Precision forecasting of the next Catalina rain (an experiment)

After looking at last night’s model run, and the many model outputs before last night, here’s the “skinny” as this forecaster sees it (“as I see it”, means this is an experimental forecast to see how close it can be called.  Its gaming the weather. Here goes:

There is a 100 % chance of rain in Catalinaland on Saturday, November 10th (sometimes referred to as “football day” this time of year).  The rain will begin between 5 AM and 11 AM that day.  It should last a couple of hours or maybe a bit more.

It will be horribly cold.   You don’t want to be out on Saturday, November 10th.

The amounts?

In a “mental ensemble” of the best and worst outcomes for this rain situation, I see a bottom (only a 10% chance of LESS) in this rain event as a puny 0.05 inches and the top (10% chance of MORE), 0.40 inches (nice!).  To get the best estimate of what will actually fall, take the average of these two, 0.225 inches.  So, that’s my forecast, 0.225 inches on Saturday here in Catalina.  Get your micrometers out!  hahahaha.

Here is the model depiction (WRF-GFS from NCEP rendered by IPS Meteostar) of the air flow at around 18,000 feet above sea level.  Recall that rain is pretty much impossible here until the maximum wind at that level goes by.  Below is a snapshot of the air flow and its speed for Saturday, November 10th at 10 AM.  As you can see below, the red core of the highest winds at 18,000 feet (aka, 500 mb level) is passing overhead then.  So, expect it to be raining by then around here.  The whole loop for this level is here.

I think you can do this today, cut it so finely, and so far in advance of the event, because the model runs have been SO consistent and in the NCEP’s (Nat’l Centers for Environmental Prediction’s1),  “ensemble of spaghetti” outputs, have been indicating a strong signal, high reliability for this event for a good ten days.  So, count on it, though obviously the timing may be off a few hours, but that’s about it.  Everything else is pretty much a “done deal”, and you don’t often get to say that this far out (six days).  Below this jet map is a snapshot of the high reliability of this forecast as seen in spaghetti.  Packing together of the blue and red lines indicates where the forecast is extremely reliable, and that’s what you see throughout the West from last evening’s plot.

Since this is the cloud-maven blog and not the forecasting-maven blog, I’ve added a pretty cloud picture at the very bottom.

The End.


1formerly, and more simply, the US Weather Bureau)

From a couple of days ago, pretty sunrise Cirrus fibratus/uncinus and pretty junior Cirrus fibratus/uncinus

6:38 AM, November 2nd.

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.