2008-09-29_PERMIT FILE - C1981019A (34)

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RULE 2 PERMITS 2.04.8 Climatological Information The closest active reporting stations to the permit area are at Craig, Colorado, which is about 28 miles northeast of the area and at Meeker, Colorado, which is about 20 miles south of the area. Information from both locations is presented herein to provide the best data as related to the permit area and to indicate the variability in climatological characteristics that may be expected within short distances. Also, the data collected at the Colowyo mine site are presented. The climate of the area can be described as typical of a high plains, continental, mid-latitude region with warm summers and cold winters characterized by high diurnal and seasonal temperature variations. The low relative humidity usually makes the hot summer days pleasant. The summer nights are generally cool because of strong out-going terrestrial radiation. The combination of dry air and strong solar radiation tempers the cold temperatures of winter days. The outstanding characteristic of the climate of northwest Colorado is its aridity and is sometimes referred to as semi-arid steppe. The flow of Pacific air dominating the climate descends into the area as a warming and drying mass after depositing its moisture over the western slopes of the Sierra Nevada and Cascade Mountains. A large rain shadow is created over Nevada, Utah, and western -Colorado by the clocking action of these natural barriers to the moist, maritime air. Intense cold waves are rare because of the barriers created by the mountains of the Continental Divide. Generally, severe storms and low pressure systems bypass the region by deflecting north or south over lower elevations of the Rocky Mountains in Wyoming and New Mexico, respectively. The predominant air mass over the Rocky Mountains during the winter is usually continental polar and sometimes maritime polar and produces cold, dry air during stormfree periods. High pressure systems that result in fine, light, powdery snow tend to become established in winter over the region which lies within the mean winter storm track. During the summer months, the air masses are generally maritime polar and, much less often, continental tropical. This region is usually south of the main storm track in the summer; however, localized thundershowers do occur primarily during the afternoon, if a moisture supply is available either locally or in the air mass. Precipitation Precipitation information for Craig and Meeker is shown in Table 2.04.8-1, Monthly Normals of Temperature and Precipitation (1941-1970), in Table 2.04.8-2 Monthly Precipitation (1971-1979) for Craig, Colorado and Table 2.04.8-3, Monthly Precipitation (1971-1979) for Meeker, Colorado. Temperature Temperature data for Craig and Meeker are presented in Table 2.04.8-1, Monthly Normals of Temperature and Precipitation (1941-1970), in Table 2.04.8-4, Monthly Average Temperature (1971- 1979) for Craig, Colorado and in Table 2.04.8-5, Monthly Average Temperature (1971-1979) for Meeker, Colorado. Based on data collected by the United States Department of Commerce, the mean annual temperature of Craig is 42.4°F while the mean annual temperature at Meeker is 44.2°F. Mean maximum and minimum monthly temperatures for both Craig and Meeker are shown in Table 2.04.8-6, Temperature Summary - Means. Rule 2 Permits 2.04.8-1 Revision Date: 6/23/08 Revision No.: MR-91