Seattle nostalgia part
Got a little homesick yesterday with the weather the way it was here in Catalina. Well, after 32 years in Seattle it seemed like home. The dank, gray, low-hanging, lifeless, overcast skies of Stratus and Stratocumulus clouds hour after hour (spoken with emphasis on each descriptor using a whiney kind of emotional voice) reminded me of all the great times in Seattle, the friends, the occasional unsatisfactory girl friend (hahaha), the sports glory days in the Western International League semi-pro baseball league (well, there was one day in particular), the days as a Mariner batting practice pitcher in the equally dank Kingdome, an edifice that mimicked the skies outside, the 25 years or so of bike trips to and from the University of Washington under those same kinds of dank, gray, lifeless skies, and piddling rain we saw here yesterday.
And with people here driving around in the middle of the afternoon with their car lights on, it was the perfect replica of a Seattle winter day. Even the temperature cooperated here to mimic Seattle; it only changed a couple of degrees from dawn to the mid-afternoon high of 47 F, some 20 degrees or so below normal. Sometimes in Seattle, the temperature is the same all day because the sun is so weak and the layers of clouds, piled one upon the other, seemingly impenetrable to light and heat.
The Seattle mimicry was completed with some light rain in the morning here, raining just like it does in Seattle, barely accumulating hour after hour but there to annoy you. We only had 0.02 inches after 7 AM LST, but it stayed wet all day here just like back at my old Seattle home. The grass in the backyard there might be dry sometime in April, otherwise your shoes and your dogs come in wet everytime.
Yep, that’s what Seattle is like. I loved it there…. Hmmmm.
Well, what I really loved was being at the University of Washington during the glory days of the Atmospheric Sciences Department when all the “big guns” in meteorology were there it seemed; Holton, Hobbs, Wallace, Reed, Charlson, Fleagle, Bussinger, Leovy, Houze, and the job of flying around in clouds in the “CARG” aircraft, etc. Their kind will not be seen, clustered together like that, anyway, again. As a kid I tried to get autographs of the big stars in meteorology like Jacob Bjerknes at UCLA so that’s why being at the U of WA was so exciting. They were to me like major league ball players were to other kids, though I did like Ted Williams and the Bosox in those halcyon days. Egad, enough!
A review of yesterday’s clouds below. The first photo toward the Tortolita Mountains (obscured) and a near perfect example of Stratus, followed by two shots of Stratocumulus. 
Weather and clouds part
Yesterday was interesting in several ways. First the rain fell from clouds topping out at a modest -10 C, something we don’t see much of in Arizona.
Second, it was so dark during the day even as the clouds became shallower as the day wore on. Below are the two soundings from TUS for yesterday from the U of AZ, the first at 5 AM and the second 12 h later at 5 PM LST. Where the green and white lines come together mark where the clouds were. From that description you can see that they were topping out around 700 mb, or around 10,000 feet above sea level in the morning, and maybe 9,000 feet by evening at about -6 C. No echoes were being observed by the afternoon.
But why?
Well, the cloud savant will know that there must have been a lack of ice crystals in those supercooled clouds in the afternoon (ones whose tops, at least, were below freezing.) But why no ice? Almost certainly it was because the cloud drops in those clouds were smallish, less than 25 microns in size, there were no “ice nuclei” active at those higher temperatures (a normal situation). The lack of drizzle (fine misty rain that appears to float in the air) is evidence that the drops in those clouds did not reach sizes larger than 30 microns in diameter. Drizzle drops (those between about 100 and 500 microns in diameter, have often been associated with the onset of ice in clouds at temperatures of -4 to -10 C over the years. But not always.
BTW, the formation of drizzle helps eradicate clouds by draining them of their liquid water, causing clearings. So the absence of drizzle due to smaller drops helped “seal the deal” on a long day of overcast. Also surprising to me was the amount of underlying haze yesterday, again evident in very strong crepuscular rays late in the afternoon. See below, along with the rare example of liquid cloud mammatus formations. That haze suggested to me that the drop concentrations in yesterday’s clouds were also pretty high, and helped keep the sizes of the droplets down by spreading the “condensate” on more particles. And guess what, those likely more numerous and smaller cloud drops helped make those clouds darker than clean clouds. More sunlight is scattered back into space by dirty clouds than by clean clouds, so the bottoms of dirty clouds are darker even given the same thickness as clean clouds. (This is a HUGE issue in global climate models, drizzling and not drizzling clouds because it effects the cloud cover, and the more cloud cover you have, the more CO2 warming is offset.)
So several factors likely went into making yesterday “so Seattle”; lack of precip later in the day, small cloud drop sizes, likely due to high droplet concentrations in those clouds, at least later in the day. Lets hope it doesn’t happen again. The End
Addendum on cloud seeding potential for yesterday
Yesterday was the perfect day for seeing what you can do by seeding clouds with dry ice–dry ice is more effective on days with marginally supercooled clouds. Would there have been some rain on the ground? You betcha with those low bases. However, it is virtually certain that any rain would have been but a trace, or barely measurable. The main thing that would have happened is that clearings would have ensued in the seeding zones, seeded by the way, by aircraft dropping dry ice into those tops. So, a little precip, and some clearings, and those clearing would have likely triggered a widespread natural clearing if you could get enough holes produced by your aircraft. The last photo shows would you can do when you glaciate a relatively thin layer cloud. Were yesterday’s clouds thin enough for holes? I think so.
