Severe Weather associated with Warm-Season Stationary Fronts East of the Rocky Mountains

Warm season severe weather impacts the United States east of the Rocky Mountains, with numerous instances of tornadoes, wind, and hail. Through the work of professional and amateur spotters alike, the National Weather Service (NWS) collects and categorizes severe weather reports. While there are recognizable inconsistencies associated with the reporting of severe weather conditions, the use of NWS Storm Reports was deemed to be the best available data to determine severe weather location for this study. A crucial forcing mechanism for the initiation of warm-season severe weather events are quasi-stationary frontal boundaries. Thus, the purpose of this study is to examine the relationship between stationary fronts and severe weather events by utilizing a nine-year (2007–2015) climatology of warm-season (April-September) stationary fronts. In particular, stationary fronts lasting 24 to 48 hours were the focus of this study.

This stationary-front climatology identified fronts that occurred within 2.5 x 2.5 grid boxes east of the Rocky Mountains. The frontal location was plotted on that grid, along with severe reports. Reports were then classified by their location relative to the stationary front, with those in a common grid box to a stationary front categorized as associated and those in a grid box surrounding the stationary front categorized as proximal. Additionally the number of tornado, hail, and, wind reports with each stationary front were counted. The data shows that the greatest number of total storm reports occur with stationary fronts during the mid-warm season months, specifically June. Median value for total reports were maximized for fronts lasting 42 hours, while both associated and proximal reports had the highest median value during fronts lasting 36 hours. Future research will expand this climatology and classify more precisely the location of severe weather around stationary fronts and will also compare the utility of severe weather report location to that of lightning strike data.