573
FXUS66 KEKA 040903
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
103 AM PST Thu Dec 4 2025

.SYNOPSIS...High pressure continues to build over the area,
bringing offshore flow and generally fair skies through Thursday
along with night and morning valley fog. Light rain is possible
mainly in Humboldt and Del Norte counties over the weekend.

&&

KEY MESSAGE:

* King Tides from December 4th-7th will lead to minor coastal
  flooding in low-lying areas mainly around Humboldt Bay.

* Frost remains possible Thursday morning in the colder valleys
  and along the coast.

* Dry and seasonably cool weather expected through Friday,
  followed by a chance of light rain over the weekend.


&&

.DISCUSSION...High pressure over the area is bringing fairly
robust offshore flow to the area. Northeast-East winds will be
breezy on the ridges through Thursday morning. Santa Fe
Geothermal, Knoxville Creek, and Mattole Road have all reported
gusts 25-37mph since 06z, Wednesday night. HiRes-ARW and other
high resolution models have the interior region of eastern Lake
county exposed to these Northeast winds, extending into Napa and
Sonoma counties. This should ease by 21z Thursday. Cold dry air
is of concern with winds easing overnight, allowing frost to
develop. Most agricultural interests have ended their growing
season. Tender plants left out in the cold this time of year will
perish. A frost advisory is in effect for portions of Humboldt and
Mendocino Counties for early Thursday morning. Early morning
minimums will vary widely from the mid 30`s to mid 40`s.

Thursday night into Friday morning a shortwave coming over the
ridge is expected to start bringing more cloudiness to the area.
This will likely keep temperatures warmer. It is possible this
could bring some drizzle to the northern coastal areas, but
confidence is low on this. Friday afternoon looks like the first
chance for some light rain and this may continue through the
weekend. The big question is how far south this rain will come.
The current forecast keeps most of it in Del Norte county with
less than a quarter of an inch in northern Humboldt county. Del
Norte count may see over a half inch. However this is a small
system and a slight shift farther north or south could really
change the rainfall totals. This is highlight in the 75th and 25th
percentiles from the NBM. The 25th percentile for Crescent City
shows 0.2 inches while the 75th percentile shows 1.1 inches. In
Eureka and much of Humboldt and Trinity counties those amounts
range from 0.00 to 0.5 inches. Farther south and east in southern
Trinity, Mendocino and Lake counties even the high ends amounts
are less than a quarter inch. Even if the heavier amounts make it
farther south, there aren`t expected to be many impacts.


&&

.AVIATION...(06Z TAFS)...High clouds continue to stream over
Northwest California. As the ridge continues over the area, offshore
flow will continue into Thursday morning, staving off coastal
stratus formation. As a result, coastal terminals will remain VFR
into Thursday. There is a chance for interior valley fog, however,
with the high clouds and drying winds, fog/low clouds are less
likely early Thursday.


&&

.MARINE...Northerly winds have continue to gradually ease, but
remain elevated Wednesday with gusts of 20 kts and up to 30 kts for
the outer zones and around Cape Mendocino. Winds and steep seas will
more significantly ease Thursday. Advisory level seas and winds will
linger longer, likely through Friday in the southern outer waters. A
decaying mid-period westerly swell will maintain combined seas 8 to
10 ft into Thursday morning. Winds and seas ease further Friday,
with the main exception being the expansion fan south of Cape
Mendocino. Conditions continue to improve going into the weekend as
high pressure weakens. JJW

&&

.COASTAL FLOODING...High astronomical tides are predicted through
Sunday for Northwest California. Water levels remain nearly a
half a foot above astronomical tides inside Humboldt Bay and this
may cause minor flooding again Thursday, so a Coastal Flood Advisory
has been issued. The tides continue to get higher Thursday and
Friday and additional flooding is expected around Humbodlt Bay.
Tides trend down over the weekend, however potential for coastal
flooding, will persist for Humboldt Bay. Outside of Humboldt Bay
the tide gauges are showing a slight negative anomaly as the swell
continues to diminish. At this point we aren`t expecting coastal
flooding outside of Humboldt Bay. This will need to be watched as
it gets closer. MKK


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Frost Advisory until 9 AM PST this morning for CAZ102>106-
     109-112-113.

     Coastal Flood Advisory from 9 AM this morning to noon PST
     today for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Coastal Flood Advisory from 9 AM this morning to noon PST
     today for PZZ415.

     Small Craft Advisory until 3 PM PST this afternoon for
     PZZ470.

     Small Craft Advisory until 2 PM PST Friday for PZZ475.

&&

$$

NOTE: The full forecast discussion is now regularly issued between
10 am/pm and 1 pm/am. Additional updates will be issued as needed.

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