AKA, Cumulus humilis virgae, or, with virga. While there were plenty of small Cumulus around yesterday, it wasn’t until after 1 PM that trace amounts of virga could be seen starting to emit from them as they got colder during the day. I think I did, too. By the end of the day, cloud BOTTOMS of those little clouds were about -20 C (-4 F)! Poor guys. Tops were likely only a little cooler, at -22 or -23 C. Those Stratocumulus bottoms topping the mountains in the third photo were about -5 C (23 F) already.
Here’s what happened yesterday. First, the tail of the frontal cloud band came by, dropped a few flakes on the Catalinas before rushing off. Here is that precip, barely detectable on the Tucson radar:
What are the concentrations of ice particles in those clouds shown at 1:16 PM through 2:12 PM, photos Nos. 6-9? How about in the last two photos? 25 points.
Answer: Probably less than 5 per liter of those larger than, say, 150 microns in maximum dimension in 6-9, likely 10s per liter in photos Nos. 10-11.
Why know something as arcane as this?
Because it impresses the neighbors, for one thing, because then you can go on and on about the Wegner-Bergeron-Findeisen precipitation mechanism in “mixed phase” clouds, or simply impugn them, with the words from the Walt Disney Studios science song lyric in “Water Cycle Jump1“;
“Your brain is on vacation/if you don’t know about precipitation.”
Second, if you’re into “vigilante science”, as Mr. Cloud Maven person was in parts of his science career, knowing concentrations of ice in clouds by sight will help you clean up some of the messes in the domain of cloud seeding when people report concentrations of ice that are too low. But an extra low ice concentration report benefits them because it helps make the clouds seem like they need some of that seeding to make ice and then more precipitation. Then a big contract is let based on bogus cloud reports, ones that you damn well know are goofy just by looking at the clouds, or checking out rawinsonde cloud tops when its raining from them… I could go on, and on, and on….. Someday…will tell those stories.
I hope that helps explain why this is important. If not, oh well.
The weather way ahead.
Well, you all know about the hot ahead. Now some rain pixels have shown up on March 10th. Not worth showing, but will keep an eye on them.
I am euphoric that this song is now online! I loved that song! Gritty but great, except the part where it is asserted that condensation leads to precipitation. Condensation (and the ice form of “deposition”) is only the first step. Also, if you like easy listening, boring music, don’t go to this site; it might be too much for you.
Condensation by itself can NEVER lead to precipitation. You got to have ice or those larger cloud droplets (again, let us call to mind, Hocking, 1959, Jonas and Hocking 1970 was it?) that cloud droplets do not stick together UNLESS they are around 38 um in diameter and larger, and then there have to be quite a lot of those that size and larger to “bump and stick” (sounds like volleyball) to form a true raindrop (mm sizes). You see, cloud droplets pretty much stop growing due to condensation at sizes TOO SMALL to fall out of a cloud as precip! They’d evaporate in the first 50 feet out the cloud bottom. NEVER forget that as a cloud maven junior!