Using Blue Waters to Assess Non-Tornadic Outbreak Forecast Capability by Lead Time

Derechos are a dangerous, primarily non-tornadic severe weather outbreak type responsible for a variety of atmospheric hazards. However, the exact predictability of these events by lead time is unknown, yet would likely be invaluable to forecasters responsible for predicting these events. As such, the predictability of nontornadic outbreaks by lead time was assessed. Five derecho events spanning 1979 to 2012 were selected and simulated using the Weather Research and Forecasting (WRF) model at 24, 48, 72, 96, and 120-hours lead time. Nine stochastically perturbed initial conditions were generated for each case and each lead time, yielding an ensemble of derecho simulations. Moment statistics of the derecho composite parameter (DCP), a good proxy for derecho environments, were used to assess variability in forecast quality and precision by lead time. Overall, results showed that 24 and 48 hour simulations had similar variability characteristics, as did 96 and 120 hours. This suggests the existence of a change point or statistically notable drop-off in forecast performance at 72-hours lead time that should be more fully explored in future work. These results are useful for forecasters as they give a first guess as to forecast skill and precision prior to initiating their predictions at lead times of out to 5 days.