Tag Archives: 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

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sunday Forecast Update

Updated Sat 9:21 PM — No major change in the the forecast. Sunny skies. High 66° with temperatures around 63° with winds NNW around 7-10 mph for the start of the Eagles game.

Weather and Daylight Savings Time-> Standard 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 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 and likely to 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 Eastern Standard Time makes a big difference for last minute evening updates about snow storms.

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 forecast11:20 PM10:20 PM
Canadian RGEM 24 hour forecst11:10 PM10:10 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 in 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

Oh, I just remembered, I have a forecast for Saturday and Sunday!

An upper air disturbance and a very weak trough will move through to our north on Saturday. The disturbance is visible in satellite water vapor imagery—

5 PM Friday satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine white contours) and superimposed MRMS radar. (Click on image for a larger view.)

Previously Posted Fri 8:27 PM —

Saturday

A mix of mid level clouds with some breaks of sun possible and some bright spots. Somewhat thicker clouds in the early afternoon, clearing late afternoon towards sunset. No rain. (The Canadian HRDPS has less cloudiness than our NOAA models and my forecast reflects that.)

High temperature 59º ( NBM model— location Blue Bell, PA)
High temperature 61º ( NBM model— location Philadelphia, PA)
uncertainty ± 2.6º (somewhat more spread than average)

Sunday

Mostly sunny. Light winds.

High temperature 62º ( NBM model— location Blue Bell, PA)
High temperature 64º ( NBM model— location Philadelphia, PA)
uncertainty ± 1.7º (less uncertain than average)