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

Conventional wisdom suggests that stationary fronts (SFs) can sometimes be the focus for warm-season severe weather and flash flooding to the east of the Rockies.  Furthermore, these SFs are typically ubiquitous features across this region during the warm season even though there has never been a comprehensive investigation of their interannual and interseasonal variability and distribution. Thus, this presentation will examine a nine-year climatology of SFs east of the Rocky Mountains during the warm seasons (April–September) of 2007 through 2015 composed through the subjective examination of archived four-times daily surface analysis from the Weather Prediction Center.

The climatological investigation revealed that 3528 warm-season SFs occurred over the nine-year period, 949 of which lasted at least 12 hours.  Further, there was noted interannual and intraseasonal variability in both SF frequency and spatial distribution. A typical warm season in the nine-year climatology featured between 300 and 450 sSFs, with August having the most SFs and April the fewest.  Spatially, the highest SF frequency occurred over the Midwest during the early warm-season months and near the Carolina coast during the late warm-season months. This presentation will explore synoptic and mesoscale rationale for these differences.  Future work will utilize this climatology to determine the precise relationship between SFs east of the Rockies and convection and flash flooding.