Monsoon clouds towering over Tucson have been so spectacular in the past week that even an experienced, research-minded atmospheric scientist can be wowed.

“I just about drove off the road watching the clouds at sunset because they were so amazing” one day recently, said Mike Leuthold, a research meteorologist in the Department of Atmospheric Sciences at the University of Arizona.

Leuthold provided some fascinating facts about our monsoon sky show — noting, for example, that some of those clouds jut 11 vertical miles into the sky.

Behind the spectacle

“At this time of year, when the monsoon gets wetter, it’s much more humid and muggy and that’s when we get the spectacular clouds,” Leuthold said. “Those spectacular clouds can build up even in the morning because the air is so wet and unstable.”

Monsoon clouds are often “much deeper and much higher from base to top” than clouds at some other times of the year, Leuthold said. “They’re spectacular because there’s so much more cloud to see.”

Types of clouds

Several types of clouds play a role in monsoon skies, but cumulus and cumulonimbus clouds are the superstars.

“If you look over Mount Lemmon, cumulus clouds form first — formed by heating of the sun,” Leuthold said.

Those white cumulus clouds can evolve into towering cumulus clouds, with their bottoms gradually becoming dark gray.

“Then they can gradually change into cumulonimbus, which is a cloud that has precipitation coming out of it,” Leuthold said. “The transition from cumulus to towering cumulus to cumulonimbus can sometimes be quite rapid, within 30 minutes.”

High in the sky

“Shallow cumulus clouds can be 5,000 or 6,000 feet off the ground,” with towering cumulus rising still higher, Leuthold said. “Cumulonimbus typically are 50,000 feet high, but in very strong storms here they can get up to over 60,000 feet” — or more than 11 miles high.

“They dwarf the mountains.”

Matters of moisture

It’s not possible to get an exact measure of the moisture in a massive monsoon cloud — but it’s a lot.

When temperature and other factors cause clouds to unleash a thunderstorm, as much as 2 inches or more of rain can fall. That happened recently in the Dove Mountain area northwest of Tucson.

“That 2 inches could fall over a large area,” Leuthold said. “The amount of moisture is enormous. It could be millions of gallons.”

Sometimes massive clouds form, but heating and other factors aren’t sufficient to touch off precipitation.

“Big storms can essentially die when they move into a drier air mass,” Leuthold added. “Dry air can evaporate clouds away.”

Contact reporter Doug Kreutz at or at 573-4192. On Twitter: @DouglasKreutz