COLORADO — Snow falling in the foothills west of Denver this week appeared to slam into an “invisible wall,” stopping abruptly before reaching the Front Range and the I-25 corridor. The reason? A powerful atmospheric process known as downslope wind flow.
Radar imagery showed snow across higher terrain near Central City and Georgetown, but precipitation quickly weakened or disappeared as it moved east toward Boulder, Longmont, and Denver.
A 30-Degree Temperature Difference in 18 Miles
Surface observations revealed a dramatic contrast between the mountains and lower elevations. In Central City, temperatures hovered near 19 degrees with snow falling. Just 18 miles away in Boulder, readings were near 50 degrees.
That’s nearly a 30-degree temperature difference over less than 20 miles — enough to completely shut down snowfall as it moves downhill.
What Is Downslope?
Downsloping occurs when strong west to northwest winds descend off the mountains into lower elevations. As air descends, it compresses. When air compresses, it warms. And when it warms, it dries out…