Less data, more filling

This is the best I could do, in examining the several model outputs over the past 24 h.  Below is the very wettest forecast panel that popped out for southern Arizona during the past 24 h.  The panel below is from yesterday’s 18 Z (11 AM AST) global data and is for the evening of December 15th, about two weeks.  Nothing like what is shown in this panel showed up in model outputs afterward, dang.  Doesn’t mean it couldn’t happen, but its not a good sign.  Still, I thought you should see it.

The 18 Z (11 AM AST) model run doesn’t ingest as much global data as ones at 12 Z and 00 Z, 5 AM AST and 5 PM AST, respectively.  That means that the 18 Z run is not as reliable as those other two, is more susceptible to having goofy outputs (outliers) than the other ones.  “Less data, more filling”, of rain gauges anyway.

We ARE on the brink of a major change in the flow pattern, that is, where the troughs/jet stream will be positioned.  We have been well to the south of the jet stream and all the storms carried with it.  That will change in about a week.   We will have recurring troughs here in the Southwest after that, meaning less warm days, along with occasional chances of rain. The signal for this to happen is pretty strong in the spaghetti plots.

The question is now how strong will those the persistent troughs be as they sporadically drop by in the weeks ahead.  The strong ones for now, like the one shown below that causes rain here, are outliers for the time being.  Stay tuned.  Gut feeling here is that we’re headed for a wet regime, finally.  Its due.

Valid 11 PM AST December 15th. Greens are lighter rains, blues over half an inch. These are rains foretold to fall sometime during the 12 h ending at map time.
The 500 mb pattern (about 18,000 feet above sea level) associated with all that rain in the first panel. As you can see by the yellowish and brown colored regions for wind velocity at this level, the strongest winds at this level are well to the south of AZ-Catalina, pretty much a requirement for rain here in the wintertime. This pattern is similar to the many lows that cut off last fall and winter, ones that gave us those good early rains.  So, if nothing else, this map is a prototype of what we need for some good rains here in Catalina.

The model outputs from last evening do have a little rain here on the 10th, and NOTHING on the 15th as shown above, so I am not going to show those disappointing outputs. You’ll have to go to IPS MeteoStar to see those renderings.

Today’s clouds

Cirrus moving in today, the remnants of one of those monster rainy fronts that bashed northern and central Cal for the past week or so.  Should be a great sunrise display; get camera ready.

From the U of A Wildcats Weather Department, this loop of those approaching Cirrus clouds.

How much rain in the past seven days in northern Cal?

FYI, some sites got over 20 inches.  Here’s a map of rainfall totals from the California-Nevada River Forecast Center for the past seven days.


They needed it.  The arrow shows where the author would like to have been during those seven days, filing daily reports of stupefying amounts of rain.

I mention these rains because this episode of heavy rains was pretty well indicated in the NOAA spaghetti factory plots back in mid-November.   This flooding event is a great example of those occasional situations where a forecast two weeks out can be inferred to be pretty reliable by examining those spaghetti plots.  Those likely heavy norcal rains were expeculated on here based on spaghetti in a November 14th blog.  I really think that you could’ve done this, too, by now!

The End.


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.