How Cirrus clouds grow up to be “uncinus” ones

What a glorious day yesterday was, if about 20 degrees F below normal!  So much new snow on the Catalinas down to such low elevations for almost mid-April.   Some sites in the Catalina Mountains reported over an inch of water content in that snow!  Yay!  Here in Catalina we had a bountiful 0.69 inches, more just to the north and west.  Choose April 9th, and “Tucson” in drop down menu on this U of AZCats rain page to see the amounts around here.  Truly a remarkable storm for April.

About those Cirrus “uncinus” clouds

How many saw those fabulous Cirrus clouds in the morning?  Once in awhile, during the passage of Cirrus clouds you get to see how those long, delicate strands you often see by themselves, get that way, from their initial appearance to the end point;  the long strands.  Usually you can’t because Cirrus clouds are traveling so rapidly up there at 30,000 feet or so that they have gone over the horizon before much happens.   Yesterday, an example of that “life cycle” passed overhead, moving from the W to the E at about 70-80 mph or so.   In all of the photos below, the subject Cirrus cloud is in the upper right part of the photo.

Here then is most of the life cycle of a Cirrus cloud as it happened over Catalina.  The starting point is that whitist cluster of little cloudlets, upper right.   Those strands of Cirrus below that and that appear in rows to the lower left, are old dying cirrus clouds at the end of their life cycle.   That top cluster in 1) has just appeared, probably only about 10 min old, and now the larger ice crystals are JUST beginning to leave the origin zone, much like a hiker reeling out rope to a friend stuck on a rock below.  Those strands are like that rope having been let go of, then caught by the wind on its way down and stretched to full length while falling through the air.   The remaining photos 3)-overhead view and 4)–leaving the scene, show that process continuing as the top cluster fades with longer and longer filaments of ice.  In 4), you can see one strand in a side view as it speeds away revealing the lack of wind shear (changes in wind direction and speed) in the layer in which the cloudlets first formed.  How do I and you know that?  That one tiny filament that is straight up and down pretty much reveals that

You can now see how and why these delicate strands are there.  Each long “rope” of ice represents one of the initial tufts that appeared within the cluster; each one has a contribution to make, a “rope” of ice to send downward.  Almost always, except in deep storms, the strand of ice encounters drier and drier air and the crystals fall at lower and lower speeds until its negligible.   The bottom, or lowest part of these strands then, have the tiniest of ice crystals, and the tail of the strand at this lowest point may appear almost horizontal if you could be up there.

The end.

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