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!