Tropical fetches

Flash: Very light rain (R–) falling at 5:30 AM!  Amazing…  Won’t measure though, as thickest clouds are already sliding away.  But still, great to see, to smell the scent of rain in the desert, and feel the drops in this little surprise sprinkle!

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Forgetting about that last big bust, namely the last big trough of the season that let us down by producing no measurable rain, let us now consider tropical finches, or rather, FETCHES, since an example is coming soon, one that might well bring rain.  (I know what you’re thinking; you’ve heard that before, wrongly, I might add as in the LBT-LBB).   Hope springs eternal I guess, though rain is predicted by both the USA and Canadian models, so there is some mathematical backing to this hope.  See below, as rendered by IPS MeteoStar:

Green pixelation approaches Tucson-Catalina urban complex.
Green pixelation approaches Tucson-Catalina urban complex on Friday, May 29th at 5 PM,

 

Valid for 5 PM AST May 29th.
Valid for 5 PM AST May 29th.

Yesterday’s clouds

You can see them all at once from the great U of AZ Weather Department time lapse video for yesterday here in case still shots with captions aren’t enough action for you.

5:59 AM.  Virga falls from Altocumulus opacus.  This can also be seen as like a little slice of the tops of many rainy days when cloud tops aren't below about -30 C or so. As here, those tops are usually still comprised of mostly liquid droplet clouds in which ice crystals form, grow, and fallout.  If the air is not rising to replenish the doplet clouds, then you will be left with a patch of ice and virga, a patch that will eventually die.
5:59 AM. Virga falls from Altocumulus opacus. This can also be seen as like a little slice of the tops of many rainy days when cloud tops aren’t below about -30 C or so. As here, those tops are usually still comprised of mostly liquid droplet clouds in which ice crystals form, grow, and fallout. If the air is not rising to replenish the doplet clouds, then you will be left with a patch of ice and virga, a patch that will eventually die.  Estimated top temperatures, -12 to -15 C, a little colder than shown on the TUS sounding for yesterday near this time because we are farther into the cold air aloft than TUS is.  Also, it would be unlikely that clouds like these would produce ice at the indicated TUS balloon sounding top of Altocumulus at -11 C.   With their geerally small droplets, it needs to be colder than that.  Egad!   This is way too much info!  But what kind of ice crystals would you expect in a water-saturated enviroment at around -13 to -15 C?  Yes, that’s right, pretty Christmas tree stellar crystals, maybe some aggregates of dendrites.  Remember, too, for aggregattes to form that concentrations of the crystals must be more than about 1 per liter.  Too, since they are falling through a droplet cloud with droplets  larger than 10 microns in diameter, you would expect those stellar crystals and aggregates of dendrites to exhibit some riming, that is, have impacted some of the cloud drops as they grew and fell through the cloud, though keeping in mind that the crystals must attain a diameter of about 200-300 microns in diameter before riming commences, helped by the fact that stellar crystals (planar ones) fall face down like a clown does when he’s trying to make people laugh and trips over something.  Also, I think someone in that big house on the right is about to have a baby.
9:40 AM.  With all the cool air over us, it wasn't long before Cumulonimbus clouds began boiling upward, giving someone some rain.
9:40 AM. With all the cool air over us, it wasn’t long before Cumulonimbus clouds began boiling upward, giving someone some rain.
9:53 AM.  While Cu boiled up quickly on the Catalina Moutains, and iced-out a plenty, they never really got the depth required to produce much more than sprinkles and virga.  Can you spot the little bit of ice on the right side of this Cumulus mediocris?
9:53 AM. While Cu boiled up quickly on the Catalina Moutains, and iced-out a plenty, they never really got the depth required to produce much more than sprinkles and virga. Can you spot the little bit of ice on the right side of this Cumulus mediocris?
10:30 AM.  Nice example of the tremendous amount of ice being produced by such modest clouds (see right side here--nothin' but ice).
10:30 AM. Nice example of the tremendous amount of ice being produced by such modest clouds (see right side here–nothin’ but ice).
1:01 PM.  By early afternoon it was all over, the clouds too shallow, the tops too warm to produce ice even though they were still well below freezing.  Just the way it is.  Guess warmer than -10 C (14 F) at cloud top when you see a sky like this with no ice.
1:01 PM. By early afternoon it was all over, the clouds too shallow, the tops too warm to produce ice even though they were still well below freezing. Just the way it is. Guess warmer than -10 C (14 F) at cloud top when you see a sky like this with no ice.
6:47 PM.  Sunset so-so as high clouds to the NW blocked the sun so it didn't under light these clouds.  Here, Cu flatten as the heat of the day, such as it was at 85 F,  cold for late May, dies away,
6:47 PM. Sunset so-so as high clouds to the NW blocked the sun so it didn’t under light these clouds. Here, Cu flatten as the heat of the day, such as it was at 85 F, cold for late May, dies away,

The End.