Potential Urban Effects on Precipitation in the Winter and Transition Seasons at St. Louis, Missouri

Abstract

Two datasets were used to investigate the potential presence of urban-related precipitation anomalies in the fall, winter and spring seasons St. Louis, Missouri, and to ascertain under what conditions anomalies occurred- if indeed they did occur. The 1971?75 METROMEX dense raingage network data were used along with 1941?80 data from NWS stations in the area. Spatial and temporal analyses of seasonal precipitation showed the reality of urban-related influences northeast of St. Louis in all seasons, plus urban-related increases to the east and southeast in winter and fall. The maximum alterations in precipitation were northeast of St. Louis with increases of 14% in spring, 5% in winter, and 7% in fall when averaged over the 40-yr sampling period. Topographic effects that increased rainfall, particularly in the winter and fall, were quite evident in the hill and bluff areas southwest and southeast of St. Louis. Studies of snowstorms during 1971?75 revealed 5% to 10% less snowfall over the city than over adjacent rural areas. Only 10% to 15% of the rain events related to areas of urban increases were altered in each season, and in most cases, they occurred with well-organized precipitation systems having convection. This agrees with the METROMEX summer findings. Good agreement between the precipitation patterns of METROMEX and climate network stations suggest that future studies of urban influences on winter and transition season precipitation can be based on the less dense climatic network of NWS.