Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 222302

National Weather Service Eureka CA
402 PM PDT Thu Jun 22 2017

.SYNOPSIS...Heat will continue over the next few days, with relief
expected to arrive early next week. Widely scattered thunderstorms
will be possible across interior areas over the weekend.


.DISCUSSION...The primary weather story throughout the region
continues to be the persistence of hot afternoon temperatures, and
this is expected to continue over the next two days. While some
minor fluctuations in high temperatures will occur in various
locations, it appears that little wholesale relief can be expected
across interior valleys as a persistent upper ridge continues to
assert itself over California. However, offshore high pressure
will begin to weaken tomorrow and Saturday as an upper level low
develops, which will help to weaken gusty offshore winds and
provide heat relief for areas that are closer to the coast. Given
these factors, the heat advisories for coastal and near-coastal
areas were allowed to expire tonight as originally intended.
However, the heat advisories for interior areas of Del Norte,
Humboldt, Mendocino, and all of Trinity counties has been extended
through Saturday. Widespread heat relief can be expected Monday
and beyond as an upper level low passes through and weakens the
upper ridge, with high temperatures likely near seasonal averages.

The weakening of offshore high pressure will
also result in a southerly stratus surge, which is expected to
impact coastal areas Friday evening and beyond. This will likely
result in cooler days and cloudier, foggier mornings for coastal
areas Saturday and Sunday.

The next item of interest for this forecast period will be the
potential for thunderstorms over the weekend, as the previously
mentioned upper low is expected to pass through the region. As
this low strengthens off the California Coast Saturday, southerly
flow will begin to draw increased moisture northward and into the
region. While the bulk of this moisture will not arrive until
Sunday, sufficient moisture for a stray high-based thunderstorm or
two may arrive as early as Saturday afternoon. Chances for this
remain low, and any activity that forms Saturday will likely be
isolated. However, should a storm or two develop Saturday, it will
likely be dry in nature. Thunderstorm chances increase markedly
Sunday when moisture/instability will be maximized. Forcing from
the approaching upper level low will also contribute to the
development of showers, which will likely be widely scattered
throughout the interior mountains.


.AVIATION...Along the North Coast, skies have remained mostly
clear and breezy today under a ridge of high pressure aloft...and
a strong thermal trof protruding off the Far Northern Redwood
Coast. This pressure pattern has been a catalyst for offshore flow
and thus fair and mostly pleasant conditions at the coast.
However, haze and occasional sea spray have been prevalent across
the region with earlier reports at CEC & ACV. Skies should remain
mostly clear except a few pockets of scattered low clouds at the
coast in the morning. The main VIS restriction will once again be
haze/fog in the morning at CEC & ACV. VFR will continue over
Inland mountains and valleys including the UKI airport. TA


.MARINE...Gusty northerly winds will continue through tonight
before diminishing on Friday. During daytime today, wind gusts in
the nearshore buoys were still around 30 to 40 kt. The gusty winds
are courtesy of the tight pressure gradient off the NW California
Coast. The tight pressure gradient is due to the coupling of the
strong East Pacific High and a thermal trough along the coast of

Overnight, the thermal low will weaken as we lose the heat in
interior California. At the same time, an upper level trough will
move into the Gulf of Alaska. This upper level trough will weaken
the East Pacific High downstream. As a result, the northerly
pressure gradient will weaken over NW California waters starting
on Friday. Winds will drop below warning and advisory criteria on
Friday, and will remain like that through the weekend.

With diminishing winds, the northerly wind waves will also
subside as well starting on Friday. But for tonight, we are still
dealing with some fairly steep seas, especially over the outer
waters. Expect around 11 to 16 ft of northerly wind waves for
tonight. The northerly wind waves will subside on Friday. By the
weekend, seas will be generally less than 5 feet or so.

Forecast is still on track. Little changes were made to the
previous forecast package. Extend the gale warning for the outside
waters for a few more hours as the gale conditions may last a
little bit longer. GFS is used to update the forecast package.


CA...Heat Advisory until 8 PM PDT Saturday for CAZ102-105>108-110-111-

     Heat Advisory until 11 PM PDT this evening for CAZ101-104-112.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 5 AM PDT Friday for PZZ450.

     Gale Warning until 9 AM PDT Friday for PZZ470.

     Small Craft Advisory until 11 PM PDT this evening for PZZ410-455.

     Gale Warning until 5 AM PDT Friday for PZZ475.



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