Ever Wondered Why Rainier and Baker Occasionally Wear Cloud Hats?

Lenticular Clouds above the Olympic Mountains, with Mount Constance in the center, it’s peak hidden behind the clouds.

Living in the Seattle Metro area, perhaps you’ve seen Mount Rainier and Mount Baker don their cloud “hats” on occasion. This is a fun weather phenomenon that makes for some amazing cloud formations that occur above mountainous terrain, and occasionally in other places as well. Want to know about what causes these neat clouds? Here’s a quick blog that explains more about them and how they form!

Lenticular Clouds are a neat cloud that takes on a saucer, hat like shape. These clouds typically form in close perpendicular alignment with whatever direction the wind is traveling in and they form in the troposphere, around 12,000 meters above Earth’s surface. When air moves along the Earth’s surface, it will sometimes come upon obstructions such as buildings, or more commonly, natural obstructions such as mountains, hills, valleys, etc. These obstructions quickly disrupt the natural flow of air, and essentially create little eddies of air. How much strength these eddies possess depend on the size of the obstruction blocking the air, and the speed of the wind when it collides with the obstruction. This creates a form of turbulence called “mechanical turbulence”, meaning that is formed through something mechanical (IE, mountain, building, etc) interrupting the normal wind flow.

When humid but stable air travels over a mountain or a mountain range, standing waves can form on the downwind side of the mountains, sometimes on a larger scale. Occasionally, the temperature at the peak of the mountains will drop to the dew point, and the moisture in these humid air waves will begin to condense into visible water vapor. When this occurs, lenticular clouds begin to form. Occasionally, long strings of these clouds will form, and these are called a wave cloud. Eventually, that moist air will move back down into the low point of the wave, and then the clouds will dissipate.

On occasion, these lenticular clouds will develop over flat land as well, created by the shear winds caused by a front.

Here’s a quick little diagram of how this process works:

Diagram Courtesy of http://www.skybrary.aero/index.php/Mountain_Waves

These clouds, formed by turbulence, are commonly a sign that a front is coming. That is why lenticular clouds, affectionately nicknamed lennies by weather lovers, are usually viewed as a good indicator that rain is on the way. This was very true yesterday when we had a pretty incredible display of lenticular clouds across the Puget Sound in the early afternoon, and by late evening, most areas were under a soaking rainfall.

Here are a few images I took yesterday of these neat lenticular clouds around the region.

The Brothers obscured by lenticular clouds yesterday.

Impressive lenticular/wave cloud formations resting above the Olympic Mountains yesterday, as high clouds filled into the region ahead of a strong frontal system.

If you look closely, you can see that this image shows a double lenticular formation over Mt. Baker, one smaller one on the bottom, capped off by a larger one on top.

On another quick note, we also saw some neat Virga yesterday, which is precipitation that is falling from the clouds above, but evaporating before it hits the ground. Here’s a quick image of that as well:

Virga seen above the Edmonds Ferry Terminal yesterday.

Here is a close up of the Virga.

As always, you can find more of our photography at JB Hawkins Photography