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  • Author or Editor: Joseph T. Schaefer x
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Joseph T. Schaefer

Abstract

Techniques that have evolved during the hundred years that scientific severe thunderstorm forecasts have been prepared are reviewed. The early empirical rules developed by Finley, Showalter and Fulks, Fawbush, Miller and Starrett, and others have been corroborated by more recent theoretical work. While significant efforts have been devoted to defining the severe thunderstorm environment, it is now obvious that these storms can occur under a variety of synoptic conditions. Severe thunderstorm forecasting consists in not only identifying the time and place that an environment compatible with such storms will exist but also in identifying suitable triggering mechanisms in that environment.

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Joseph T. Schaefer

Abstract

A form of the critical success index (CSI) is used by the National Weather Service to indicate the value of warnings. This verification statistic assumes that the times when an event was neither expected nor observed are of no consequence. It can be shown that the CSI is not an unbiased indicator of forecast skill but is proportional to the frequency of the event being forecast. This innate bias is demonstrated theoretically and via example. An unbiased verification statistic appropriate for forecast of rare events is presented and applied to severe convective weather warnings. Comparisons of this score to the CSI show the extent of the penalty the CSI extracts from forecasters who work in areas that are not climatically prone to given events.

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Joseph T. Schaefer
and
Richard L. Livingston

Abstract

Since the probability of precipitation (PoP) appears in the forecasts of the National Weather Service (NWS), it is important that both the forecaster and user fully grasp the subtleties of the meaning of PoP. A brief review of the theory of PoP is presented. It is shown that although the PoP is defined as the average point probability, the guidelines outlined in the National Weather Service Operations Manual (NWSOM) also make the PoP the expected areal coverage of precipitation across the forecast area.

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Richard L. Livingston
and
Joseph T. Schaefer

Abstract

The medium-range forecast model (MRF) provides the basic guidance for the 3–5-day extended forecast issued by individual Weather Service Forecast Offices. The ability of the MRF to forecast shorter synoptic, subsynoptic, and mesoscale phenomena is examined through the use of the anomaly correlation coefficient and illustrated with several case studies. The operational implications of putting detail in the extended forecast are reviewed. Finally, several suggestions are presented to help operational forecasters determine consistency and accuracy in the extended guidance.

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