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Show Figure 11, Cumulative Snow and Avalanche Data, covering seven years' observations at Alta, gives much interesting information on the character of the middle alpine zone. It also illustrates how futile it would be to attempt to forecast avalanche hazard on the basis of gross statistics. 1. Is dangerous avalanche occurrence proportional to total snowfall? By no means. The highest frequency occurred in 1948- 49, the second highest snowfall year. The next highest frequency occurred in 1950- 51, the lowest snowfall year. Dangerous avalanche occurrence in the year of greatest snowfall, 1951- 52, was only average. 2. Is dangerous avalanche occurrence proportional to water content of the snowfall? By no means. The year of lowest water content had the highest avalanche frequency, 1948- 49. The year of highest water content, 1951- 52, had only average avalanche frequency. 3. Is dangerous avalanche occurrence proportional to average density of the snowfall? This works out fairly well on the basis of extremes. The year of highest frequency had snow of the lowest density. The year of highest average density had the second highest avalanche frequency. 4. Is dangerous avalanche occurrence proportional to maximum snow depth? By no means. 5. Is dangerous avalanche occurrence proportional to the number of days when 12 inches or more of snowfall deposited in one 24- hour period? By no means. Compare 1948- 49, 1950- 51, and 1951- 52. 6. Is dangerous avalanche occurrence proportional to the number of major storms? ( A major storm is defined as one during which there is 12 inches or more continuous snowfall or some outcome of importance.) The answer to the question is " no". Compare 1948- 49, 1950- 51, 1951- 52. 7. The statistics prove the impossibility of forecasting hazard based on avalanche frequency by months since there is no consistent pattern. Over the 7- year period, dangerous avalanche occurrence in January and March, for instance, fluctuated from zero to 7. The averages are 2.6 avalanche days per month for January and 4.1 for March. Just what would an avalanche hazard forecaster do with six- tenths of an avalanche? 8. Some points of interest which do not appear on the condensed table are: a. Maximum snow depth was attained in March for four years; in April for two years. In one year the same oiaximum occurred in both March and April. b. In the winter of 1948- 49, there was greater snow depth in January than in April. This is known locally as the winter that stopped just in time. - 27 - |