Category Archives: Commentary

SO WHAT HAPPENED TO THE STORMS?

So what happened to the storms and flash flooding expected for today?

Clearly, the models didn’t do a very good job here.  On Sunday, the models overwhelming predicted a severe weather event.  They continued to do this on Monday, but by Monday evening there was a lack of agreement, with some models showing the insignificant showers we ended up with.

By this morning, the severe weather parameters had become very unimpressive and I posted that change this morning.  Still, the Rapid Refresh model (RAP) available at 9:35 AM showed a line of storms about 4 PM.

While at work, the rest of this morning’s models became available between 10:15 and 12:40.   The NAM NEST, WRF-AWF, WRF-NMMB, RAP, HRRR and HRDPS are the models I look at for thunderstorms. (Hey, it’s almost a full-time job, but it’s still a hobby.)

By this morning’s model run, the models had really backed off considerably with even the rain, shunting anything developing to our south.   Too late to make an updated web announcement, while at work.

Interestingly, they were still talking about severe thunderstorms on the radio while driving home at 6:30 PM.

It’s always a tough call to cancel the call for severe weather when even the slight possibility could endanger people if it occurs.

Anyhow, the “elusive” search for the model that’s always correct is elusive for a reason.

Looking back, even the GFS, a large-scale model, did better yesterday than some of the high resolution models.  And if I had to hang my hat on a model yesterday, the Canadian HRDPS probably called it the best at the earliest time.  But it’s not always right…

THE FV3-GFS WEATHER MODEL

Today, with its morning model run, the National Center for Environmental Prediction (NCEP) will have upgraded the GFS model (version 14) to the new and improved FV3-GFS (GFS version 15.1.1). The FV3-GFS becomes the main global model of the National Weather Service today.

The FV3-GFS (Finite Volume Cubed Sphere) has been in development for well over 10 years and has been in testing for the past three. It uses a different three dimensional geometry to reduce errors inherent in all numeric weather models. It includes different modeling physics and new parameters.   Significant information on the FV3-GFS can be found here.  Background information is here.

The model data has been available on university web sites in a very limited fashion for awhile.  Over the past two weeks, the NCEP made the data available on the main weather model download server, “NOMADS”.

The FV3-GFS has been heavily evaluated and is considered “equal or better” than the current GFS.

DAYLIGHT SAVING TIME & WEATHER MODEL FORECASTS

My post from last year about Daylight Saving Time and the forecasts you see on the 10 and 11 PM TV news is useful information to check out.

The short version is that the latest runs of the GFS and other global models are not completed nor available in time for the late night TV weather segments when we switch to Daylight Saving Time on the east coast.

Indeed, the first “products” of the GFS model first become available about 11:32 EDT.

With the exception of the NAM, the forecasts you see on the 10PM or 11PM (east coast)  news/weather can only be based on older model runs from the short range models and [possibly] the newest NAM.   Indeed, some of the short range models at those times are, in turn,  “initialized” from the earlier afternoon NAM model, not necessarily the latest!

WEEKEND FORECAST UPDATE -SUNDAY

Last Updated

Wow, the clouds never broke today and temperatures remained in the 40s!  Yesterday’s NAM had predicted temperatures remaining in the 40s and I ignored it; I thought it was a modeling error because it was so far off.  So one model was an outlier, yet it turned out to be correct.

from earlier this morning:

The rain will move out later this morning. Some of the models are forecasting a break in the clouds after noontime for a few hours, so we may get some sun.  If not, certainly brighter skies.

I know you may have heard about a high of 61 today.  Only the GFS has been predicting this high.  Most of the models have a high in the low to mid 50s.  I guess we’ll find out.

A cold front will move through between 4 and 6 PM. Widely scattered showers and some cloudiness moves through at that time. Temperatures drop into the low 30s by daybreak Monday.

It will become very windy this afternoon and even more so this evening.

Contrary to an often-heard incorrect explanation on TV forecasts, high winds are NOT due to a “wind tunnel effect”.

High winds and wind gusts are principally due to 1. Rapid changes in atmospheric pressure, specifically, the rate of change of pressure over time.  (dp/dt).    2. Thermodynamic effects that cause a mixing down of normally high winds aloft down to the surface.

If you’re looking for “Wind tunnel effects”, they can be felt on the corner of Walnut and 15th streets in Center City on windy days.

Every time I hear a TV person attribute windy conditions to a wind tunnel effect, I wince.