Synoptic Mechanisms behind Extreme Precipitation Event Frequency in Omaha, Nebraska, 1948–2018

Daily extreme precipitation events (EPEs) within the top 1% of the 1948–2018 precipitation event distribution are identified for Omaha, NE. The frequency of EPEs significantly increased over the 71- year period by approximately 1.1 events decade–1, based on a linear regression of 11-year running sums. Embedded within the long-term increase is a multidecadal oscillation where over 40% of its variance can be explained by the phase of the Atlantic Multidecadal Oscillation. Using a temporal synoptic index classification methodology, the synoptic weather types associated with the 71 EPEs are identified and analyzed. Eight weather types, which encompass over 75% of the events, are examined in detail. Weather types are assigned to general categories of extratropical cyclones, frontal passages, stationary fronts, and southeasterly flow. Each of these broad categories contributed near equally to extreme event totals, ranging between 22% and 28%. The frequency of one type, Stationary Front #1 (STF_1), can explain approximately 12% of the variation in EPEs. STF_1 significantly increased in frequency from 1948 to 2018, contributing to the overall increase in event frequency. The increasing occurrence of EPEs may have far- reaching implications to various societal sectors, particularly with respect to water resource management and agricultural productivity.