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:
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 NAM.