Dewpoint rises above zero degrees! Upper low to pass over Catalina!

Moisture’s not flooding in quite yet, but just to see the dewpoint creep above 0 F lately has been satisfying.  Here, from the U of AZ Weather Department, this plot from early this morning:

Plot of surface station data for 4 AM AST this morning.
Plot of surface station data for 4 AM AST this morning. Numbers on the lower left are dewpoint temperatures; 18 F (!) at TUS, but 38 F over there in Yuma.   Even higher dewpoints are headed our way!

 

Currently, ejecting out of equatorial waters toward Catalina, are banks of middle and high clouds, which, along with lower level moist air from the Gulf of California and waters to the south, will be moving into SE Arizona en masse tomorrow and Friday.   You can see this process unfolding here from the University of Washington’s Weather Department’s western hemisphere satellite loop for the past 24 h. Take a look down in the lower right hand corner of these images, by the Equator, and watch those clouds begin to roll northward.  Pretty exciting to think that clouds that were near the Equator will be here in 36 h or so.

US model has a paucity of rain, whilst the Canadian mod continues to have a much “juicier “solution for us as the big upper low now over southern Cal wobbles around for a day or then trudges east.  The  Canadian mod calculates, as it consistently has, that this low will be going slightly farther south as it passes over Arizona than the US model, with the center of the low eventually crossing directly over Catalina on Saturday at 5 AM AST.

A more southerly trajectory means more moisture is like to wrap into our low before it gets here.  The best of the rain would fall just before the center arrives.

The start of scattered showers in the area is still later tomorrow and would continue through Saturday morning.  The range of amounts for Catalina/Sutherland Heights  is still probably “light”,  in the range of 0.05 inches to 0.25 inches.  However, with thunderstorms likely at times, a lucky hit might make that top end a much greater amount.

For quantitative predictions, go to the U of AZ mod output, ones that will be based on the US overall model, but downscales what the US model predicts a much finer grid of local terrain.  So, those calculations, which weren’t done yet from the 11 PM AST data,  are likely to be a little less even that what CMP sees.  It will be interesting to see which of us has foreseen the more accurate future, the Beowulf Cluster at the U of AZ, or CMP in the game of “Beat the Computer.”  (The human usually loses….)  ((Oops, just saw now that there is no updated run from last night’s data, a shame, and may be due to lack of funding.  How bad is that?))

Should have clouds similar to yesterday today, which is already what’s out there this morning.

Moving ahead to yesterday…

Yesterday’s clouds

Started appearing around mid-day yesterday, those non-Cirrus clouds we call Altocumulus. Some lenticularis here and there as well.  I was pretty happy for you now that you could see some non-Cirrus for some excitement.

How high were they?  Oh, about 17,000 feet above sea level, or about 14,000 feet above Catalina. Here’s the TUS sounding profile, launched about 3:30 PM.  Where the two lines pinch together is where the clouds were, and, if you follow the sloping lines of temperatures to the lower left, you will see that the top temperatures of those clouds were pretty cold, -16 C, around 4 F, cold enough for some ice crystals to form, but not a lot.  Below a few shots or your cloud day yesterday.

Tucson balloon sounding ("rawinsonde") for 5 PM AST yesterday.
Tucson balloon sounding (“rawinsonde”) for 5 PM AST yesterday.

 

1:02 PM.  Altocumulus lenticularis dot sky north of Catalina.  No ice visible.
1:02 PM. Altocumulus lenticularis dot sky north of Catalina. No ice visible.
DSC_0280
1:02 PM looking south from Catalina. Altocumulus perlucidus patches with scattered lenticulars. Here’ where you should have been logging your first ice sighting. Look at the delicate, very transparent veils between the clouds. Of course, you would have been estimating less that one per liter concentrations of ice, too, in your cloud diary.  The droplet clouds are easily detectable because “cloud condensation nuclei” are far more numerous than ice nuclei.  Here, droplet concentrations are likely 100-200 thousand per liter; ice crystals, less than 1 per liter!  Those factors make droplet clouds sharply defined, and ice clouds “wispy.”

 

4:38 PM.  Droplet Ac clouds with ice falling out below.  Interestingly, nature's ice nuclei like to form a liquid drop that then freezes rather than form a crystal directly (except at really low temperatures, like -35 C or so).
4:38 PM. Droplet Ac clouds with ice falling out below. Interestingly, nature’s ice nuclei like to form a liquid drop that then freezes rather than form a crystal directly (except at really low temperatures, like -35 C or so).

 

7:24 PM.  Ended up with a nice sunset again.  Some ice falling from these Altocumulus clouds is visible, with a hint of a "sun pillar".
7:24 PM. Ended up with a nice sunset again. Some ice falling from these Altocumulus clouds is visible, with a hint of a “sun pillar”.

 

Blazing heat still in the cards once our low passes on Saturday;  temperatures will “recover” rapidly to max temperatures of 100 F or so for a good week beginning next week, but a an early June rain is also shaping up.

The End.