The rain before the storm

Our models have been showing a batch of scattered showers on Thursday for some time, a precursor to the Big Change day on Saturday.  Skepticism prevailed at this keyboard since there didn’t seem to be much going on off’n Baja where this moisture was supposed to come from.  Here is an upper level chart demonstrating that assertion: don’t see any contour circles out there do you?  Just a wandering, single contour off Baja, not much going on compared to that behemoth trough blasting the Pac NW.

But, by golly, there IS a patch of clouds and moist air in that weak circulation off Baja that is going to be swept out of the eastern Pacific by the “broom” of the flow around that giant upper trough that moves toward us from the Pacific Northwest into the Great Basin area on Friday and Saturday, generating a powerful low center at the ground as it does.   Some Cumulonimbus clouds have even formed off Baja in this weak tropical circulation, and here, that should mean some nice Altocumulus castellanus clouds tomorrow, likely with virga.  Cirrus will also be around for a real visual treat.  As we remind reader (s), get your cameras ready.   Could be some spectacular scenes;  sunrises and sunsets.

Here is a link to what is going on out there (from the Huskies, of course, the Washington ones.)  Those white specs that appear and disappear off’n Baja are little Cumulonimbus clouds, showing that the middle levels of the air out there is very unstable.  (Those are a type of Cumulonimbus that sit on top of boring Stratocumulus clouds, FYI)

What could be tremendous for us is that the Wildcat model (here), has off and on showers from this tropical surge for no less than 24 h!  Amazing.  I just now saw this from last night’s run.

Could it happen?

Well, this model is smarter than you and me, and so you figure there is going to be a lot of mid-level clouds and castellanus (spire-clouds) the size of small Cumulonimbus clouds as we see offshore now in the sat images.  And with that, the likelihood of some thunder here and there.   This preliminary action is getting to be so much greater than I possibly could have imagined;  rain in the immediate offing, not waiting until Saturday!

One of the things that will happen tomorrow, too,  with this little slug of moisture and clouds,  is that the lower level humidity will be increased some as well; it won’t be just middle and high level clouds that increase.  That will help juice up the air before the Big Trough gets to us, maybe helping that Saturday rain out just a bit.  Ironically, this little thing ahead of the BT might well produce more rain in a thunderstorm than the BT with all of its drama, the strong SW winds on Friday, frontal passage and wind shift to the NW overnight or early in the morning, and such.

With BT, strong winds are guaranteed on Friday, it will really seem like the season has truly changed which is kind of cool.  Rain still looks marginal from BT; could be just a few hundredths, though the “window” is still there for more than a quarter of an inch if everything is optimized (storm hangs on longer, jet stream is a little farther S than predicted, etc.)

The weather ahead

It does appear that we’re headed for a new wet regime after our long, warm dry spell since mid-September with persistent high pressure over us and the West Coast.   Last night’s global data, crunched by our super model WRF-GFS,  had rain on SEVERAL days after these two chances go by tomorrow and Saturday due to the passage of more troughs plunging in from the Pacific.  The pattern we’ve had, warm in the West, cold in the East is fairly common one because the jet stream seems to like to do that, sometimes, as we have seen, for weeks at a time.

But now that pattern is disappearing and a new jet stream pattern is taking shape, one that will likely mean normal or above normal rains here over the next month or so as this new pattern gets locked in for awhile.  With those once-in-a-while rains will be below normal temperatures.

A pattern like this, “cold in the West”,  almost always means warm in the East, and so the really cold air those unfortunate folks affected by Sandy have been experiencing will soon be gone, a good thing.

Here’s an example of a trough predicted to be over us from last night’s global data on November 15th:

Nice, huh?


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.