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Donald S. Foster and Ferdinand C. Bates

A technique for forecasting the size of hailstones accompanying thunderstorms is presented. Hailstone size is related to its terminal velocity which in turn is related to the updraft velocity of a thunderstorm as derived from parcel buoyancy. This updraft velocity is approximated from positive area measurements on a thermodynamic diagram. The technique is tested on proximity soundings taken near the site and prior to known hail occurrences.

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Robert M. White and Agnes M. Galligan

Forecasts of the pressure-height variations at eight stations in the eastern United States are prepared by a statistical technique employing empirical influence functions. The accuracy of such forecasts is found to be comparable with that attained by synoptic techniques.

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Konstantine P. Georgakakos and Michael D. Hudlow

Quantitative hydrologic forecasting usually requires knowledge of the spatial and temporal distribution of precipitation. First, it is important to accurately measure the precipitation falling over a particular watershed of interest. Second, especially for small watersheds and/or for longer forecast lead times, forecasts of precipitation are critical to the achievement of the greatest possible hydrologic forecast accuracy and longest possible lead time. This paper describes the current hydrologic forecasting program of the U.S. National Weather Service (NWS) and highlights the relevance of Quantitative Precipitation Forecasting (QPF) products to real-time hydrologic forecasting. Specific requirements for QPF products in support of hydrologic forecasting applications are defined and current operational QPF procedures are reviewed to determine to what extent they meet these requirements. It is concluded that no known QPF procedures capable of fulfilling all desired requirements are currently available operationally, although much valuable QPF information is available to meet parts of these requirements. Some recent advances in mesoscale QPF research are examined and these techniques are treated in two categories: those uncoupled dynamically from and those dynamically coupled to hydrologic forecasting procedures. Finally, a summary of possible future directions toward achieving improved use of QPF information in hydrologic forecasting applications is presented.

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William H. Klein

The forecast research program of the Techniques Development Laboratory is summarized. This program combines dynamical, statistical, and synoptic techniques in an effort to improve and automate operational weather forecasting. Principal accomplishments of the Laboratory during the five years of its existence are described, and plans for future work are outlined. Weather elements for which forecast techniques are being developed include temperature, precipitation, humidity, wind, ceiling, visibility, severe local storms, wave heights, and storm surges.

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Myron K. Cox

A thunderstorm forecast technique is evaluated on a day by day basis during the months May through September, 1960. The over-all verification probability is 0.92. In a comparison test with persistence forecasts, the semi-objective method has a 24 per cent greater verification probability and shows more than thrice the skill factor.

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CAPTAIN Wilburn R. Schrank

The evaluation of the operational utility of new forecast techniques has presented meteorologists with a difficult problem for many years. Both the per cent correct score and the commonly used skill score possess rather serious limitations which are discussed in this paper. Finally, a new evaluation score is proposed which retains most of the good features of the other two scores but does not retain their primary limitations.

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John L. McBride and Greg J. Holland

Questionnaire replies from forecasters in 16 tropical-cyclone warning centers are summarized to provide an overview of the current state of the science in tropical-cyclone analysis and forecasting. Information is tabulated on the data sources and techniques used, on their role and perceived usefulness, and on the levels of verification and accuracy of cyclone forecasting.

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Ralph D. Reynolds

A procedure for using the 700-mb dew point temperature as an objective aid for forecasting the occurrence or nonoccurrence of cumuloform showers in southern Arizona is presented with verification data.

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Bernard W. Magor

The tornado forecast becomes a small-scale problem as the tornado-generating severe-thunderstorm area approaches a particular locality. Consequently, much of this problem can be solved by the best possible analysis of surface synoptic weather data. Various tornado occurrences were investigated and found to be associated with meso-lows. These meso-lows were depicted either by the intersection of two instability lines or by the intersection of a squall line with a northeastern boundary of rain-cooled air. An explanation is given for the formation of tornadoes along this intersection.

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Alexandra K. Anderson-Frey and Harold Brooks

Evaluating the success of a forecast is a necessary step in the development of a rigorous and useful forecast system; robust forecast evaluation can identify the situations in which the most substantial improvements can be made ( Brier and Allen 1950 ), and ideally also provides a roadmap for the application of those improvements. Choosing the metrics by which we evaluate forecasts, however, is a process that is far from trivial. Murphy (1993, hereafter M93) identifies three distinct types of

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