Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 182201

National Weather Service Eureka CA
301 PM PDT Fri Aug 18 2017

.SYNOPSIS...Offshore winds over far northwestern California and
southwest Oregon will continue to transport smoke from inland
wildfires across portions of coastal Del Norte and Humboldt Counties
through the weekend. Otherwise, near normal temperatures are
expected through the next week, with thunderstorms possible over
Trinity and interior Del Norte Counties Tuesday afternoon.


.DISCUSSION...An upper-level anticyclone over the NERN PAC is
forecast to amplify during the weekend. As that occurs, a cut off
low will materialize in the vicinity of coastal SRN CA. Zonal flow
aloft is then forecast to develop across the PAC NW early next week,
followed by the passage of a trough during mid week. In the low-
levels, high pressure positioned over the NERN PAC and lower
pressure over the intermountain west will favor strengthening NNELY
winds across the region, with the strongest inland speeds occurring
over portions of Del Norte County. These winds will aid in advecting
smoke from inland wildfires across portions of the Redwood Coast
through the weekend, as well as contributing toward elevated to
locally critical fire weather conditions tonight through Sunday
(reference the fire weather discussion below). Offshore winds are
forecast to dissipate by early next week as a frontal system
partially breaks down the offshore surface high.

During Tuesday, a cut-off low positioned south of the region is
forecast to aid in the northwestward advection of cooler midlevel
temperatures. This cooling will yield destabilization favorable for
thunderstorm development over the mountains of Trinity and interior
Mendocino Counties Tuesday afternoon/evening. An upper-level trough
is then forecast to move across the region during Thursday, but
current model guidance indicates moisture will be scoured out of the
area, which will preclude precipitation development.


.AVIATION...The marine layer pattern has been fairly typical and persistent.
However, today presented sort of an irregularity with the Cigs/Vis,
especially for the CEC air terminal. A thick layer of smoke
continued to flow off the coast over CEC. This appears to have
inhibited mixing. Last night Cigs were mainly MVFR with a smoke
layer anywhere from 050-090 feet. Basically stratus Cigs were IFR-
LIFR. Also, the ridge has played a part in compressing the marine
layer. Therefore Cigs and Vis continued to have "some" impact on
flight operations, specifically at ACV. By 2:30 PM, Vis Sat Picture
showed the stratus/fog had pushed back over Humboldt Bay to Trinidad
keeping conditions in IFR-LIFR. The Mendocino Coast remained quite
saturated in stratus again.  MVFR-IFR/LIFR conditions to prevail.
Inland mountain/valley areas: Expect mainly VFR, although afternoon
pilot reports indicate some smoke obstructions to about 10,000 feet.



.MARINE...Winds and seas remain elevated, mainly over the northern
outer waters. The evening ASCAT showed winds of 15 to 30 kt over
the northern outer waters. The gale warning looks to be on track
and a second warning was added to upgrade the watch for the
southern outer waters. On Saturday the stronger winds will likely
push into the southern inner waters and SCA is now in effect to
to address that. There is the potential that a hazardous seas
warning will be needed over the inner waters due to the large
waves propagating into them. Will hold off on that for now.

Monday models are in decent agreement that winds will diminish
fairly dramatically as the ridge of high pressure breaks down.

Waves will mainly be locally generated and steep. There will also
be a small northwest swell with a period of around 10 seconds.


.FIRE WEATHER...Northeasterly winds gusting to around 10-20 mph
are expected within the mid/upper-slope thermal belt in Del Norte
County tonight. Northeasterly winds are forecast to strengthen
another 5 to 10 mph Saturday night, and when combined with poor
overnight RH recovery (values in the teens and 20s) and sufficiently
dry fuels, will favor a locally critical fire weather threat.
Therefore, a fire weather watch has been issued for locations above
1500 feet for fire zone 203 late Saturday afternoon through late
Saturday night.


CA...Fire Weather Watch from Saturday afternoon through late Saturday
     night for CAZ203.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 3 AM Saturday to 11 PM PDT Sunday for

     Gale Warning until 9 PM PDT Sunday for PZZ470.

     Gale Warning from 3 AM Saturday to 11 PM PDT Sunday for PZZ475.



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