A Climatology of Dryline Convection in the Southern Great Plains

Synoptic-scale processes regulate dryline formation and intensity and are thought to “prime” the dryline environment for deep, moist convection (DMC). However, the precise nature of how these processes lead to convection initiation is not well understood. For instance, if synoptic-scale ascent conditions the environment for DMC, how much lift is required to make the mesoscale circulation at the dryline more likely to sustain deep convection? Conversely, if mesoscale lift is strong enough are there scenarios without significant synoptic-scale forcing that favour DMC?

The primary aim of our research is to improve our understanding of how forcing for synoptic-scale ascent determines the initiation and morphology of convective storms along the dryline. The first phase of our study was to create a climatology of DMC within the southern Great Plains. Archived Weather Prediction Center surface analyses were obtained for April, May and June 2006-15 to identify occurrences of drylines. Doppler radar imagery was used to identify convective drylines; where DMC was deemed to have been associated with the dryline circulation. Visible and infrared satellite imagery was also used to determine whether the dryline was the initiating boundary. Only radar echoes within 100 km of the dryline were considered, with a minimum threshold applied to radar reflectivity.

On average there were 33 dryline days per season. Drylines were most frequent in May and least frequent in June, with the lowest frequency towards the end of June. DMC was associated with the dryline on average 21 days per season, with highest frequency occurring in May. Drylines often occurred in temporal clusters, defined as consecutive days with an identified dryline. Approximately 64% of drylines occurred as part of a multi-day sequence. However, convective drylines were less likely to occur in clusters. Approximately 41% of convective drylines occurred as part of a multi-day sequence. These results raise several questions. For instance, why are convective drylines occurring in smaller temporal clusters than drylines in general? Given the presence of a dryline, are certain synoptic environments more conducive to DMC? Future work will attempt to answer these questions by determining how the timing and location of convection initiation relates to synoptic-scale features.