OCR Text |
Show its aftermath. But it would "be incorrect. The fact remains that sufficient snowfall in favorable terrain is all that is necessary to produce an avalanche and that in the absence of either one, no avalanche can take place. Climate Analysis Like terrain, climate to the snow observer is a combination of a number of factors! snowfall type and quantity, wind force and direction, temperature, humidity, barometric pressure* storm characteristics. Their roles in the rise and fall of avalanche hazard are analyzed in the next section. The discussion here is limited to the general character of an alpine winter climate, specifically, Altars. It is not the same as that of any other alpine area, even in the vicinity, and is described merely as a sample of what the snow observer needs to know. The Wasatch Mountains are a steep and high range rising abruptly at the edge of a semi-desert. The altitude of the canyon floor at Alta is 8500 feet and the surrounding peaks reach or exceed 11,000 feet. When the westerly, moisture-bearing winds strike these mountains, the result is impressive. Snowfall at the rate of an inch an hour is not uncommon. Storms which deposit 3 feet or even more of new snow in one continuous downpour are not unusual. Alta^ desirability as a ski area and the character of its avalanche hazard depend on the individual traits of these storms. Alta's typical snowfall is dry; that is, there is not enough free moisture in the snow crystals so that they will adhere when squeezed in the glove. It is varied in type: flake, granular and pellet in all sizes and combinations. Its weight averages .092 of an inch of water per inch of snow, which is heavy for a ,!dryu type of snow. These characteristics promote rapid settling and cohesion, those qualities of flotation without stiffness, and packing without becoming icy, which delight the heart of the skier. Alta's winds, generally westerly, are highly erratic in direction and force in contract to the Alps, where wind direction is practically a constant. For an elevation of 8,000 to 10,000 feet, Alta's temperature is comparatively mild. Throe or four days only of below zero weather during the season are normal. Daytime maximums are apt to be above freezing. The bulk of the temperature curve lies between 12° and 32° Fahrenheit. This is in marked contrast to temperatures in the alpine regions of Colorado where the average and the extremes are considerably lower. Corrected barometric pressure and relative humidity records for Alta are not available. Both fluctuate rapidly and widely. The following table gives cumulative snov; data for the past b years. It yields interesting sidelights on the variability of some of the major factors with which the snow ranger must deal. For example, there are the monthly snowfall extremes of 18 inches in January 19^5 and 165 inches in March 19^+8; or the water content extremes of .18 of an inch of water per inch of snow, January 19^5 against . 06 of an inch, December 19^7. |