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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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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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Lars van Galen
,
Oscar Hartogensis
,
Imme Benedict
, and
Gert-Jan Steeneveld

Weather forecasting is critical not only for social activities for the general public but also for transportation, energy supply, water management, agriculture, and many other crucial infrastructures and business decisions. Weather forecasts have become increasingly more accurate in recent decades due to improved numerical weather prediction (NWP) systems as a result of advances in understanding physical processes, data assimilation techniques, and computing capacity ( Bauer et al. 2015

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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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Russ S. Schumacher
,
Aaron J. Hill
,
Mark Klein
,
James A. Nelson
,
Michael J. Erickson
,
Sarah M. Trojniak
, and
Gregory R. Herman

Excessive rainfall, and the flash flooding it often causes, remains one of the most difficult forecast challenges in meteorology ( Fritsch and Carbone 2004 ; Sukovich et al. 2014 ; Novak et al. 2014 ). Unlike many other weather hazards, the definition of “excessive rainfall” varies from location to location, depending on the local and regional climatology. Likewise, the flooding that results from a given amount of precipitation depends strongly on the characteristics of the underlying land

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Kristin M. Calhoun
,
Kodi L. Berry
,
Darrel M. Kingfield
,
Tiffany Meyer
,
Makenzie J. Krocak
,
Travis M. Smith
,
Greg Stumpf
, and
Alan Gerard

Serafin et al. (2002) stated the need for a national testbed, closely linked to an operational center, where suggestions for model improvements would be subjected to rigorous systematic evaluation. Participants would be intimately involved in the testing, with access to the full operational data stream and knowledge of the operational staff. The interactions between the research, academic, and operational communities would provide a direct transfer of research into operational 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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