Probably most people didn’t notice much yesterday, but at times, especially in the mid-afternoon it was spectacular up there due to delicate little patterns within Cirrus and Cirrocumulus clouds. Some examples below.
5. The after life of those Cc and Ac clouds was Cirrus!
The Tucson rawinsonde sounding indicated that these initially liquid droplet clouds (Cirrocumulus and Altocumulus) were at 26,000 feet (at the 330 millibar level) above Catalina at -30 C (-22 F) . So, being that high, its no wonder those delicate Cirrocumulus clouds (Cc) became fuzzy masses of ice. Long ago it was noticed that nature liked to produce a droplet cloud before it froze to become ice, even at these low temperatures. Only around -35 to -40 C does ice form directly without going through the water phase, though liquid drops have been reported at -44 C!
To watch some of this transition happen before your very eyes, go to the University of AZ time-lapse and, about 1:02 from the finish (about 15:35 PM if you can read the time on this movie!) before the end of the movie, a really nice patch of Cc appears on the left, but by the time its about to exit the field of view, it has magically transformed into a thin patch of ice cloud. This little patch of Cc in the movie is likely the same one I shot at 15:32 PM in photo number 4.
Just ahead, our upper air anticyclonic summer regime
And with that big mound of hot air over the Southwest US, the first onset of summer rains are now indicated in the models twelve days from now, around June 25th. Too far in advance to bother showing, but am very hopeful of an earlier onset of the summer rain season, and we hope, a LONG, juicy one!
In the meantime, we will be in a trough for a few days, but, as tantalizing as that is, the models still see insufficient moisture for rain in AZ when the trough peaks over us this weekend. However, rain is shown in Sonora near the AZ border this weekend so its not impossible that a few Cumulus might get overly enthusiastic and bust those model predictions of complete dryness this weekend in the mountains. If rain did unexpectedly develop over the weekend from our little trough, it would probably fall from very high-based Cumulonimbus clouds producing mostly virga.