2014-10-31_PERMIT FILE - C1981044A (2)

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2.04.8 CLIMATOLOGICAL INFORMATION The climate of the EC Permit area can be described as typical of a: high plains, continental, mid-latitude region with warm summers and cold winters characterized by large variations in diurnal and seasonal temperatures. The effect of high summer temperatures is moderated by low relative humidity, and summer nights are generally cool due to the rapid loss of accumulated terrestrial heat. The dominant climatic characteristic of northwest Colorado is the general lack of significant precipitation. The area is generally classified as semi-arid. The flow of pacific air extending over this region typically loses its moisture while passing over the Sierra Nevada and Cascade Mountains and tends to pick up moisture as it moves eastward. This dominant air flow pattern creates a "rain shadow" over Nevada, Utah, and northwestern Colorado by effectively blocking other movements of moist maritime air. Major storms and low-pressure systems generally bypass the northwest Colorado region, deflecting northward or southward through major topographic breaks in the Rocky Mountain chain. During the winter, continental polar air masses may displace the dominant pacific airflow. This event can produce very cold climatic conditions. The EC Permit area lies in the west central portion of the Rocky Mountain winter storm track. During the summer months, this region is usually south of the main storm track. However, localized thundershowers do occur primarily during the afternoon when climatic conditions are favorable. The closest active reporting weather station to the EC Mine site is at Craig, Colorado, which is located approximately seven miles [o the north of the EC mine site. Data from the Craig weather station is submitted herein. Available weather information is presented to allow accurate evaluation of meteorological trends and variations in the permit and adjacent areas. Preci nation Precipitation is directly related to local topography. In general, winter precipitation falls as snow over large areas at a time; whereas summer precipitation is most likely to fall as scattered local showers and/or thunderstorms. Precipitation is normally heaviest over and near the mountain areas. The average precipitation for the EC area is 13.88 inches with an average monthly high of 1.64 inches in August and an average monthly low of 0.83 inches in March. Precipitation information for the Craig weather station is shown on Table 31, Precipitation Summary-Craig. Measurable snow has been recorded nine (9) months out of the year at the Craig weather station. The only months in which snow has not been recorded are June, July, and August. Most snow falls in the month of December with an average of 18.6 inches and least in May with an average of 0.6 inches. Temneramre Average monthly temperatures for the area range from 21°F to 31°F during [he winter and from 50°F to 65°F during the summer. Recorded high and low temperatures at the Craig weather station between the years 1951 and 1970 were 99°F and -45°F respectively. Temperature data from the Craig weather station is presented in Table 32, Monthly Average Temperature-Craig. Temperature extremes including record highs and record lows for the Craig weather station are shown on Table 33, Temperature Extremes-Craig. All of the temperature data presented herein, is based on records maintained by the United States Department of Commerce, National Oceanic and Atmospheric Administration located in Fort Collins, Colorado, The growing season for the EC area is approximately 120 days. Wind Air movements in the EC area are characterized by prevailing westerly winds, which influence air quality in the region. The direction and speed of surface air movements are greatly affected by topography. Near calm conditions Permit Revision 04-34 2.04-26 Revised 7/2/04