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DONALD L. JORGENSEN

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DONALD L. JORGENSEN

Abstract

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DONALD L. JORGENSEN

Abstract

A chart for the graphical solution of the skill score is developed on the basis that the number of cases is held constant. A procedure is suggested by means of which the chart presented may be used for any number of cases. The overall range of the skill score is shown to be restricted by limiting values of the number of correct and expected correct forecasts. Other characteristic features of the score are pointed out.

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DONALD L. JORGENSEN

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Variables obtained from synoptic sea level and upper air charts are investigated to determine their significance in the estimation of concurrent rainfall. Eight variables consisting of sea level pressures and pressure gradients, pressure heights and height differences, and the temperature-dew point differences at two upper levels are combined into a graphical procedure to estimate the probability of occurrence of rainfall. With the probability of occurrence rising to above 50 percent, supplementary charts are used to estimate the amount of rainfall to be expected.

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DONALD L. JORGENSEN

Abstract

The issuance of forecasts in probabilistic terms introduces the problem of the measurement of the forecasting skill which goes into the preparation of this type of forecast. The applicability of the conventional skill score to the evaluation of probability forecasts is investigated. It is shown that the skill score can be generalized to give the amount of skill involved in the issuance of forecasts at the various probability levels. The conclusions reached throw some light on the use of the skill score when applied to the conventional two-category type of forecast.

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DONALD L. JORGENSEN

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A 20-year record of winter precipitation data for San Francisco is used to determine frequencies of periods of rain and no-rain of various lengths and the frequencies of periods of a given type of weather followed by the same type of weather. The observed frequencies are compared with those expected on chance and are examined for evidence of persistence of rain and no-rain. The use of persistency as a forecasting aid is discussed and its skill determined.

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DONALD L. JORGENSEN

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No Abstract Available.

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Donald L. Jorgensen

Abstract

The Wadsworth-Bryan method of specifying atmospheric circulation patterns is used as a basis for developing a hurricane forecasting procedure. Regression equations have been calculated using persistency and circulation parameters to give 24-hr components of motion for hurricanes threatening the middle and north Atlantic coast regions. The final forecast is expressed in terms of probability areas.

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Donald L. Jorgensen

Abstract

The observed polarization of the light emitted from certain illuminated areas in a ceilometer beam during rain is explained as due to the polarization of light rays by reflection and refraction in passing through the raindrops. The theory developed indicates that 96 per cent of the light from the area in the beam corresponding to the primary rainbow is made up of the component with the electric vector vibrating in the plane perpendicular to the plane of incidence. It is suggested that the fact that the light resulting from the “rainbow effect” is partially polarized may be used to differentiate between bright areas caused by rain and those caused by clouds.

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Donald L. Jorgensen

Abstract

As part of the investigation into the problem of forecasting heavy snowstorms in the eastern and central United States, a synoptic climatology of the precipitation associated with winter storms has been derived. In order to facilitate the derivation, a procedure was developed by which the necessary computations were carried out by means of an electronic computer. The computational procedure was designed so that given the position of the storm center (or some other storm feature) and observations of a weather element over a sufficiently dense network of reporting stations, the computer would derive and print out the areal distribution of the weather element over the grid network. The resulting synoptic climatology is presented.

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