Catalina dust to be vanquished today (?)

“?”?  It goes with the predicting the future territory…

Raining at 4:19 AM!  Pretty good sized drops!  Wow. Current NWS forecast now says rain only after 11 AM so an early start is excellent.

Moisture is moving rapidly into southern Arizona.  As an example, look at this uptick at Sells, AZ to the SW of us (green line in top panel).

The satellite view is also promising with a bank of Stratocumulus with buildups (castellanus-like) to the SW moving rapidly this way.  Take a look at this, courtesy of the U of AZ, and if you look closely you’ll see some whiter specs appearing indication that a few of these clouds are getting colder tops compared to surrounding clouds.

Those whiter tops would be small Cumulonimbus clouds with rainshafts in that mass of clouds entering AZ.  So, there’s a whole mass of those little guys scattered here and there in that mass of clouds heading for us.

Not likely to get too much rain out of them, however.  The rain from the clouds over us now and immediately upwind is falling from clouds that are not connected to the ground and so the updrafts in them tend to be not so great.  Higher updrafts usually means that more falls out the bottom if the tops of the clouds can reach that magical -10 C level up there where ice can begin to form.

Later in the day, as it warms up, the updrafts will be rooted at the ground and be stronger as the moisture revs up and with that, the chance of an organized line of showers moving in during the evening, one that might last an hour or two, goes up.

One caveat:  The U of AZ mod from their 11 PM AST run (here) doesn’t see ANY rain in Catalina today, tonight, or tomorrow, which seems surprising (and likely bogus as estimated from this keyboard).  It could be those clouds to the south, and the moisture intrusion we’re now getting were not seen in the data at the beginning of the model run.  This output does, however, indicate that we are in a marginal rain producing situation. Usually this model is quite good.

24 h rainfall ending 5 AM tomorrow, October 12th, a truly horrible depiction.


Don’t really know what’s wrong with the model, but it does seem like measurable rain will fall in Catalina, though its likely to be less than 0.25 inches.  Will be pretty happy, since it is a marginal situation, if we get more than 0.10 inches, something to settle the dust and clean the desert vegetation up a bit.  At the least, there will be some interesting clouds to look at!

A few more drops here at 5:13 AM!  Excellent.

Looking way ahead, 14 days or so.

In the longer view, more rain for Arizona is seen, of course, in the 10-15 day model prognosis, possibly substantial ones.  But last time this was predicted in the models,  “upon further review” we saw that those rains were associated with a model run was an outlier of some kind, plain goofy, when we looked at the NOAA-NCEP ensemble-spaghetti plots, dammitall.  So all that rain in AZ in THAT model run was almost certainly bogus.

But, once again the the models came up with some pretty good rains in Arizona, these rains derived from the model run using 5 PM AST global data from last evening.  These rains are more “robust” in terms of confidence.

In fact, the situation we have right now, and the one predicted in 14 or so days, are rather similar in appearance in the spaghetti plots.   Our current incoming upper low center was quite well predicted more than 10 days in advance when one examined the “spaghetti” plots.

How about the rain prediction below, goofy or what?

To answer that query, we’ll go to our friend, the NOAA NCEP ensemble-spaghetti plots here.  We need to have a trough in upper levels, just like now, to have rain in the cool half of the year.  Will there be one?

Gee, can’t do that based on last night’s data.  No ensemble “bad balloon” plots done yet.  Will have to wait, but the spaghetti plots from the night before last were encouraging.   Will update this discussion when the new spaghetti plots are producted.  So, after all this discussion, we’ve kind of ended up with nothing!


This word just in minutes ago from NOAA-PSD where the ensemble plots are displayed.  “System down for maintenance.  Should be available later today.”   Great. Then I can really ruminate on those spaghetti plots!

Pretty clouds out now (8:46 AM), take a look if you have a chance.

Tomorrow, we’ll talk about CLOUDS!


Valid for Friday mroning, 5 AM, October 26th. The green areas indicate the rainfall the model expected in the prior 12 h. As you can see there is a lot of coverage in AZ.





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.