Yesterday’s higher based Cumulonimbus clouds were hyper-electrified for some reason. Their bases were running about 11-12 kft above the ground over Catalina at 5 C (41 F). Here’s are two examples of the tiniest thunderstorms I have ever seen (and I seen a lot of ’em, having chased them in the southern Cal deserts in the late 1950s and early 1960s, and for a few days here in the summers of 1964 and 1965. (Egad, you’re thinking; me, too.)
Here are those “tiniest thunderstorms” in the first two shots.
At this point in mid-afternoon, even though the temperature was a baking 104-105 F here in Catalina, hot enough to send plumes of warm air into the ionosphere you would think, the cloud situation for rain was not looking so great upwind toward the northeast.
But those big rollers came, didn’t they!
What these little thunderstorms were telling us about the big boys that grumbled in from the NE eventually, and the ones that developed near us later, was that they were going to throw a lot of electricity at us.
They did not disappoint, though we only received 0.04 inches here in Catalina at this site.
The frequency of cloud to ground strikes was incredible, I think the most frequent I have seen. Here are some shots, in case you were inside watching TEEVEE and Olympics’ beach volley ball from London, which is somewhat understandable:
Some rainfall tables for you to peruse for yesterday:
Pima County Alert gages: http://188.8.131.52/temp/pptreport.txt
U of AZ rain network rainlog.org
“Cocorahs” for Pima County, another, but national rain collecting network
Why were our Cumulonimbus clouds so hyper-electrified?
The simple answer is, I don’t know.
We know that electrification is related to updraft speeds in clouds and separation of hail/graupel (soft hail) and smaller ice crystals like dendrites, which leads to separation and build up of charge centers in clouds because, after bumping into one another, they collect in differents areas of the clouds. They build up charge and spark to one another, and to the ground. I am really oversimplifying this, but that appears to be the main source of cloud electrification, and why stratiform (“flat”) raining clouds and clouds that produce rain without ice, do not spark.
There was nothing in the lapse rate from the TUS sounding yesterday afternoon to suggest higher updraft speeds would develop that I could see. Was it the extreme heat that drove this occurrence? Also, crystal type in the clouds may have something to do with it.
Idle speculation: It has seemed to this observer, that the warmest based Cumulonimbus clouds have not been highly electrified here, at least, not like the ones yesterday. Warmer bases lead to different collections of ice crystals in the clouds, such as huge concentrations of columnar types (rods) called needles and sheaths (hollow columns). At lower cloud base temperatures, these do not occur except at very great heights, and very low temperatures, not in the middle of the cloud as needles and sheaths might.
The weather ahead…
Today: I could not find a single model that had rain here in Catalina today. It’s supposed to dry out due to dry air invading from the east. You can see that here in this water vapor loop from the U of WA Huskies. That dark area in New Mexico and extending into the central Plains is how the imagery represents dry air as seen by a satellite. You can see that while we are moist air right now, i.e., dewpoints are high, we have mid-level Altocumulus castellanus around, distant Cumulonimbus clouds to the WSW as I write, this moisture over us will thin. Still, I have to think we’ll see something in the way of a Cb off somewhere, probably not here, though.
Tomorrow: About the same as today, the mods say. Darn.