Category Archives: Commentary


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.


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.


This Sunday morning,  Eastern Daylight Saving Time changes to Eastern Standard Time — the early morning hours get lighter (at least initially), the afternoons gets darker earlier, and the daylight hours that are already shortened seem even shorter.

What could possibly be good about this?

Well, there’s at least one good thing —  the weather models (which are run on Universal Time”UTC” (previously called Greenwich Mean Time “GMT”) are available an hour earlier! On the east coast, this makes a giant difference.

Every evening, the National Center for Environmental Prediction begins incorporating the latest weather data measurements including weather balloon radiosonde data at 00 UTC, which is 7 PM Eastern Standard Time and 8 PM Daylight Saving Time.

The incredible amount of data to ingest and the number of calculations needed for models to output takes 2 – 4 hours to complete, even on super computers.

Since last March (the beginning of DST), every meteorologist, TV station, etc. on the east coast has had to make their evening  and 11 o’clock broadcasts without the latest GFS model data, simply because the first 24 hours of GFS forecast data hadn’t become available until 11:38 PM EDT — after the 11 o’clock news was over.

With the change to Eastern Standard Time, the GFS now becomes available at 10:38 PM EST— plenty of time to update the weather on the 11 o’clock news.

Similarly, the NAM whose 24 hour forecast data became available about 9:57 PM EDT will now become available at 8:57 PM EST.

For those interested, the exact model time availability can be found here.

For amateurs who enjoy weather forecasting and for those who do it professionally, this one hour difference makes all the difference in the world.

It’s a small conciliation for the shorter days and the colder weather, but it’s something. 🙂

Over the years, I have talked about this on previous blog posts—here,  and here.

BTW, the GFS is showing a frigid outbreak for the time period around Nov 12th.


I find it fascinating that most of today’s models didn’t predict the rain that developed in a narrow, persistent band over Philadelphia. Interestingly, little rain developed at the shore to this point.

Radar 4:30 PM Friday, courtesy of

Going back to last night’s models, the WRF-NMMB and to a lesser extent the WRF-ARW were the only models to predict this rain last night.   However, the same models run this morning didn’t show it as much and the GFS, NAM really were off about this.

The unexpected rain was the result of some vorticity and vertical lift in the mid levels of the atmosphere, captured on this afternoon’s 2PM RAP model analysis—

RAP Model 2 PM Friday Analysis showing lift and vorticity at the 500 mb level (~18,000 feet)

I don’t know why, but as I mentioned last week, hurricanes seem to throw off the model forecasts, often in big ways.

This rain is expected to clear out later today.  The weekend looks to be beautiful with sunny skies and comfortable temperatures in the 70s.  I’ll do a brief update later this evening.