Verification of a daily thunderstorm probability forecast contest using the National Lightning Detection Network

Since 1983, a thunderstorm probability forecast contest has been organized by the University at Albany, State University of New York, during the summer months (defined as June, July, and August). The forecast contest involves predicting the probability to the nearest 10% that thunder will be heard during a 24-h period (starting at 1800 UTC on the forecast day) at each of ten locations across the continental United States. The forecasts are verified by standard Automated Surface Observing Station (ASOS) reports, and are scored against consensus and a 16-year thunderstorm climatology (1988–2003). In recent years however, there have been several instances, particularly during overnight hours, in which a thunderstorm failed to be reported in the ASOS observations despite its occurrence. During such instances, the forecast contest was verified by (i) contacting the attendant National Weather Service office directly, and (ii) examining Weather Surveillance Radar-1988 Doppler and National Lightning Detection Network (NLDN) data.

Given that the NLDN has continuous space and time coverage, an average detection efficiency in excess of 90% and mean location errors of ~500 m for cloud-to-ground (CG) lightning flashes, this presentation will examine the utility of using the NLDN to verify thunderstorm occurrence at the ten ASOS stations currently used in the Albany Thunderstorm Contest. In particular, an updated 15-year thunderstorm climatology (1995–2008) from Global Summary of the Day station observations will be compared to an NLDN-verified lightning climatology. Questions such as (i) how close to an ASOS station does CG lightning need to strike for a thunderstorm to be reported and does this distance vary by ASOS station, and (ii) are there detectable trends and interannual variability in thunderstorm occurrence, will be addressed in this presentation.