Fun Weather Facts: Wave Clouds

Every time I drive around Enumclaw delivering flowers I realize how lucky I am to have such great views of Mt Rainier.  Especially now that fall is coming and the storms that go with it, I marvel at all the interesting clouds (a weather geek’s delight) around the mountain.

The atmosphere is full of waves, but we can’t always see them.  All it takes is wind blowing over mountains, but even hills will do.  Waves can be also caused by thunderstorms and other disturbances.  Wave clouds, sometimes called cap clouds, if they are right on top of a mountain, are part of the fun cloud viewing. 

Most people know that the wave cloud is stationary, but do not realize that air is continually flowing through the cloud.  As air flows towards the mountain some of it tries to flow around, but only some of it can do this, the rest is lifted up as it hits the mountain. As the air is lifted it cools by expansion (see my earlier blog “Warm Air Rises and Cold Air Sinks---Doesn’t it?”) and if the air is cooled enough the dew point is reached and clouds form.

On the downwind side of the mountain the air then descends (again reaching the dew point) and the cloud evaporates. 

The mountain can trigger a series of waves downwind which can produce a string of wave clouds trailing off into the distance.

The best conditions for wave clouds over Mt. Rainier are when a storm is approaching.   Layers of moisture are streaming out of the storm, but they might not have yet reached the dew point.  These moist, but still not cloudy layers are crucial for fun wave cloud viewing. 

I’ve included a picture of Mt. Rainier wave clouds where multiple moist layers flowed up and over the mountain.  The other picture is a logo I cooked up for Enumclaw.  Since it has wave clouds in it I used it to show the airflow through the clouds.  See if you can find the elk head and fish in the snow on the mountain.