A couple of cloud pics, and the next pretty big US-Canadian model divergence coming up (updated)

Updated-at-lunchtime bulletin

This is tremendous, filled with rainy portent for AZ.   I am getty excited again as I perused the 6-day (144 h) mod output from Enviro Can, our friends to the north, most of whom live close to the US border because they like us so much and we like them:  Take a look at this map, valid for 5 AM, Oct. 2nd.  The main things to note and get excited about yourself is that the flow is “caving in” over the Pac NW.   Our little low is sitting off Baja, awaiting the southward moving trough over British Columbia.  As that trough edges south and southeastward, that low will “open up”, stop being a circle of flow and be a “trough” like its big brother over BC and eject to the northeast.  And, if that is not enough, this model   output also has a tropical storm that will, in the event these things fall into place, be swept up by the trough off Baja and rake Arizona with substantial rains!   OK, so I have filled in some “blanks” here, but, with a victory in the weather computing wars by the Canadians vis a vis our USA model recently, why not ride their coattails into the next major AZ rain? Rain would get here most likely beginning on the 3rd.  Could be a little floody here, too, if it works out the way I am projecting, but then I have just had some extra coffee and am a little overexcited right now.  In fact, look at the size of this paragraph!

I’ve added arrows as one would drawing up a play in touch football. I’ve shown where I think things will go based on this output valid for 5 AM AST Ocotber 2nd. The Canadians don’t post longer range views from their model, so I had to become an weather offensive coordinator to show where I think they should go.

6:05 PM.  Residual Cumulus clouds, no ice falling out because they are warmer than -10 C at top.
6:17 PM. A Cumulonimbus cloud just over the border in Mexico shows how painfully close deep clouds and showers are.


The weather ahead; will it rain or not in a week?

Still a chance of rain of rain between October 4 and 8th as two pulses were shown in yesterday’s WRF-GFS 5 AM AST outputs. Of course, those AZ rains are gone now in the 11 PM AST run from last night, but does that mean it won’t be back in a future model output?  Of course not.

The computer models are flummoxed by these weak patterns we have now and we again have a model “divergence” between the USA! and Canada.   While the USA NOAA WRF-GFS model has backed off rain in AZ as of last night’s run, the Canadian model, ironically is pointing TO RAIN in AZ (instead of taking it away, as it did with the remnants of poor hurricane Miriam, winding down, lost at sea).  It will be interesting to see which one pulls the “trickeration” this time.

The conundrum involves whether a weak upper air circulation that could rotate tropical air in here by the 4th, stays along the southern California coast, or recedes to the west, as the latest US models are indicating.  The Canadians think its going to hang around, not go west, at least so far.

Environment Canada model has an upper low (at 500 millibars) hanging around off southern California at 5 PM AST October 1st (upper left panel). Westerly jet stream, shown by bunching of lines in western Canada on that panel, bulges ever so slightly to the south and a big fat high is west of the Duck-Beaver nations (Oregon).  Note winds over AZ are from the SW, always a good thing.
In the NOAA WRF-GFS model for the afternoon of October 1st,  the same time as the Enviro Can map above, that upper center is a tad farther west, but is blocked from eastward movement by a big fat ridge of high pressure with no real center as was shown in the Enviro Can map. Also, here, the jest stream in western Canada bulges to the north. That jet stream “needs” to collapse toward the south to help bring that wandering low off California toward Arizona.  In this US model run, it doesn’t shift southward until its too far away from that wandering low.  Note, too, that the winds over Arizona in this prediction, are from the north-northwest, not from the SW as shown in the Enviro Can map.  Air from the north tends to sink and dry out;  air from the SW tends to have clouds and rising motion.

































Yesterday, that rain for AZ predicted by the WRF-GFS model happened because that jet stream coming into the Pacific NW and western Canada collapsed southward and literally grabbed that low off California and threw it toward Nevada and its tropical moisture came roaring up into AZ as that happened.  Last night’s run is not even remotely similar to yesterday’s!  Oh, well.  Such is weather forecasting in the modern era.

Hoping for another “retro” model solution today or down the road.

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.