Uncommon Cool Temperatures over the Pacific Northwest Results in Sturdy Winds and Energy Outages in California

Reposted from the Cliff Mass Climate Weblog

Saturday introduced document or near-record chilly temperatures to the Pacific Northwest, and surprisingly sufficient, that led to uncommon Diablo winds over northern California, with the regional utility PG&E slicing energy to 1000’s to scale back the prospect of one other main wildfire.

Chilly temperatures probably producing wildfires?   Ironic, maybe, however true.
Late final week an uncommon slog of chilly air, related with an higher degree trough, pushed into the Pacific Northwest, with the cool, dense air related to excessive stress at low ranges.  That chilly air/excessive stress combo prolonged inland after which southeastward into the Intermountain West (from japanese Oregon down into Nevada).   And excessive stress north and east of California resulted in sturdy, dry downslope, northerly to easterly circulate that may produce harmful wildfire situations:  the dreaded Diablo winds.     Let  me illustrate this for you!
Beneath are a collection of mannequin forecasts throughout the interval in query, together with heights ( suppose stress, stable strains), winds, and temperatures round 5000 ft (truly the 850 hPa stress degree).
At 5 AM Thursday, the chilly air was beginning to transfer in (bluish colours).

A day later (5AM Friday), the chilly air was pushing inland.

Saturday morning at 5 AM, greater heights (and stress) and funky air had prolonged into Oregon, with a really sturdy stress (peak) gradient over northern CA and Nevada.   Sturdy stress gradients produce sturdy winds!

And by Sunday at 5 AM, the excessive stress (and nonetheless cool air) pushed farther east and south, leaving a really sturdy stress/peak gradient throughout the Sierra Nevada and northern CA.  Decrease heights and stress are alongside the coast.  That is precisely the sample that produces the dry, windy situations referred to as Diablo winds, which were related to main CA wildfires, such because the Nov. 2018 Camp and Oct. 2017 Wine Nation fires.  No marvel PG&E determined to close off the facility in some communities.

Actually, winds did gust to 60 mph in some places north of San Francisco (see under)

And over 45 mph gusts hit north and east of Paradise, CA, the situation of the horrific Camp Hearth final yr.  With a poor energy infrastructure, PG&E has to close the facility off to stop their energy strains from beginning new fires.  One useful factor this time of the yr–vegetation remains to be comparatively inexperienced, notably after a really moist spring.

Having such sturdy Diablo winds may be very uncommon this time of the yr, since usually these sturdy downslope winds keep away from the summer season.
Why?  As a result of they’re pushed by chilly, inland excessive stress that’s uncommon throughout the summer season.     To point out this, here’s a determine from a paper on Diablo winds written by UW grad pupil Brandon McClung and myself (I’ve a NSF grant to review Diablo winds, by the best way).   Diablo winds on the western facet of the Sierra Nevada are uncommon in mid-June and rare across the Bay Space.  Huge enhance in fall as cool air strikes inland.

So why the weird June Diablo winds this yr?  Unusually chilly temperatures.  Right here is the climatological of temperatures at 850 hPa (once more round 5000 ft) at Quillayute, on the Washington coast, versus time of the yr.  The blue strains symbolize the document low temperatures for the date.  I put a marker on Friday’s worth—just about tied the document low.  No marvel there was snow on the Paradise ranger station on Mt. Rainier on Friday and early Saturday!

However the temperatures have been much more uncommon in Oregon and neighborhood.  This map, courtesy of NOAA, exhibits places of document low most temperatures on Friday for that date.  LOTS of them over southern Oregon and Idaho.

And there have been even some document low minimal temperatures for that date as properly.

Much more spectacular, there have been some MONTHLY data for low most temperatures.  THAT may be very uncommon.

So the potential for main wildfires in CA is straight related to colder than regular temperatures extending into the Pacific Northwest and into Nevada.  Much more fascinating, international warming, which might in all probability cut back such cold-air durations, might properly cut back the variety of Diablo winds and thus wildfire menace durations like this occasion.   That is one thing I’m researching utilizing excessive decision regional fashions run for a century. 

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