REGIONAL UTILITY OF NOAA/CPC SEASONAL CLIMATE PRECIPITATION FORECASTS

Authors: Schneider, Jeanne; Garbrecht, Jurgen

Submitted to: Proceedings of the World Water and Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2003
Publication Date: 12/15/2003
Citation: Schneider, J.M., Garbrecht, J.D. Regional utility of NOAA/CPC seasonal climate precipitation forecasts. CD-ROM. Proceedings of the World Water & Environmental Resources Congress. 2003. Environmental and Water Resources Institute, American Society of Civil Engineers.

Interpretive Summary: Experimental climate forecasts for 3-month total precipitation appear to offer information that could reduce uncertainty and risk in the management of water resources. However, assessments of forecast performance at regional scales are not offered with the forecasts. The potential utility of these forecasts for practical applications is assessed using three measures: usefulness, dependability, and effectiveness. Usefulness measures the frequency and degree of departure of the forecasts from normal climate conditions. Dependability measures the ability of the forecasts to accurately predict either wet or dry departures. Effectiveness is the frequency of dependable forecasts of wet and dry departures. Collectively, these measures indicate that the utility of these forecasts varies strongly across the contiguous United States, and that dependability can be different for forecasts for wet vs dry departures. In many regions, the effectiveness is so low that opportunities for practical use will be rare. The highest potential utility has been in the Desert Southwest, California, the Pacific Northwest, and along the Gulf and Southern Atlantic Coasts.

Technical Abstract: Experimental climate forecasts for 3-month total precipitation are issued monthly by the NOAA Climate Prediction Center (CPC) for lead times from 0.5 to 12.5 months. Among these forecasts, the CPC probability of exceedance maps and graphs for 102 forecast divisions covering the contiguous United States present information on expected shifts in the probability distribution of precipitation amounts, relative to climatological distributions. The statistical character of these forecasts support a wide range of possible applications in water resource management. We have examined forecast utility over the years 1997-2001, for all lead times and all forecast divisions. Utility is assessed using three simple measures: usefulness (degree and frequency of forecast departures from climatological distributions), dependability (correspondence between direction and magnitude of forecast departures and actual occurrences), and effectiveness (the frequency of dependable forecasts with useful departures). Using these measures, forecasts during the study period are shown to have widely varying degrees of utility, with the highest utility in the Desert Southwest, California, the Pacific Northwest, and along the Gulf and Southern Atlantic Coasts.