More strato; less Cu (again)

Day started out as expected, but instead of Cu fluffing up into congestus and Cumulonimbus clouds yesterday as expected, a higher layer of Altocumulus (with ice plumes) filled in the sky indicative of “slab lifting” due to our incoming trough, and with the strengthening winds mixing things all up, the Cu went flat on us. So about three days in a row, the kind of clouds expected didn’t happen. First time this has happened since four days ago.

But, we did have Cumulonimbi in the area, those deeper clouds indicative of the cooling aloft that had occurred during the day, if you noticed the OCNL LTG to the NW-N after dark. Thought, too, for a moment around 8 PM a cell was erupting overhead as sparse large drops fell, always the melted remnant of graupel (soft hail) aloft indicating a Cumulus turret up there, but it didn’t mature into a full blown Cumulonimbus. So, only a trace of rain from all those many sprinkles yesterday afternoon beginning just after 2 PM through about 9 PM. Darn.

—————distraction—————-

BTW, I must direct your attention to a great new weather site by local U of AZ forecasting expert, Mike. It has gorgeous graphics and will be a real contribution for weather-centric folk.

Mike joins “Bob” in doing some great, professional-style weather discussions for TUS and vicinity, not at all like the ones found here.

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Yesterday’s clouds

11:43 AM. From Romero Ruins Trail. Small Cu begin to form to our SW-W.

1:20 PM. Cu continue to grow and expand in coverage as wind picks up and small cloudlets of Altocumulus shedding ice roll over on top. Getting pretty cloudy at this point. No congestus anywhere.

1:36 PM. Lots of ice dropping out of those Cu now merging with a higher layer of Sc. But no sign of anything deep.

2:20 PM. Really looking kind of bleak as the overcast thickened with no sign of a strong shaft (which would indicate a buildup), just “gentle” virga and light rain showers reaching the ground.

3:14 PM. Shafts of virga and rain reaching the ground are more evident, but suggest “mounding tops” not ones jutting up much.

6:50 PM. Strong TSTMs had erupted by this time to our NW toward PHX and vicinity. Here the darkness on the horizon is a dust plume, not a rain shaft, a plume generated by heavy precip to our NW. It wasn’t long that some LTG was observed NW-N of us.

6:50 PM. Close up of a weak ‘boob-like feature driven by strong outflow winds. Spread out and flattened racing toward Avra Valley.

6:51 PM/ Dust cloud riding a wind shift to the N approaches Catalina. The temperature here dropped about 10 °F in half an hour about this time when the wind turned to the N. So much promise, so little production.

Should see some nice Cu today, though, as our upper puddle of cold air slips away from us. Early birds may have noticed some lingering Cumulonimbus tops to the NW-N at dawn. Probably won’t see any more of those except off in the distance to the N during the day.

The weather way ahead

Notice that the red lines are in Baja and this strongly suggests troughing (cooler than normal air aloft) in our region. Looks pretty Niño-ish. So, it would appear that we’ll continue to have an occasional blast of cooler days, rather than just a long series of clear, warm days.

Still looking for significant rain next week, between the 6th and 8th, but our best model from last evening’s (00Z, 5 PM AST) global data thinks that rain in AZ will mainly be to our north with little if anything here. However, I have rejected that analysis and am clinging to the thought that at least 0.25 inches will occur in Catalina next week during the aforementioned window. I recommend that you be kind of clingy, too.

Valid May 15th at 5 PM AST. Those who are able to look into spaghetti and read the strands know that this map promises a pretty nice spell of weather, temperatures often below normal, through at LEAST the middle of May. No — Valid May 15th at 5 PM AST. Those who are able to look into spaghetti and read the strands know that this map promises a pretty nice spell of weather, temperatures often below normal, through at LEAST the middle of May.

The End

By Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.

View all of Art Rangno's posts.

1 comment

Hi Art: not a lot of clouds of any kind here. We’re starting off may with another heat wave-could see the high 80’s on Monday. just wanted to correct something I said earlier to you; Looking at that picture of the high clouds with virga that I sent you last week (with the 2 other pictures) I can now see it is indeed altocumulus rather than cirrus. The ice crystals kind of masked the typical formation of Ac for me. RD

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