Area Forecast Discussion
Issued by NWS Eureka, CA

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855
FXUS66 KEKA 122204
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
204 PM PST Tue Dec 12 2017

.SYNOPSIS...Mainly dry conditions, accompanied by mild afternoons
and cool nights, will persist this week. Rain chances may
increase early next week.

&&

.DISCUSSION...An upper ridge axis was located over coastal
portions of NRN CA Tuesday afternoon. Farther west, a trough was
positioned over the WRN Gulf of Alaska. Strong subsidence was
evident in satellite imagery over CA/NV, while active SWLYS were
observed from the ERN Gulf of Alaska into NWRN Canada. Model
guidance shows this upper height pattern persisting through
Thursday...with northerly midlevel flow spilling over the ridge
across coastal CA during Wednesday, which will aid in clearing
wildfire smoke. Thereafter, an upper disturbance is forecast to
break down the upper ridge during Friday, with increasing mid and
upper-level cloudiness being the primary impact across NWRN CA.
The ridge is then forecast to rebuild during the weekend, followed
by a digging upper trough over the NERN Pacific early next week.
However, model variability is very large next week, and confidence
in the outgoing forecast is subsequently low. Nevertheless, rain
chances could potentially increase if the trough evolves according
to the 12Z GFS.

&&

.AVIATION...Today, southern fires allowed smoke aloft to drift
into Northwest California and partially obscure skies above 8,500
feet...especially at ACV where haze also briefly dropped VIS to
MVFR in the afternoon. A ridge of high pressure will remain in
place through Wednesday afternoon. Mild and dry conditions will
continue across the region with mostly VFR Sky and VIS. Some areas
of minor haze obstruction can be expected in the afternoon near
the coast. Pockets of patchy fog will develop again across a few
interior valleys in the morning, but early morning frost will be
widespread...including at the UKI air terminal.

&&

.MARINE...We are starting to transition into more active marine
weather. For today, we are seeing light north winds over NW CA
waters. A thermal trough will develop along the coast of
California, while a high pressure builds in from the northwest.
This will tighten the northerly pressure gradient over our coastal
waters. North winds will be on the increase tonight into
tomorrow, with winds of 10 to 15 kt expected. By Wednesday night,
winds will increase to 15 to 20 kt with gusts to 25 kt for the
southern outside waters. Elsewhere, north winds of 10 to 20 kt
expected.

A stronger high will build into the Pacific Northwest on Friday,
and this will further increase the northerly pressure gradient
over our area. This will lead to further increase of northerly
winds over southern outside waters, with north winds of 15 to 25
kt with higher gusts starting on Friday. There is a small craft
advisory for gusty north winds from Wednesday night through the
first part of the weekend.

Seas will also get more agitated as the week goes on. We have a
background westerly swell with wave period of around 16 to 18
seconds and magnitude of around 6 feet through the week.
Meanwhile, we will have a developing northerly wind waves moving
into our waters due to the strengthening northerly winds. The
combined seas will be around 6 to 7 feet through middle of the
week, then increasing to around 9 to 11 feet for the second half
of the week into the weekend. /RCL

&&

.SNEAKER WAVE POTENTIAL...There will be an elevated risk of
sneaker wave from Wednesday morning through Thursday evening. We
have a persistent long period west swell moving into NW CA waters
with a period of around 16 to 18 seconds. The magnitude of the
swell will be around 6 feet. Meanwhile, we will have northerly
short period wind waves starting to develop on Wednesday. However,
the magnitude of these wind waves will be small and intermittent,
such that the energy of the swell may not be easily diminished.
With this set up, there is an elongated period with elevated
threat for sneaker wave. Thus, issue a Beach Hazard Statement for
Wednesday morning through Thursday evening.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Wednesday morning through Thursday
     evening for CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 3
     PM Wednesday to 3 AM PST Sunday for PZZ475.

&&

$$

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