The trace

We had a trace yesterday in SH.  There was not ONE but TWO periods of rain, the first at 1236 to 1237, and the second from 1240 to 1240:30, both from the same cloud, but likely from different turrets protruding above the base.  The drops were very small, barely mm-size, with considerably horizontal separation between them.  Likely were from a few ice crystals that rimed up, became soft hail, then melted and evaporated on the way down to those tiny 1-mm sizes.

Here’s the key to recording trace events:   First of all, you have to “want it”; have to have the fire in your belly like I do,  that a day in which a small amount of rain falls is not getting by you as a zero rain day.  In effect, you have to have a linebacker’s mentality.  Be out there when it might happen, park your car outside overnight after cleaning the front and back windows before nightfall.   Dust on it is especially good.

Now for yesterday and what happened, presented in detail so that you can improve your trace measuring skill set:

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12:17 PM. Cumulus congestus lined up to pass over Sutherland Heights.  Have to be ready.
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12:29 PM. Its getting closer.  Looks great for targeting. Was thinking with a little luck, a little more heating I’ll get shafted. No sign of ice at this point. None around either, so hopes are pretty exceptional.
12:36 PM. Isolated drops falling, there's one over there, and I thought I felt one, arms extended. But cloud is slipping slightly to east of me! No shaft coming out!
12:36 PM. Isolated drops falling, there’s one over there, and I thought I felt one, arms extended. But cloud is slipping slightly to east of me! No shaft coming out!  But great looking cloud bottom.  Will go into that collection.

:

12:35 PM. Just before first drops felt.
12:40 PM. Another surge of little drops, can hear them on porch roof!  Bottom not looking as generous as a couple of minutes ago.
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12:44 PM. Its over, cloud moving away now, feeling exhausted. Maybe I’ll have a cigarette.  Not as much came out of the cloud as I had hoped for,  No shaft ever developed;  maybe a trace of ice visible overhead is all.  But, nice view of the Catalina Mountains!

 

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Now, for that smog bank that moved in during the afternoon….THAT was a horrible sight, and kind of ruined the late afternoon sky views.  The deep blue seen in the first shot was replaced by this whitish, hazy look, lots of “crepsucular” rays, in fact the whole sky got a bit “suckulent”, to misspell another word with purpose….  Take a look:

3:51 PM. Smog attack under way.
3:51 PM. Smog attack under way.

Likely will have the same stuff today. Origin? Well, seems to be coming out of the southwest and Mexico, but also may be old southern Cal smog.  Here’s the GOES aerosol optical depth (AOD) image for later yesterday afternoon, 3:15 PM.

GOES AOD for 3:15 PM. Be glad you're not in Bakersfield, CA! But note some smog over and to the SW of Tucson heading this way.
GOES AOD for 3:15 PM. Be glad you’re not in Bakersfield, CA! But note some smog over and to the SW of Tucson heading this way around low in central AZ.  Colored regions denote smog;  blue small amounts, orange and red, ugh, gimmee a handkerchief! Can’t measure AOD if too many clouds are present.

Today? Some smog, some pretty-but-dirty Cumulus clouds (ones with extra high droplet concentrations, likely darker bases than they really should have due to the “dirt” inside’em), and not much more. Maybe a Cumulonimbus off on the horizon somewhere.

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.