GFS stands for Global Forecast System. It is a common prog for developing the extended forecast (3 to 10 days out). The GFS model is available on UNISYS weather at: http://weather.unisys.com/mrf/9panel/mrf_500p_9panel.html The trough / ridge pattern can be used as a medium range-forecasting tool. If the GFS model has a good handle on the evolution of the trough / ridge pattern, the forecast will do reasonably well. Keep in mind that beyond about 5 days, the GFS data output can change quite dramatically from one model run to the other. Small changes in the initial input into the model result in dramatic difference beyond the 5 day forecast period (i.e. butterfly effect). The trough / ridge pattern determines which regions will be cooler or warmer than normal and which regions have a higher likelihood of precipitation. Temperatures tend to be cooler than normal under amplified troughs and warmer than normal under amplified ridges. Precipitation tends to occur to the right of a highly amplified trough axis, along fronts and along shortwaves. The graphical output visual appearance from the GFS is similar to the NGM and ETA, just sometimes can be harder to read on the Internet because of the small panel size. |