A Conditional Lightning Climatology for the Florida Keys

Florida leads the United States in cloud-to-ground lightning strikes each year. As such, protecting lightning-sensitive interests has become a primary concern for all National Weather Service offices in the state. The NWS office in Key West, Florida, serves a diverse population over a widespread area. The general public, and especially the aviation and maritime communities have a vested interest in the NWS office's ability to accurately forecast the occurrence of lightning along the island chain and over the surrounding waters. Emphasis in the office is placed on the short term forecasting of probable lightning, and the nowcasting of lightning once convection has begun.

To assist the forecast staff, a conditional lightning climatology has been developed to provide a robust measure of the seasonal, monthly, and daily temporal patterns of lightning that occur in the region. Of particular utility is the development of hourly lighting probabilities for the Key West International Airport. This analysis revealed that there is a temporal minimum of lightning activity that occurs just after 2 pm local time, between the typical mid-morning and late-day rounds of convection. This lull in lightning activity is most clearly discernible in the early warm season months when convective potential is generally low. Additional analysis revealed the role local wind regimes play on the probability of lighting occurrence. Locally induced cumulus-line convection is the most probable source of thunderstorm development during light wind regimes. In contrast, widespread excessive lightning events are usually the result of convection developing outside of the region, and moving into the study area. Specifically, the most prolific lightning events are often the result of outflow boundaries or density currents originating over South Florida or Cuba. This presentation will summarize this work, as well as ongoing efforts designed to improve our short-term decision support services to our partners in the Florida Keys.