2016-12-23_PERMIT FILE - C1982056A (8)

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Extremes, 1971-1978. Based on data collected by the United States Department of Commerce, the mean annual • temperature at Steamboat Springs is 38.7 degrees F with recorded extremes of 96 degrees F and -50 degrees F. Mean monthly temperatures range from 15.4 degrees F in January to 16.8 degrees F in July; mean daily maxima range from 29.3 degrees F in January to 82.8 degrees in July; and mean daily minima range from 1.5 degrees F in January to 40.9 degrees F in July. Freezing temperatures can occur during any month of the year. The average annual growing season (above 20 degrees F) of irrigated land near the Yampa River and Steamboat Springs is 102 days according to the Colorado Water Conservation Board and USDA, 1969. Mean temperatures at Hayden are about 3 to 4 degrees F warmer than corresponding mean temperatures in Steamboat Springs. Monthly means at Hayden range from 17.3 degrees F in January to 65.9 degrees F in July. Mean daily maxima range from 31.0 degrees F in January to 85.3 degrees F in July. Extreme temperatures of 100 degrees F and -45 degrees F were recorded at Hayden in 39 years of observations, freezing temperatures can occur during any month of the year in Hayden. Wind The east -west orientation of the Yampa Valley is conducive to easterly downslope breezes during nighttime hours and stronger westerly upslope winds during the day. Local terrain has the effect of shielding the valley with respect to surface air motion, and consequently, calm or near -calm conditions are common, especially at night and in the early morning. Preliminary information on atmospheric stability and associated air motion has been collected near Craig and may be used as an indication of air movement patterns farther up the Yampa River Valley. Four stability categories are is defined: stable, unstable, neutral and transition conditions. Stable conditions occur when the air lavers close to the ground undergo cooling with associated low wind speeds; neutral conditions occur with cloudy skies and/or high wind speeds; transition conditions occur in the short period of time following the breakup of stable conditions and prior to the onset of unstable or neutral conditions. Stable layers, at ground level, occurred approximately 60 percent of the time. Such layers are typically as deep as 1,100 feet and can persist for several days during winter and spring. Under stable conditions, surface winds are light and variable. Local influences control the surface wind about 40 percent of the time. Ordinarily, local influences are caused by the valleys of tributaries to the Yampa River. However, the drainage air that flows down these smaller valleys is typically only 100 to 200 feet deep. The existence of stable layers is most common from 7 p.m. to I I a.m., followed by upslope, or westerly winds through about 6 p.m. The gradient westerly winds have higher velocities than the drainage winds and are associated with neutral or unstable conditions. In the transition period between stable and neutral or unstable conditions, surface winds tend to be light and variable. Wind data from the Federal Aviation Administration at the Hayden Airport (the closest reporting station collecting wind data) show that wind velocities of 3 to 15 miles per hour blow from the east to northeast 16.3 percent of the time and from the west to southwest 31.3 percent of the time. Also, winds with velocities exceeding 15 miles per hour blow out of the west-southwest 7.5 percent of the time. Winds so light that their speeds were not detectable (0 to 3 miles per hour) occurred 6 percent of the time. The remaining 34.4 percent of the observations occurred randomly. Weather Station at Energy Mine No. I • A weather station was operated at Energy Mine No. I for the period of 1977 and 1978. Temperature and precipitation information from the weather station are found in Table 19, Weather Data - Energy Mine No. 1 Station. MR 97-154 2.04-46 Revised 10/02/97