Warm-Season Stationary Fronts East of the Rocky Mountains: Intraseasonal Distribution and Variability

Stationary fronts (SFs) are sometimes associated with warm-season severe weather and flash flooding to the east of the Rockies. Additionally, SFs are typically present over this region during the warm season. However, there has never been a comprehensive investigation of their intraseasonal variability and distribution. Therefore, this presentation will offer the findings from a nine-year climatology of SFs east of the Rocky Mountains during the warm seasons (April–September) of 2007 through 2015 created by the subjective analysis of four-times daily surface maps from the Weather Prediction Center. 

A total of 3528 warm-season SFs were recorded over the nine-year period, 949 (358) of which lasted at least 12 (24) hours. There was prominent intraseasonal variability in both SF frequency and spatial distribution. When considering all 3528 warm-season SFs, it was noted that July and August had the largest amount of SFs, with 664 and 658 respectively, while September had the fewest with only 473. Spatially, the highest frequency of SFs during the early (late) warm-season months was concentrated over the Midwest (Carolina coast). This presentation will further elucidate the spatial trends of the intraseasonal variability and distribution of SFs across the eastern two-thirds of the United States. Future work will utilize this climatology to determine the association of SFs east of the Rocky Mountains with convection and flash flooding.