West Texas Roll Cloud
December 28, 2007
The photo above shows a daunting looking roll cloud in western Texas, near U.S. Highway 285. It was taken one year ago today (December 28, 2006) when a cold front moved into western Texas from New Mexico. The camera is looking north toward eastern New Mexico, with the Guadalupe Mountains (in the background) about 40 miles (64 km) to the northwest. This attention-getting cloud was moving rapidly east and had a perceptible rolling action. Despite the patch of clear skies seen in the picture immediately behind the cloud, heavy cloud banks quickly moved in, and the temperature dropped rapidly with the cloud’s passage. Snow began to fall on the Guadalupe Mountains shortly after this picture was snapped.
Roll clouds are tubular shaped clouds associated with storms or advancing cold fronts. They're formed when down drafts usher in cold air toward the ground. This colder, denser air then spreads out along the surface in the direction the storm or front is advancing and undercuts warmer air. When moisture in this tumultuous near-surface air condenses, and if conditions are favorable, a roiling, rolling cloud occasionally forms.