Cloud of the Week #12: Cirrocumulus

May 11, 2011 Maria

Cirrocumulus (on the right) All photos by M. Ruth

I hope everyone was outside yesterday watching the skies clear for our 24-hour high-pressure respite from the rain. I walked out the front yard just after high noon and, what to my wondering eyes did appear, these miniature clouds and no sign of rain, dear.

I ran back inside for my polarized sun glasses and my camera, then my chair and my laptop, then some meteorology books and articles. I was going to camp out and watch the show of these tiny little ice-crystal cloudlets called cirrocumulus--our long-overdue-but-worth-the-wait Cloud of the Week #12.

From what I could see from my front yard facing west (below), the lower, thicker stratocumulus clouds were moving eastward over the Black Hills and were lifting, eroding, scattering as they traveled inland.

Around midday, upper-level clouds started moving in aloft--these cirrocumulus at chilling heights of 16,500-45,000 feet. It seemed as if they were condensing into ice-crystal clouds in the swath of sky between the Black Hills and my home 20 miles to the east. Because these cirrocumulus clouds appeared in bands (below) they are called cirrocumulus radiatus.

I had never seen--or perhaps never took the time to see--the very irregular shapes of the individual cloudlets that made up these clouds (below). These cloudlets are often described as "rice grains" to distinguish them from the much larger and lower altocumulus cloudlets which are more "bread-roll" sized. But calling them rice grains makes it sound as if the cloudlets were uniform in shape and size. The clouds yesterday were neither. They were more whimsical and energetic, kind of like what would happen if you dipped a cat's paws in white paint and set him loose on a blue tarp with a moth.

Because I am trying to understand what really made these clouds, I consulted the National Weather Service forecast report for Olympia yesterday and its seems that we were enjoying a weak high pressure ridge. This is what that looks like on a weather map:

For more details on this and a time-lapse of yesterday's clouds, go to www.cliffmass.blogspot.com

What's funny (to me) is that the National Weather Service report predicted "Just scattered clouds this afternoon..." Just scattered clouds? I think not. Here they are (below)

Now, you can see in the left side of this photograph the faint trails of ice crystals, called virga, in the wake of the cloudlets. And then, because I couldn't go inside (or stop looking up), I watched a jet fly through a thickened layer of cirrocumulus (cirrocumulus stratiformis), cutting a dissipation trail ( distrail). At first it looked like this:

And then it began to deteriorate into a cloud from I believe few people would recognize (below). Had I not been out in my front yard not writing, I would not have see the jet (the smoking gun) and the initial disstrail to know what this weird fanged cloud was. Oh, just scattered clouds.

And then the whole show ended with another set of undulating clouds (below) lining up like sardines in first class--not too crowded. What a day.