Temporal Distribution of Flooding WWAs Associated With Warm-Season Stationary Fronts East of the Rockies

Due to the slow moving nature and their known association with summer precipitation, stationary fronts may have a greater risk of causing flood events. As stationary fronts generally remain over the same area, the associated convective precipitation has the potential to remain in one area for an extended period of time. This project examines the temporal distribution of National Weather Service flooding watches, warnings, and advisories (WWAs) associated with warm-season (April-September) stationary fronts east of the Rockies.

Five years (2007-2011) of archived flooding WWAs (flood, flash flood, areal flood, coastal flood, and lakeshore flood) were imported into ArcGIS and examined to test our hypothesis. These WWAs were then compared with the position of warm-season stationary fronts from a 9-year (2007-2015) climatology. Using surface analysis archives and the coded surface front bulletins, the average daily position of fronts was also imported into ArcGIS for stationary fronts with a duration of at least 24 hours. The type of flooding WWA, time issued, date issued, location relative to the front, and duration of the front it was associated with were recorded.

The diurnal, intra- and inter-seasonal temporal distribution of flooding WWAs associated with stationary fronts were examined. Diurnal results reveal that 58.2% of Areal Flood advisories and 53.9% of Flash Flood warnings occur between 1800z and 0200z. Other flooding WWAs are observed to have greater diurnal variability and occur during any time of day. Monthly results show a distinct pattern for all Areal Flood, Flash Flood, and Flood WWAs. Inter-annually, 2007 had the least amount of Areal Flood and Flood WWAs, while the most Areal Flood advisories were in 2011. The majority of flooding WWAs were issued for 36 hour fronts.