Gale Watch 8, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
357 PM PST Wed Feb 14 2024

.SYNOPSIS...An active weather pattern has begun today with an
ongoing storm system bringing moderate rain and isolated heavier
showers. A stronger storm system more focused in the southern half
of the forecast area will then impact the area Friday into the
weekend. An additional impactful storm system will bring more rain
and gusty southerly winds by late Sunday.

&&

.DISCUSSION...A cold front is passing through this afternoon while a
surface low has formed off the Oregon coast. As post frontal showers
and a brief period of isolated thunderstorms (15%) develop over most
of the forecast area, trailing moisture behind the surface low will
direct steady, moderate rainfall focused over Del Norte County
through Thursday. This will lead to 1 to 3 inches of additional
rainfall for this county through Thursday, and minor urban and
small stream hydrological issues may develop as a result. Some of
the more vigorous showers may contain gusty winds this afternoon.

A stronger system continues to be forecast for late Friday
through late Saturday as the broad North Pacific low pressure
system pushes east into the NE Pacific region and stronger
disturbance eject off of it. Broad ascent and upper diffluence
will first spread over CA late Friday. Chances then increase for
moderate to heavy rainfall and stronger southerly winds as an
atmospheric river storm system arrives through Saturday.
Hydrological and wind issues look likely through the weekend,
particularly for the southern portion of the forecast areas from
the King Range and south. A strong shortwave or even compact
surface feature looks to form and locally enhance winds and
rainfall late Saturday. The track of this feature is yet to be
fully resolved, but has been inconsistently modeled to impact
somewhere along our coastal forecast area with around 60 kt 950 mb
winds, but higher resolution guidance will be needed for
confidence.

An additional larger area of low pressure looks to then cutoff
and stall off the CA coast Sunday, bringing the potential for a
prolonged period of stronger southerly winds and rainfall (heavy
at times) Sunday night and into next week, so the extended
forecast should be watched closely due to exacerbating
hydrological issues from the potential succession of storm
systems. Rainfall from this system may be again focused in our
southern zones for this system, but the uncertain track of the
cutoff low decreases confidence.

There is a high probability (60 to 100%) for greater than 3 inches
of rainfall Saturday through Monday. The favored terrain enhanced
location along the King Range and south have a modest shot (20 to
50%) at greater than 5 inches through the same time period. Advisory
level winds (gusting to 45 mph) are looking likely (up to 70%) over
at least some of the ridges and coastal headlands late Friday
through Saturday. Higher gusts will be possible if a compact
surface low moves in. There looks to be a better shot of stronger
winds for the Sunday night/Monday System. The EFI (Extreme
Forecast Index) is showing 0.9 vs 0.7 for QPF, meaning
climatologically anomalous rainfall for Saturday. Overall, most
likely rainfall forecasts show 2 to 4 inches throughout Lake and
Mendocino on Saturday. Such rain will be falling on freshly
saturated soils and will be more evenly spread to lower
elevations, increasing the risk of urban and small stream
flooding. /JJW

&&

.AVIATION...All terminals have been in and out of IFR during a cold
frontal passage beginning late this morning, significantly reducing
ceilings and vis with locally heavy downpours. The last few bands of
strong showers are traversing the southern Humboldt and Mendocino
coasts, inundating ACV and UKI. Visibility's should gradually improve
as this area of low pressure progresses east, but conditions will
remain unstable through the TAF period with CAA at upper levels
steepening lapse rates. As a result, isolated thunderstorms are
possible along the coast through the rest of this evening.
Otherwise, mid to low level ceilings will keep terminals MVFR with
continual rain showers through early Thursday morning. Gusty S winds
and light LLWS will hang on in CEC while ACV and UKI winds will
gradually diminish overnight. Additional waves of moderate rainfall
will be confined to CEC and ACV through the day on Thursday while
UKI should lift to VFR ceilings and VCSH by Thursday morning.

&&

.MARINE...Gusty southwesterlies and sig waves are beginning to
diminish as an area of low pressure moves onshore. Overall, the sea
state has been a bit chaotic with competing NW and SW swells
mingling with wind waves triggered by a frontal passage this
morning. Winds and seas will remain elevated in the northern waters
with continual wind wave response, while lighter conditions in the
southern waters will quickly rebound to small craft early Thursday
morning as a long period westerly swell fills into the waters. A
lull in the sea state is expected late Thursday into Friday ahead a
stronger storm arriving on Friday as a landfalling AR. Responsive
southerly wind waves will begin in the outer waters early Friday and
slowly progress into the southern inner waters. Models have been
consistently hinting that the frontal boundary will stall offshore
until weakening early Saturday morning, thereby allowing gale gusts
to persist. Steep and hazardous seas will result as two long period
westerly swells decay and build alongside steady southerly wind
waves. Sig waves are forecast to be 16-18 ft across the waters with
the potential for high surf along the coast. Winds and seas will
diminish slightly for the second half of the weekend, but wave
heights do not look to drop below 10 ft before next week.

&&

.HYDROLOGY...Two atmospheric river type storm systems will bring
periods of moderate to heavy rainfall to the region Saturday and
again late Sunday through Monday. Additional rainfall may
continue into next week from a potentially stalling weather
system. The CNRFC is projecting the Russian River at Hopland to
reach flood stage late Saturday with other rivers (such as the Mad
River, Eel River at Fernbridge and South Fork Eel) showing
probabilities of 40 to 60% of reaching Monitor Stage. Clear lake
has increasing chances for reaching Monitor Stage of 8 feet as
well. WPC has now included us in a "Slight Risk" for excessive
rainfall through the weekend. The forecast should be monitored as
the situation evolves. /JJW

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory until 3 PM PST this afternoon for CAZ102.

     Winter Weather Advisory until 4 PM PST Thursday for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PST Thursday for PZZ450-455-
     470-475.

&&

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

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