Objective Forecast of Precipitation over the Western Region of the United States
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Objective Forecast of Precipitation over the Western Region of the United States
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  • Description:
    The case classification by 500-mb flow types described in the first chapter represents an objective synthesis of synoptic information which has subjectively and successfully been used by experienced forecasters in predicting the weather. This information is presented in the form of a climatology of 500-mb winter flow patterns. It consists of the frequency of occurrences of seven tharacteristic 500-mb height configurations and associated patterns of vorticity, vertical velocity, higher and lower pressure levels, dew-point depressions, frequency of precipitation, etc. This stratification of probabiIity of precipitation represents a refinement in the forecast of precipitation probabilities over simpleĀ· climatology. The type classification is used as a stratification criterion in the second chapter to obtain predictive equations for precipitation probability. Different predictive variables are stressed within the different types. Based on the reduction of variance and the Brier P-score, it appears that the stratification leads to signigicant improvement in the regression equations. In effect, the stratification includes a pattern comparison which could never be included infinite regression equations. The results are promising and the method can presently be applied in operational forecasting at very minimal computer cost.
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