Tag Archives: FV3-GFS

Commentary

NEW GFS MODEL COMING

The main model used in US weather forecasting is the GFS (Global Forecast System), a model that continues to be developed and improved. The last major upgrade to the GFS model occurred in June 2019 with the release of the GFS-FV3 which was “version 15” in its evolution.

I wrote a brief post about this model back then, describing the changes in “FV3” ( Finite-Volume Cubed Sphere Dynamical Core) geometry that the model uses to divide up the atmosphere into geometric units that can be handled mathematically. The complexity of these models is amazing and the NOAA scientists that create these models can only be admired.

The new version of the GFS model continues with the FV3 geometry (in the long line of this model evolution, this will be GFS version 16) and it has just become available this past week on a full time NOAA server. It’s available in what is referred to as a test “parallel mode”, meaning that it is running at the same time the current operational version (v 15) is running.

If you’re into technical stuff, or just want to be dazzled by the science of these models, check out this early presentation from the NOAA Model Evaluation Group. It gives a brief history of the GFS model development and also presents the improvements, short-comings and challenges of the new GFS v16 model. The official GFS v16 evaluation website can be found here with plenty of additional information.

If all goes according to plan, it should become the GFS model early February 2021.

I would expect general improvements in weather forecasts with its release. Additionally, the GFS model is used to set the boundaries and initial conditions for several other models—

GFS-MOS
UKMET
MAG
HRRR
RAP
NWPS
NBM
HWRF
HMON
GEFS

So several other models’ accuracy will benefit when the GFS v16 becomes operational early 2021.

What could be a better example of the new GFS model’s improvement than today’s cloud forecast? Last night’s operational GFS had forecast for it to be sunny here at 3 PM today, keeping the clouds to our west —

Current GFS model showing clouds stay to our west at 3 PM (Click on image for a larger view.)

 

The new, soon to become operational GFS version 16, had a correct cloud forecast for today at 3PM—

New GFS (version 16) had the correct cloud forecast for this afternoon, showing clouds overspread much of the area.  (Click on image for a larger view.)

Last night’s indecision about cloud cover for today would have been less of a dilemma had I used the new GFS.

One of the issues of the new GFS is that the new model’s data size is almost twice as large as the existing GFS. NOAA is concerned about the data download size issue and it is expected to limit data download rates within the month for all their models. We’ll see how that plays out.

Another minor issue— the higher complexity of the new GFS takes more computational time. As a result, the new model take 7-12 minutes longer to complete. As an example, the first 24 hours of the current GFS become available about 10:37 PM EST. With the new GFS model, the first 24 hour forecast data will become available about 10:46 PM EST.

Those 11 PM TV weather entertainers are going to have even less time to update their forecasts during Eastern Standard Time.

The new model is an overall improvement, but not without its problems. It tends to handle tropical systems not so well, sometimes developing systems that don’t actually form. Certain parameters used for forecasting thunderstorms are understated, especially when soil moisture is low. Forecast temperature biases, while improved, also have their issues. You can be sure that scientists are already hard at work with a future version 17.

One more thing— the HRRR and RAP models were updated earlier this month and have shown improved forecasting accuracy and an increase in model forecast length. The HRRR has become a full 48 hour model and the RAP a 51 hour model. These same models are expected to start using the same FV3 core geometry used by the GFS in their own next iterations.

Several other high resolution models (HIRESW and HIREF) have been upgraded to the FV3 core geometry and are planned for release in the next few months. Their output is now available as “parallel” models.

Philadelphia Weather Outlook

FORECAST REVIEW & WEEK WEATHER OUTLOOK

There are widely scattered showers around most of the area right now (4:49 PM Sunday)

NexRad Radar at 4:49 PM (source- https://www.weathertap.com )

Most of today’s models missed forecasting these showers entirely or forecast much less coverage, somewhat later, about 6-7 PM.  The NAM and NAM-NEST were particularly disappointing today.  The GFS and ARW2 were close, but no cigar.   Even this morning’s HRRR didn’t predict showers.

However NOAA weather scientists are on top of it, developing the next generation of weather models.

Here’s a forecast from one of their still-experimental SAR-FV3 models  (SAR = “Stand Alone Regional”)

(FV3 = Finite­ Volume Cubed-Sphere dynamical core)

SAR-FV3 Model forecast

I’d love to use this SAR model all the time, but it’s run once a day at 8 PM and takes much of the next day before it becomes available.  It has limited available parameters and no raw data feed available yet.

Over the next two years, some of these new models under development will become available.

As mentioned yesterday, new improvements and time extensions in the HRRR and RAP models are to be released next week.

The process of rewriting the HRRR with the new FV3 core is planned to start shortly.   An FV3 version of the HIRESW is currently running experimentally as well. So I think you can expect large improvements in forecasts over the next few years.

Speaking of FV3 core models, the GFS went to a FV3 core last year and here’s what it’s forecasting for this week’s weather-

GFS Forecast 1AM Tuesday  (Click on image for a larger view.)

The weather setup is complex with an “omega block”, closed upper low and surface low in the Midwest and a coastal low with some tropical characteristics moving northeastward.

The current general consensus for this week’s weather is cloudy, windy and somewhat chilly, but most if not all of the rain will be suppressed to our south and east by high pressure in eastern Canada. 

Things should settle down by Memorial Day Weekend.