6.1
Establishing a 10 year climatology of 101.6 mm (4 inch) rainfall days, part I
Norman W. Junker, NOAA/NWS, Camp Springs, MD; and R. H. Grumm, R. Hart, and L. F. Bosart
A climatology of 4 inch rainfall events across the conterminous United States has been constructed for the 10 year period (1991-2000) from the official Hydrometeorological Prediction Center precipitation analyses (Olson et al.1995, McDonald 2001). From these analyses, a list was compiled of: 1) the date each event, 2) the states affected by 4 inches or more or rainfall during that 24 hour period, 3) the maximum analyzed rainfall, 4) the approximate center (latitude and longitude) of the maximum precipitation area, and 5) comments about type and/or scale of the event. The number of days when 4 inches or greater rainfall was observed were then totaled by state and season. These data were then plotted on a map to show the number of events by state and season. In the winter, the maximum number of 4-inch days is concentrated along the west coast and over the Southeast. There were no 4-inch events observed across the northern plains. The frequency of 4-inch rainfall events increased across most of the southeastern United States during the spring. The largest increase was observed over the central and western gulf coast states and central and southern plains where there was a seasonal maximum. During the spring, there was a marked decrease of events along the West Coast while the number of 4-inch events increased significantly across the Central Plains and upper midwest. The number of events decreased over the central and eastern Gulf States during summer. Only one 4-inch event was recorded along the west coast during the summer, possibly due to the northward shift of the polar jet and the relatively low mean precipitable water across the western United States. During the autumn, the number of events increased across Louisiana, Texas, Florida and along the West Coast while the number of events decreased dramatically over the northern plains and upper midwest. Mean monthly charts of various parameters were inspected to help understand the observed seasonal shifts. Possible reasons for the seasonal changes in frequency will be discussed.
Session 6, Winter Weather and Climatological Studies
Wednesday, 14 August 2002, 8:00 AM-10:00 AM
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