Alton, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

265
FXUS66 KEKA 201002
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
202 AM PST Sat Dec 20 2025

.SYNOPSIS...A mainly dry day is expected Saturday. More heavy
rainfall returns Saturday night into Sunday. Monday is expected to
be relatively dry, however the active storm track continues to
bring additional heavy rainfall and a flooding threat, strong
winds, and lowering snow levels much of next week.

&&

.DISCUSSION...Saturday morning is expected to see dry weather
with more rain starting to moving into the area in the afternoon
and evening. This is expected to arrive in Mendocino and Lake
counties first where the focus of the rain is expected to be. This
rain is expected to continue through Sunday afternoon. IVT Values
from the GFS and EC ensembles show nearly 24 hours of over 500
kg/m/s. There are still some differences in the ensembles, but
confidence is fairly high that there will be quite a bit of rain.
The current forecast is showing 3 to 6 inches in Mendocino, Lake
and southern Trinity. Farther north 1 to 3 inches is expected in
Humboldt, Del Norte and northern Trinity counties. Have expanded
the flood watch north into southern Trinity county. For now it
looks like southern Humboldt will see around 2 to 3.5 inches which
isn`t expected to be enough to cause much flooding. The NBM does
show the potential for close to 6 inches in southern Humboldt if
there was a shift north with the event. So this will need to be
watched as it gets closer. See hydrology section for more details.

Gusty winds are also expected with this event over southern
Mendocino and Lake counties. 850MB winds on the NAM over southern
Mendocino and Lake counties are expected to be near 45 to 50 kt.
However, the strongest winds are expected to remain aloft with a
fairly stable layer near the surface. This stable layer is also
expected to limit the potential for thunderstorms. Snow levels
with this next system are expected to remain high through the
event, but start to come down as early as Monday.

Sunday night into Monday the main system is expected to move out
of the area, however southwest flow continues and this is expected
to keep skies clouds and some rain showers around. Snow levels are
expected to be around 4,000 to 6,000 feet, but any snow that does
fall should be fairly light.

Monday night into Tuesday the next weather system is expected to
move into the area from the south. However, there is still quite
a bit of uncertainty on when exactly this will move in. Heavier
rain is expected initially in southern Mendocino and Lake
counties gradually spreading north on Tuesday. Snow levels
currently are expected to be around 4,000 feet in the north and
6,000 feet in the south. This will likely bring snow to Scott
Mountain Pass on Hwy 3. There is certainly the potential for this
colder air to move slightly north or south and impact hwy 199 and
hwy 299. So this will need to be watched as it gets closer.
Rainfall amounts are expected to be lighter with this colder
system, but with the previous rainfall this may cause some
flooding. See the hydrology section for more details. There is
also the potential for some stronger winds with this system in
Mendocino and Lake counties, but there is a high level of
uncertainty with this still.

Wednesday may see a break in the rain or least a break in the
heavier rain. However snow levels may be lower if there is any
precipitation and there could be some light snow. Heavier rain is
expected to return Wednesday night and Thursday. Again, this looks
like a colder system. Currently the NBM is showing snow levels
around 4,000 feet, but this could easily end up a thousand feet
higher or lower. This will also bring the potential for some small
hail. Additional rain and snow is possible on Friday with
generally drier conditions possible by Saturday. MKK

&&

.AVIATION...(06z TAFs)...Upper level winds are quite strong but have
not mixed down to effect landing approach with low level wind shear.
The recently departed Atmospheric river has left standing water and
flooded streams and could have standing water on runways or taxi.
Post frontal showers have eased but another integrated water vapor
plume is due by late Saturday afternoon or evening. This round will
be focused on Mendocino and Lake county terminals. UKiah will likely
have reduced visibility on  the backside of the front with showers
and ceilings at or below 15,000ft. Otherwise expect an unsettled
weather pattern for the next few days with flight categories
variable. /EYS

&&

.MARINE...A west to northwest swell has been building, and has
reached around 8-10 feet at 11 seconds -per the latest buoy
reporting. This will slowly diminish Saturday.

Another weather system is expected Saturday night into Sunday yet
there is wide variability in the model solutions. The models are
currently struggling to resolve the location of a strong area of
low pressure and where it will exactly track. The locations of
this storm will dramatically impact the strength of the coastal
winds, so looking at multiple models can give a better idea of the
potential winds formation. The NAM is now showing weaker winds
more like the GFS, yet the ECMWF seems to capture the influence of
the coastal terrain the best so a 2:1 blend has been made with
the previous forecast. This yielded winds of around 20 kt. This
seems reasonable for now, as confidence remains low, yet there is
still the potential for a stronger winds with only a slight
variation in the forecasted strength and/or track of the low.

Monday and Tuesday the winds look to generally remain fairly light
with the next storm system likely to bring gales on Wednesday or
Thursday. MKK/EYS


&&
.HYDROLOGY...Additional rain starting Saturday evening and
continuing through Sunday has the potential to bring flooding. The
heaviest rain is expected to be south of Cape Mendocino. It may
extend into southern Trinity county so have added a flood watch
there. This will again pose a threat for quick rises in streams
and creeks along with rock and mudslides. Risk for rock and
mudslides will again increase and could impact travel on area
highways.

At this time, none of the main stem rivers are forecast to exceed
action/monitor stages with this next system, although the Russian
river likely will get the closest. The next weather system on
Tuesday and Wednesday will have a higher potential for main stem
rivers to reach flood stage. The Russian River at Hopland has a 35
percent chance of exceeding flood stage Tuesday night. The Navarro
River has a 20 percent chance. The Eel River has a 35 percent
chance of reaching flood stage on Wednesday. These mid-week
systems have a particularly high level of uncertainty in the
location and amounts of rainfall so these river levels will need
to be watched.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Flood Watch from Saturday afternoon through Monday
     afternoon for CAZ108>115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PST Saturday for PZZ470.

&&

$$

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