Temporal and Spatial Frequency of Warm-Season Stationary Fronts in the Eastern and Central United States

Stationary fronts (SFs) are a common feature across the United States that are often associated with flash flooding and severe convective storms. Previous research using gridded reanalysis data found that SFs are present over the eastern two-thirds of North America between 1.5 and 3.5% of the time. However, there has not yet been a thorough study conducted that focuses on actual SFs. Thus, this presentation examines the intraseasonal and interannual frequencies and spatial distribution of SFs east of the Rocky Mountains by creating a nine-year (2007–2015) warm-season (April–September) climatology of SFs. From this study, 3,528 individual SFs were identified. There is a substantial interannual variability of SFs, as 2014 had the most with 451 SFs, and 2008 had the fewest with 301 SFs. The intraseasonal variability features an increase in SFs from 549 in April to 664 in July, with a subsequent reduction to 472 SFs in September. Overall, the spatial distribution reveals that there are two maxima in SFs. The first is over Kansas and Oklahoma with the second along the Carolina coast. SFs from 2007–2011 most frequently occurred in the first region, while from 2012–2015, SFs most frequently occurred in the second location. Similarly, the concentration of SFs shifted from over the Central Plains in the early months of the warm-season to the east coast of the Carolinas during the late warm-season months. This warm-season climatology of SFs can be of importance to forecasters especially given the high-impact nature of warm-season convection that often develops along these boundaries.