the GFS joins the rest of the models with rainfall of about 0.3″. Rain moves in during the early afternoon Friday.

As for today, Thursday, the latest NBM appears to be running low again and this time with a standard deviation of over 3º, indicating high spread with the model forecasts. For today, we’ll use the Canadian HRDPS which tends to run just a bit high—

03-14-24 06z Canadian HRDPS high temps for today, Thursday. Contours are 1º intervals (Click on image for a larger view.)

Posted Wednesday 03/13/24 @ 9:17 PM — Today’s high temperatures were predicted by the NBM, but only if the standard deviation was added to the mean temperature. The mean was too low, something I’ve seen before. With more sunshine on Thursday, I’ve taken the liberty to add the sd to the NBM mean temperature forecast for Thursday—

As for Friday, a cold front moves through during the day. There’s a wide range of forecasts for Friday’s rainfall with the latest GFS having low pressure develop along the front with significant rain during the evening (0.8″) Most other models have significantly less (0.20″ -0.0.35″) The GFS has some light shower activity during the day Friday, with heavier rain at night. Other models are much drier during the day. So an uncertain forecast for Friday at this time.

Posted Tuesday 03/12/24 @ 8:53 PM — It still appears that we’ll have some mid-level cloudiness late morning into at least mid-afternoon on Wednesday. High temperatures upper 60s to approaching 70º in some areas—

03-12-24 18z NBM high temperatures for Wednesday All have a standard deviation of approx 1.6º which is normal uncertainty. (Click on image for a larger view.)

Posted Monday 03/11/24 @ 7:47 PM — A quick update to the forecast for the week. Latest GFS shows some cloudiness on Wednesday as warm air moves in aloft. Also, Thursday is now looking cloudy.

First Posted Mon 4:20 PM —Deep low pressure stacked vertically high in the atmosphere with a strong pressure gradient along with a strong jet flow aloft of over 200 mph has given us the high winds over the past 36 hours. It will move off to the northeast and winds should gradually subside.

Here is the current satellite water vapor image showing the low pressure east of Maine and the next weather systems down the road—

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. Warm dry air (orange shading) will move in for Tuesday through at least Thursday. (Click on image for a larger view.)

The weather map (NAEFS model) corresponding to the above water vapor image is below. A building ridge in the middle of the country will move eastward with warmer air. The system labeled (1) will affect our weather next weekend—

NAEFS statistical “mode” version model combined with GEFS “bias-corrected” precipitation model forecast for 5 PM today, corresponds to the above satellite image. (Click on image for a larger view.)

The warmer temperatures have been well advertised on the radio/TV weather. Here’s the NBM forecast highs for Blue Bell (add about 2º-3º for Philadelphia.)

03-11-24 18z NBM forecast high temperatures for Blue Bell, PA . Add about 2-3º for Philadelphia. (Click on image for a larger view.)

Overall, sunny through Wednesday. Some gradually increasing cloudiness on Thursday with the high temperatures at or above 70º

Weather and Standard Time-> Daylight Saving Time

Twice a year, I feel compelled to talk about Daylight Saving Time and how it negatively affects timely access to updated evening weather model data before bedtime for those of us on the east coast.

Frankly, I love Daylight Saving Time and the extra hour of daylight we get in the late afternoon. The problem for us weather people is that major weather models are run worldwide at “00z” (Coordinated Universal Time or what used to be called Greenwich Mean Time). This corresponds to 7 PM Eastern Standard Time, but 8 PM Eastern Daylight Time. That hour makes a big difference.

Since numerical weather models take 2-5 hours to ingest data, compute and process, many of the major models become available too late in the night to be any use for us on the East Coast for planning our activities the following day.

When you hear “tune back in at 11″, you’re not going to see any change in the 5 day forecast at 11PM during Daylight Saving Time and you’ll likely see little change in the next day forecast; new model data simply hasn’t become available yet.

So for us weather people, the return to Daylight Saving Time has a negative impact on last minute evening updates regarding the next day’s weather.

Here’s some of the changes in some model availability (eastern time) :

Model Name (00z model run)Daylight TimeStandard Time
GFS 24 hour11:46 PM10:46 PM
GFS 5 day12:20 AM11:20 PM
NAM 24 hour forecast10:05 PM9:05 PM
NAM-NEST 24 hour forecast10:12 PM9:12 PM
HREF 48 hour forecast11:25 PM10:25 PM
Canadian HRDPS 24 hour forecast11:50 PM10:50 PM
Canadian RGEM 24 hour forecst12:10 PM11:10 PM
ECMWF*2:00 AM1:00 AM
ECMWF (free open data version)3:15 AM2:15 AM
* Partial runs of the ECMWF may be available earlier for paid subscriptions.

I’ve written extensively about Daylight Saving Time over the past years—

Little Known Facts about Daylight Saving Time and TV Weather Forecasts

Daylight Saving Time and Weather Models

“Check Back at 11” — TV Weather and Daylight Saving Time