What causes upslope snow
25 Mar 2009
We are about to get a facefull of upslope snow tomorrow along the Front Range of Colorado including Fort Collins. What does this have to do with web development? Nothing, except maybe I’ll get to ski to work.
Weather is one of my favorite topics, which is good for my health since I’m a pilot.
Upslope snow in Fort Collins happens this way: A low pressure area passes to our south. The flow around a low pressure area is counterclockwise, which causes the surface wind to come from the east, a little unusual for our area. That air originated well southeast of here near the Gulf of Mexico (visualize that large-scale counterclockwise flow), so it’s wet and moist and thinks it might be fun to take a little vacation in Colorado.
As the moist air flows from the east to the west aiming at the Front Range, it is moving uphill. The elevation in Fort Collins is just over 5000 feet MSL. The elevation at the eastern edge of Colorado is about 3500 feet MSL. The air coming at us is indeed moving “upslope”. As the air is forced westward it’s also forced upward and the gain in altitude causes the air to cool down, which (if it cools down enough) causes the moisture in the air to condense, or if it’s cold enough, to sublimate and precipitate out as snow.
As long as that low pressure sits to our south pumping the air westward and upward against the Rockies, it will continue to snow. If it sits there long enough like it did in 2003 we could get three feet of snow. This time the storm should keep mozying along and we’ll get 6 inches or so by Friday morning.