Your Christmas Day clouds:
More of the same types of clouds are streaming toward Catalina today (sat imagery with radar here), but the winds aloft are increasing as another upper level trough approaches, this one in two parts. Today more Cirrus, Altostratus, and probably some Altocumulus with lenticularis clouds here and there, especially downwind of Mt. Lemmon, as one part of it goes overhead. These clouds will be drifting off to the south of us over the next 24 h as the second trough approaches with much colder air, and lower clouds, bringing with them a chance of a little rain later tomorrow and overnight. We should see Cumulus and Stratocumulus dangling icy virga by tomorrow afternoon and evening. Any rain will be pretty light, likely not more than 0.15 inches.
The weather ahead
Still looking for more rain after this marginal rain chance tomorrow night. But, mods now have rain moving in much sooner, before the end of the month, on Sunday, December 30th due to wild changes in model runs. Formerly, the rain waited until early January. View latest (06Z, 11 PM AST last night) run here.
Wildness? Look below at two model runs valid for the same hour, 5 PM AST New Year’s Eve. Sobering, which is probably a good thing on New Year’s Eve.
The Canadian model has our end of December low lurking off southern Baja (upper left panel below), while the USA model has it scooped up and merged it with another trough dropping down out of the north before it can get cut out of the flow. Vastly different takes!
Take a look at these model depictions and have sympathy for your local weather forecasters trying to deal with this mess (“model divergence” is what we might call it, to sound more scientific, but its really just a mess for us).
How to decide which one has more truth?
Check the spaghetti.
Sadly, this chart, also valid for New Year’s Eve, makes the low far off Baja less likely to be realized (as suggested by the few red lines wandering off the Baja coast), that is, the Canadian model calculations have come up with an “outlier” result, one not so likely to be realized, though not impossible. Dang! If that low had hung around off Baja for a couple of days, and THEN ejected northeastward, as the prior model runs had been repeatedly showing until lately, we’d had the possibility for a very substantial rain.
Now we seemed doomed to something much less potent as a rain/snow producer, and very cold.