Using DCIN and DCAPE to Evaluate Severe Surface Winds in a Case of Elevated Convection

Using DCIN and DCAPE to Evaluate Severe Surface Winds
in a Case of Elevated Convection

Paula Sumrall¹, Patrick Market¹, and Scott Rochette²

¹University of Missouri, Columbia, MO

²SUNY-Brockport, Brockport, NY

Abstract

A case study was done to demonstrate how the downdraft convective available potential energy (DCAPE) and downdraft convective inhibition (DCIN) can be used to help forecast/nowcast damaging wind at the surface when a near-surface inversion may be present. DCAPE, DCIN, and their ratio, are examined and applied as tools to help estimate the potential for a downdraft to penetrate through the depth of the stable surface layer. The evolution of this storm was studied to determine the relationship between the DCAPE, DCIN, and the DCIN/ DCAPE ratio, and the type of severe weather that occurred.

The case in question occurred over Iowa on 29 May 2011, with the first report of severe weather at 1121 UTC; this was an event with a significant number of severe wind reports (28). An elevated mesoscale convective system developed over western Iowa in the overnight hours. The storm moved from west to east, north of a warm front. The early phase of the severe reports was dominated by hail, reported in eastern Nebraska/western Iowa. As the storm strengthened, it produced primarily severe winds. Skew-T log p analyses were used to determine the DCAPE and DCIN values. Using an analysis of the DCIN/DCAPE ratio, it was found that as the storm switched from producing severe hail to severe wind, the DCAPE values increased while the DCIN values diminished to near zero, providing a ratio near zero which, indicates a high probability of strong winds reaching the surface.