Gale Watch 8, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
245 PM PDT Mon Mar 10 2025

.SYNOPSIS...Gusty south winds are expected late Tuesday night
into Wednesday afternoon. Heavy rain and heavy mountain snow is
forecast late on Wednesday. Additional bouts of rain and mountain
snow expected to follow late week into the weekend. Snow levels
are forecast to fall below 2000 feet Wednesday night and Thursday
as rain showers persist. Small hail Wednesday night into Thursday
could create icy and hazardous road conditions.

&&

.DISCUSSION...
KEY MESSAGES:

-Rain and mountain snow to return Tuesday night and Wednesday.
 Wet and unsettled weather to continue for the remainder of the
 week through the weekend. Heaviest precipitation expected on
 Wednesday and again over the weekend.

-Strong wind gusts for high elevations late Tuesday night into
 Wednesday. Greatest risk for populated areas along shore and in
 Lake County. Stronger winds possible over the weekend.

-Snow levels will drop through the week, dropping below 2000 feet
 by Thursday with periods of heavy snow possible over highways
 299, 36, 3, and 199.

-Small hail and hazardous road conditions possible Wednesday
 night through Thursday

WEATHER PATTERN OVERVIEW:

A series of deep troughs will bring a return to wet and unsettled
weather by late Tuesday through the end of the week. Southerly
wind will begin to increase ahead of the troughs by late Tuesday
afternoon, peaking Wednesday morning. A moderate jet of 35 to 50
kts at 800 mb is forecast to sweep the area early Wednesday
morning. This jet supports a 60% to 90% chance of gusts to 45 mph
or more over ridges and coastal headlands. NBM 90th percentile
gusts are on the order of 60 mph for SW Humboldt and portions of
Lake County, mostly over the ridges and right before frontal
passage. Such speeds are consistent with a minor risk of tree
damage and isolated power outages. With that said, we issued a
wind advisory considering the instability and mixing near the
frontal boundary. Most lower elevations have much lower
probabilities for gusts to 45 mph, about a 20 to 40% chance.
Deterministic NAM12 BUFKIT soundings indicate downward momentum
transfer around 35-41 kts at both KCEC and KACV airports. ECMWF
ensemble mean gusts are under 40 mph with a few members 45-53 mph.
This will need to be watched for possible expansion of the wind
advisory to the lower elevations once within range of the CAMS
and HREF statistics.

A consistent supply of moisture along the trough will help
generate widespread rain across the area, mostly during the day
Wednesday. Moisture transport is generally consistent with an weak
to moderate atmospheric river event (AR1), though the duration of
the AR appears limited to less than 24 hours. Most likely rain
totals are about 2 to 3 inches at higher elevations and 1 to 2
inches at lower elevations. Down sloping effects will generally
greatly decrease low elevation rain amounts, especially around
Humboldt Bay. Such amounts will generate minor to moderate urban
and small stream flooding concerns with less than a 10% chance of
minor flooding along any mainstem rivers. Rivers, streams and
creeks will rise rapidly in response to the rainfall run-off,
however once again the short duration of the heavy rain will
mitigate the risk for significant flooding. Convective potential
increases late Wednesday and persists into Thursday with more
showery precipitation and a slight risk for small hail as 500mb
temperatures plunge to -30C. Another pulse of organized rain and
perhaps strong southerly winds is probable on Friday.

The deep nature of the troughs will advect cold air across the area,
peaking Wednesday night into Thursday. Though snow levels will
starts as high as 4000 feet Tuesday night, there is a consistent
signal than snow levels will drop below 2000 feet Wed night into
early Thursday with upslope and evaporative cooling helping to
drop snow levels as low as 1000 feet, especially in Trinity County
by Thursday evening. Though precipitation will be inconsistent by
this time, impactful snowfall is expected on high elevation
highway passes of 299, 36, 199, and 3 by early Thursday. 4 to 8
inches of snow is generally most likely. Snow levels will most
likely reach their minimum early Friday morning, with a 25 to 50%
chance of 1 inch of snow as low as high elevations of highway 101
in Mendocino County and around Cobb.

