Most of us will obsess over clouds and other rain-related weather phenomena this summer. It’s a popular pastime in the West. Clouds bring rain, and so much depends on rain.
We’ve had some typical May rain as of late, though that’s typical only if you consider there’s really no such thing as typical spring weather in the Rocky Mountains. One year back in the ‘90s, when I lived in the Bitterroot, we had one of the driest winters ever. With the mountains surrounding the valley mostly free of snow by the time May rolled around, we were expecting a summer of river closures and forest fires.
Then it started to rain, and it didn’t stop until August. That Montana summer turned out to be the most smoke free I can remember.
The clouds that come with the weather add to the spectacular scenery of Montana. The other day, while driving through Bozeman trailing a storm that had rolled through the Gallatin Valley, the clouds appeared to be clinging to the top of the Bridger Mountains. The clouds rose up from the east and poured down the west face of the range just beyond the M.
Clinging is an illusion. Mountains don’t attract clouds, they create them. Air rising up and over the range causes water vapor to condense and become visible in the form of clouds. The clouds don’t really travel over the mountains so much as they are constantly recreating themselves on the windward edge then disintegrating as the air rolls down the other side.
I’ve learned these pillows of water vapor are called orographic clouds, a category that includes a variety of cloud formations caused by the lifting and falling of air as it travels over mountain ranges. It’s also not unusual to see a series of cloud waves out in the valley downwind from the mountaintop. These waves probably aren’t breakaways from the mountain mist, but clouds that recreate themselves as the air continues to oscillate as it drifts across the plain.
Clouds form as the air rises. Then, like those “clingy” clouds on the mountains, they disintegrate as the air descends. This process becomes clear when you watch one of those time lapse videos of cloud formation. Orographic clouds disappear and reappear in the same place.
Maybe the most dramatic kind of orographic clouds are the lenticular type. Lenticular clouds form atop mountains or on the leeward side. The mountain disrupts the flow of air, and then the lens shaped clouds form in the stratified air currents. Sometimes just one lens cloud forms, but sometimes they can form a stack, like upside down saucers.
The clouds look a little like the flying saucers so common in science fiction movies of the black and white era. I think you’d have to be a little bit drunk, or crazy, to confuse a cloud for a space ship, but there are plenty of folks in the Rockies who fit one or both of those descriptions so maybe there’s truth to the legend.
I’ve seen quite a few lenticular clouds over the years. I lived in Flagstaff, Arizona, and the 12,000-foot extinct volcano on the edge of town creates all kinds of bizarre clouds as the prevailing winds drive past toward the Hopi Mesas. But the best lenticular I’ve seen was a stack of four or fives lenses downwind from Heart Mountain east of Cody, Wyoming.
I see the waterfall clouds, like the one I saw pouring over the Bridgers last week, from time to time. They form over the hills near where I grew up in Southern California, but only in winter when the air was cool and moist enough to hold water vapor as the currents push inland from the Pacific.
That’s what passes for winter weather down there. A few clouds and an occasional monsoon rain shower. That’s my kind of winter.
Rob Breeding writes and teaches when he’s not fishing or hunting.