Small Craft Advisory 106, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
513 AM PDT Tue Oct 15 2024

.SYNOPSIS...A weak cold front may generate light drizzle along the
coast this afternoon but otherwise calm conditions will persist in
the interior. A stronger cold front Wednesday will bring increased
cloud cover and coastal drizzle with cool and gusty conditions to
end the week.

&&

.DISCUSSION...A subtle shortwave alongside a weak surface cold front
is forecast to cross the area today. Though providing some lift,
this system has very little moisture to work with. Little more than
light coastal drizzle is expected with NBM showing only a 10 to 25%
chance of even 0.1 inches of rain mostly concentrated right along
the Humboldt and Del Norte coasts. The cold front will most likely
even struggle to lift mid level clouds across the interior with
mostly clear skies persisting through the day aside from a lifted
marine layer along the coast.

A much deeper and stronger trough and surface cold front will dip
across the area during the day Wednesday. Though stronger, this
system will remain moisture starved with no noticeable moisture plume
from the south. Still the stronger forcing will bring slightly
higher chances (20 to 40%) of 0.1 inches of rain, still concentrated
right along the north coast but with a very slight chance (10%) of
wetting rain extending as far south as Mendocino county. At the very
least, this second front will be strong enough to pull midlevel
clouds across the interior.

The strongest impacts of the front will be felt Thursday into
Friday. First, very dry, cold air behind the front will bring some
of the first chances of frost for the season to interior valleys.
Cooling will be especially strong Thursday night as skies clear
within the cold air mass. Especially in Trinity County, NBM has a 80
to 90% chance of freezing temperatures. Frosty conditions are likely
(40 to 60%) chance to extend into interior Humboldt and Del Norte.
There is very little chance, however, of such cool conditions in
Mendocino and Lake counties, mostly thanks to stronger winds keeping
overnight conditions warmer.

In addition to cold air, strong north winds will build in behind the
front, especially as the front aligns with the Central Valley and
contrasts with high pressure rapidly rebuilding over the eastern
Pacific. Winds will most likely peal early Friday along the rim of
the Sacramento Valley and along the Russian River Valley with most
likely wind gusts of 25 to 35 mph in exposed areas. At high
elevations, NBM shows a 10 to 20% chance of isolated gusts as high
as 45 mph. Winds are highlighted as unusually strong with EFI
values above 0.8.

Essentially all cluster ensemble members show high pressure briefly
building this weekend. About 80% of ensemble members show high
pressure then giving way to a positively tilted trough, thought he
exact strength and timing of the trough varies widely. Most models
show just enough moisture transport along the trough to generate a
weak atmospheric river. No models show anything more than light
rain, however, with most likely rainfall concentrated along the
North Coast of 0.2 and 0.5 inches. The evolution of any trough is
unclear with very high uncertainty by early next week. About 50%
models show a dry pattern with the other 50% showing continued rain
chances.
/JHW

&&

.AVIATION...Light offshore flow overnight has helped stave off widespread
IFR/LIFR conditions for coastal terminals. HREF indicates high
probabilities of broad low level cloud cover just at the coast early
this morning, with potential periods of low visibility and ceilings
at coastal terminals. A broad shield of mid level clouds visible on
satellite will continue to progress eastward as the cold front
approaches the coast, gradually turning winds northerly through
today. MVFR/IFR conditions are likely by late afternoon or early
evening, with some light drizzle possible by then. UKI will avoid
inland penetration of stratus and remain VFR through the TAF period.
/JLW

&&

.MARINE...A NW swell continues to gradually deteriorate through the coastal
waters. Broad northerly flow will prevail across the waters today as
wave heights diminish. Winds and seas are expected to increase in
the southern waters by late Wednesday as a deep upper trough axis
traverses the region. Seas up to 10 feet are possible Thursday and
Friday, especially nearshore and downwind of Cape Mendocino, as
small craft wind gusts approaching 30 knots combine with a decaying
NW swell. JM

&&

.FIRE WEATHER...Generally warm and moderate conditions will prevail
across the interior through Wednesday. A well defined cold front
will increase fire weather concerns Thursday through Friday. Cool
but very dry air will build behind the front, dropping minimum RH
into the low teens throughout the interior. Strong surface
inversions will help promote poor RH recovery at night, especially
in Lake County with maximum RH as low as 40 percent. As the cold
front stalls in the Central Valley, it will generate a strong
pressure gradient along shore. This gradient will promote moderate
to strong north winds along the rim of the Sacramento Valley and
within channeled terrain such as the Russian River. Winds will be
strongest Thursday night into Friday when north winds combine with
the normal diurnal flow. Strong winds and dry air will best align in
Southern Lake County, generating critical fire weather conditions.
Wind gusts will most likely peak overnight with gusts of 25 to 35
mph on exposed ridges. NBM indicates a small chance (10 to 20%) of
gusts as high as 45 mph. Fire weather conditions will ease with much
calmer winds this weekend. /JHW

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Fire Weather Watch from Thursday morning through Saturday
     evening for CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 AM PDT this morning for PZZ450-
     455-470-475.

&&

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https://www.weather.gov/images/eka/zonemap.png