PROBABILISTIC GREAT-LAKES HYDROLOGY OUTLOOKS

The Great Lakes Environmental Research Laboratory developed a semiauto matic software package for making hydrological outlooks for the Great Lakes. These include basin moisture storages, basin runoff, lake heat storage, lake evaporation, heat fluxes, and net lake supplies, one or more full months into the future. The package combines GLERL's rainfal l-runoff and lake evaporation models with near real-time data reductio n techniques to represent current system states. Users select historic al meteorologic record segments as candidate future scenarios to gener ate deterministic near real-time hydrological outlooks. GLERL has exte nded the package to make probabilistic outlooks for a decision-maker w ho must estimate the risk associated with his decisions. GLERL matches National Weather Service meteorologic outlook probabilities by select ing groups of historical meteorologic sequences, and constructs embedd ed outlook intervals for each hydrologic variable of interest. Interva l probabilities are assigned from comparisons over a recent evaluation period. This physically-based approach for generating outlooks offers the ability, as compared to other statistically-based approaches, to incorporate improvements in the understanding of process dynamics as t hey occur in the future and to respond reasonably to conditions initia l to a forecast (such as heat and moisture storages), not observed in the past.