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  • Author or Editor: ALLAN H. MURPHY x
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Allan H. Murphy

This paper briefly examines the nature of hedging and its role in the formulation of categorical and probabilistic forecasts. Hedging is defined in terms of the difference between a forecaster's judgment and his forecast. It is then argued that a judgment cannot accurately reflect the forecaster's true state of knowledge unless the uncertainties inherent in the formulation of this judgment are described in a qualitative and/or quantitative manner. Since categorical forecasting does not provide the forecaster with a means of making his forecasts correspond to such judgments, a categorical forecast is generally a hedge. Probabilistic forecasting, on the other hand, presents the forecaster with an opportunity to eliminate hedging by making his (probabilistic) forecasts correspond exactly to his judgments. Thus, contrary to popular belief, the desire to eliminate hedging should encourage forecasters to express more rather than fewer forecasts in probabilistic terms.

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Paul R. Julian
and
Allan H. Murphy

Recent developments in six areas of statistical meteorology are described and the importance of interdisciplinary research in these areas is indicated. The areas are stochastic-dynamic prediction, assimilation of observed data, time-series analysis, statistical weather forecasting, probability forecasting, and precipitation modification statistics. Several problems are identified within each area and the need for further interdisciplinary research to solve these problems is emphasized.

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Allan H. Murphy
and
Barbara G. Brown

This paper reports some results of a study in which two groups of individuals—undergraduate students and professional meteorologists at Oregon State University—completed a short questionnaire concerning their interpretations of terminology commonly used in public weather forecasts. The questions related to terms and phrases associated with three elements: 1) cloudiness—fraction of sky cover; 2) precipitation—spatial and/or temporal variations; and 3) temperature—specification of intervals.

The students' responses indicate that cloudiness terms are subject to wide and overlapping ranges of interpretation, although the interpretations of these terms correspond quite well to National Weather Service definitions. Their responses to the precipitation and temperature questions reveal that some confusion exists concerning the meaning of spatial and temporal modifiers in precipitation forecasts and that some individuals interpret temperature ranges in terms of asymmetric intervals. When compared to the students' responses, the meteorologists' responses exhibit narrower ranges of interpretation of the cloudiness terms and less confusion about the meaning of spatial/temporal precipitation modifiers.

The study was not intended to be a definitive analysis of public understanding of forecast terminology. Instead, it should be viewed as a primitive form of the type of forecast-terminology study that must be undertaken in the future. Some implications of this investigation for future work in the area are discussed briefly.

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Allan H. Murphy
and
Barbara G. Brown

Worded forecasts, which generally consist of both verbal and numerical expressions, play an important role in the communication of weather information to the general public. However, relatively few studies of the composition and interpretation of such forecasts have been conducted. Moreover, the studies that have been undertaken to date indicate that many expressions currently used in public forecasts are subject to wide ranges of interpretation (and to misinterpretation) and that the ability of individuals to recall the content of worded forecasts is quite limited. This paper focuses on forecast terminology and the understanding of such terminology in the context of short-range public weather forecasts.

The results of previous studies of forecast terminology (and related issues) are summarized with respect to six basic aspects or facets of worded forecasts. These facets include: 1) events (the values of the meteorological variables): 2) terminology (the words used to describe the events); 3) words versus numbers (the use of verbal and/or numerical expressions); 4) uncertainty (the mode of expression of uncertainty); 5) amount of information (the number of items of information); and 6) content and format (the selection of items of information and their placement). In addition, some related topics are treated briefly, including the impact of verification systems, the role of computer-worded forecasts, the implications of new modes of communication, and the use of weather forecasts.

Some conclusions and inferences that can be drawn from this review of previous work are discussed briefly, and a set of recommendations are presented regarding steps that should be taken to raise the level of understanding and enhance the usefulness of worded forecasts. These recommendations are organized under four headings: 1) studies of public understanding, interpretation, and use; 2) management practices; 3) forecaster training and education; and 4) public education.

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Allan H. Murphy
and
Robert L. Winkler

This paper describes the preliminary results of three experiments in subjective probability forecasting which were recently conducted in four Weather Service Forecast Offices (WSFOs) of the National Weather Service. The first experiment, which was conducted at the St. Louis WSFO, was designed to investigate both the ability of forecasters to differentiate among points in a forecast area with regard to the likelihood of occurrence of measurable precipitation and their relative ability to make point and area (including areal coverage) precipitation probability forecasts. The second experiment, which was conducted at the Denver WSFO, was designed to investigate the ability of forecasters to use credible intervals to express the uncertainty inherent in their temperature forecasts and to compare two approaches (variable-width intervals and fixed-width intervals) to credible interval temperature forecasting. The third experiment, which was conducted at both the Great Falls and Seattle WSFOs, was designed to investigate the effects of guidance (i.e., PEATMOS) forecasts upon the forecasters' precipitation probability forecasts.

