Hanging virga on tap (its not a beer)

Cloud patches and upper level trough approaching this morning.  They’ve got some precip in’em, but its a little dry underneath those cloud patches coming toward us so that only a few ice crystals/flakes will make it to the ground from the isolated, hanging virga we’ll see in the later morning hours.   Should be kind of pretty though, big, long trails of snow coming down from really cold Altocumulus, Stratocumulus, and small Cumulus (coldest tops likely to be below -25 C, -13 F).

Trough apex and wind shift aloft goes over us at mid-day (seen here from the U of WA), and you know what that means.  Those morning clouds will move off, leaving only small, COLD-like-us, Cumulus clouds since the atmosphere is mainly moving downhill behind the upper level trough wind shift line, and that means a clearing.

Here are the temperatures around this morning;  “milder” on hillsides, colder in low spots hereabouts, as you know from experience.  Cold air drains like water off hillsides, is replaced by warmer air just above that is not in contact with the cooling ground surface.  The air then cools at the surface,  slides down hill and fills up washes and lower elevations in general.  (Right now, 6:43 AM update, holding steady at 29 F, but down the road and down the hill, in Black Horse Ranch, its 23 F.  See map here.)

Happens over and over again, and so if you have a temperature trace to watch, and you live on a hillside, you will see blobs of warmer and colder air passing by soon after dark, usually just at one or two miles per hour.  Even the smallest little creek beds have little, slow downhill moving streams of cold air.  If you live in a bit of a low spot on the side of a hill, you’ll know this from, say, walking the dog along a road along the hillside.

Check this nice graphic below from the U of AZ of regional temperatures with the infrared satellite image overlain on them.  Tucson was 26 F at that time while here in the little hills above Catalina it was 29 F at 4 AM).  HUGE difference…  Well, its something.

Note -14 F at the Grand Canyon, -15 F at Bryce Canyon, UT.  Only 7 F at Big Bear Lake, CA (L35 on map), 33 F right on the coast of southern Cal at NFG1, by San Diego.  It’ll get colder yet at most of these stations in the hours before sunrise.

You can also see in this graphic the cloud patches that are heading our way in SE Cal and western AZ.

Map for 4 AM AST today.
Map for 4 AM AST today.


Other than today, precip chances have been diminishing after a model “feint” indicating some snow on the 14th.   Its gone now, like so many model-indicated precip days.  It now is looking more likely that January will end as another dry month, even if it rains some near the end of the month (beyond the current dry-for-15 days model predictions).

Some scenes and clouds from yesterday.

First this nice shot of the Catalina Mountains…  OK, I really didn’t get a picture of them yesterday, and so this will have to do.  Its what the Catalina Mountains WOULD look like if they were 11 inches high and it had snowed on them, and it was windy when it was snowing.  Here’s another one of the effect of wet snow on our dried out from summer grasses.  I thought it was kind of pretty how the snow stuck on stems.







10:11 AM along Equestrian Trail Road.
10:11 AM along Equestrian Trail Road.









Now some scenes of those great, if chilly-looking blue skies dotted with small Cumulus clouds yesterday; no ice detected falling from them by these eyeballs.  Should see similar sights today, except ice/snow should be hanging down (he sez).

8:45 AM.  Pretty Stratocumulus hovers over Oro Valley.
8:45 AM. Pretty Stratocumulus hovers over Oro Valley.








1:28 PM  Cumulus humilis forms over Oro Vally.  No ice haze visible though cloud tops were, from the TUS afternoon sounding data, -11 to -13 C, below the usual ice-forming temperature here of about -10 C.
1:28 PM Cumulus humilis clouds form in a line over Oro Vally. No ice haze visible though cloud tops, from the TUS afternoon sounding data,  were -11 to -13 C, below the usual ice-forming temperature here of about -10 C.  A second factor in ice-formation is drop sizes in the clouds.  The smaller the drop size (as in small clouds like these, or in lenticular clouds) the lower the temperature required to initiate ice (from U of WA studies).







1Oceanside Camp Pendleton Marine Corps Air Station