Spatial Coherence of Monthly Precipitation in the United States

Abstract

Factor analysis and an orthogonal rotation to the varimax criterion are used to identify the synoptic-scale regions of the United States over which monthly precipitation amounts show the greatest spatial coherence. The regions are consistent with previously documented cyclone trajectories. The seasonal continuity of the patterns is seriously disrupted only in summer. Regional values of the Palmer Drought Index correlate most highly with the precipitation pattern amplitudes averaged over 13?18 months in the central United States and over 7?9 months along the East and West Coasts. Associations between the regional precipitation and local 700 mb height parameters are strongest with the geostrophic wind components in the Ohio Valley and Great Lakes regions, and with geopotential height and vorticity in the Northern Plains. Sea level pressure anomalies over broad areas of the Atlantic and Pacific Oceans are associated with regional precipitation in the central and eastern United States, while the correlations with precipitation along the West Coast are somewhat more localized.