Massive virga pummels air above Catalina; some drops reach ground elsewhere

A Cumulus cloud!  Then traces of ice spewing from them as they deepened and spread over the sky!  Then masses of VIRGA,  snow drifting downward toward the parched desert, which is mostly parched all the time anyway.  What a day, Mr. and Mrs. Catalina!

12:14 PM. Can this really be happening? A cloud has formed over Ms. Lemmon, or close to her.
12:14 PM. A closer look to make sure its not an illusion. In a real boo-boo, cloud maven person estimated the base was only 10,000 above Catalina, when in fact, it was probably about 13,000 feet above Catalina at this time, and as bases do on sunny days, rose some more as the afternoon heating carried on, reaching a 100°F here!
12:14 PM. There even more tiny Cumulus clouds out over the desert to our north! What is going on?
2:08 PM. How wrong CMP was in his cloud height estimate is becoming clear as ice began to form in great quantities by this time. They had to be much higher than was originally estimated. Its fun saying you were wrong about something because it illustrates humility, and lack of fear about an error, increases your stature with others even if you’re actually upset about it and only pretending to be “happy” and gracious in admitting error.
3:50 PM. Those Cumulus clouds look pretty dark, but were only about 5,000 feet thick. Notice nice heavy trail of virga in the center. The darkness was likely not the result of so much depth, but the high droplet concentrations. When clouds are full of high droplet concentrations, the droplets are smaller overall, and reflect more sunlight from their tops, making them seem darker on the bottom.   Clouds with larger cloud droplets in them, such as those found over the oceans (away from continents) would be less dark looking with the same cloud depth.
3:51 PM. Looking toward the southwest at more virga.
4:07 PM. We really should have a covered grandstand for folks to just sit and watch the sun and shadows highlight our beautiful Catalina Mountains.  Here the Sutherland Trail out of Catalina State Park is highlighted.
6:43 PM. Some drops appear to be reaching the ground, center, right.

How high up were the bottoms of those Cumulus clouds with all that ice?  Oh, about 17,000 feet above sea level, 14,000 feet above Catalina by mid-to late afternoon.  The base temperatures, as you could tell with all that snow virga hanging down, had to be way below freezing, about -9°C, about 16° F.

Now, with all that ice, can you guess how low the temperatures had to be up around the tops of those clouds?  Remember, if the top is about -12°C in a thin cloud, the droplets are very small because they haven’t been lifted upward much, 1000 to 1500 feet or so, there’s probably not going to be any ice.  The smaller the drops, the harder it is for nature to create an ice crystal.  So guessing that the tops were 1000-1500 feet above the base would be a good starting point, but horribly WRONG for those clouds with a lot of ice!  A cloudwise neighbor,  hearing that estimate, might start laughing, or at least sniggle.

With all that ice up there, and cold based clouds, a good estimate would have been -22.3°C, because adding the decimal would make it appear that you know more than you really do.  Here’s the sounding from the U of AZ for yesterday afternoon when all the ice was in full display, down thataway as well as here:

Ann 2017050600Z_SKEWT_KTUSSo you can see that tops were about -25°C, about right for all the ice we saw come out of those clouds.

As you know, the actual rain from this incoming system doesn’t get here until late tomorrow.  We have to go through a dry slot aloft before the Pacific moisture gets here. The U of AZ Beowulf Cluster output is suggesting that we here in Catalinaland should get at least a tenth of an inch as an upper level vortex goes by (run is not complete as of this writing).  But, because this vortex aloft that’s going to affect us is rather small,  a slight position error could mean much more than that.  It would seem the potential rain amount here might range from a least amount of 0.05 inches to ten times that amount, or 0.50 inches, more uncertainty than usual! Good chance of some thunder with this situation, too, to remind us that the summer rain season is getting closer.

The NOAA spaghetti factory had indicated this situation and the chances of rain on the 8th more than 10 days ago, and that is the power of those crazy maps, to give us some insight farther out in time than we normally can do any reliability.  The scenario of “troughiness” over us continues well into May in those plots, and that should mean temperatures are moderate, not “ovenly” as we like to say here.  Check it out here.

But that  also means very windy at times, too, along with a chance for additional rain.

The End.

2 thoughts on “Massive virga pummels air above Catalina; some drops reach ground elsewhere”

  1. Hi Art: we had a pretty good example of virga here on Thursday evening after a warm day (High around 80F). A series of thunderstorms moved up the coast in the evening). A sudden fall of rain/hail occurred after that virga moved overhead.

    1. Interesting weather, Roland! I heard there were a lot of strikes in western Washington.


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