FORECASTING WINTER PRECIPITATION 36 TO 48 HOURS IN ADVANCE AT DES MOINES, IOWA

An Experiment Using the Prognostic Chart as a Data Source

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  • 1 Short Range Forecast Development Section, U. S. Weather Bureau, Washington, D. C.
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Abstract

To determine the accuracy with which a precipitation forecast can be made from the features of the prognostic charts currently disseminated, an objective forecast system using only those features has been developed for the Des Moines, Iowa, area. As a means of finding predictors, sets of composite sea level and 700-mb. charts were made up for very dry situations and for situations in which heavy precipitation occurred. In the final system, the various predictors are combined in scatter diagrams to give a forecast, comparable in accuracy with that of the district forecast, of the occurrence of precipitation at Des Moines during a 12-hour period beginning 12 hours after the valid time of the 30-hour sea level prognostic chart.

Abstract

To determine the accuracy with which a precipitation forecast can be made from the features of the prognostic charts currently disseminated, an objective forecast system using only those features has been developed for the Des Moines, Iowa, area. As a means of finding predictors, sets of composite sea level and 700-mb. charts were made up for very dry situations and for situations in which heavy precipitation occurred. In the final system, the various predictors are combined in scatter diagrams to give a forecast, comparable in accuracy with that of the district forecast, of the occurrence of precipitation at Des Moines during a 12-hour period beginning 12 hours after the valid time of the 30-hour sea level prognostic chart.

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