For each experiment, some background material is presented; the design of the experiment is discussed; some preliminary results of the experiment are presented; and some implications of the experiment and the results for probability forecasting in meteorology and probability forecasting in general are discussed. The results of each of these experiments will be described individually and in much greater detail in a series of forthcoming papers.

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Allan H. Murphy
and
Robert L. Winkler

Some results of a nationwide survey of National Weather Service forecasters with regard to probability forecasting in general and precipitation probability forecasting in particular are summarized. Specifically, the questionnaire which was used in the survey, the participants in the survey (i.e., the forecasters), and the nature of the results are briefly described, and some recommendations based upon these results are presented.

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William R. Bergen
and
Allan H. Murphy

Severe downslope windstorms are an outstanding feature of the winter weather in Boulder, Colo., and property damage associated with these storms averages about $1 million each year. Recently, efforts to develop a numerical model capable of forecasting downslope windstorms have yielded encouraging results. The possibility that short-term forecasts of these storms might become available on an operational basis led to a study of the societal impact of improved windstorm forecasts in the Boulder area, and this paper describes the results of that study.

Surveys were conducted of selected samples of Boulder residents and businesses concerning the potential economic and social benefits and disbenefits of improvements in downslope windstorm forecasts. The survey questions concerned five basic topics: 1) perception of the windstorm hazard; 2) the desire for improved windstorm forecasts; 3) the use of windstorm forecasts; 4) the value of improved forecasts; and 5) possible forecast dissemination techniques. Personal interviews were conducted with local businesses and public service agencies to supplement and extend the results of the surveys.

All segments of the community were found to be concerned about the windstorms because of the possibility of serious injury and/or major property damage. The responses also revealed a strong desire for improved windstorm forecasts, although the level of desire was found to depend upon the accuracy of the forecasts. Moreover, significant increases in the use of a variety of protective actions would occur if accurate (i.e., 80% accurate) windstorm forecasts were available. The results of the surveys and interviews indicated that accurate forecasts could reduce residential property damage by approximately $200 000 annually, and the potential savings to local businesses were estimated to be an additional $150 000. These benefits appear to greatly exceed any incremental costs associated with formulating and disseminating the forecasts and any economic losses suffered by local businesses due to decreased windstorm damage. In addition, the residents expressed a willingness to support a local windstorm forecasting system if governmental funding was not available. Finally, while no completely effective procedure for alerting a significant fraction of the community to an approaching windstorm was identified, it was recognized that this problem is not unique to forecasts of downslope windstorms and requires further study.

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Allan H. Murphy
and
Robert L. Winkler

This paper summarizes the responses of the forecasters of the Travelers Weather Service to a questionnaire concerning probability forecasting. The questionnaire was designed to elicit information from the forecasters relative to the process of precipitation probability forecasting (e.g., the information sources examined, their relative importance and order of examination), the relationship between judgments and forecasts, the effect of the definition of precipitation on the forecasts, the meaning of the forecasts, the effects of feedback and experience on the forecasts, and related matters. The responses to the questionnaire and subsequent discussions with Travelers Weather Service and National Weather Service forecasters suggest the presence of a number of “problems” related to probability forecasting. Several of these “problems” are considered in some detail in a separate paper (Murphy and Winkler, 1971).

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Allan H. Murphy
and
Robert L. Winkler

The responses to a questionnaire which was administered to forecasters actively involved in probability forecasting are summarized in Murphy and Winkler (1971). These responses and subsequent discussions with forecasters reveal the presence of a number of “problems” concerning probability forecasting. In this paper, we identify several of the more important problems, describe their nature, indicate some approaches and results which clarify certain aspects of the problems, and make some recommendations related to research studies and operational practices in probability forecasting. In particular, we discuss the formulation of judgments and the assessment process, the interpretation of probability forecasts, the occurrence of “hedging” by forecasters, and the evaluation of probability forecasts and forecasters.

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Allan H. Murphy
and
Robert L. Winkler

The case for an operational program involving the formulation and dissemination of probabilistic temperature forecasts is presented. First, the need for information concerning the uncertainty in temperature forecasts is discussed, and examples of formal and informal decision-making situations in which such information would be useful are described. The results of experiments in probabilistic temperature forecasting are then reviewed, and it is concluded that experienced weather forecasters can quantify the uncertainty inherent in temperature forecasts in a reliable and skillful manner. Finally, the essential components of an operational probabilistic temperature forecasting program are outlined, and some suggestions are made regarding specific temperature events that should receive probabilistic treatment on an operational basis.

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