482
FXUS66 KEKA 092207
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
307 PM PDT Thu Oct 9 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 was centered offshore
the Oregon coast, with an associated frontal boundary extending
southward into California offshore waters this afternoon. This
feature is bringing mid to high level moisture across much of the
of the area. Pre-frontal light showers or light isentropic upglide
rainfall is expected this afternoon and evening.

Rain chances increase tonight into Friday as an occluded frontal
system approaches the area. Southerly winds will increase along
the North Coast late tonight/early Friday morning 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

.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...(18Z TAFS)...Thick and opaque clouds covered much of the
forecast area today. All forecast terminals (KACV, KCEC and KUKI) continued
to have VFR ceilings, generally above 4000-5000 feet. Some sprinkles
or light showers may occur with the upslope S-SW flow into the mountain
ranges, otherwise VFR ceilings for the terminal forecast sites will
continue for much of tonight. Increasing risk for MVFR ceilings and
lower vsby is expected toward early morning Friday with light to
moderate rainfall with an 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...Winds have been light under 15 kt today. NW swell around
5 ft at 10 seconds will continue through the week with perhaps
another build up to 7 ft on Sunday. Main concern continues to be
the potential for strong and gusty winds with downdrafts associated
with showers and possible thunderstorms late tonight into Friday
morning. Initially threat for strong wind gusts will be late
tonight into 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 until 3 PM PDT this afternoon for
     CAZ103.

     Coastal Flood Advisory from noon to 3 PM PDT Friday for
     CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS...None.

&&

$$

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