Dry thunderstorm forecast procedure
Due to the seemingly innocuous conditions preceding dry thunderstorm development across the western United States (west of the Rocky Mountains), forecasting dry thunderstorm events can prove challenging and inconsistent. NWS Reno WFO developed WA04, a conceptual model of dry thunderstorms that includes the pressure of the dynamic tropopause, jet streak dynamics, equivalent potential temperature, and upper level lapse rates in conjunction with the High Level Total Totals (Milne 2004). Isentropic analysis was added to WA04.
This procedure was applied to several studies from past five years including the dry lightning events across all regions of the western United States. Dates of the investigated events are June 25-27, 2006, August 16-18, 2006, July 16-18, 2007, June 20-21, 2008, August 1, 2009, and August 20-21, 2009. These events show the diversity of dry thunderstorms in terms of development, location, and timing. The procedure proved useful in determining the potential for dry thunderstorm development in the preceding days and hours to the initiation of the event and if the event lasted more than one day. This paper summarizes these case studies, and describes the dry lightning forecast procedure.