Climatology, Synoptic Conditions, and Misanalyses of Mississippi River Valley Drylines

Abstract

he dryline is an important focal point for convection initiation. Although drylines most commonly occur on the southern Great Plains, dryline passages and subsequent severe weather outbreaks have been documented in the Mississippi River valley. This study presents a 15-yr (1999?2013) climatology of these Mississippi River valley drylines and associated severe weather. Additionally, synoptic patterns are identified that may result in drylines moving atypically far eastward into the Mississippi River valley. In total, 39 Mississippi River valley drylines (hereafter referred to as MRV drylines) were identified from the North American Regional Reanalysis (NARR) dataset through the study period. Mean and anomaly synoptic composites were created for these drylines. MRV dryline events typically occur under synoptically active conditions with an amplified upper-air pattern, a 500-hPa shortwave trough to the west or northwest of the dryline, and a strong surface cyclone to the north. These boundaries are often misanalyzed or inconsistently analyzed as cold fronts, stationary fronts, or trough axes on surface maps; of the 33 cases of identified MRV drylines for which the Weather Prediction Center archived analyses were available, only 6 were correctly analyzed as drylines. Drylines moving into the Mississippi River valley often result in severe weather outbreaks in the Mississippi River valley, the Midwest, and the southeastern United States.