GIS assessment of GCM forecasts of upper air circulation and expected impacts on winter precipitation in Western North America

This study assesses the impact of global warming on northern Rocky Mountain States April 1 snowpack as influenced by 50 kPa synoptic fields for lx and 2x CO2 warming scenarios generated by the CCC GCM-II. The synoptic pattern observed was subjectively classified into one of seven 50-kPa winter time synoptic patterns that explained almost ninety percent of the non-average annual snowpack patterns in the study area. Two analysis were completed: fIrst to compare the 1 xCO2 predictions of synoptic type frequency to historical data, and secondly to compare lxCO2 predictions to the 2xCO2 simulation. The lxCO2 run of the GCM was found to statistically simulate the historical patterns well for all but one of the seven synoptic patterns. Comparison of the 2x and lx run of GCM indicates a statistically significant increase in a synoptic pattern associated with wet conditions in the north of the study region and dry conditions in the south, and a decreased frequency of patterns resulting in dry conditions in northern regions and relatively wet conditions in the south. From this analysis is expected that the decrease in mid-latitude jet occurrence over the southern regions of the study area could result in lower snowpack conditions over this region in a warmed scenario.