The challenge of flash flood forecasts continues to perplex forecasters. This system offers a paradigm shift in our thinking about flash flood predictions. To date, the main focus of advances in assessing the possibility of flash floods has been on operational mesoscale models and improved quantitative precipitation forecasts, despite the fact that many studies indicate the serious shortcomings of convective parameterization schemes (Gallus). Even with rapid advances in processing speeds, the forecast community has reached a plateau in flash flood prediction which will likely not be changed until cumulus scale models are quasi-operational, perhaps within 5 years. While cumulus scale models may hold high hopes, many areas will still be at risk of flash flooding during the next half decade of development. This system offers a bold initiative to increase advance watches and warnings of flash flooding, specifically for the Middle Atlantic River region, but with applications elsewhere in the nation.

The foundation of this system is the research by Grumm and Hart (1999) establishing a real-time operational assessment of climatological anomalies of various model forecast fields based on derived monthly means from the NCEP reanalysis work (1948-2000). Since October 1999, the National Weather Service Office in State College has been producing graphical displays of model forecast anomaly fields for the Eta, Aviation, and the locally run MM5 computer models. Anomaly fields consist of the vertical mass-weighted mean anomaly for height, temperature, wind and moisture. These parameters are compared to the climatological mean to determine the anomaly. This anomaly system, developed by Grumm and Hart, is being used to create anomaly fields for historically significant rainfall events over the MARFC domain dating back to 1948. These significant rainfall events will be chosen based on the observed/estimated rainfall values. Once anomaly fields have been created, a pattern recognition exercise will be conducted to classify these events by time of year and significant types (ie. narrow cold frontal rain bands, mesoscale convective systems, etc.)

This project will determine the atmospheric anomalies associated with flash flooding in each month over the MARFC domain. The premise of this project is that there are characteristic signatures of flash flooding in the departure from mean fields of a variety of NCEP reanalysis data variables. That is, by month and season, flooding and flash flooding in the Middle Atlantic region has a fingerprint, so to speak, of anomalies that when predicted by current operational models and assessed by the Grumm-Hart model comparison fields will yield an early alert to flooding.