The frequency of occurrence of frozen precipitation forms relative to the frequency of occurrence of non-frozen forms is determined as a function of geographical location and of the mean temperature (or thickness) of the layer from 1000 mb to 500 mb. The results are derived from the data for a large number of stations in the United States during two winter seasons. A map of the thickness values for equal probability of occurrence of frozen and non-frozen forms illustrates the effects of altitude and continentality.
It is found that the form of the precipitation can be specified with a confidence of 75 percent or more when the thickness value at a station is 100 feet or more from its “equal probability” value. Some refinements of the technique are discussed.
1The research reported in this article has been sponsored by the Geophysics Research Directorate, Air Force Cambridge Research Center, under contract AF 19(604) 1305.
