509
FXUS66 KEKA 092313
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
313 PM PST Thu Jan 9 2025

.SYNOPSIS...Weakening cold front will bring a chance of light rain
and drizzle to Del Norte and northern Humboldt on Friday. Gusty
northerly winds along the coast and robust offshore flow across
the interior mountains will return this weekend. Drier air mass,
clearer skies and light winds in the valleys will make for cold
and chilly mornings this weekend into early next week.

&&

.DISCUSSION...Stretch of dry weather will be temporarily disrupted
on Friday by a decaying front currently approaching 135W as of 2
PM Thu. The front will not pack much rain with 0.05 to 0.10 for
Del Norte County and a few hundredths for the greater Humboldt Bay
area. Shallow push of moist air behind the front will probably
result in a ramp up of fog and low clouds in the interior valleys
Friday night into Saturday morning.

High pressure is forecast to build back quickly Friday night into
Saturday, resulting in locally breezy northerlies by Saturday
morning. Pressure gradients tighten up on Saturday and winds
should increase for coastal areas and across the interior
mountains. ECMWF ensemble has been signaling the potential for
anomalous wind speeds for coastal areas with EFI`s of 0.5-0.7,
particularly from Cape Mendocino southward. Deterministic
soundings show stable conditions as winds shift to NE winds to
around 20-25kt, 1500-2000 ft AGL. The increased stability and
easterly component will make it harder for stronger winds aloft to
mix down to mean sea level. Even worst-case NBM 90th percentile
speeds (30-35 mph) are below advisory criteria, but may still have
impacts on outdoor activities this weekend. Around Cape Mendocino
over the coastal headlands and ridges in SW Humboldt (King Range)
gusts to 50 mph or more are highly probable. For now will message
the potential for gusty northerly winds along the coast in a
weather story graphic and social media post.

Offshore flow in the interior over the last several days will
finally decrease and become onshore on Friday in response to a
transient shortwave trough. This trough will be another inside
slider type and may turn out to be stronger in terms of winds
over the higher elevations. E to NE winds will increase across the
interior mountains this weekend with gusts o 25-35 mph over
exposed ridges. Most notable will be across southern Lake County
where NBM 24-hour probabilities for gusts over 50 mph increase to
30-50% Sunday night into Monday as the 500mb trough aloft cuts
back across the area. Granted those probabilities are confined to
the ridges and not the lower elevations. Deep east and northeasterly
flow and steeper surface pressure gradients will bring a potential
for stout NE winds to Lake County and possibly Mendocino County.
Ridges and exposed terrain will gust to 50 mph or more for sure.
How strong winds get in the lower elevations remains uncertain.
Strongest NE winds look to occur Sunday night into Monday. Current
indications (based on NBM 90th percentile gusts) are for places
like Cobb and portions of highway 175 to gust to 40-45 mph. This
is very close to criteria and a wind advisory will need to be
considered over the next couple of days.

The airmass will be slightly cooder and drier this weekend,
bringing near or below freezing low temperatures for lower
elevations, and possibly for coastal areas too. Low dewpoints,
clear skies and light winds at night will allow for ideal long
wave cooling. Frost and freezing temperatures are probable this
weekend into early next week, both along the coast and in the
interior valleys.

Offshore flow, a blocking large scale flow pattern and dry weather
will continue into early next week. Ensemble means keep the forecast
area in a dry and stable regime for the remainder of next week
too. Model chaos increases and ensemble members diverge mid to
late next week. So far there is no definitive signs for wet and
stormy weather. NBM hints at more piddly light rain late next
week, but nothing that looks long-lived and significant. DB

&&

.AVIATION...Apart from some occasional bouts of coastal haze, with
perhaps a brief contribution of smoke from a small fire well
northeast of the terminal, VFR conditions are prevailing. Surface
and near surface winds are light, with the exception of Southern
Lake County where northeast winds aloft up to 38 kts through the
1500 to 2000 ft AGL level will continue to create a threat for low
level wind shear in that area. High clouds will begin increasing
tonight in advance of a weak front that will move through on Friday.
Ceilings will begin lowering into MVFR levels with some chances for
light rainfall towards the end of this 18Z TAF period. Chances for
IFR, with a potential for patchy fog have been trending higher for
Friday morning, at 15 to 25% with a scenario of a faster arrival
time of the front. Chances for MVFR ceilings with movement into IFR
increase again through Friday afternoon as the front passes. JJW

&&

.MARINE...Northerly winds ticked up a little this afternoon. A long
period swell will begin filling in this evening and will rise to
around 6-8 feet in the 15 second area through Friday. A weak front
will also move through Friday, and there will be some up to 25 kt
gusts as it passes by through the morning hours. Northerly winds
will quickly increase Friday afternoon behind the front with a
tightening pressure gradient between a passing trough to the north
and a strong area of high pressure west over the Pacific. Gale
conditions will develop by Friday evening over the outer waters and
around Cape Mendocino. Winds will continue strengthening, and look
to be strongest Saturday and Saturday night when gusts of over 40
kts are forecast. Short period seas will become steep and hazardous
in response to these winds, building up to 16 feet. Gale conditions
look to likely hold through Sunday, when a 50 to 60% chance of gust
of 34 kts in the northern outers and 84% chance for the southern
outers currently exits. The pressure gradient will collapse through
Monday when winds and seas will begin an easing trend. A Gale Watch
is out for the outers starting Friday evening. Held short of
extending the watch into the inners for now. At least advisory level
winds with portions of gale strength gusts will exist in the inner
zones Friday night through Sunday, and probabilities for gusts over
34 kts are higher in the southern inners. JJW

&&

.BEACH HAZARDS...A long period westerly swell will begin filling in
this evening as a mid period swell fades. The swell will continue
building tonight through Friday, up to around 6 to 8 feet at 15
seconds, and as the dominant wave group. A High Risk for sneaker
waves can be expected by early Friday morning with these expected
conditions. JJW

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Beach Hazards Statement from late tonight through Friday
     afternoon for CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PST Friday for PZZ470-475.

     Gale Watch from Friday evening through Sunday morning for
     PZZ470-475.

&&

$$

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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png