Pretty excited up there, as usual.
The Cumulus and Stratocumulus clouds began filling in yesterday, and some shed ice/snow virga in the late afternoon. With that a few drops of rain (melted snow, of course) plopped down on Catalina. In case you missed those drops, here they are.
Note the trails of virga dropping out of Stratocumulus clouds near and over the Cat Mountains in shots 3 and 4. That was the “worst” of our “storm” right then when the clouds got their deepest, which wasn’t all that deep, maybe 3,000 feet or 1 km.
By now, too, you will know instantly that the top temperatures of those clouds, to be able to produce ice, were lower than -10 C (14 F). This kind of knowledge about local clouds and ice, is also a great “ice breaker” at parties and barbecues. In fact, the TUS sounding suggests that the general top was about -12 to -13 C, with likely momentary tops protruding to -15 C or so. This would suggest marginal ice formation in clouds with bases as cold as ours were, about -7 to -8 C (about 18 F). (Strangely Believe It: warmer cloud bases with the same top temperatures as we had yesterday, leads to more ice formation, and precip.)
Below the photos is the mid-level weather map for the time the sprinkles occurred from the University of Washington. Since the wind follows the green contours on this map, you can see two things. The wind maximum at this level (500 millibars) is south of us over northern Mexico, and that the wind was on the verge of shifting to the WNW above us at map time (5 PM AST yesterday). That wind shift line is referred to as a trough, and at, and ahead of the wind shift line, clouds and precip are stimulated, while behind it, the air gets drier and clouds are mashed down or disappear. You could even see that happening to the west of us yesterday afternoon while the clouds were heavy and precipitating over the Catalinas. Those clouds over the mountains, too began to whither, and the virga ended, not JUST because it was heading toward evening and getting cooler, but also because of that trough was passing to the east at that time and the drier, descending air was moving in over us.
In this map, you will also see the much stronger trough over northern California, one that is racing toward us and will bring rain as early as tomorrow morning! Yay! However, the U of AZ massive Beowulf Weather Calculating Computer Cluster foretells only about a tenth of an inch from this next storm (here). Boo! I will suggest that might be a little on the light side, but that’s because I am biased and strongly want more rain than a tenth from this new storm; I’ll venture 0.25 inches or so here in Catalinaland by Wednesday morning.
More storms after this next one? Oh, yeah!