WMOD00301 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I As air is forced over mountains it cools and moisture condenses out forming clouds and precipitation. After passing over the tops of the mountains, the air slides down the lee side. The downward movement of the air results in slight warming and the warmer air has more capacity to hold moisture as water vapor. Thus the cloud droplets evaporate and the clouds disappear. When an air mass approaches the Uinta Basin from any direction, it must pass over mountains or high plateaus. The Wasatch Mountains to the west of the Basin form a barrier of about 8,000 to 10,000 feet. An air mass approaching from the west is lifted and cooled to the 8,000 level, and considerable moisture is condensed out. Although some moisture remains in the air mass, further lifting (above 8,000 feet) is required to continue cloud formation and precipitation. Further lifting occurs for the portion of the air mass that passes over the higher Uinta Mountains and precipitation is produced in those areas. The air passing over the southern slopes of the Uinta Mountains (less than 8,000 feet) or over the Uinta Basin, descends in elevation. Clouds dissipate and no precipitation results even though there is still moisture in the air. The moisture that is carried downwind will be deposited as precipitation when it is condensed out by further lifting processes (i.e., when the air mass is lifted above 8,000 feet as it passes over the Rocky Mountains of Colorado). The Effects of Storm Fronts Large air masses tend to take on and retain certain characteristics for relatively long periods of time. Air masses which stagnate over polar ice and snow fields are usually very cold and dry. Air masses that travel long distances over warm oceans are usually warm and moist. A "storm front" occurs when a warm air mass is pushed against a cold air mass. The warm air mass slides up and over the cold air mass. As the air rises and cools, moisture condenses and clouds are formed. Further cooling and condensation results in precipitation. For these reasons, clouds and precipitation are associated with storm fronts. , j Winter and spring storm fronts pass over the Uinta Mountains, the Wasatch Mountains or the high pbteaus into the Uinta Basin on a regular basis. These fronts are affected by topography. To understand the linkage between frontal storms and topography, net lifting can be divided into two components: (1) lifting within the storm system (warm moist air being lifted as it moves upward over the cold air mass) and (2) lifting of the storm system itself as it moves upward over a mountain range (or subsidence, as it descends mountainous slopes). A frontal storm moving toward the Basin will be lifted as it approaches the Wasatch Mountains. The topographic lift of the storm system enhances the frontal lift of the storm. This lifting intensifies the storm and increases precipitation on the windward side of the mountains. As the storm moves into the Uinta Basin, it descends the mountains and the descent of the storm system tends to counteract the frontal lift that occurs within the storm. At times, the descent of the storm system may be rapid enough to negate the lifting within the storm and little or no precipitation results. At other times the frontal lifting within the storm is rapid enough that the slow topographical descent as the storm system moves down-slope, counterbalances only a small part of the frontal lifting within the storm system. Under this situation, precipitation may be copious, even though it is slightly reduced from what it would be if there were no mountainous descent.