Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 122344

National Weather Service Eureka CA
344 PM PST Mon Nov 12 2018

.SYNOPSIS...Mild afternoons, chilly nights, and very dry
conditions will continue during much of the week. Areas of fog
will impact portions of the coast, with hazy sunshine inland. Areas
of smoke and haze will continue to expand across most of
northwest California through mid- week.


.DISCUSSION...An upper-level ridge straddling the West Coast will
temporarily give way to a series of upper-level troughs over the
next few days. However, the ridge will remain established to our
south, and the main impacts of any fronts associated with the
passing upper-level disturbances will stay to our north, across
Washington and northern Oregon. All this will translate to
continued dry weather for the week ahead across northwest

The main short-term challenges are going to be marine stratus and
fog along the coast, along with low temperatures presenting a
frost threat for inland areas tonight. Temperatures are running 5
to 15 degrees cooler along the coastal plain compared to
yesterday, mainly due to the switch to light onshore flow which is
allowing this stratus to drift onshore along the immediate Del
Norte and Humboldt coast. General light southeast flow developing
tonight may tend to keep this stratus from pushing much farther
inland, but areas that do see the fog push in will likely have a
tough time clearing out until mid to late morning Tuesday. Model
guidance does not have a very good grip on these clouds, but does
indicate more of a stratus and fog threat Tuesday night and
especially later in the week as the flow turns more predominantly
onshore. The marine air has also resulted in a substantial
increase in dewpoints along the coastal plain, which should limit
the frost threat to inland areas. Have issued a frost advisory for
the Mattole Valley and inland Mendocino where the growing season
officially continues for a bit longer. Areas farther inland will
be even colder, though a few degrees milder on average than the
past few couple of nights.

Meanwhile, smoke has thinned across much of Mendocino county
compared to yesterday, but smoke and haze aloft has spread
farther north across portions of Humboldt and Trinity County. More
smoke from the Camp Fire in Butte County is taking aim at
Mendocino and Trinity Counties through Tuesday. Farther north and
west toward the coast and up to Del Norte County, the smoke will
tend to be thinner aloft with hazy skies, but better overall air
quality and visibility compared to eastern Mendocino and Trinity.

The rest of the forecast through this week remains relatively
quiet and unchanged. Upper-level ridging will rebuild late in the
week after the last of the aforementioned troughs passes by well
to our north and east late this week. Overnight and morning
coastal clouds and fog during the mid to late week period should
tend to dissipate or drift farther offshore heading into the
weekend, with the potential for weak offshore flow and more in the
way of sunshine. At this point it is looking like any rain should
hold off until the middle or end of Thanksgiving week. /AAD


.AVIATION... The stratus is temporarily back for coastal forecast
terminals (KACV and KCEC). Subsidence due to the ridge axis overhead
has strengthened the inversion offshore, allowing for a marine layer
to form this morning. This cloud bank has now moved northward and
onto land with the afternoon seabreeze, lingering along the
coastline and bringing inconsistent IFR conditions. Upper level
cirrus and weak offshore winds later tonight may act to weaken the
bank by early tomorrow morning, allowing for a return to VFR
conditions. HRRR-experimental smoke model indicates smoke
continuing to drift northwest as well tonight into tomorrow as
southerly to southeasterly winds develop. Thus it seems possible
that haze and smoke may impact KACV and KCEC with reduced vsby and
sky obscuration due to haze. Confidence is not high on this and
have not reflected this in the current tafs. Smoke from the CAMP
FIRE in Butte county also continues to impact KUKI and vicinity
with IFR to MVFR vsbys but still not quite as bad as the previous
few days. /TDJ


.MARINE... Light winds and low seas are expected through Tue as a
weak front forces a ridge axis over the coastal water. There will be
a messy set of small swell groups as well as shorter period wind
waves that will combine to produce seas generally around 5 ft or
less. The main components, after the northerly wind waves subside,
appears to be a long period southerly swell that for the most part
remains offshore over the outer waters, along with shorter period
wind wave chop from light southerly to southeast winds.
Forerunners from a more significant swell group from the west will
arrive on Wed and peak through Thursday. Winds in the offshore
waters also strengthen Wednesday into Thursday, generating
associated rougher seas in the offshore zones, however conditions
are expected to stay below advisory levels. /TDJ


.FIRE WEATHER...An exceptionally dry airmass, characterized by
afternoon RH values still only 5 to 15 percent this afternoon,
followed by poor overnight RH recoveries, will remain in place
across the region for another day or so, followed by gradual
improvement during mid to late week. Elevated fire weather
conditions will persist due to these low RH levels, though winds
will be very light and mainly terrain-driven for the next several
days. Rainfall is not expected through the beginning of next


CA...Frost Advisory from midnight tonight to 9 AM PST Tuesday for



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