Winter Storm Watch 8, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
555 AM PST Tue Feb 27 2024

.SYNOPSIS...Cooler air settled in this morning behind a front
tonight. A multifaceted, powerful and very cold storm system will
then unleash brief heavy rain, strong winds, heavy snowfall and
small hail Thursday into the weekend.

&&

.DISCUSSION...The boundary layer is effectively decoupling this
morning with robust radiational cooling dropping coastal temps
into frosty and some freezing levels. The forecast for a major
winter storm is largely on track. On Wednesday a deepening, cold
trough will begin descending from the north. Rain chances will
increase from north to south throughout Wednesday under increasing
upper diffluence. Southwest winds will strengthen Wednesday
afternoon and become strong by early Thursday morning. A High
Wind Watch is out for gusts up to 65 mph on the ridgetops. An
Advisory may also be needed for lower elevations not included in
the watch. A strong cold front with an IVT plume will then arrive
Thursday. The front will initially deliver a round of widespread
moderate rainfall, with a briefer period of heavy rainfall for
portions of the North Coast and on some favored higher terrain.

Sounding analysis shows the potential for a sharp drop for snow
levels by around late Thursday morning. This colder scenario is
looking more likely given the adiabatic and dynamic cooling in
part from the orographic lift from the strong southerly winds.
Moreover, some high resolution guidance is resolving heavy
rainfall rates along a banding feature which could drive down the
cold air aloft. Have lowered snow levels Thursday to include the
Willow Creek and Hoopa Valley where sounding support exist for
now for at least light snow impacts. There will be a warm nose
ahead of the front which will further complicate this aspect of
the forecast.

The dynamic, very cold trough will continue to descend in,
bringing waves of embedded disturbances and fronts which will
steadily drive down snow levels. This looks to include a couple
small surface lows which could locally enhance precipitation and
winds, depending on where the track. Total precipitation has
slighlty decreased for the event through the weekend when the
trough axis passes through. Snow levels of 500 to 1000 feet are
most likely in Trinity, Del Norte, and Humboldt early Saturday
morning. Even south in Mendocino and Lake snow levels of 1000 to
1500 feet are most likely. The most likely snowfall forecasts
Friday through Saturday still shows multiple feet at high
elevation locations like Collier Tunnel and Berry Summit. The
Prairie Creek pass on 101 and stretches of 101 near Laytonville
in Northern Mendocino County can expect snowfall and travel delays.
NBM shows a 30 to 50% chance of accumulating snow as low as
Clearlake in Lake County and Blue Lake in Humboldt County early
Saturday morning. Increasing instability and forcing, along with
the very cold air aloft will also create an environment favorable
Friday into Saturday for dangerous and widespread accumulating
small hail. JJW

&&

.AVIATION...Winds will continue to be relatively calm along the North
Coast into the late morning. Light winds, generally from the north
and east, will persist until more northerly gentle to moderate
breezes take over by the afternoon. VFR conditions are expected at
all terminals through the TAF period. More cloudiness will develop
as ceilings begin to drop toward MVFR by the very end of the TAF
period as a low pressure system begins to approach the area.

&&

.MARINE...Northerlies strengthened behind yesterday`s frontal passage
with gusts in the low to mid 20 mph range. Advisory level
northerlies will generally diminish, but persist into the early
tomorrow morning, especially in the southern waters. A fresh NW
swell fills in around 12 ft at 13 seconds. Seas are expected to
trend downward by mid-week, but will soon build back Thursday and
into the weekend as a series of fronts approach. A large W swell is
expected late this week, with wave heights reaching around 20 ft.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     High Wind Watch from Wednesday evening through Thursday
     afternoon for CAZ101-102.

     Winter Storm Watch from late Wednesday night through Friday
     morning for CAZ102.

     High Wind Watch from late Wednesday night through Thursday
     afternoon for CAZ104>106.

     Winter Storm Watch from Thursday morning through Friday
     morning for CAZ105-106.

     Winter Storm Watch from Wednesday evening through Friday
     morning for CAZ107-108.

     Winter Storm Watch from Thursday afternoon through Friday
     morning for CAZ111-114.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 AM PST this morning for PZZ450.

     Gale Watch from Wednesday evening through Thursday morning
     for PZZ450-470.

     Small Craft Advisory until 2 AM PST Wednesday for PZZ455-
     475.

     Small Craft Advisory until 6 PM PST this evening for PZZ470.

&&

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