A METHOD OF FORECASTING THE FORMATION OF 500-MILLIBAR BLOCKS USING STATISTICAL PARAMETERS
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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An investigation is made of the statistical properties of blocks at the 500-mb level along the latitude belt 50-55N covering 180 degrees of longitude including the block area. From the results obtained a method of computing a 72-hour forecast of block formation is developed. From the space correlations in SSW Selfridge, S., N. Stevenson, and E. Wood, The development of a weather-typing system for extended-range forecasting. Masters Thesis, U. S. Naval Postgraduate School, 155pp., 1960 the expected frequency of block days in all four sectors which they investigated is 903 block days out of a possible 2168 days. Of these block days, 209 were initial formation days. The remaining block days were rejected from the total, since only initial block days and non block days were used in testing. The climatological expectancy of block formation was 0.142 per day. The climatological expectancy of non block days was considered to be 1-0.142 equals 0.858. From the sample summarized, a forecast accuracy of 87 percent and a skill score, based on the climatological expectancies, of 0.73 were obtained.