The Flatirons in Fall

Lenticular clouds form when strong westerly winds are forced upward by the Rockies. Rising air cools, which causes the moisture in the air to condense as the air approaches the crest of the range. The lenticular or mountain wave cloud that forms marks the crest of the wave-like airflow that develops. As the air passes the crest and descends again, it warms and the cloud evaporates. Lenticular clouds are a sure sign of high winds aloft. The cloud appears to be stationary, but only because the cloud forms on the windward side as fast as it dissipates on the leeward side. Often the wave-like motion in the westerly flow initiated by the mountains continues for several more waves to the east of the Rockies, creating a series of lenticular clouds that form at the apex of each wave. An impressive example of such a cloud had formed over Boulder’s famous Flatirons one fall morning when the sumac along the edge of Chautauqua had turned bright red. The rising sun painted the cloud fiery pink. Reflected light from the cloud enhanced the red tones of the already vibrant sumac and created the spectacular natural color you see here.