A Statistical Analysis of Precipitation Frequency in the Conterminous United States, Including Comparisons with Precipitation Totals

Abstract

An alternative measure of time-aggregated precipitation for use in short-term climate studies is developed. This measure, precipitation frequency, is defined as the number of days per month or season with total amounts ≥ 2.54 mm (0.10 inch). Newly created data sets for the period 1951–80 are used as a basis for describing large-scale spatial and temporal features of precipitation frequency for the mainland United States. Comparisons between precipitation frequency and the conventional statistic, total precipitation, indicate that frequency is more normally distributed and more spatially coherent than total precipitation. Factor analysis and an orthogonal rotation to the varimax criterion are used to identify synoptic-scale, spatially coherent regions of precipitation frequency. The regions are generally consistent with previously documented cyclone trajectories.