Comparison of Warm Season North American Precipitation Variability Observations to CFSv2

Previous analysis of observed regional precipitation variability over the US during the April through June (AMJ) season has revealed a strengthening of variability over the northern Great Plains and southeast U.S. during the 1950-2010 time frame. The strengthening of the variability was shown to be related to changes in the primary modes of North American low level jets (NALLJ). With observed NALLJ variations showing a stronger connectivity to sea surface temperature (SST) variability during 1980-2010 than the earlier 1950-1979 period. To further characterize SST influence on NALLJ and precipitation variability, the observational analyses are repeated using the National Center for Environmental Prediction Climate Forecast System Version 2 (CFSv2) AMIP simulations. CFSv2 simulations consist of 12 ensemble members with monthly output from 1950-2010. Analyses of the CFSv2 AMIP simulations are compared to observations to investigate the interannual variability of regional North American precipitation for the AMJ and July through September (JAS) seasons. Comparisons and correlations of these simulations to observations will aid in determining the importance of SST variability to the trends and interannual variability of precipitation over the U.S.