OCR Text |
Show - 3- complicated climatic factors. It is suggested that the distribution of new snow densities, as graphed in Figures 1 through 5, is a climatic character-istic of a given área, reflecting influences of altitude, prevailing temperatures, and particularly winter storm characteristics. In order to compare readily these distributions from the different áreas, the approximate envelopes of the bar graphs are ali plotted to the same scale in Figure 6. Vertical amplitude of each envelope has been adjusted to a record of 300 snowfall days. It will be noted in Figure 6 that the curves for Alta and Stevens Pass are very similar. These exhibit a relatively low peak around 0.08 gm/ cc, and a strong skew toward higher densities. Rather frequent deep snowfalls are com-mon in these áreas, possibly being responsible in part for the more frequent occurrence of higher densities, as discussed separate below. Both of these stations receive most of their snowfall from the regular winter cyclo-nic disturbances which originate in the Gulf of Alaska and sweep across the northwestern United States. Both are in áreas of strong orographic lifting, the Cascades providing a barrier to air masses from the Pacific Ocean and the Wasatch Mountains a barrier to those crossing the Intermountain Basin. Berthoud Pass presents a contrasting picture. New snowfalls at higher densities are quite rare, and the curve is only slightly skewed. Most snow falls are concentrated in a very narrow range of 0.04 to 0.09 gm/ cc. There is no imnediate explanation for the marked double peak in this curve. It is difficult to conceive any physical explanation of why Berthoud Pass snow is so reluctant to be recorded at a density of 0.06 gm/ cc. It seems much more likely that this anomaly is an accidental product of the techniques of observation and conputation. Berthoud Pass receives much of its snow from the same storms which affect Stevens Pass and Alta, but at the same time |