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HARRY R. GLAHN

Abstract

The regression screening and principal component techniques for developing forecast aids are investigated for their applicability to the objective forecasting of rainfall probabilities. The forecasting of summer rainfall in the Mississippi Delta is the particular problem studied. Subjective forecasts made for the area as well as objective forecasts are verified in terms of reductions of variance and saving over climatology. It is found that many of the forecast equations developed by regression screening and principal component techniques are not stable on test data. The results indicate that subjective screening of predictors is desirable before the regression screening is accomplished. It is found that useful aids can be developed with these linear techniques; at the same time the desirability of an approach that better integrates the physical processes of the atmosphere is indicated.

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Harry R. Glahn

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Harry R. Glahn

Abstract

There is a popular misconception that the secant form of the Lambert conformal map projection is “better” than the tangent form. It is shown here that the two forms are equivalent; they are different only in the sense that the scale of the map quoted is usually true at the two secant latitudes for the secant projections and at the single tangent latitude for the tangent projection.

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THE USE OF DECISION THEORY IN METEOROLOGY

With an Application to Aviation Weather

HARRY R. GLAHN

Abstract

The concepts of decision theory are discussed, especially in the light of their application to meteorology. The use of the principles of decision-making under risk requires certain probability information to be available. The issuance of forecasts in probability terms has a firm basis in theory and has been shown to work well in practice. The best verification statistic of these forecasts is their usefulness to the user and this can be measured and compared with some standard if the utility matrix is known.

A multi-dimensional contingency table technique is used to estimate the conditional probability distribution of the 5-hr. projection of ceiling height at Washington National Airport. Three predictors are screened from 164 possible predictors according to the utility criterion. Developmental and test data results are presented.

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Harry R. Glahn

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Harry R. Glahn

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Harry R. Glahn

Abstract

Complete automation of public weather forecasts will exist when forecasts are prepared entirely by computer and are disseminated to the final user through associated communications facilities. Preparation of such a forecast must start with observations of various kinds and proceed through the collection and analysis of those observations, the running of numerical and statistical models to arrive at digital forecasts of the pertinent weather elements, and the preparation of the forecast in its final format.

Observing the atmospheric variables used as input to forecasting models is far from automated, although much has been done in this area in recent years. The assembly and analysis of the observations have been largely automated at national centers, although work must continue on incorporating new types of observations and making more efficient use of those already available. Numerical models are being run which do a good job of predicting the future state of certain atmospheric variables. Statistical models are in operation which translate these “atmospheric” forecasts into “weather” forecasts. Automatic preparation of the forecasts in final form has received much less attention than have other aspects of automation, but experimental computer programs do exist for this purpose. And finery, the AFOS (Automation of Field Operations and Services) program of the National Weather Service provides a feasible means for monitoring and communicating the forecasts, if not to the final user—the public—at least to the media which do make the forecasts available to the final user.

This paper describes the automated public weather forecasts issued by the National Weather Service—such as probability, amount and type of precipitation, maximum and minimum temperature, clouds, winds and severe weather—and the progress made on formatting these into a worded message.

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Joseph R. Bocchieri and Harry R. Glahn

Abstract

An automated system for forecasting the conditional probability of frozen precipitation was put into operation by the National Weather Service in November 1972. The Model Output Statistics (MOS) concept was used to develop the system, and both teletypewriter and facsimile products have been distributed to field offices twice daily. In this paper, guidance forecasts from this system are compared to subjective (local) forecasts prepared at Weather Service Forecast Offices. The local forecasts have been archived since September 1973 as part of a combined aviation/public weather forecast verification program within the National Weather Service. The comparative verification between the guidance and locals for two different data samples shows the guidance has produced better forecasts for the 18, 30, and 42 h projections.

In attempting to improve the operational system, we experimented with the Regression Estimation of Event Probabilities (REEP) screening technique. The operational system had been developed with the logit model, but our logit computer program does not objectively screen predictors as REEP does. A comparison of the REEP and logit systems on independent data shows logit to be better.

We used the logit model to develop a new operational system. Five winters of developmental data were used for the new system; the old system was developed from three winters of data. A comparison between the new and the old systems on independent data shows that they are equally accurate for the short-range (12 h) projection but that the new system is more accurate for the longer-range (36 h) projection.

The predictors in the new system include the 850 mb temperature, boundary-layer potential temperature, 1000–500 mb thickness, and 1000–850 mb thickness. These variables are forecast by the National Meteorological Center's primitive equation model. The new system was made operational during the winter of 1975–76 and provides forecasts for the 12, 18, 24, 30, 36, 42, and 48 h projections twice daily.

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JOSEPH R. BOCCHIERI and HARRY R. GLAHN

Abstract

The model output statistics (MOS) technique consists of determining a statistical relationship between the forecast output of numerical prediction models and a predictand. This paper presents some results obtained in applying the MOS technique to the prediction of ceiling height by means of screening regression.

Data from 3 winter seasons and 95 eastern U.S. stations are combined in a generalized operator approach to develop multiple regression equations. The potential predictors subjected to screening include surface variables observed at 0700 GMT and forecast output from both the National Meteorological Center's primitive-equation model and the Techniques Development Laboratory's subsynoptic advection model. Prediction equations are developed for 5-, 11-, and 17-hr forecast projections representing ceiling height forecasts valid at 1200, 1800, and 2400 GMT, respectively.

Ceiling height is treated both as a categorized and as a continuous predictand. Where ceiling height is categorized, the regression estimation of event probabilities (REEP) screening technique is used to develop probability forecast equations. Where ceiling height is treated as a continuous variable, specific ceiling height forecast equations are developed by ordinary screening regression.

The independent sample used for testing consists of data for 20 stations in the eastern United States from the winter of 1970–71. Several verification scores, including the Brier P-score, Allen utility score, Heidke skill score, and percent correct, are presented. The verification results indicate that forecasts from the REEP equations are generally better than those from the equations that produce specific heights. Also, the REEP forecasts are better than persistence and climatology.

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Joseph R. Bocchieri and Harry R. Glahn

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No abstract available.

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