A past and future look at the Rapid Update Cycle for the 3 May 1999 severe weather outbreak

The Rapid Update Cycle (RUC), running at NCEP and developed at NOAA/FSL, has become a key forecast tool for predicting environments conducive to development of severe convective weather. The one-hour assimilation cycle allows for the rapid impact of asynoptic weather observations and the availablility of a new 12h forecast suite based on these observations every 3h. The operational 40km version of this model was available and used by forecasters on 3 May 1999, the day of a major outbreak of tornadoes and severe weather in Oklahoma and surrounding states.

The performance of the operational RUC from NCEP on 3 May 1999 was mixed, giving some indication of strong moisture convergence where the first storms initiated in southwestern Oklahoma, but then failing to predict much precipitation.

In this presentation, we will compare operational RUC forecasts available in real time on 3 May 1999 with experimental RUC forecasts made with a few key differences: - inclusion of wind profiler data that was missing at NCEP due to a temporary timing problem - an improved version of the 40km model, including improvements in the Grell convective parameterization, use of MM5 cloud microphysics, boundary-layer and surface physics. - the new 20-km version of the RUC to be made operational at NCEP later this year.

Through these experiments, we will examine what improvements from RUC guidance might be expected for a similar situation in the future with a more complete data assimilation and an advanced version of the RUC model.