May 06, 2011

Northwest's Signature Cloud

If someone asked you what the number one cloud was over the west side of the Northwest, what would you say? The cloud we see most frequently during every season. The cloud that sends Californians back to their Jacuzzis in the Bay Area or LA.

There is little doubt it is the cloud we saw quite a bit of on Friday: stratocumulus.

Here is an example:

Stratocumulus is a relatively low cloud, with the entire cloud below roughly 8,000 ft and the base far lower. It is generally made up of large, dark, lumpy elements, with bright sections in between. They form in a generally moist lower atmosphere, where weak convection is blocked by a stable layer aloft. Most are completely dry (no precipitation), but they can produce light rain or snow.

Friday there was lots of these fellas: take a look at video from the UW looking towards the Olympics (see link below). As you watch the video I want you to notice something. Early in the video the cloud base was clear and distinct. During the afternoon the cloud base became blurry and you can't see individual elements.

That happens when precipitation starts. So if you see a cloud base blur....time to get your raincoat!


  1. I have figured out when the clouds start to blur, get the laundry off the line!

  2. Thanks Cliff, your blog is very interesting to read. I remember chatting with a local meteorologist about our NW cloud, and Jim Bosely I believe was his name. He said that 1/10 of a degree F could make the difference between a day that was forecast to clear off and be sunny, and one that ended up being like the video on your blog. It could be real headache when the phone calls started coming in complaining that the sun never came out.

  3. Two questions:

    1) At about 16:30 and again around 17:00, a white point distortion appears in the upper left quadrant briefly; is this an equipment glitch?

    2) What is a "raincoat?"

  4. Interesting and timely post. On Friday evening I sat up on Phinney Ridge in my west facing living room with the lights off just watching the the cloud dance from about 8:15 PM until about 9:20 when it was too dark to distinguish the different layers. The clouds were very beautiful against the western sky - which was still light. Interesting to watch the different layers of clouds move at the different speeds and even directions!


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