All’s well that ends well

What a nice day yesterday was, ending with this fabulous, but run-of-the mill sunsets we get to see here in the Catalina area on a regular basis.  Yesterday was interesting because we had two graupel (soft hail) showers, the first about noon, and the second with a blast of thunder (1) at 1605 PM.   If you weren’t lucky enough to get any, measure it and report it to the National Bureau of Standards, or the NWS, here’s what it looked like on our old chaise lounge a  couple of minutes after it fell (see below).  Some of it was “conical graupel”, pointed on one side, though that is not visible here.  Graupel, soft hail form when there aren’t many ice crystals in the cloud and the cloud is chock full of droplets at below freezing temperatures.  Those droplets freeze instantly onto the ice crystal as it makes it way down to the ground, eventually losing all of its identity as it become a little snowball.  Usually, where this happens in the cloud is in a very limited region, and, it usually doesn’t last for a long time.  So, consider yourself especially “lucky” to see graupel/soft hail, hail.  I do.  If you want to relive yesterday’s clouds, as seen from the U of A, go here.   “Above Catalina” is at the left, beyond Pusch Ridge.

What’s exciting now is that something akin to an atmospheric iceberg is barreling down on us (SE AZ) from the north.  This “cold low” center, representing a column of extraordinarily cold air in this case, goes from the ground all the way up through the “troposphere.”  IN this case, the troposphere is squashed down to less than 20,000 feet over Wy0ming right now. The stratosphere is above that, and above “cold lows”,  the stratosphere dips down over them.  Usually its twice that height at our latitude.

Here’s what I am talking about, shown in this morning’s 500 millibar pressure map (about 18,000 feet above the ground) or usually half way up through the troposphere (map courtesy San Francisco State U.)  The winds flow along the green lines, ones that bend gently toward the west over the Great Basin.  That bend in the wind represents an area where a small low center amid this giant river of wind will form in the next 24 h and that little center of circulation should pass right over us!

Now, not a single model output that I saw from last night’s runs had enough moisture in this forming upper center to have snow even fall on Mt. Sara Lemmon (e.g., the U of AZ regional model from last night).

A few days ago, the Canadian model was suggesting a signficant storm here from this center. I really believe it.   Well, that’s “bye-bye” since the center is not well to the west of us as that Enviro Can model indicated it would be, but rather will end up right over us (which means much drier).    The U of WA model run from this morning’s data says that a little “L” will be right over my house on Thursday morning (see reddish map below) !  Man, it will be cold over me!    Might lose some plants in this one before its over.

However, I am going to stick my neck out and expect (hope) there will be just enough moisture for flurries around here (Catalina area) anyway tomorrow into tomorrow evening.

BTW, the U of A has just issued a special weather discussion here.  You’ll want to check this out!











































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.