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<br />(l 0 \.1';)2 ~ <br /> <br />Start Times of Storms <br /> <br />Knowill3 the time of day when storms occur is iJrq;lortant since traffic <br />compounds problems of snow removal and employees sometimes work overtime <br />when snow falls in the early evenill3 or overnight. Observations are not <br />taken frequently enough at most cooperative observer sites to determine <br />time of fall. Researchers have studied time of fall at several sites in <br />Colorado, however, (Grant, ed., 1969; Crow, 1969) and their findill3s, <br />discussed below, are used to assign start times of each storm. <br /> <br />Figures 1-4 show variations in times of recorded snowfall at Hot <br />Sulphur Sprill3S in central ColoradO and at OUray, Durango and Silverton <br />. in the southwest. A marked peak in frequency durill3 the early morning <br />followed by a dip around noon is typical at Hot Sulphur Sprill3S and at <br />other stations in the north and central parts of the state (Grant, ed., <br />1969). The pattern at OUray is somewhat similar. aut in Durango, snow <br />is more likely to fall in the mornill3 and less likely to fall in the late <br />afternoon and evenill3, and in Silverton snow is most. likely to fall in <br />the late afternoon. Grant, ed., (1969) attributes these differences to <br />exposure--that is, to the location of observation stations relative to <br />surroundill3 mountains. <br /> <br />We used the probabilities of occurrence of snow depicted in Figures <br />1-4 to assign a start time to each storm randomly. The Hot Sulphur <br />sprill3S variation was used for counties in north and central Colorado; <br />Ouray, Silverton and Durall30 variations were used for OUray, San Juan, <br />and La Plata counties, respectively. <br /> <br />we assumed that the probability of storms startill3 at a given hour <br />is, in the lOIl3 run, identical to the probability of snow fallill3 during <br />the same hour. If, for exaJlIlle, snow at a given station is twice as <br />likely in the early mornill3 as in the early afternoon, the model assigns <br />start times that reflect this pattern. <br /> <br />-11- <br />