Tag Archives: Daylight Saving Time

Philadelphia Weather Outlook

WEEKEND WEATHER PREVIEW & DAYLIGHT SAVING TIME

A cold front will move through around daybreak Friday. Light rain is expected with the frontal passage (less than 0.20 inches).

Skies are expected to clear after the frontal passage and should remain sunny and cooler Friday.  A secondary cold front moves through early Saturday. 

The weekend should be mostly sunny, windy and cooler although some cloudiness is possible during part of the day Sunday as a weak upper air disturbance moves through.  High 48-50º Saturday and 53-56º Sunday.

The fairly dry weather pattern is expected to continue.

Of course, Sunday morning is the beginning of Daylight Saving Time.  I love the extra daylight at the end of the day, but for “weather people”, Daylight Saving Time means the models come out an hour later. (Weather models are run at UTC – Coordinated Universal Time).   For “weather people” on  Eastern Daylight Time, the models really come out a little too late!  I’ve written extensively about this 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

The new GFS version 16 launches on March 17th. Due to the increased complexity of the new model, (there are new parameters and it’s computed at many additional levels -layers of the atmosphere), the GFS v16  will take an additional 8 minutes to compute its forecasts.  Several models that depend upon the GFS for their “initial conditions” will also run later.   

That means the GFS model’s next day forecast (for the next 24 hours) won’t be available until 11:45-11:50 PM EDT, way past the 11 o’clock TV news and past bedtime for most of us! 

 

Commentary

“CHECK BACK AT 11” : TV WEATHER & EASTERN DAYLIGHT TIME

With the change to Eastern Daylight Saving Time, the TV weather forecasts you will see on the 10 and 11 PM news won’t/can’t be based on the latest models.  Why?   Read my post from March 2018.

I tried to further explain this snag in another post last year.

Over the past year and a half, I’ve been directly downloading weather model “grib” (gridded binaries) data from NOAA for these forecasts instead of relying on the adequate, but limited data freely available from university sites on the Internet.

Over the past day  I’ve been redoing my scripts/programs to have them run properly starting at 2 AM Saturday night.

To give you an idea of how late some of these weather models become available in Eastern Daylight Saving Time, here’s a few of the changes I need to make:

NAM model  9:38 PM EST —> 10:38 PM EDT
GFS model  10:38 PM EST —> 11:38 PM EDT (first 24 hour forecast data)
HIRESW Models 10:10 PM EST —> 11:10 EDT
HIREF ENSEMBLE: 11:19 EST. —> 12: 19 AM EDT
CMC GDPS  11: 45 PM EST —> 12: 45 AM EDT
ICON Model 11:21 PM EST —> 12: 21 AM EDT

To those times, add 5-10 minutes to download the data, time to review the data and you’re well into the wee hours of the morning.

Even the hourly HRRR, RAP and NBM models require several hours to incorporate  the changes in the upper air measurements (also done an hour later.)

So when you hear “check back at 11” for the weather on the TV during Eastern Daylight Saving time, you’re not going to get an updated forecast on new data.  It’s true for the next day forecast and even more so  for the five day forecasts.