Similar maps…

When some of you were weather browsing this morning, and you saw this forecast map from IPS MeteoStar, valid for next Tuesday, which shows a very late in the season tropical storm off Baja heading toward the Southwest US, while a vigorous winter storm bashes the West Coast, I had a feeling that it reminded you immediately of one of your early weather memories of a similar situation.  First, the IPS map.

Valid at 11 AM AST, Tuesday, November 24th.  This from last evening’s 5 PM AST global data. The green and blue areas are regions where the model thinks it has rained during the prior 6 hours.

The map below is from an era when you were a little child and maybe you, too,  were clipping weather maps  out of the Los Angeles Daily News, if that’s where you lived:

Sandwiched between storms 002
Actual map from the Los Angeles Daily News, November 30, 1951, clipped by the present writer.   Note that with isobars the Daily News was not afraid of challenging its readers with a non-Mickey Mouse weather map.  The tropical storm on this map is down there to the lower right where the scale of miles is.  Like this winter season, 1951-52 was a Niño year, though not of the great magnitude of this one.


Looking back,  but a little closer,  like yesterday and the day before…..

Nice storm we just had.    0.65 inches fell in Sutherland Heights.  Would not have predicted that much over these past couple of days to be honest.  Total for month now 1.10 inches or a little above the 38 year average of 0.97 inches.

After a long dry spell though at least the next week,  November will close out on a dry or wet note, which is pretty encouraging.

Yesterday’s clouds, ice and sun: a soliloquy on ice

 Fair amount of ice yesterday in our low clouds.  As you would guess on your way to becoming a cloud maven, bases AND tops were especially cold for AZ.  Afternoon cloud bases were running about -8° to -9° C, whilst tops were about -15° C.  Still ice was not plentiful.   How’s come?  Well, it seems the amount of ice in clouds is dependent on both the cloud top temperature and the droplet sizes in the coldest parts of the clouds (see Rangno and Hobbs 1994, Quarterly Journal of the Royal1 Meteorological Society)  (Hell, no one’s going to read this, though it is now available without having to go through a “pay wall” and the page linked to above has been updated  with new pdfs!)

In sum, a cloud with a base of -10° C and a top of -20° C will have LESS ice than a cloud with a base of 0° C with the same cloud top temperature (-20° C) because with a warmer base, the drops near the top of the cloud in second example will be larger.

That seems to be the way it works.  So, yesterday’s thin cloud with cold bases had smallish drops, and ice production was a little limited.

Also, if you monitored Ms Lemmon, and the Catalinas in general, you probably were thinking, “Where’s the ice?”, in those cold Stratocumulus clouds as they piled up against them.

Well, when you have strong winds at cloud level as we did yesterday, and with ice crystals taking a little time to appear from some of the droplets that freeze in the cloud stream, grow, and eventually fall out, you’re not going to see much evidence of ice on the windward side of the mountains in these kinds of situations.  The ice is going to appear and fallout as snow or virga downwind a good distance downwind, and that’s what was happening yesterday to nearly all of those deeper clouds (with slightly colder tops and larger cloud droplets in them) that formed over the Catalinas.

If you don’t believe me, yesterday’s time lapse movie from the our great weather resource, the University of Arizona, shows this.  You’ll see a lot of precip and virga falling of those clouds as they stream eastward from the Catalinas.  So, we didn’t get to SEE much ice from those Stratocu clouds but it was there.

Lastly, the sun, as it appeared yesterday at sunset in the dust-haze kicked up by that powerful low that brought us our rains.  The jet stream, as was pointed out by a friend, was about 200 mph overhead of TUS at 40 kfeet.  Wow.

5:21 PM.  The sun.  Stratocumulus sans virga at top.  Droplets too small, temperature too high at cloud top apparently.
5:21 PM. The sun. Stratocumulus sans virga at top. Droplets too small, temperature too high at cloud top apparently.  Sun seems to be free of blemishes, too.  Are we still in a sunspot minimum,  thought to drive cooler climates, one that might rival the Maunder Minimum?  I don’t know.  I am a weatherman, not an astrologist.


The End.


1″Royal”–that is so funny; “hey”, guys,  wake up, its the 21st century!

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.

1 comment

  1. Art: You reminded me a lot of my youth when I used to cut out the weather maps from our local paper (The Vancouver Sun). I still have a lot of those maps in a bag (looking rather dusty, I admit). Anyway, lots of rain up here this month! This is already my wettest month of the year.

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