Characterizing the Extremely Wet 2022/2023 Winter in the Southwestern United States

The record wet 2022/2023 winter was out of the expectation of operational forecasters – with extreme precipitation particularly snowpack in the southwestern United States. However, the reason behind the extreme precipitation remains elusive. This study examines this extreme wetness from the perspective of synoptic patterns. During December 2022 – January 2023, the deep south trough pattern occurs on 34 days, while the climatological value is 13 days. This trough pattern accounts for most of the total precipitation received in the southwestern United States during the two months. This deep south trough pattern is closely related to atmospheric rivers that made landfall over the southwestern U.S. An increasing trend in the frequency of the deep south trough pattern has been found partially contributes to the record high frequency of this pattern in the winter, subsequently the extreme precipitation.