Dry, dry, hot, dry, all mixed up, then, blammo, the storms roll in again

Well, it will be pretty obvious, ludicrously so to spaghetti lovers, the sequence shown below.  It goes from “warm in the West (again);  cold in the East pattern to another undercutting flow from the Pacific, the kind we’re having right now under the “soft underbelly” of a big blocking high, except that the tropical flow from the Pac this time is a little too far to the north to give us anything.

But, it will be another floody situation for northern Cal in the coming days.   Some places, mainly north of “Frisco”,  have already picked up 4-6 inches in the first blast which hit yesterday.  Ten to 20 inches more is likely over the next week at favored locations.  Having quite the water year there, really a lot of water year.

You may recall that the current situation, alluded to in the “break on through to the other side” refrain used here about ten times,  was well predicted about two weeks in advance!  That’s what spaghetti can do for you!

OK, enough jabbering, let us move on to the current exciting examples that popped out from last night’s global data ( there are outputs after adding little errors at the start of the model run, to see how the flow is changed with them in it.  Sounds crazy, I suppose, but is considered a huge advance in forecasting, a stupendous tool, that is, to make errors in models at the beginning of the run).  Heck, they even do that in climate models that simulate 30-50 years from now, and you’d be amazed at how the tiniest fraction of a degree change the beginning makes (see Deser et al 2012).

Valid on
Valid Sunday evening, 5 PM AST, February 12th (TIme at the top is Zulu Time, as we used to say,  or CUT, Central Universal Time, which takes in a lot of territory IMO.  This is one you look at and say, “Its gonna happen.”  What?  A big blocking high pressure ridge along the West Coast in a little more than a week.  Done weather deal.  Period. The dip to the south in the blue lines over there by the Great Lakes says that cold air will be extruding into the eastern US.  So, we have a Nike swoosh in the jet stream across the whole Pacific and then it makes a sharp left turn up into Alaska, and NW Territories of Canada.  They must be jumping up and down now, seeing this.

Well, the first one’s not so exciting since we’re dry and hot for this time of the year, and its a common one that can get stuck for weeks at a time, so you REALLY hate to see models project a bulging ridge poking north along the West Coast.  It could mean a rainless February here, if it persisted.

Here’s the exciting follow up, though, pretty unexpected given the above, showing a sudden collapse of the West Coast ridge regime, and strongly suggesting that wet spell has begun in Arizona, including regions of Catalina and Saddlebrooke:

Valid at 5 PM AST, Friday, February 18th.  Given a day or so off, we would be looking at a rainy spell beginning somewhere about this time or a day or around it.   The thing that really jumps out is the clustering of the red lines (564 decameter) contour lines. ALL the way across the Pacific right into central Cal and the Great SW.  This means that the jet stream will once again break through a ridge at lower latitudes just as its doing now, but in this case, a little farther S, which should mean periods of rain for us, keeping those washes going, or restarting the flow in them if we’re lucky.

So, you’ll want to get outdoor work done before this.

Historical note of interest, added value content,  etc.

Some of you may remember that the 564 decameter contour (those red lines) at this level (500 millibars or around 18,000 feet above sea level on average) was used in the early years of forecasting before computer models (50s and early 60s) by southern California forecasters to demarcate where rain would fall in California–at and north of where that 564 decameter contour intersected the coast when upper troughs came in.    The Old Forecaster remembers, though not much else…

So those red lines barging into southern Cal after a LONG fetch from the subtropical Pacific in the plot above mean central and southern Califs better watch out for some major rains a little before we ourselves get a dousing around the 18th of Feb.

Isn’t it great what spaghetti can do, that is, constrain our future weather to fairly certain outcomes two weeks in advance!

There was a sunset yesterday, btw:

6:06 PM. Altostratus with tiny virga illuminated by a setting sun. haha Guess I didn't need to say the sun was setting
6:06 PM. Altostratus with tiny virga illuminated by a setting sun. haha Guess I didn’t need to say the sun was setting.

Upper level snow flurry passes south of Tucson!  Trying to generate some excitement here….

8:56 AM, Feb 1st.
8:56 AM, Feb 1st.

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.


  1. Lots of snow here on the ground again. I ‘m finding this winter to be quite a “roller coaster” type. Last week we were up on the hill with sunshine and mild dry conditions. Since Friday we’ve gone back down into the trough, and then, if I’m understanding you correctly we’ll have a big ridge over us again the next week?

    1. Looks like it, Roland. It has been one of great changes in pattern runs, that’s for sure, and repetitions of similar, if somewhat unusual patterns.

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