You know the rest of the words to this song, the punch line, “…pretty ugly.” Yes, who can forget Johnny Rotten….?
Gorgeous clouds yesterday, but no rain is going to follow them (the “ugly” part)! I had really hoped for a splotch of glaciating Stratocumulus clouds this morning after the great display of….the tongue twister, Altocumulus (Ac) perlucidus undulatus, a mid-level cloud with a honey-comb of elements (“perlucidus”), and those elements also aligned in rows (“undulatus”). If you looked off toward Twin Peaks, you saw that the the back edge to these clouds was very smooth looking and did not advance toward us. That was an Ac lenticularis cloud that started the whole shebang. That lenticular cloud, as often happens, devolved into little cloudlets and rows; its smooth lenticular form devolving into cloudlets that trailed downwind over us here in Catalina. See pretty pictures below. One has the crescent moon in it.
Now it looks “pretty ugly” here for rain since there are no clouds this AM! “Dang”, as a friend would say.
Why get excited about the chance of a sprinkle, or at least some pretty virga this morning because of the two layers of clouds yesterday afternoon? No model indicated any rain. First, it doesn’t happen often, but to HELL with models, they can be WRONG. Don’t bet against them too often, though. You will lose everything.
So, if you were just eye-balling the movement of those two cloud layers later yesterday afternoon and using the crescent moon as your fix, you saw that those mid-level Ac clouds were jetting along at a tremendous speed as they passed it.
How fast?
The NWS balloon sounding indicated that at the height of those pretty Ac clouds, about 20,000 feet above ground level, they were blowing along at no less than 80-90 mph (70-75 knots)! This is a really strong jet for May! And it indicated that the jet stream must be right over us, or darn close, and it was blowing from the SW. If you no doubt know, Buys-Ballots Law, in the northern hemisphere means that a low or trough is to the west of you, and in this case; above you, not at ground level since you’re looking at higher clouds.
Also, the small Cumulus were beginning to cluster into Stratocumulus over the Catalina Mountains. Getting pumped because there movement was showing more southerly now; the wind was more southerly at that level than it had been in the morning, also suggesting the influence of the trough to the west. Here they are. If you really want to relive yesterday’s clouds, particular in the afternoon and evening, our friends at the U of Arizona Wildcat Department of Atmospheric Meteorology have captured them
here. For the really sharpies who DO go here, you’ll see that these cloudlets were further devolving in this time lapse to “ghosts” of their former droplet selves in the form of barely visible, icy little veils as they exit the area. So, can you guess the temperature of those clouds? Piece a cake: probably -20 C or less (-4 F or less). Sounding indicates -20 C, BTW.
Perhaps, I mused yesterday afternoon in a bout of wishful thinking, that in the core of that trough heading for us, there’ll be a smidgeon of Pacific moisture left within its interior, enough for some thicker lower clouds than now, and those clouds will be cold enough, too, so that they will form ice inside them and we’ll see some virga (trails of snow fall out of them) or get a sprinkle (in spite of what the models were saying)! Many of you will remember that according to Willis and Rangno (1971–Final Report to the Bureau of Reclamation by EG&G, Inc) that rain can only fall in the wintertime here when you are in the interior of a trough. I’m sure many of you have this report, and can look it up jf you don’t remember.
Well, we should still see a few isolated Cumulus around, small ones, maybe as big as “mediocris” stage (1 km thick or so, 3300 feet). And, with the coldest air over us this afternoon and evening, I am going to stick with an expectation of some ice in those clouds! And you will here about it tomorrow if there is one crystal up there!
Finally, for cloud technicians, how cold will it have to get at cloud top to have ice in those small clouds around here in Arizona today? Well, between about -10 and -15 C (14 to 5 F)–this is somewhat higher than for those mid-level clouds. So we will check that out tomorrow, too!
“The end”, unless I think of something else later.
Footnote: It now appears that last night’s model run of the “Beowulf Cluster” at the U of A has some precip on the Catalinas, between 3-4 PM LST today. Interesting that after I had this thought based on a crude conceptual model, that the “Cluster” would now have that thought as well…. Hmmmm.
