Altocumulus clouds, Cirrocumulus clouds, Definitions, Iridescence, Lenticular clouds, Something about the 60s Pretty cloud day October 30, 2013 Art Rangno One of the best, really, never mind all that wind yesterday. No rain, of course, in our future, not even fantasy rain these days. See usual rehash of yesterday’s clouds, the 60s, in case you forgot, below: 8:49 AM. This Altocumulus perlucidus cloud behaved like a lenticular, holding in place for at least 2 h, but did not have the classic pancake or sliver look of lenticularis clouds. Air likely too unstable (temperature dropped with height rapidly) and allowed tiny cumuliform elements to form. Only on the very right edge where it first formed, did this cloud appear “lenticular” in any way with its smoothness 10:15 AM. More classic looking, sliver Altocumulus lenticularis beyond the Catalinas. Cloud forms on the right edge, dissipates on the left as the air rises and falls slightly. 11:58 AM. Cirrocumulus (delicate granulation) on the fringes of Altocumulus (larger elements on the right). 12:01 PM. These clouds change by the second as the degree of moisture in the air jetting along up there ebbs and wanes. Look how much larger that fine granulation on the left got in just a couple of minutes. 2:09 PM. One of the many examples of iridescence seen yesterday in those Cirrocumulus clouds, or on the very thin upwind edge of Altocumulus lenticularis clouds. Its due to the formation of extremely tiny droplets, a few microns in diameter, that cause diffraction in the sun’s rays (see link for a more complete explanation and nice examples). Do you remember that white light has the wavelengths of all the colors in it? Here you can see some of them, and photograph them by performing a replication of the Black Power salute of Tommy Smith and John Carlos from my alma mater, San Jose State, one that beat the Wyoming Cowboys recently in fubball. I added a link in case you forgot and wanted to get worked up again. Yes I was at SJS when that happened down Mexico way, minding my own business doing weather forecasts with a political slant (left, of course, because that’s what made you popular during the rad lib days) for the college paper. Suddenly, I feel like going to San Francisco, putting some flowers in my hair.… 2:19 PM. Cirrocumulus and Ac lenticularis in the same layer. Recall Cc can’t have shading, not that it matters that much. 4:39 PM. This dramatic scene amid the dust and wind. This would be an Altocumulus lenticularis, one that devolves into Altocumulus perlucidus (honeycomb pattern seen downwind from the distant leading edge). The End.