The Spatial Scale of Daily Precipitation in North Carolina

Abstract

One of the major geographical characteristics of precipitation is its spatial pattern. Many studies have described and explained the spatial variation of monthly and annual precipitation totals in various regions. For North Carolina these patterns, clearly demonstrating such phenomena as the orographic effect or the influence of sea breezes or coastal storms, are well established and underpin much of our concept of the climate of the state ( e.g. Kopec and Clay, 1975). Much less is known, however, about the pattern of precipitation on the daily time-scale. Individual daily conditions are routinely considered by the National Weather Service for forecasting purposes, and this has led to an informal classification of precipitation into two types (Robinson and Henderson, 1992). First are the cyclonic days associated with widespread, often gentle rainfall from travelling depressions. Second are the convective days with localized, frequently intense, precipitation from short-lived thunderstorms. The relatively infrequentvisits oftropicalsystems tothe statearefrequently a mixture of these two types, and are not considered separately here. It can be suggested that the cyclonic days should dominate in winter, and that there should be a mixture of cyclonic and convective activity in summer (Epperson et al., 1989). In addition, topographic effects should lead to differences between the mountains and the rest of the state. Thus, on the average, there should be different patterns ofd aily precipitation between winter and summer and between the mountains and the lowlands. The focus of this paper is to investigate these seasonal and topographic differences in daily precipitation patterns. In more personal terms, it considers the question "If it is raining at my location, what is the probability that it is raining at another place in the state which is of interest to me?"