What is the difference between the AVN, MRF and GFS models?
The NOAA National Centers for Environmental Prediction (NCEP) used to have the AVN and MRF models. The MRF was run once a day and it was a long-range forecast (2 weeks or so). The AVN was run 4 times a day out to 5 or so days. I'm not sure exactly how long each of these forecasts went out to. Then NCEP stopped running the MRF but extended the AVN out to 2 weeks or so 4 times a day, and renamed it to the GFS. There is information about NCEP's global models at http://www.nco.ncep.noaa.gov/pmb/products/.
In READY, the GFS data are at 3-hour intervals on a one degree grid. Details about our forecast datasets are at http://ready.arl.noaa.gov/READYmetdata.php.