6:43 PM. Trailing raindrops. The lack of visible ice at cloud top indicates low updrafts, and marginal ice formation, tops just barely reaching the temperature level where ice forms. That level tends to change some each day due to different aerosol and droplet concentrations, but is generally near the -10 C to -12 C level in Arizona. In oceanic regions, where clouds have larger drops and form drizzle and rain before reaching the freezing level, ice first forms in clouds closer to the -5 C level.2:09 PM. No ice or virga present.
“So what gives Mr. Weatherblogperson? Most clouds had no ice and a very, very few did, ones that had some rain fall out of them. Below I have handcrafted a diagram with too many arrows and text on it, just for you, my friend, to help explain the mystery of yesterday’s clouds. I think, or rather hope, the excess text and arrowing will be self-explanatory…..
The balloon sounding data from Tucson yesterday afternoon at 5 PM AST (launched around 3:30 PM, actually).
Overhsooting tops? Here’s the biggest one of the day yesterday. Most however, because they are colder than the environment, collapse quickly and as is often the case in days like yesterday, there is NO overshooting top by the time the ice and rain start to fall out the bottom of the cloud. But, you can bet before that happened there was one.
3:21 PM. Looking SSW toward Tucson at light rainshower with an overshooting top above most tops. Need a fatter arrow. That top is above and beyond the slope down part of Pusch Ridge.7:01 PM. The large patch in the distance would be Stratocumulus formed by the spreading out of Cumulus cloiuds.
Forgot the nice sunrise and another faint rainbow, two mornings in a row! In case you missed them, again, here they are:
6:01 AM.5:54 AM. Ac opacus.
While yesterday’s Cumulonimbus clouds were sparse, their “overshooting” tops told you that they had pretty violent updrafts in them, ones that carried the top of the cloud past the tropopause (the boundary where the decline in temperature as you go higher stops). Above the tropopause sits the stratosphere, normally cloud-free and extremely dry.
These “overshooting” tops are due to inertia generated by the strongest updrafts in the cloud below them, they end up being much COLDER than the surrounding air in the stratosphere because the air is still expanding and cooling as the cloud punches through the tropopause. Like stones in water, they plummet back down quickly as they drift away from the root updraft. The worst volcanoes, like El Chicón in the early 1980s and, of course, Pinatubo in 1991, do this, too, and to a lesser degree these overshooting tops also inject aerosols and moisture into the stratosphere. These tops are usually easily recognized as a bulb-looking, whiter top above the flat anvil, the anvil representing cloud top ice that has been stopped by the tropopause barrier and has spread out.
Some examples:
1:10 PM. Violent looking Cb with an overshooting top, one that punches through a flatter anvil cloud. There were many of these yesterday, regrettably so far away you couldn’t even see the rain shaft! Boohoo. Here, looking SSW from Catalina, range about 50 miles or so.2:51 PM. I thought this cluster looked especially “volcanic” with how tight the Cumulus tops were in the foreground. When the updrafts are strong from the base on up, you have a lot of aerosol particles taking part in the condensation melee, cloud droplet concentrations are extremely high, the clouds are extremely dense inside, might not be able to see the wingtip of your aircraft. For this reason they look like granite on the outside (center). When ice forms, such as in the higher tops, the concentrations are less and the cloud “softens” in appearance (highest top, left of center), one that appears to have punched through a flatter anvil cloud.2:56 PM. Many Rim Cbs also had overshooting tops. In our worst storms, with frequent cloud-to-ground lightning and blinding rain, you can pretty well be sure that you’re under one, or close to it.1:38 PM. Mt. Lemmon did join the Cumulonimbus producing fray in the distant mountains around us, but they were about a magnitude smaller than the ones in the distance, and, as you saw, the several that formed could not leave the high terrain.
Seems we have a day similar to yesterday ahead for today, but the models suggest an uptick in activity tomorrow. When the thunderheads are more isolated, they are more photogenic I would have to say, especially against the backdrop of the darker blue skies we have now. And with no haze around, something that often can accompany higher humidities such as we have had over the past week or two, our cloudscapes are especially pretty I think.
The End.
About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
