Let’s look at December and the beginning of the second Catalina rain season

A day of pretty Cirrus and a nice sunset yesterday:

5:35 PM.








Now for some more of that Catalina climo, featuring December

(Most of these data below are due to the folks at Our Garden right here in Catalinaland just off Columbus._

First, the rainfall frequency chart for December.  Not much going on.  Chances of rain on any day about the same as any other, no trend up or down during the month, except for that one peak.  Below this chart, in the monthly averages for the October through September “water year”, you’ll see that the average rainfall has jumped up considerably in December from November. Yay!

 But will it rain at all in December 2012?

Let’s check…and also look, just for the HECK of it, whether any trough/storm is headed here in the 11th-13th rain frequency peak shown in the first plot…to see whether the atmosphere “likes” to have a little rain in Catalina in that time frame this year.

Below, the USA WRF-GFS model output, again rendered by IPS MeteoStar, from the global data taken at 5 PM AST valid for Monday, December 10th at 5 AM (close enough):


Astounding!  A strong trough with rain IS predicted in about that time frame where the chance of rain in our 35 year record peaks, though a bit early.  If this map verified, rain would be ending at about the time of this map, 5 AM AST on the 10th,  it would be very, very cold, probably in the upper 30s in that rain.   Amazing.

But let’s check with the superior Enviro Can model from the Canadians, our friends to the north, because-its-built-on-the-Euro-model-where-they-have-more money-for-big-computers-and-better-models-than-we-do.

(PS:  You’ll be pretty upset when you read this–Model comparisons Science-2012-Kerr-734-7 —about US and Euro models.)

Not even close to the prediction by the USA model!

Unbelievable difference, in fact.  In the USA model, the apex of the trough is over us in Catalina and in the superior (or will it be?) Canadian model,  its over the “‘Braska” Cornhuskers, Lincoln, NE, maybe ONE THOUSAND miles farther east!

Unbelievable2.  This is a phenomenon, BTW, which does happen from time to time, that is called, “model divergence”, to put it mildly.

So where do we check to find out where the truth lies, if the truth can lie at all (to borrow a line from Harry Shearer)?

The NOAA spaghetti factory, which I have annotated for you below:


Outstanding forecast reliability is indicated in the Pacific,  off Asia, but who cares?
Sadly, only mediocre reliability indicated here in the Great SW USA, as shown in the wanderings of the blue lines.
But will a trough be close to us?
Pretty much count on that because so many blue lines feint to the south in interior of the western US. I think we’ll surpass the Canadians this time…
There’s still a chance of rain on the 9-10th, but its pretty slim.  Having cold air invade us, to varying degrees is pretty much guaranteed even if sans rain because that nearby trough will drag cooler air this way as it goes by.
Its the AMPLITUDE that matters here, and in our USA model, that is not so well known.  In fact, the blue lines, with so many of them north of us are telling us that the actual forecast map from last night’s global data is an outlier model run;  can’t count on it.  It will likely come and go on the future model runs.
The End.