Snow Billows Above the Colorado Rockies
March 31, 2010
What appear to be ghostly clouds on the above photo are actually vortices of snow coming off of the high peaks of the central Colorado Rockies. On the morning of January 25, 2010, high winds near the Eisenhower Tunnel on Interstate 70 were redistributing much of the previous night's snowfall. The snow billows were fascinating to watch as their appearance rapidly changed – they’re made visible by the snow they entrain. They seemed to be positioned slightly beyond the ridgeline and perhaps 600 – 1,000 ft (183 - 305 m) above it. I’m estimating that their velocity was 60-70 mph (97 to 113 kmh).
This phenomenon is evidently caused by rotor turbulence, which occurs in the lee of mountain ranges when strong winds blow nearly perpendicularly to the ridge axis. Rotor cells always occur in clusters and can be responsible for dangerous turbulence that may even threaten small aircraft.