Soft underbelly, storm passageway, from the subtropics to Cal and AZ under contruction

Its never too early to talk about rain and storms in old AZy.

A couple are already on the move and will arrive here between the 3rd and 5th of January.  Confidence is quite high, more so that on the last failed medium range forecast, which I think says something1.

However, its after those first couple of storms that it gets really interesting, given the Big Niño in progress.  Scrutinize this hint of future weather below, valid some two weeks from now:

Valid January 12th at 5 PM AST.
Valid January 12th at 5 PM AST.  Red lines represent tracks of the “subtropical jet stream.  Blue lines more or less the Polar jet stream.  Notice that the red lines are nearly ALL far south of the SW US, while the blue lines bulge northward into AK and the Bering Sea.  This would be a strong split flow pattern, where storms coming out of the western and central Pacific are forced to stay at lower latitudes rather than move north.  Yippee!

Cloud maven person admits that this is his very favorite pattern since he was a kid, the one that’s being suggested above, so subjectivity,, the enemy of science, could be creeping in.

The Big Fat Ridge (representing a blob of deep, relatively warmer air compared to the air hundreds of miles around it) has overextended itself into the Gulf of Alaska and Arctic.  It looks like too much of it has extruded into the Arctic areas.

What always happens when the BFR extends to the north over thousands of miles is that the westerlies, with their series of storms moving along in them, “break on through to the other side”, as Jim Morrison might say if he had been a meteorologist.    But they are shunted by the BFR  “underneath”  and travel at relatively low latitudes north of Hawai’i toward the West Coast.

That means those low pressure centers carried along in the westerlies travel over warmer water than usual,  arriving along the Cal and Baja coasts with Hawaiian style wetter clouds.  Some of the great rainfalls in Cal and AZ occur in these situations.

How much can it rain from storms like those, should they materialize with vigor?  Check this 24 h rain table out for Cal for January 21-23, 1943.  These are all just 24 h amounts for a storm that gradually shifted southward along the West Coast.  Broke 24 h precip records from Cal to Colorado:Cropped Jan 1943 rain table--typed by the author

The storm that produced these prodigious totals originated near the Hawaiian Islands a few days before the rivers of atmo water struck the West Coast.  The above table was typed by the writer (hah, “typed”, then “writer”2) on a Hermes 3000 typewriter in about 1962 or ’63.  Only those amounts over 10 inches in a day are shown.  Shows you what can happen when storms barge in from warmer waters, and when they are strong (have deep low centers with them that produce strong winds against the mountains.)

So, while the first coupla storms are pretty much (he sez,  in the bag, will be watching to see if the above “Lorenz plot” (aka, spaghetti plot) has seen something two weeks out.  Usually only the strongest signals show up that far out, and what is shown above is darn strong for a ridge, trough underneath in the eastern Pac.

Add a pinch of veracity, too,  due to the Big Niño we have now.  Niños are phenomena that  enhance the southern portion of the jet stream/westerlies in the eastern Pacific and SW, and that means stronger lows out there, too.

Exciting days ahead in old AZy!

The End.



1In a sense it was quite accurate for so many days ahead.  While there was NO precip, it WAS, in fact, quite a storm of cold air.

2Another silly-ism.  There’s a real quarry of them here in this blog.  But I hope to indulge listeners not only with an occasional “silly-isms”, but I also hope to educate the listener with  one or two facts, one of which is often correct.  Are you listening?