Low Level Airflow in Southern Wyoming during Wintertime by Aircraft

Abstract

The winds persistently blow in southern Wyoming for the same reason that the region was a popular route for early pioneers who migrated to the western United States in the 1800’s. Today it is still a popular route with truck drivers and railroad operators. The continental divide is very low in this section of the Rocky Mountain Barrier. The Great Divide Basin in southern Wyoming at ~ 2000 m MSL is the lowest region along the continental divide between Montana and New Mexico and provides a natural passageway for the low level airflow through the Rocky Mountain barrier. The rest of the Rockies in Colorado, Wyoming and Montana are above 3000 m with numerous peaks above 4500 m. During the winter and spring, pools of cold, stable air regularly collect in the extensive Great Basin of Idaho, Nevada and Utah, west of the continental divide. The cold air promotes the maintenance of a quasi-permanent anticyclone during the winter months. The anticyclone, usually in conjunction with the frequent cyclones in the lee of the central and northern Rockies, provides a strong pressure gradient force which accelerates the low level airflow over the continental divide, particularly through the narrow gap or wind corridor in southern Wyoming. The topography of southern Wyoming (Fig. 1) channels the low level airflow through the Wyoming wind corridor. The Park Range Mountains south of Rawlins (RWL) and the Medicine Bow Mountains south of Medicine Bow (MB) establish the southern boundary, while the intermittent mountains between the Wind River Mountains and Laramie Peak comprise the northern boundary of the wind channel. The northern boundary contains a number of gaps through which flows a significant amount of air from the Great Divide Basin. The terrain through the wind channel was aptly dubbed the “wind corridor” by Kolm (1977) and is generally level at 2000 m MSL except for a few ridges near RWL. Eastward from MB the terrain gradually ascends ~150 m to Wheatland Reservoir (WR). The WR area provides a natural gap in the Laramie Range. From WR, the terrain descends abruptly into the Great Plains region of eastern Wyoming.