Island Mountain, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

577
FXUS66 KEKA 190822
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
1222 AM PST Fri Dec 19 2025

.SYNOPSIS...Moderate to heavy rainfall will taper off to the south
through Friday afternoon. More heavy rainfall returns Sunday. An
active storm track will bring additional heavy rainfall and a
flooding threat, strong winds, and lowering snow levels much of
next week.


&&

.KEY MESSAGES...

- Pacific storm track remains active with additional heavy
  rainfall and chances for strong southerly winds this weekend
  and through much of next week.

-Flooding risk trends higher as more rounds of heavy rainfall
 occur over saturating grounds.

-Focused areas of heavy rain and strong winds create a forecast
 challenge to pinpoint areas of greatest risk.

- Snow levels gradually drop by early next week, and could be as low
as 3500 to 4500 ft by Wednesday.

&&

.DISCUSSION...The threat for sharp rises in creeks and streams
will diminish this afternoon as rainfall turns light. Winds in
excess of 50 mph have been recorded at coastal Del Norte and the
prominent exposed headlands and ridgetops.

Widespread moderate to heavy rainfall rates up to 0.5 inch per
hour will continue to move from north to across the region
Friday. The threat for minor flooding will exist from this
rainfall. By early Friday afternoon the last of the moderate to
heavy rainfall will pull south of Lake County.

The persistent ridge that has been south of the region will then
eject east as a strong NE Pacific trough takes shape. Models
diverge on development of a new frontal wave and northward surge
of IVT ahead of the trough, but heavy rainfall looks to be focused
in more of a narrow band, and could become more persistent over
one area. It is likely that Lake and Mendocino will be in the
bullseye for this focus of moderate to locally heavy rain. The
precip max could easily shift northward Sunday as we have seen
many times before.

NBM 75th percentile 24 hour rainfall amounts Sunday are generally
2-3 inches north of Cape Mendocino, with 3 to over 4 inches south
of the Cape, including southern Trinity County. Currently, the
higher probabilities for over 4 inches in 24 hours is south of the
forecast area in Sonoma County. Looking at the ensembles, the
greater uncertainty is revealed. There is very high variability
for many locations in Mendocino and Lake County, which is expected
for more of a narrowly focused moisture plume. A narrow area of
very heavy rainfall rates of 0.4 to over 0.6 inch per hour may
develop. An additional Flood Watch will likely be issued to cover
this threat.

Going into early next week, ensemble guidance continues to keep the
storm door open, but the position of the systems are uncertain. Some
ensembles keep the bullseye to the south of the area towards the Bay
and some keep the bullseye in Mendocino and Lake Counties. A
potent shortwave trough or perhaps a compact closed low with
heavy rainfall and strong winds has been modeled to arrive around
Tuesday or into Wednesday. This system could pack strong winds,
possibly localized, as well as heavy rainfall. The exact location
and timing of this feature yields the ensemble uncertainty. There
is then the potential for a strong Pacific cyclone to imact N CA
late next week. If precipitation is near- continuous for several
days, more significant flooding impacts (such as main- stem rivers
nearing flood stage) are possible.

Snow levels remain high into the weekend and early next week. Snow
levels begin to fall going into early to mid next week, potentially
as low as 3500-4500 ft, which could bring us our first impactful
snow event to the higher mountain passes or even lower. Stay
tuned!


&&

.AVIATION...A cold front is bringing strong southerly winds to the
coastal areas and the higher ridges. There are stronger winds at a
couple thousand feet creating some wind shear This is also bringing
heavy rain with it and IFR to LIFR conditions. This is expected to
gradually shift south through the morning. Behind the front there is
expected to be a fairly dramatic shift of northwest winds, but these
will be much lighter, likely only around 10 to 15 kt. Friday night
fog is likely in the valleys again and UKI will likely be included
in this. The coast is expected to see some light offshore flow and
this may clear skies out. MKK


&&

.MARINE...A cold front moving through the waters is bringing near
gale to gale force southerly winds. This is building wind waves as
well. The front is expected to move past the area before sunrise in
the north and by midday in the south. Winds will quickly become
northwesterly behind the front, but remain only 5 to 15 kt. A west
to northwest swell is also building in this morning to around 10
feet at 11 seconds. This will slowly diminish on Saturday.

Another weather system is expected on Sunday but there is wide
variability in the model solutions. The models are currently
struggling to resolve a strong area of low pressure and where it
will exactly track. The NAM is now showing weaker winds more like
the GFS. Confidence is still low on this so blended the NBM with the
90th percentile of the NBM. This yielded winds of around 20 kt. This
seems reasonable for now, but confidence remains low, and there is
still the potential for a stronger winds with only a small shift
in the strength 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


&&

.HYDROLOGY...The threat for minor flooding and sharp rises in
creeks and streams will diminish this afternoon as rainfall turns
light.

Additional rain starting Saturday night and continuing into early
next week has the potential to be more impactful. There is still
some uncertainty on the positioning and how long the heaviest rain
will last, but the heaviest rain will start around Cape Mendocino
and southward. 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
highways 299, 36, 101 and 199.

The storm track will remain active through much of next week with
much more rainfall likely. Additional Flood Watches will be
likely with increasing confidence on impactful accumulation
totals.

At this time, none of the main stem rivers are forecast to exceed
action/monitor stages. Rivers in narrow basins may once again
quickly rise with heavy rain on Friday. This is not too uncommon for
our rivers. Ensembles are showing slightly higher probabilities for
main stem rivers to reach flood stage within the next 10 days. The
highest chances are mid to late next week, but some potential is
there Sunday-Tuesday. Over the next ten days the RFC gives the
Russian River at Hopland now has a 42% chance to reach minor
flood stage. The Navarro River at Navarro has a 24% chance to
reach minor flood stage. The Eel River at Fernbridge has a 20%
chance to reach minor flood stage and a 51% chance to reach
action/monitor stage. The Mad River at Arcata has a 40% chance to
reach action/monitor stage but no ensemble members show flood
stage as a possibility in the nearer term.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory until 8 AM PST Friday for CAZ101-102-105-106.

     Flood Watch from midnight PST tonight through Friday
     morning for CAZ101>106.

     Wind Advisory until 8 AM PST Friday for CAZ103.

     Wind Advisory until 10 AM PST Friday for CAZ104.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Warning until 9 AM PST Friday for PZZ450-470.

     Small Craft Advisory until 9 AM 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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