The weather ahead – Page 34

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!

Snowball Earth? Well, maybe a Snowball Tucson on the doorstep!

The computer models are diverging significantly on the “tail of the scorpion” on this incoming front and the two troughs that pass over us in the next few days. First, a Pacific front blows through on Monday with its upper air accompaniment racing to the northeast. But then this monumentally strong wave disturbance barges in from Canada over the Rockies and actually deploys toward the SSW while intensifying and curling into an upper center, this center trailed by a gigantic mass of cold air that oozes over most of the US. High pressure levels in the cold air, 1060-1065 millibars initially, may set some records here and there in the northern Rockies.

The “best/worst” full display of this predicted sequence is here from our friends at Environment Canada, and the output from last night, of which one panel is shown below.

This panel at left, from that Canadian model run, is the most exciting panel of future weather I have seen this winter!

Now, if you’re a bit jingoistic about models and want to know about our US model results for this situation, I have to tell you, sadly, that they do not have this “good” a configuration over the SW as far as precip goes.

There is no upper vortex, Virginia, over western AZ in the US models, as in shown in the upper left panel here.

And that makes all the difference in whether AZ will get much precip out of this second of a two part event. In the US models, such an upper low does not form over AZ but rather just a bitterly cold slug of air, mainly dry, intrudes on us and that second strong upper trough just trucks on by.

So, its a dicey situation, but, because my dad was Canadian (from Winnipeg) and I really want to see some precipitation here after a rainless January, I am going to say that this Canadian model is the correct one, jingoism aside.

Furthermore, in order to have precipitation, which I believe will be rain changing to SNOW here at about 3200 feet on Wednesday, there will first have to be clouds (silly, haha), the latter my specialty at the University of Washington.

I love clouds and the way they present themselves in this gorgeous Sonoran Desert environment that we are so lucky to live in. So, there oughta be some interesting clouds beginning today as the cirrus zipping on by begin to announce this monumental change from our mundane, but glorious weather of late. And, of course with that fast moving river of air called the jet stream settles over us, there’ll be some windy periods, too.

The worst part of this scenario is the bitter cold that will likely get here after this mammoth upper low center goes by, and if the US models are correct, it will only get here that bit sooner.

Below, this morning’s cirrus, full of portent, over Mt. Sara Lemmon.

Catalina-Smog before the storm

Those of us awaking this morning were literally a-palled by the amount of smoke around. Not even Twin Peaks was visible, some 10 miles to the SW. See examples of smog in the photos below.

Where did it come from? Back trajectories, ones that end in Tucson as of this morning at 5 AM shown below, suggest the smog came from the SE of us (red and blue lines. The green line for air around 12,000 feet, represents where the air came from that air came from the off the California coast ; it was too high to be involved in our smog episode. Best guess, could be smog from El Paso and/or from burning in northern Mexico, that in the presence of light winds, has kind of muddled around and drifted N into Tucson.

Note the pooling of smoke in the low valley ahead in the Golder Ranch area in the first photo. Probably the result of wood-burning stoves used in the small housing development back there. What it shows you is the persistent nighttime inversion that forms in that bowl, the flat top of the smoke indicating a temperature inversion. You then see a “clear slot” of little smog and then the overall deeper smog layer above that, also very laminar in appearance. With the sun’s rise over the mountain, that kind of structure/separation is soon removed as bubbles of warmer surface air float upward and are replaced by downward moving blobs, mixing all the structure you see in the first photo out. In the last photo, a few tiny cumulus fractus clouds composed of droplets have formed over the Catalina Mountains. The droplets in those clouds are probably 10 microns in diameter (about 1/10 the size of a human hair). These droplets are about 100-1000 times bigger than the aerosol particles making up the smog. This makes the clouds to tell from transparent haze blobs because the smog particles are too small to scatter much light while the cloud particles even in small clouds, prevent you from seeing through them. Well something like that.

Hang on to your hat tomorrow; windy, thinking momentary gusts here in “Catalina Heights” will hit 30-50 mph by late afternoon and overnight before a very strong cold front rolls through around dawn tomorrow. This is an unusually strong upper level AND lower level system with a deep low expected to form over southern Nevada during the day tomorrow. Looks like the rain could change to snow above 3,000 feet after the front goes through, too. That would be terrific! The clearing after the front goes by will probably be late in the day with passing light showers possible until early Friday morning. The ones later in the day and overnight, are likely to be snow flurries above 3,000 feet . Don’t expect the temperature to do much tomorrow. And, the amounts of precip are likely to be substantial putting us at or above normal for the month. Yay! Well, this what it looks like to me; check the NWS for the official forecast!