Abstract
A mesoscale analysis of surface variables is presented for an AYE-SESAME case, 10–11 April 1979, when 89 severe weather events were reported, including the Red River Valley tornado outbreak. Two severe weather outbreaks, the first along the Red River Valley and the other in north-central Texas, were found to be associated with two sub-synoptic low pressure centers. The first low formed between 1900 and 2000 GMT over the Texas Panhandle, moved outward, and was located near Wichita Falls at 0000 GMT 11 April, the time of the deadly tornado there. It then moved slowly northeastward, having a lifetime of 7–8 hours. Barograph traces showed that a second low formed quickly at about 0120 GMT near Abilene causing additional severe storms to occur throughout the night in central Texas.
After the formation of each sub-synoptic low, moisture convergence increased in the area, creating a local environment conducive to severe storm formation. In addition, the second surge of severe weather in north-central Texas was accompanied by an eastward protrusion of the dry line. Tegtmeier's idealized sub-synoptic low (SSL) dryline wave (DLW) model agreed well with the present study. Severe thunderstorm formation occurred northeast of the SSL and also along the DLW in accordance with his conceptual model.
