Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 280431
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
931 PM PDT TUE SEP 27 2016

.SYNOPSIS...A gradual cooling trend will continue through Friday as
an upper ridge drifts slowly east through the week. Some light
rain is expected to develop over the weekend. Rain chances will
continue into early next week as multiple systems move through the
region.

&&

.MARINE UPDATE...Hoisted a Small Craft Advisory for the N near
shore waters. Winds over the extreme N portion of the zone have
ramped up to around 25 kt sustained. Seas were already forecast to
reach marginal advisory criteria, and this forecast may be a bit
conservative. The advisory will run through noon on Wednesday.
/SEC

&&

.PREV DISCUSSION... /issued 318 PM TUE SEP 27 2016/

DISCUSSION...Northwest California remains located on the western
periphery of an upper level ridge today. The marine layer inversion
has once again become established and coastal stratus/fog formed
last night. Similar conditions are in store tonight with increasing
trapped low level moisture likely resulting in more widespread fog
along the coast by Wednesday morning with partial clearing Wednesday
afternoon. A deepening marine layer Wednesday night into Thursday
will reduce the potential for dense fog but likely result in longer
lasting stratus through much of the day.

A gradual cooling trend is in store for the next few days as an
upper trough deepens off the Pacific Northwest coast. 1000-500 mb
thickness values will descend to near 550 dam on Friday. Thus, high
temperatures on Friday across the interior will range from the 70s
in the valleys to 50s in the mountains while coastal areas stay in
the 60s throughout the week.

The upper trough will bring increasing moisture to the region Friday
into the weekend. Guidance has slowed the initial onset of rain
chances to Friday night/Saturday morning, but overall the pattern
remains similar to yesterday`s model runs with the chances for rain
showers remaining over the northern half of the area Friday night
through Saturday as the upper trough moves inland. There remains
some uncertainty as to the exact strength and trajectory of
subsequent shortwaves moving east-southeast on the backside of the
trough. The ECMWF is predicting stronger systems with greater
moisture, resulting in heavier shower activity than the GFS on
Sunday. The best chances will remain in the north, particularly in
Del Norte and northern Humboldt counties through Sunday night. Snow
levels will fall to just below 6000 feet Saturday into Sunday
resulting in some light accumulations on the highest mountain peaks.

The most significant system will likely move through the region on
Monday as a strong early season front brings the chance for
widespread light to moderate rainfall to the region. Rainfall
amounts are still highly uncertain. Southerly winds on Monday are
currently expected to be near 25-35 kt ahead of the front, thus wind
advisory conditions are not currently anticipated but model trends
will be closely monitored. Snow levels will rise to near 7000 feet
on Monday. /RPA

AVIATION...Shallow stratus and fog will likely return to coastal
terminals late evening...resulting in prevailing LIFR conditions
both for ceilings and visibilities that will remain through tomorrow
morning. Gradual improvement can be expected along the coast by late
morning/early afternoon...but this will be a gradual process that
may only result in a few hours of clearing during the mid afternoon.
VFR conditions will continue at UKI. /BRC

MARINE...A summer-like pattern will remain in place through at
least late tomorrow, with an inland thermal trough and high pressure
across the Pacific. This will result in a continuation of strong
northerlies across primarily the offshore waters, with a narrow
strip of somewhat variable but primarily southerly winds along the
immediate coast. As is often the case, mariners can also expect some
of the strongest northerly wind gusts...perhaps to around 30
kt...between Cape Mendocino and Shelter Cove and also just offshore
from Point Saint George.

This summer-like pattern will begin to shift Thursday, as an active
storm track will develop across the Pacific Northwest. Several fast-
moving storm systems will traverse through the waters late in the
weekend...initially resulting in weakening winds on Thursday that
will eventually become very erratic over the weekend as each system
quickly moves through the waters. From a birds-eye perspective, wind
speeds will be generally low despite brief periods of stronger
southerlies, which should help to prevent waves from reaching full
maturity albeit while also being somewhat chaotic. The lack of a
large, coherent northwest swell will also help keep seas somewhat
low through at least early next week. Still, mariners should prepare
for rapidly changing conditions over the weekend, complete with
periods of rain and gusty southerly winds particularly across our
northern waters. /BRC

&&

.EKA Watches/Warnings/Advisories...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until noon Wednesday for PZZ450.
     Small Craft Advisory until 9 AM Thursday for PZZ470-475.

$$

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