April 03, 2024

Undulating Clouds

Last evening around 6 PM I was enjoying a run with my dog around Seattle's Magnuson Park and noticed some amazing clouds.

The bottom of the cloud deck was distorted by strange waves and structures.  So unusual that several people sent me pictures and the nearby National Weather Service office posted some pictures (see some samples below).

Picture courtesy of the NWS Seattle Office

Picture provided by John McBride

These stunning clouds have an impressive name: Undulatus Asperatus.   Often they are simply called Asperitas clouds.

You can get another perspective on these clouds from the SpaceNeedle PanoCam at 6 PM.   Pretty scary!

Or you can view from space, using the NOAA/NWS GOES satellite at 35,000 km above the surface (I have placed a red arrow pointing to Seattle's Magnuson Park),    You can see the massive cloud shield of a frontal system moving in at this time.  And a lot of wave-like undulations in the clouds.

Asperitas clouds are one of the newest additions to the cloud classification system, joining its more familiar cousins about a decade ago.

The limited research that I have seen suggests that Asperitas clouds are associated with atmospheric gravity waves, waves in the atmosphere analogous to water waves on the ocean surface.   These waves can distort the base of clouds in impressive ways.

Yesterday, during the late afternoon, a frontal system was moving in and winds aloft had strengthened.  Looking at the Seattle PanoCam a few hours before (4:30 PM) showed many lenticular clouds in the sky (they look like flying saucers!).  Clearly, there was a lot of wave activity aloft:  a sky full of waves produced by the Olympics interacting with the strengthening flow.

Here is a schematic of such mountain waves.

As the front came through, the clouds associated with the frontal motions were distorted by all the mountain waves downstream of the Olympics, producing an impressive show of Asperitas clouds.

I think this is a plausible hypothesis of what happened, but certainly interested in other ideas.


  1. Yesterday evening, as I looked East from Everett, towards the Cascades...massive, beautiful cloud formations were dominating the view...one formation was very much like the representation of a Mushroom cloud , suggesting an Atomic bomb!..The top was rising quite high, perhaps 25-30 thousand feet. I anticipated eventual thunderstorm activity--no such luck!

    1. Of course! Northwest thunderstorm predictions usually disappoint. It's the thing I miss most about East Coast living, on par with swimming in the ocean, crickets, katydids, and flaming orange maples in the fall.

  2. It would be interesting to find out what your physics professors think of the gravity wave theory. My limited understanding of gravity waves is that they are typically measured in proton level distances bending space-time over several kilometers using LIGO installations in a interferometer method. Something this noticeable to our naked eye probably is fluid mechanics element associated more with the motion of the air over the terrain at certain velocities being less turbulent and causing these effects.

    1. tharrylock.... you are thinking about the wrong gravity waves. I am talking about ATMOSPHERIC GRAVITY WAVES in which the restoring force of gravity is central. Look it up..cliff mass

  3. I guess I am with tharrylock. I get that you are just relating to us what meteorologists have decided to call this phenomenon, so not criticizing you at all, but the name suggests that the undulations in the cloud thickness are caused by undulations in the gravitational force, which is most definitely not what is happening here.

    1. No...not implying that at all. Gravity waves are a well-known atmospheric phenomenon. Gravity is the restoring force. You are confusing another field of study.

    2. Ocean waves are another example of gravity waves by this definition. Gravity waves by the cosmologist's definition, propagating undulations of a gravitational field, require very sophisticated equipment to detect (e.g., LIGO).

  4. In Arlington that night there was 1very impressive lighting strike that occurred, was very impressive for western washington


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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