Cold shock

A really strong trough scrapes Catalina today on its way to Texas.  Just ahead of the coldest air aloft, is a cold front sweeping southward toward Catalina this very minute.  Should arrive with a “pressure check”–barometer turns sharply upward–before 10 AM AST.  You’ll know it when you notice the wind has picked, then go outside to see what’s going on, and find that its blowing out of the north-northwest in gusts to 20-30 mph.   You will also notice that the temperature isn’t going anywhere, may top out in the upper 40s today even though its starting out in the low forties as we speak, figuratively speaking.

Also with this trough up there is a band of clouds (higher based Stratocumulus ones) producing  light precip down into central AZ now.  Cloud tops are running well below -15 C, and so you expect stuff to fall out the bottom in the form of virga because its cold enough for ice and snow to form in them.  Here’s the satellite “skinny” (from IPS MeteoStar) as we used to say so long ago:

For 5:45 AM AST this morning, Sunday, February 24th.
For 5:45 AM AST this morning, Sunday, February 24th.

 

You can follow the progress of this front here, too, by noting where the temperature is LOWER than where it was yesterday.  (Remember, as a CMJ, you always refer to temperatures as “higher” or “lower”; places you above the “pack”, though it is a bit snooty I suppose.)  ((But this is who we are, we don’t call sprinkles, “drizzle”, and we don’t call rain mixed with snow, “sleet”.)) ((( Face turning red just thinking about those common misperceptions.)))

24 h temperature change for 5 AM AST.
24 h temperature change for 5 AM AST.
Valid for 11 AM AST. That core overhead, usually the boundary between precip and no precip to the ground here in the great SW, suggests light snow on the Catalinas today.
Valid for 11 AM AST. That core overhead, usually the boundary between precip and no precip to the ground here in the great SW, suggests light snowshowers on the Catalinas today. (Our best model outputs for local situations, from the U of AZ (“hey”,  how about Wildcat basketball this year!) has no precip on the Catalinas today, just a close call to the N and E, so we’re going up against the BEST over a trace of snow :}

The weather ahead

After the dustup today, its cool for awhile, below normal for us, but then this happens at the beginning of March (based on the global data taken at 5 PM AST last evening).   I’ve added two arrows with question marks to see if you have been paying attention.

What do the arrows point to, that is, what are the technical terms for these bulges and dips in the 500 millibar pattern (answers below, not printed upside down because WordPress doesn’t know how to do that):

Valid for 5 PM AST, March 2nd, a Saturday.
Valid for 5 PM AST, March 2nd, a Saturday.

Answers to quiz: “Gi-normous ridge” (in the West) and “gi-normous” trough in the East.

This is the CLASSIC, often observed pattern of “warm in the West” and “cold in the East”, and as far as the “ensembles of spaghetti” go, you can HARDLY have more confidence that this will happen, even though its about a week away.   This is a very strong signal for both regioins  So it abnormally hot here in the early part of March.  People will be complaining back East about cold; count on it.

OK, now lets look at a WEAK signal in these plots, weak just about everywhere, meaning anything can happen. This is for the end of the calculation period where they deliberately input slight errors to see how much of a difference it makes in the model outcomes:

Valid for 5 PM AST, March 10. Not much help, suggestion of a weak, dry trough in this region.
Valid for 5 PM AST, March 10. Not much help, suggestion of a weak, dry trough in this region.  These plots mostly look like this “bowl of rubber bands”  15 days out.  That’s just the way it is, slight differences can make a huge difference in weather that far out.  Tipping points can be relatively small.

Finally, our present trough will be a huge weathermaker in the South. While it would be great to chase this trough as generates exciting weather, you also KNOW that there is going to be some significant damage from severe storms and tornadoes with it.

Ending this now (6:49 AM) with Stratocumulus clouds with virga visible W-N; not yet to Cat Mountains. Want to finish before I see too much; wouldn’t be fair to U of AZ model… hahaha, sort of.

The End.

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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.