A potentially powerful low pressure system will impact the
forecast area with more heavy rain and strong winds this weekend.
There is still considerable variability, but based on NBM
probabilities for gusts to 50 mph or more, impactful and damaging
wind gusts are possible (40-60% chance for lower elevations and
70-90% chance for the ridges and headlands). Snow levels should
increase above 3000-4000 feet and travel impacts on route 36 and 3
are possible. There is considerable uncertainty on the snow
levels and just 500 feet lower will make a huge difference.

FORECAST CONFIDENCE AND DEVIATIONS:

Timing of the incoming system has remained remarkably consistent over
the past several model runs, with rain and wind set to begin to
Tuesday evening and peaking early during the day Wednesday. Rain
amounts, however, have proved more variables. While the chances of
high rain amounts have generally diminished, there remains a 20%
chance of localized amounts over 4 inches in terrain favored areas.
Such amounts would bring more moderate flood potential.

Similarly, the overall wind risk has trended downwards, but there
remains significant uncertainty, mostly dependent on the exact
strength and track of surface low pressure which remains very
uncertain. Generally speaking, however, only 10% of ensemble members
show a 800 mb jet any stronger than 50 mph. This generally caps the
overall maximum wind speed. In line with this, ensembles now show
essentially no chance of wind gusts over 70 mph along high terrain
with chances for damaging wind gusts over 55 mph dropping to near 30
mph even in the most exposed areas. Of note, however, the
possibility for stronger wind next weekend has actually increased
with 20% of models showing a low level jet up to 70 mph. As the
midweek event has generally trended more moderate, some attention
will have to paid to the weekend event.

On the snow side, confidence has remained high that snow levels will
drop strongly by Wednesday night. There is an 80% chance of
accumulating snow at locations such as Berry Summit and Collier
Tunnel by late Wednesday evening. These locations serve as a good
indicator of when the strongest impacts are most likely along area
highways. Snow is more uncertain further south and later in the
week. That said, the low snow level signature remains strong, most
of the uncertainty has to do with waning QPF potential during the
coldest periods. The possibility for impactful snow at Cobb and
along highway 101 bears close watching, but the potential for 1
inch or more of snow in these locations remains relatively low
around 30%.

DB

&&

.AVIATION...High pressure over the area is bringing VFR conditions
and dry weather. Tonight an approaching trough is expected to start
shifting the wind and allowing stratus to form along the north
coast. The HREF is showing a 50 to 70 percent chance of ceilings
below 1500 feet at KACV and KCEC by 12 to 15Z on Tuesday. This may
take some time to clear, but they should clear or lift to VFR
conditions by midday Tuesday. The inland valleys may also see some
low clouds and fog again tonight, but this is not expected to
include UKI. MKK

&&

.MARINE...High pressure has temporarily built in today, shifting
winds northerly. Winds are generally light, but some stronger
breezes of 15 to 20 kts in the lee of Cape Mendocino are possible
through the evening, before easing overnight. Combined seas are
hovering around 9-10 ft, but these will gradually subside into
Tuesday. An approaching system will turn winds southerly and bring
gusty winds Tuesday night into Wednesday. High-res is showing
greater confidence on gale force gusts in the northern outer waters
ahead of this front. The northern inner waters could see near-gale
force gusts up to 30 kts, but some models do show gale force gusts
reaching the coast. South of the Cape, winds are forecast to be near-
gale ahead of the front Wednesday morning. Seas Wednesday will be
characterized by steep to hazardous southerly wind waves and a long
period westerly swell of 10-12 ft. Winds ease Thursday, but another
system approaches the area Friday bringing another round of near-
gale to gale force southerly winds and steep wind waves. JB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Winter Storm Watch from Wednesday afternoon through
     Thursday afternoon for CAZ102-105.

     Wind Advisory from midnight Tuesday night to 2 PM PDT
     Wednesday for CAZ104>106.

     Winter Storm Warning from 2 AM to 8 PM PDT Wednesday for
     CAZ107-108.

     Wind Advisory from 7 AM to 5 PM PDT Wednesday for CAZ115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Watch from Tuesday evening through Wednesday morning
     for PZZ450.

     Small Craft Advisory from 9 PM Tuesday to 3 AM PDT Thursday
     for PZZ455-475.

     Gale Warning from 6 PM Tuesday to 9 AM PDT Wednesday for
     PZZ470.

&&

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