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season below 5,000 feet of 140-150 days. Above 9,000 feet, frosts • have occurred during all months of the year. Heating degree days in the Rifle-DeBeque region average 5500-7500. WIND While gradient winds are prevalently from a west-southwest direc- tion, local wind flow patterns are a strong function of local topography. Parachute Creek lies in a relatively deep and narrow valley cut through the Roan Plateau which has a range in elevation from about 8,600 feet above mean sea level (msl) in the upper reaches, to about 5,100 feet msl at the confluence of Parachute Creek and the Colorado River. The Roan Plateau lies at a mean elevation of about 8,000 feet msl. The downslope of the valley, with increasing downwind distance, results in the local air flow regimes being shielded from gradient wind flow fields, especially • winds within the valleys. The shielding effects of the mountains to the west also cause an increase in mechanically-induced turbu- lence above the plateau region, giving way to the more important thermally-induced turbulence within the valley reaches. Special meterological conditions are produced by local terrain features during the absence of strong gradient flow patterns. Within the valley regime, during warm afternoons, the laterally- constricted but vertically-expanded air tends to flow up the valley. This phenomenon occurs simultaneously with upslope winds caused by differential heating along the valley walls and floor. The opposite flow condition occurs during clear nights and low gradient wind speeds. Air near the valley walls cools more rapidly than that out over the valley floor. This cold and dense air flows downslope along the valley axis. This causes the stable air along the axis to be set in motion and is forced downslope and out of the lower reaches of the valley . system. K-10