Yesterday was as rare a day in Catalina, Arizona as seeing the marbled murrelet in Olympia, Washington.1
Our bit of rain (0.12 inches in Sutherland Heights) was only due to that formed by the collision-coalesence process, some times called the “warm rain” process, or more technically, non-brightband rain2.
No ice needed.
Usually clouds at inland locations like Arizona have so many droplets in them , a few hundred thousand per liter or more, larger drops that can collide and coalesce don’t form because the condensed water is spread over so many of them.
So I could feel the excitement out there as that frontal band got closer. Perhaps you saw the drizzle-mist rainbow on the Tortalitas, looked at cloud tops, and saw no ice. If you said you saw some ice yesterday you were mistaken or lying to impress your friends.
Let us review yesterday in clouds:
Skipping a LOT of pretty scenes now…..
Valid for 10 AM, yesterday. Output was from the 11 PM AST model run, a diagram with a lot of writing on it.
The rest of the day was overcast, cool with a period of light rain around 2 PM, with the temperature dropping to a remarkable 58° F here in Catalina.
The last TUS sounding seemed to confirm this unusual rain day, indicating that the stratiform tops near and over the site were at 0° C.
Our final rain total in Sutherland Heights was a respectable 0.12 inches from a rarely observed event. 0.47 inches fell on Ms. Lemmon for the highest amount around.
Might add more later, but am quitting now to go “lunge” and ride a horse..
PS: I have added more, re-written some not so great “formulations”…
1If upon reading that sentence you would like bail on reading about clouds and rain here in Arizona and read about that bird, please consult:
2When steady rain is occurring, returns have a bright band, or a augmented return from the layer in the atmosphere where snow is melting into rain. On days like yesterday, throughout the Tropics, along the West Coast, among many places, non-brightband rain is fairly common. Typically it falls from clouds with tops warmer than -5° C. Ice usually onsets at temperatures between -5° and -10° C in such clouds. Hawaii is a good example where “warm rain” produces most of the prodigious rain totals there on the windward slopes, such as that at Mt Waialeale on the Island of Kuwai where the average rainfall is more than 450 inches!
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