What goes up (to Alaska) must come down…to Catalina

Yesterday’s cloud of the day

7:16 AM.  Altocumulus castellanus virgae. Hope you got this right.
7:16 AM. Altocumulus castellanus virgae. Has light snow falling out of it in tiny filaments,  Aircraft measurements show that those filaments, snow fibers, that are falling out right below the base are only 10 to about 30 yards (meters) wide.  “Floccus” would be OK, too.  Notice that there are two turrets, one is older, has holes in it on the left, while the younger one on the right side looks more solid, firmer.  The younger one has not yet formed a strong virga trail, but will as it ages.  These are Cumulus to Cumulonimbus transitions in miniature and in slow motion.

 Today’s sunrise of the day

7:20 AM.  Altostratus.
7:20 AM. Altostratus.

 

 

 

 

 

 

 

 

 

 

 

 

About up and down…

That giant low pressure center, so needed by us droughty folks here in the SW,  has materialized in the western Pacific, shoving gigantic amounts of heat and clouds poleward (up) toward Alaskans.  We like to call them Eddy or Eddys; they keep the poles from getting too cold and the Equator too hot by shoving air around.   This low in the western Pacific has forced a big northward bulge in the jet stream up that way where it had previously been pretty much a west to east flow.   A region of higher pressure is created aloft when there are injections of warm air into the northern latitudes by storms1.

When air surges northward and builds a region of higher pressures in the jet stream like that, it buckles and turns southward on the downwind side of the high pressure (or ridge) almost immediately.   In this case, and lucky for us, the buckle is toward the south over the western US and ultimately down into Mexico, but not too far, we hope.

What goes “up” in latitude must go “down”, more or less.

Take a look at these maps for current conditions, ones from the Navy Research Lab, Monterrey:

Surface weather map with satellite imagery for 11 PM AST last night.
Surface weather map with satellite imagery for 11 PM AST last night.
500 millibar map for 11 PM AST.  Ridge pilling up in AK-Bering Sea, about to turn jet southward into the western US.
500 millibar map for 11 PM AST. Ridge pilling up in AK-Bering Sea, about to turn jet southward into the western US.

So, that inconsequential looking area of clouds and low pressure which appears to be jetting across British Columbia and Alberta in the first map, will suddenly begin enhancing and expanding southward, new low pressure centers will form in the Great Basin area.  It will get windy here for a time.  Very exciting.

I guess what I am trying to say, too,  is that old timey weather folk like this writer would look at a map like these above, even without the satellite imagery, and think, “Oh, my”, “Change gonna come“, as Sam Cook so sweetly sang so long ago, a drastic change for the area downstream of the giant low and its heat plume.

Things are out of balance at this “map moment”;  weather “Koyannisqatsy“, too much swirling low in the west part of the Pacific and strangely quiet downstream over the US at the SAME latitude as that giant low is reaching down toward out there far to the west of us.  “This will not stand”, as someone once said about an invasion of a Middle East country.  And the “quiet” in the West won’t  stand, either.  Balance in latitudes affected by storms is a key proviso of weather, a kind of conservation law2 we used to talk about a lot, and still do in undergraduate courses.

We could go back all the way to the Middle East to see the roots of the storm that blew up in the western Pacific. It was already a strong upper level wave that showed up in the Middle East as the snow situation there was beginning to take place.  As a strong upper level feature, it was the trigger for the stupendous low that formed when it exited the Asian continent, found heat and temperature contrast that are the building blocks for strong storms.

The clouds and storm ahead

Models have been wetting it up more and more here, sometimes the US model have no rain at all as the trough and its clouds passed too far to the SOUTH of us.  But lately, that US model has been increasing the amount rain here, not taking the low so far south.  The Canadian model has had rain here in every run for days, so its been more consistent on this pattern, not taking the low too far south.

Valid at 11 AM Friday, December 20th.  The colored regions are those in which the model has calculated precip over the prior 6 h.  Note heavy band over Catalina! (Dried up a lot on the next run at 11 PM AST, though.)
Valid at 11 AM Friday from IPS MeteoStar, December 20th. The colored regions are those in which the model has calculated precip over the prior 6 h. Note heavy band over Catalina! (Dried up a lot on the next run at 11 PM AST, though.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Due to the variable nature of the precip amounts seen by the mods, you have to figure there’s an awfully wide range of amounts that can occur here in Catalina from a tenth of an inch on the bottom, to as much as .75 inches if everything goes really well.  U of AZ mod will have more to say about this in the next 48 h.

Of course, as cloud mavens, we’re interested in the sky as well as the storms.  Lots of precursor high clouds today again like yesterday, and if the usual trend continues, those clouds will lower some as the day goes on from just Cirrus, Altostratus,  sometimes augmented by Altocumulus.  These kinds of clouds can lead to some fantastic sunrises and sunsets, so have camera ready.  You only have a couple of minutes to capture the peak of the “blooms.”

The End.

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1Remember, low density air (air filled with warmth and humidity), if deep, leads to a small change in pressure as you go up in the atmosphere, and so by the time you’re at 50,000 feet, you’re in a HIGHer pressure region than those regions where the air is not so warm.   How odd.  So surges of warm air and clouds from the Tropics build regions of high pressure aloft, and that’s what we’re seeing now.

2Conservation of absolute vorticity.