Completing the Forecast Characterizing and Communicating Uncertainty for Better Decisions Using Weather and Climate Forecasts (2006) / Chapter Skim
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1 Introduction
1 Introduction
Pages 5-14
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For the purposes of this report, "hydrometeorology" will refer to the The concept of the Enterprise is now sufficiently widely accepted that the combined fields of meteorology and hydrology from the short time scales American Meteorological Society has formed a Commission on the Weather of weather prediction to interseasonal climate forecasting. and Climate Enterprise to facilitate dialog among Enterprise participants.
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as the forecasts progress. In summary, the chaotic character of the atmosphere, coupled with inevitable inadequacies in observation quality 1.1 THE UNCERTAIN ATMOSPHERE and data assimilation, model physics and numerics, bound AND HYDROSPHERE ary conditions, and model resolution, result in forecasts that Uncertainty in hydrometeorological predictions, often always contain uncertainties that generally increase with described in terms of probability (Box .)
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INTRODUCTION BOX 1.1 Interpretation of Probability This report has many references to the notion of probability. While often treated as a synonym for uncertainty, it is better described as one of many ways in which uncertainty can be expressed.
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suggested stochastic better numerical models, and rapidly increasing model reso dynamic forecasting, in which forecast errors are explicitly lution, further enhancing the dominance of a singlesolution, considered during model integration, but computer process deterministic approach to forecasting. ing power was not sufficient to support this method at that The first operational probabilistic forecasts in the United time.
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Faster computers allowed the initiation of overlapping temperature and precipitation "outlooks" for global ensemble prediction at major operational prediction each month up to a year ahead. Several different methods centers such as NCEP, the European Centre for Medium (e.g., dynamical models, analogs, cannonical correlations Range Weather Forecasts, and the Canadian Meteorological with El Niño/Southern Oscillation)
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Even predictions) , relatively little headway has been made in though such deterministic forecasts are without scientific supplying actionable uncertainty information to most of the basis and suggest a level of forecasting skill that does not user community.
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research on how to effectively communicate uncertainty information to its users. 1.4 REASONS FOR SUPPLYING UNCERTAINTY exist, media presentation of these forecasts has multiple INFORMATION drivers in addition to the science.7 Problems with the dominance of deterministic forecast The American Meteorological Society's "Statement on ing information are compounded by the poor communica Enhancing Weather Information with Probability Forecasts" tion of the limited uncertainty information that does exist.
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A retrospective study of management strategies for large There is an extensive literature documenting the potential reservoirs in California (WSAT, 000) showed that using socioeconomic value of uncertainty information over tradi uncertainty information from a seasonal ensemble resulted in tional deterministic forecasts (e.g., Katz and Murphy, 997)
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But such uncertainty information was not provided to the public 1.5 THE NEED FOR AN ENTERPRISE-WIDE or even other federal agencies. RESPONSE With the availability of uncertainty information, users -- each with their own sensitivity to costs and losses and with The shift of hydrometeorological prediction to a scien varying thresholds for taking protective action -- could better tifically valid approach that fully considers, communicates, decide for themselves whether to take action and the appro validates, and appropriately applies forecast uncertainty will priate level of response to hydrometeorological situations.
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would encourage new links and feedbacks between forecast NWS forecasters will need to master the underlying ideas producers and forecast users within the Enterprise. Last, of ensemble prediction and forecast uncertainty and will the introduction of new uncertaintyexplicit forecasts will require retraining to deal with the new probabilistic forecast generate the need for continuing validation, producing feed communication systems of the future.
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