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THE PREDICTION OF SURGES IN THE SOUTHERN BASIN OF LAKE MICHIGAN

Part III. The Operational Basis for Prediction

LAWRENCE A. HUGHES

Abstract

The development of operational surge prediction in southern Lake Michigan is reviewed through the 10-year span starting with the disastrous surge of June 26, 1954 which took several lives in the Chicago area. Particular emphasis is given to the application of the work of others, especially Platzman, to the surge-prediction problem. Considerable detail is given on the surge of August 3, 1960, for which a successful prediction was made. This example, with its messages to the public, could serve as a model for future surge predictions. Finally a set of steps is given by which a prediction is made, followed by comments on those items still needing research before we can evaluate all parameters for an operational surge prediction.

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LAWRENCE A. HUGHES

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No Abstract Available.

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LAWRENCE A. HUGHES

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No Abstract Available.

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Lawrence A. Hughes

Abstract

A number of problems that arise in making probability of precipitation (PoP) forecasts are noted and discussed, and solutions are given where known. This effort is based on a long-standing extensive verification of PoP's issued by 66 offices of the National Weather Service's Central Region. Verification results were sent monthly to each office and each forecaster for the past 13 years. Some additional problems and solutions dealing in general with verification and evaluation of PoP'S are discussed. These include modifications of scores generally used, plus factors to consider when trying to compare scores of offices having different climatological conditions.

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Lawrence A. Hughes
and
Wayne E. Sangster

Abstract

Using screening regression procedures, an attempt has been made to standardize probability of precipitation Brier scores for difficulty. Climatological factors affecting the difficulty of forecasting used are: precipitation frequency, time persistence and small amount frequency. Standardizing equations were derived for three-month seasons from seven years of data. Four-term regression equations were developed for each season and lead time. Local forecaster improvement over guidance scores varied inversely as the Model Output Statistics (MOS) scores, indicating that poor machine forecasts are easier to improve upon than good machine forecasts.

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Lawrence A. Hughes
and
Wayne E. Sangster

Abstract

Two methods are discussed for combining the routine forecasts of the 12 h probability of precipitation made by the National Weather Service, for use when longer period probabilities are desired but cannot be created independently. Both apply a year's forecasts from 28 forecast offices to basic equations of probability to adjust for the obvious dependence of the precipitation events among the forecast periods. Both methods suggest that warm season precipitation events are more independent than cold season ones, as would be expected. One method gave unrealistic results for probability combinations outside the range of those actually used. The other method applied realistic constraints to eliminate this undesirable feature. The largest deviations from probabilities for independent events occurred when combining probabilities of 60%, but the deviations wore only about 5% in the warm season and 10% in the cold season. Tables and an equation for combining probabilities are given.

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