We’ve had some windy days lately. Two days ago (October 20, 2019) we had gusts up to 40 mph (miles per hour) — it was hard to walk in that wind!
As we battled the blustery weather while walking the dogs, I happened to look to the west, where I saw lens-shaped clouds hovering over the tops of the mountains.
Once inside, I decided to clean up some photos on the computer. I happened across this shot of Longs Peak from near Estes Park from fifteen years ago.
North Face of Longs Peak, October 2006
What caught my eye initially was the odd shaped cloud over the east face of the mountain top — just like what I’d seen while walking the dogs. This is called a ‘lenticular cloud’, meaning lens-shaped. Lenticular clouds indicate that the wind is really ripping, pulling relatively moister air up to the top of the mountain, where it forms a cloud as it crosses over. Although these clouds seem to stand still, in reality, they are constantly forming on the near side, then evaporating on the far.
Notice the snow blowing off the ridge to the right (west) and dropping into the basin below the summit. This extra snow helps build glaciers.
According to the Rocky Mountain National Park Service Wind page, in the winter, the average daily wind speeds on Longs Peak are 65 mph, so the average is higher than our peak wind speed on Sunday. It often blows at over 100 mph, and the maximum wind speed recorded was in excess of 200 mph!
Suddenly, I’m more appreciative of our relatively calm air.
Where did all the snow go? Last week at this time, the Front Range was entirely blanketed in several inches of the white stuff. Today, it’s almost gone. Where did it go?
The Answer: Chinooks.
Chinooks are warm dry winds. They get their name from a Pacific Northwest Indian word for “snow eater,” because when the chinook blows, the snow goes. With gusts that blast up to 120 miles per hour, pushing the temperature up 40 degrees F in minutes, chinooks along the eastern side of the Rockies are the most violent in the world. You always suspected that, didn’t you?
What causes a chinook? Chinooks are cool air pushed down by the weight of a high pressure front above them. Squeezing the cool air warms it up, to become warm dry, air. In winter and spring, chinook winds often buffet the areas just east of the mountains from Canada all the way to Mexico.
At ground level, the now-warm dry air is no longer under pressure. Like any compressed gas, it expands when released, and rips along the surface at 50 to 120 miles per hour as a chinook, melting and evaporating snow as it goes. By definition, chinook winds are warm and dry, and they suck the moisture out of plants, soils and people as they blow.
Foehn wall hanging above the Front Range (not visible in this photo).
When a chinook blows, look toward the mountains. A bank of smooth clouds often hangs above the highest peaks. This is known as a foehn wall; it is created as the cool, wet, air crosses the mountains and is then forced down by high air pressure above that causes the chinook as well.
As the cool wet air containing the foehn wall is pushed down, it is compressed by the air above it; as it is compressed, it heats; as it heats, the amount of water it can hold increases (dew point rises) and the foehn wall cloud evaporates.
Chinooks also have the odd habit of “bouncing” over the land. They swoop down, blast some poor place with hurricane-force winds and then bounce back up, totally skipping over a locale just a few miles down the road.
In California chinooks are called Santa Aña winds, and in Europe, foehn (German for “warm”, pronounced “phone”. Actually, I heard a native German-speaker pronounce this word and it was closer to the way Peter Sellers and Steve Martin did it in the “Pink Panther” movies: “fun” as in “Your fun is ringing.”).
My mom sent me this website a couple of weeks ago. http://hint.fm/wind/index.html It shows the direction and speed of surface winds for the entire country. This screen shot doesn’t do it justice, because on the webpage, the wind lines flow. Beautiful.
In addition to being mesmerizing and beautiful, the map is very educational. When you look at it closely, you’ll see that the winds are flowing from blank areas to areas where they curl and swirl. The blank areas are areas of high air pressure, pushing extra air out; the swirls are areas of low pressure, where the air is sucked in.
Even more interesting is that the swirling lows often represent bad weather with high winds. The lows pull in moisture, in this case from the Gulf of Mexico. This is the moisture coming in for our storm tonight.
The Wind Map was created, not by the National Weather Service, or similar group, but as an art project from Point B. Studio. http://memory.org/point.b/windmap.html