021
FXUS66 KEKA 111153
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
453 AM PDT Tue Mar 11 2025

.SYNOPSIS...Gusty south winds are expected late tonight 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 tonight 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 tonight 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 tonight through the end of the week. Southerly
wind will begin to increase ahead of the troughs by late this
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 tonight, 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 this
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...Lingering low level clouds are being observed along
coastal terminals. MVFR/IFR conditions with brief periods of LIFR
categories will be present through the morning until atmospheric
mixing evaporates away the condensation late in the morning. Strong
southerly winds will build over the next 24 hours due to an incoming
low pressure system arrives to the PacNW. Rainshowers, gusty winds,
and degraded visibilities bringing conditions to MVFR/IFR through
tonight into tomorrow morning. A fast moving low level jet will
create Low Level Turbulence overnight tonight through Wednesday
morning with 35-40kt winds @ 1.5kft AGL.

&&


.MARINE...Today, marine conditions will begin to change due to a
series of storms heading the the coastal waters through the rest of
the week and through the weekend. Southerlies will build through the
day to strong breeze gusts by sunset. The winds wont stop there
however, an incoming low pressure system heading towards the
Washington State / British Columbia area will create gale force
winds with strong gale force gusts from tomorrow evening through the
early morning in the northern waters, and near-gale to gale force
gusts in the southern waters. Hi Res Model Guidance is suggesting
winds in the southern waters will be lighter, peaking at near gale
force sustained winds with a 60-80% probability of gale force gusts
in the upper parts of the southern waters early Wednesday morning.
Gale Warnings have been issued in response to this increase in
forecast confidence. Winds are currently forecasted to subside below
gale force to strong/fresh breezes by mid-morning on Wednesday.

Wind waves will build rapidly as gales enter the waters, and are
forecasted to rise from 3 feet to >9 feet in 6 hours overnight
Tuesday through Wednesday morning. These wind waves, in addition to
a long/mid period swell at 12 feet, will create hazardous
conditions, even after the Gale Warning has expired. This means seas
will continue to remain chaotic and increases the potential hazards
for smaller watercrafts through Wednesday and Thursday.

More storms entering our area will arrive on Friday morning and
again from Saturday afternoon through Sunday night. More details on
these storms and their impacts on marine conditions will be available
when models begin to align and resolve better within the next couple
of days. DS



&&

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

     Wind Advisory from midnight tonight 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 Warning from 9 PM this evening to 9 AM PDT Wednesday
     for PZZ450.

     Gale Warning from 2 AM to 9 AM PDT Wednesday for PZZ455-475.

     Gale Warning from 8 PM this evening to 9 AM PDT Wednesday
     for PZZ470.

&&

$$

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