The contribution of mesoscale convective weather systems to the warm-season precipitation in the United States.

Abstract

The contribution of precipitation from mesoscale convective weather systems to the warm-season (April-September) rainfall in the US is evaluated. The distribution and geographical limits of the precipitation from the convective weather systems are constructed for the warm seasons of 1982, a 'normal' year, and 1983, a drought year. Precipitation characteristics of the systems are compared for the 2 years to determine how large-scale drought patterns affect their precipitation production. The frequency, precipitation characteristics and hydrologic ramifications of multiple occurrences, or series, of convective weather systems are presented and discussed. The temporal and spatial characteristics of the accumulated precipitation from a series of convective complexes is investigated and compared to that of Hurricane Alicia. It is found that mesoscale convective weather systems account for approximately 30% to 70% of the warm-season (April-September) precipitation over much of the region between the Rocky Mountains and the Mississippi River. Changes in the large-scale circulation patterns affected the seasonal precipitation from mesoscale convective weather systems by altering the precipitation characteristics of individual systems. It is concluded that mesoscale convective weather systems may be a crucial precipitation-producing deterrent to drought and an important mechanism for enhancing midsummer crop growth throughout the midwestern US.-from Authors