What is the difference between the models?

[David Toner]

This afternoon I was explaining a forecast to a friend when he asked what the difference between the models was. I started to explain what the acronyms stood for (You know, North American Model or Global Forecast System) but that wasn't what he was asking. He wanted to know what the pros and cons are of each and if one handles something better than the others. I came to the realization that while I have developed a bias for the NAM I couldn't explain why? My bias isn't scientific, rather more of a superstition that I've developed over the years. The closest I can come to explaining a model is the RUC being rapid updating and short/near term.

So I ask you, what is the difference between the ECWMF, GFS, NAM and the others?

 

[rdale]

http://www.meted.ucar.edu/nwp/pcu2/

http://www.meted.ucar.edu/nwp/course/modules.php

 

[Dave Rennie]

Danny Neal: You seem to be good at answering questions. Would you like to take a stab at David Toner's question? I've been wondering about model differences as well, but don't care to register for classes to satisfy my curiosity.

 

[Jason Boggs]

Dave, nothing against you personally, but sometimes you do have to do a little work to get something in return. Links were provided, so expecting to be spoon fed an answer won't happen a lot of times.

 

[Dave Rennie]

Well, David, I did some looking and maybe this will help answer your question:

GFS, NAM, ECMWF, WRF-GFS, MM5-NAM, RUC, etc. are all acronyms for the complex computer models that forecasters may use to aid them in preparing a weather forecast. The models are based on mathematical equations that describe and try to reproduce the physics that control how the atmosphere changes over time. These models are run by different organizations all over the world, frequently on powerful super-computers, and the data is shared with the various academic and meteorological organizations. Many of these models, including the ones run by the National Weather Service (NWS), are available to the general public via the internet.

* The GFS stands for Global Forecast System and is one of the two main models run by the National Weather Service. The GFS is run 4 times per day based on the synoptic data times (00Z, 06Z, 12Z, 18Z) and the output is in two different resolutions, 90 kilometers (GFS90) and 40 km (GFS40).

* The other main NWS model is the NAM which stands for North American Mesoscale (model). The NAM is a mesoscale regional model, meaning that it has higher resolution than a hemispheric model like the GFS. There are trade-offs between using higher resolution mesoscale models and lower resolution hemispheric models. The NAM is also run 4 times per day with output coming in two resolutions, 40 km (NAM40) and 12 km (NAM12).

* The ECMWF is the model that the European Center for Medium Range Weather Forecasting uses, and is comparable to the GFS.

* The Canadian is the model that Canada's weather service, "Environment Canada" uses and is also comparable to the GFS.

* The RUC is short for "Rapid Update Cycle" and is a model that is run every hour. The main use of the RUC is in forecasting rapidly changing conditions. An example of this would be thunderstorm outbreaks that can occur in the midwest.

* More localized organizations, such as the University of Washington or our forecast office in Salt Lake City, run their own computer models, usually high resolution models that help account for detailed local effects such as terrain or bodies of water. These high resolution models include the MM5 model and the WRF model.. These computer models are 'initialized', or start with the initial conditions from either the GFS or NAM model, then the models continue on with their own forecasts. The models are frequently run at resolutions as small as 4 km, and forecasters often look at and refer to them to get some idea of what kind of impact the small scale effects may have.

Hope this helps, as it did me, and I didn't even have to register for classes to find it!

Thanks to the NWS Forecast Office, Salt Lake City, UT, for the above information.

 

[rdale]

but don't care to register for classes to satisfy my curiosity.

Those "classes" are actually good for you... Sorry that the requirement to register pushed you away, but it's free. You did answer the question factually, but to put the models to use operationally you'll need some training. The METED classes are great (and cheap!)

 

[Dave Rennie]

rdale: Thanks for the response. It wasn't the registration, per se, that pushed me away, but just that looking at the curriculum it appeared to be a longer term commitment than I was looking for at this point in time. I may check it out when things quiet down.

Jason Boggs: No offense taken, but I don't think I'm expecting to be spoon fed. I'm currently reading Tim Vasquez's Weather Map Handbook, Severe Storm Forecasting, and Storm Chasing Handbook; George Elliott's Weather Forecasting: Rules, Techniques and Procedures. I have signed up for Tim's forecasting class at ChaserCon, and I'm currently enrolled in the Spotter Network's training course. Adding the course that rdale linked to seemed a bit much at this point in time.

 

[David Toner]

I appreciate the answers and thanks for the link. I'm going through the COMET courses now.

 

[Jason Boggs]

rdale: Thanks for the response. It wasn't the registration, per se, that pushed me away, but just that looking at the curriculum it appeared to be a longer term commitment than I was looking for at this point in time. I may check it out when things quiet down.

Jason Boggs: No offense taken, but I don't think I'm expecting to be spoon fed. I'm currently reading Tim Vasquez's Weather Map Handbook, Severe Storm Forecasting, and Storm Chasing Handbook; George Elliott's Weather Forecasting: Rules, Techniques and Procedures. I have signed up for Tim's forecasting class at ChaserCon, and I'm currently enrolled in the Spotter Network's training course. Adding the course that rdale linked to seemed a bit much at this point in time.

I hear ya Dave. I probably could have worded it better, but didn't have much time when I wrote that. Sorry if I came off harsh...I didn't mean to be. I'm always willing to help out, but from time to time some members always want something for nothing. Take care!