While waiting for a “better” numerical model output….

As we say, “if you don’t like the model run now, wait 6 h and get a new one with different results.”

Last night’s model run based on global data taken at 5 PM Arizona time, was truly mediocre in rain in Arizona in the week to two weeks ahead.  Sure, great storms bash northern California, where they need rain desperately this year, and Washington and Oregon as well, ones that are likely to make the news, the jet stream was again retracted to the north in that run.  Take a look at this, courtesy of IPS Meteostar for Sunday, January 22nd and notice where the reddish area is compared to the output I showed yesterday (below).  The impacting jet stream is now centered over Portland, Oregon, fer Pete’s Sake!  Its outrageous.  No rain is imminent here with a map like that!  We’re on the wrong side of the jet stream as anyone can see.  Just yesterday, we had the kind of output from global observations that showed the Pacific jet stream (JS), this on model calculations from only six hours earlier than the output shown in the first panel.  As you can see, in that slightly earlier run, the JS is shown bursting into California at almost the exact same time on January 22nd instead of into Oregon.  That second panel was loaded with rainy portent for Arizona (see last panel)!   So, its worth checking into IPS Meteostar, a weather provider I favor for their nice imageries, later today to see what the 5 AM AZ Time global obs say.

Why do these fluctuations occur that prevent confidence in weather predictions more than a few days out?  Well, we have a reason:  “bad balloon.”  (Or “missing balloon.”)

While small changes in initial conditions in themselves can cause vast changes in model outputs many days ahead, sometimes these problems are caused by errors in measurements and probably more often, missing measurements in the global network.   The models then have to guess what is happening in the missing data regions, usually with the help of satellite measurements, and/or use the prior model run’s prediction of what was supposed to be in the missing region.

I am getting the impression that the quality of the 00 Z runs are not as high in reliability 1-2 weeks in advance as those at 12 Z.

In the meantime, while waiting for a new more better model run, a word about today’s clouds…

Right now (8:44 AM AST) we have an overcast layer of Altocumulus (Ac) with patches of Altostratus (As) clouds. The former are mostly composed of droplets while the latter are ice clouds. The TUS sounding indicates that the Ac layer is based at -20 C (-4 F). Those Ac clouds are ultraripe for aircraft produced ice, and right this minute, I would say that much of the virga around is due to aircraft on those “supercooled” clouds. This is particularly evident if you see straight lines of virga, or a hole with ice in it. Here’s a line of virga (those downward hanging protuberances called “mammatus”, to the SW of Catalina right now that looks suspiciously like it may have been produced by the passage of an aircraft through some Ac.  That passage would cause tremendous numbers of ice crystals to form, and then fall out as fine snow we call virga.

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.