Category Archives: Commentary

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.

Commentary

SO WHAT’S WITH THE (UN)FORECAST SNOW?

So what’s with the snow falling (which was not forecast)?   That’s a great question.  Here’s the short answer—

I wasn’t even looking for the possibility of snow today.   But as soon as I saw the snow, I went back to the high resolution NAM NEST model and saw that it was forecast to 32º or below at key levels of the lower atmosphere with plenty of precipitation occurring after 11 AM.

NAMNEST model 32º F (isotherm) temperatures at 6000 and 3000 feet above sea level (lavender and violet lines) and simulated radar (blue/green shading)

Add to this strong vertical motion and heavy precipitation with dynamic cooling and we got the brief period of snow.

I wish I had forecast that possibility, but I skipped over the thermal profiles this weekend, thinking snow wasn’t a consideration.

As for the professional forecasters and the talking heads on TV,  I don’t know what their excuse is.

Anyhow, this is what makes the weather so interesting.   The forecast might have been off, but at least we know why.

Put another way, often we blame the models for being wrong.  This time, the wrong forecast was due to the forecasters.