| description abstract | Areal extents of monthly and seasonal North American snow cover were correlated with precipitation totals, precipitation frequency, and severe weather associated with the North American monsoon. Significant relationships were found to exist between monsoon variables and snow-cover extent over western North America. Synoptic composites of the summertime atmosphere revealed that during years of low snow-cover extent, 500-mb heights were higher across much of the United States and 850-mb specific humidity values were increased over the desert southwest compared with high snow-cover extent years. Seemingly, displacement of the 500-mb ridge across the United States displaces the Four Corners high, which in turn affects the strength of low-level moisture advection into the southwestern United States. In beginning to assess the possibility of anticipating the strength of the North American monsoon using winter and spring snow-cover extent, data for anomalously large and small snow-cover years (50% of the data record) were input into stepwise multiple regressions. Using the limited data record, results showed that winter and spring snow-cover variables explained significant portions of the variance in precipitation totals (83%), precipitation frequency (95%), hail (81%), wind (82%), and total severe weather (98%) for the monsoon region. The results lead to optimism regarding the development of seasonal forecasting algorithms that are centered upon the use of winter and spring snow-cover extent to assess the potential intensity of the subsequent North American monsoon season. Accurate prediction of general monsoon intensity several months in advance would be invaluable to many different aspects of life in southwestern North America. | |
