461
FXUS66 KEKA 100800
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
100 AM PDT Fri Oct 10 2025

.SYNOPSIS...A frontal system will bring periods of moderate to
locally heavy rainfall and gusty southerly winds on Friday.
Isolated thunderstorms expected over the coastal waters and along
the North Coast. Colder air aloft will bring the potential for
frost and some freezing conditions across the interior valleys
this weekend. A colder storm system is forecast early next week,
and will bring additional rainfall and the potential for some
mountain snow.

&&

.KEY MESSAGES...

-A cold upper low will bring light to moderate rain over the
 region for the next few days.

-The instability and dynamics of this low will be favorable for
 oceanic to coastal thunderstorms capable of strong wind gusts of
 40 to 50 mph and potentially some waterspouts.

-Colder trending overnight lows will bring chances for frost and
 freezing temperatures for the interior.

-A colder frontal system is forecast early next week which will
bring additional rainfall and a chance for mountain snowfall


&&

.DISCUSSION...A slow-moving Pacific cyclone centered offshore
between California and the Oregon coast, progresses westward with
an associated frontal boundary. This feature is bringing mid to
high level moisture across much of the of the area. Light showers
with a few 50db radar returns and lightning strikes are presently
being observed insitu, as of 08z Friday morning.

Rain chances increase today as an occluded frontal system
approaches the area. Southerly winds will increase along the North
Coast as a low level jet forms in advance of the front. Gusts
from 25 to 35 mph are likely over the more prominent coastal
headlands and exposed ridges in Del Norte and Humboldt counties.
High resolution models show light to periods of moderate to
locally heavy rain moving onshore early Friday morning over the
coastal ranges in Del Norte and Humboldt counties. Colder air
aloft will subsequently spread across the West Coast Friday
morning. As result, instability will increase to around 100- 200
J/kg of CAPE Friday afternoon and evening. Instability could allow
for some isolated thunderstorms (15 to 30% chance) over the
waters and right along shore, but any storms will be weak and
short lived. Rain showers are expected to continue to move east
and southeast through Friday night, before another round of
showers move in on Saturday. Total rainfall amounts from this
system are forecast to range from 0.50 to 0.80 inches from early
Friday morning through late Sunday morning in Del Norte and
Humboldt counties. Locally up to 1.30 inches focused over the
southwest windward facing terrain. 0.1 to 0.5 inches total
rainfall amount forecast for Trinity and northern Mendocino
counties. The lowest amounts are forecast for southern Lake County
with total rainfall from a trace to few hundredths expected.
/ZVS /EYS

.From Previous Discussion...

Overnight temperatures will trend much lower through the weekend
beyond the passage of a cold front. Frost and freezing temperatures
are currently forecast for the portions of the interior. How cold
it gets will be highly dependent on the amount of clearing/drying
that happens. The upper low will be slow to depart the region
before the next low begins its quick descent. Cloudcover and
lingering showery weather would moderate some of the cold
subfreezing overnight lows, but Saturday and particularly Sunday
have the potential to clear out.

There is increasing confidence for a colder area of low pressure
to dive straight over our region from the north early next week.
Additional rainfall and some mountain snow look probable based on
ensemble and cluster analysis. There is currently a 30-40 percent
chance for 24 rainfall over an inch through Monday. Given the
pattern of the setup, snow levels will need to be watched for the
mountains as the forecast period nears. JJW



&&

.AVIATION...(06z TAFs)...Thick and opaque clouds from the
outer band of the low pressure system continues to move through the
forecast area early Friday morning. Coastal regions have a brief
chance for scattering or clearing very early Friday before the main
front begins moving through a few hours before sunrise. VFR
conditions are mostly expected for coastal terminals with
the potential for MVFR with the passage of heavier rain and showers.
Some sprinkles or light showers may continue with the upslope S-SW
flow into the mountain ranges. A general increasing risk for MVFR
ceilings and lower vsby is expected toward early morning Friday with
light to moderate rainfall with the incoming front. Low level
shallow turbulence possible over the coastal range early Friday
morning with a 35-40kt of winds 2kft to 3kft above mean sea level.



&&

.MARINE...Southerly winds will increase to just below small crafts
throughout Friday as the front approaches. NW swell around 5 ft
at 10 seconds will continue through the week with perhaps another
building to 7 ft by Sunday. The main concern continues to be the
potential for strong and gusty winds with downdrafts associated
with showers and possible thunderstorms starting Friday morning.
Initial threat for strong wind gusts will be early Fri when a
925mb speed max peaks around 35-45kt.

Shear with this low level jet along the coastal terrain does not
quite line up with the greatest instability and CAPE farther
offshore, however. Risk for strong outflow winds to 35 kt, or more,
will persist through the day on Friday as the cold core aloft moves
across the area. Gusty shower activity may continue overnight Friday
and possibly into Saturday morning, before more stable conditions
and northerly winds build by Sunday. We issued a marine weather
statement to call attention to this threat for wind gusts to 35 kt
or more with showers and thunderstorms. Strong winds will generate
large steep waves that could capsize vessels.

&&


.COASTAL FLOODING...The perigee moon cycle is generating above
normal high tides. The tides are forecast to be higher again on
Friday, reaching 7.94 ft MLLW around 2:15 PM local time. Southerly
winds ahead of the system may increase the anomaly which could lead
to minor coastal flooding. If the 0.85 to 1.0 positive tidal anomaly
persists, the North Spit high tide will reach 9.0 feet. Minor
coastal flooding occurs around Humboldt Bay at tides of 8.8 ft at
locations such as King Salmon, Jackson Ranch Road, and the Arcata
Bottoms. The large tidal swings will also create stronger than
normal currents through channeled waterways.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Coastal Flood Advisory from noon today to 3 PM PDT this
     afternoon for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Coastal Flood Advisory from noon today to 3 PM PDT this
     afternoon for PZZ415.

&&

$$

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