Category Archives: Dust devils

An extraordinary June 16th

Not only did Tucson set a daily record for rain on June 16th with 0.29 inches, breaking the old record of 0.20 inches that fell in 1918 (!), but here in Catalina, the 0.11 inches was the first measurable rain on June 16th in the 35-year combined record maintained at Our Garden, and then here for the past few years.

It was only the second day with measurable rain in Catalina since mid-April, and that prior rain was only a paltry 0.01 inches that fell in mid-May.

Regional rainfall totals for yesterday’s magnificent day can be found here, courtesy of the Pima County Flood Control District.  Two sites in the Catalina Mountains got hit hard, with 0.94 inches at Pig Spring, and a whopping 1.54 inches at CDO at Coronado Camp.  Those two gages are close to one another near the top of the CDO watershed.  Here is a map having those locations.  You can also get 24 h rain totals, ending at 7 AM today, from the U of A network here.

The best part, though, may have been those desert aromas that spring out of the desert when it rains,  and that cool air that rushed around Catalina yesterday afternoon and evening.  Makes you happy to be alive.  However, those two close lightning strikes were somewhat unsettling when you’re running around outside with a camera..

The drop in temperature as the rain hit was stupefying, about 35 degrees, from 100 F to 65 F!

Here are some photos, since I am still alive, the first ones of the Altocumulus perlucidus clouds that were mutating into Cirrus uncinus, a bit of an oddity.  The TUS sounding indicates that these droplet Altocumulus clouds were extremely cold, -30 C (-22 F).  And their presence was another live demonstration about how odd ice formation is in the atmosphere, still not completely understood.

By late morning the Cumulus were sprouting over the Catalinas, and the Altocumulus/Cirrus were gone. Those Cumulus clouds were a great sight since the models had very little rain indicated, and these were fattening up nicely suggesting those models might not have gotten “the scene” for yesterday right; there was more hope for rain after all.

Ice clouds on the left, droplet clouds on the right side.
Parhelia (sun dog) in the fallstreak of a former Altocumulus flake.
1:16 PM: Cumulus mediocris, center right, portends a good shower day.
2:11 PM. We are underway!
2:32 PM: Heavy rain falls on the upper CDO wash watershed.
3:01 PM: A strong shower complex appeared to the S toward TUS, giving hope of some rain here.
3:02 PM: Two very strong dust devils developed ahead of the outflow winds coming into Marana. They seemed odd since they were under the cloud cover and you start looking up to the base to see it there is a tube up there, and whether it is one of the dry tornado funnel cases.
3:09 PM. The thunderstorms over the Catalinas propagated to the west and here Saddlebrooke gets a dump.
7:33 PM: After our nice little rain, and as happens so often here in the summer rain season, we polish the day off with a spectacular sunset.
























The weather ahead

The next chance for rain, the best one I could find, of course, is next Friday and Saturday afternoons. For Friday afternoon, this, from the U of WA’s model.  The lightly colored, filled in areas represent rain.

Looking for just Cumulus today, maybe a very isolated Cumulonimbus cloud.

Dr. Dust Devil, Peter C. Sinclair

With no weather in view for the next week or so, and with June being “dust devil” month in Arizona, it seemed appropriate to reference the work of Dr. Peter C. Sinclair, University of Arizona, Institute of Atmospheric Physics, 1960s.   Read all of his journal articles because I liked dust devils myself….  Don’t we all like to see them, are fascinated by them, when we don’t have a jumping castle about to be tipped over by one?

I know a lot of you out there, too, are fascinated by dust devils and even while driving, take snapshots of dust devils you’re particularly fond of.   The photo below is from a friend who’s particularly fond of dust devils, as an example.

Here’s one of Dr. Sinclair‘s pioneering efforts from 1964.   Also, from a Google image collection, these.  Some are fantastic!

Dr. Sinclair put stuff on his car, the kind of stuff shown in this article above, and drive into dust devils, getting measurements of the temperature, pressure and winds inside them.  He was the first person to do that, to get measurements inside them,  and so was making a real contribution.  He was kind of a hero of mine since I, too, had a fascination with dust devils, though of a more visceral nature; I just jumped into them sans instrumentation when they crossed our San Fernando Valley school yard.  Its a gritty experience.   Hair gets messed up, too, but who cared about girls then?

Here’s a post-dust devil kid shot, entitled, “little Artie’s hair” for some reason.  (I hope it was a post dust-devil shot! I always laugh when I see this photo and hope you do, too.)


Note that in the article referenced above, Dr. Sinclair, shown standing next to his equipment, has hair that is perfectly in place.  I don’t think he jumped into them, to really KNOW them, like I did…

Plenty of sun all day, high sun angle, with resulting surface temperatures that could melt lead leads to tremendous instability at the ground and “superadiabatic” lapse rates here in Arizona.  In these situations, the air right at ground level, within inches, might be 120 F, and the air just above, “only” 100 F.

The atmosphere gets rid of that excess heat at the ground via thermals, bubbles of warm air that lift off and is replaced by cooler air overhead.  Our afternoon winds, ones that come up suddenly, then die out, and repeat that sequence over and over again, are evidence of those thermals.  Leads to a very bumpy temperature trace since its warmer, then cooler, warmer, then cooler, etc.

Sometimes, when the bubble lifts off, perhaps suddenly, air swirls in to take its place, and by conserving its angular momentum, develops a tube as the air spins more rapidly as it approaches the the central lift off point.  A more recent explanation is that small volumes of air already have rotation and become tilted upward over hot surfaces, as shown here.

Below, one taken by the arthur on a U of WA research flight over eastern Washington where dust devils are particularly numerous as well.  You might think about spending some time in the desert there, since you could get into quite a dust devil, but it wouldn’t be as hot.  Still have to have those superadiabatic lapse rates at the ground, however.

The weather ahead…

Man, the models of late have come up with an exceptional trough in the West.  While no rain is expected here, it is quite extraordinary, and is pretty much supported by the ensemble plots (aka, spaghetti plots).  Here is the upper air anomaly plot showing how extraordinary this forecast for the heights of the 500 millibar surface are for June 17th, ten days from now.  This would mean exceptionally cool air over southern California and Nevada, and some cooling here, though not so much is indicated for us at this time since the low stays west of us.  Inside the strongest winds around this low at this level would be the areas having precip, or in Nevada and central California only.

At this time of year, we need a tropical fetch for us to get rain, and that isn’t forecast right now.  But the models are having a hard time with this situation, and it may be that some tropical air can be caught up on the faouter boundary of this low if it moves off to the west.  Such moist air is already foretold to invade over New Mexico and west Texas, lucky guys.


The End.