Lenticularis in July?

Altocumulus lenticularis, to be exact.   Of course, as the discerning, eruditeful cloud person that you have become, I didn’t need to tell you this.

Well, yep, here they are, courtesy of the U of A Wildcats website. And, if you missed them locally near Catalina, here are a coupla shots.  In this movie, you will see sliver clouds that appear absolutely motionless above the Cat mountains.  Those sliver clouds are “Ac len.”   Cloud droplets form on the upwind side (to the right) and evaporate on the downwind side (on on the left) in this film.  They are stationary because they are in a bump in the airflow caused by the mountains, and since the mountains aren’t going anywhere very fast, the bump remains in the same location as long as the winds are steady.  As the air moistens and dries out, those Ac len clouds can expand upwind or disappear since the bump or hump in the airflow is bigger than what you see when the air quite dry.  I will get my 1o1 cartoon of this situation out. (I actually taught 101 one summer at the prestigious University of Washington’s Department of Atmospheric Sciences.  Poor students!  Those weather jokes!  Poor University, too.  I had,  and have, only a Bachelor’s Degree and I am sure that this Lectureship caused a decline in Washington’s accreditation that year.  As you know, to teach even the most simple class, a University must have Ph. D.’s. Experience gained in research and in the “school of hard weather knocks”, etc.  have no real impact on a university’s accreditation as we know1.  Gotta have the big Ph. D.  Whining here, and off task, but it feels good.

Lenticulars are an odd site for July.  Why?  Because lenticularis clouds are associated with stronger winds aloft AND a modicum of moisture and we don’t usually see BOTH in July.   However our influx of tropical air, not fully arrived yet, is associated with a stronger than usual flow pattern.  The NWS rawinsonde (balloon) sounding indicated winds of 30-35 mph at cloud levels.  Here’s what the sounding looked like as depicted by the University of Wyoming Atmos. Sci. Dept.:

Where the dark lines pinch toward each other are where clouds might have been.  Since at sunset some of these Ac clouds shed ice, you would have to guess that they were NOT at the lower level where the lines pinch in  (“600” mb or 14,000 feet or so above sea level) but rather near 20, 000 feet (or at the “450” mb level or even at the “325” level, close to 30,000 feet (!) that highest point where the lines pinch in showing a moist layer.

Quitting here, looks like first chance for rain today after the interruption of the summer rain season….  Excellent!  Gorgeous sunrise “blooming” now, too.  Ac opacus with scattered virga.











Below a simple diagram modified for the Catalina mountains showing what the airflow might be like under strong, semi-moist westerly flow with Ac lenticulars occurring downstream from the peaks: