Mesoscale Precipitation Fields. Part I: Statistical Analysis and Hydrologic Response

Abstract

A statistical objective analysis (SOA) scheme was developed to adjust estimates of rainfall accumulation from the WSR-88D in central Oklahoma using rain gauge measurements from the Oklahoma Mesonetwork. Statistical parameters of these rainfall fields were obtained from a time series of 2-km Constant Altitude Plan Position Indicators at 2 km ? 2 km resolution for accumulation time intervals of 15, 30, 60, and 120 min. Results document that the Twin Lakes WSR-88D underestimates rainfall rates by 28% on average. In turn, these errors generate large errors in the streamflow simulations performed for the Dry Creek watershed in north-central Oklahoma. Mean normalized expected error variances of the accumulated rainfall over 1?2-h duration were reduced up to 25% by the SOA scheme. These results are discussed in the context of a hydrometeorological forecast system that uses the analyzed rainfall field to adjust rainfall rates for nowcasting (0?3 h), to improve rainfall forecasts (0?12 h) via its assimilation into mesoscale models, and to verify the accuracy of these rainfall forecasts.