Winter Storm Watch 7, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
500 AM PST Mon Feb 26 2024

.SYNOPSIS...Light to moderate rainfall will move through the North
Coast today along a cold front. Cooler air will settle in behind the
front tonight. A multifaceted, powerful and very cold storm system
will then unleash heavy rain, strong winds and heavy snowfall late
in the week and into the weekend.

&&

.DISCUSSION...A cold front is quickly moving through from the north
this morning, and will bring areas of moderate rainfall from
Northern Humboldt through Del Norte. There remains a chance (30-40%)
for an inch of total snow accumulation over Berry Summit and Collier
Tunnel as snow levels will be very quickly dropping throughout the
day. Some breezy northerly to westerly winds will arrive behind the
front today.

On Wednesday a deepening, cold trough will begin descending from the
north. Subtropical moisture with origins near Hawaii will
advect north before being delivered to our coast ahead of the
first front Wednesday. There will be quite effective moisture
transport, looking at deep-layered strong southerly flow and IVT
values (Integrated water vapor transport) nearing 500 kg/ms. The
PWAT (precipitable water) values will become somewhat subdued (up
to 0.86 inches) after the passing of the airmass near the Gulf of
Alaska along the trough. Widespread moderate rainfall will still
occur, with areas of heavy rainfall rates expected late Wednesday
and Thursday. A quick initial round of 2-5 inches with this front
through late Thursday. This will be followed by more steady
moderate rates as snow levels come down. There will be some quick
river rises and the potential for minor urban and small stream
flooding impacts.

Winds will be strongest Wednesday through Thursday. Smith River -
Doctor Fine Bridge has up to 25% of hitting Monitor Stage Thursday.
Advisory level southerly winds currently look likely, and areas
of High Wind criteria will have to be monitored for. There will
initially be very strong winds aloft on approach late Wednesday,
but it does appear that there will be weakening as these winds
near the coast. NBM has consistently held 50-70% chances for peak
wind gusts to exceed 60 mph down to some coastal ridges and out at
Crecent City. There are similar chances for gusts over 70 mph for
the higher inland ridges of Humboldt and Del Norte counties, this
includes Kneeland (55%). EFI highlights this risk area.

Model soundings hint at a sharper drop in temperatures aloft late
Thursday, and this will need to be monitored regarding potential
valley floor snowfall for interior Humboldt. The dynamic, very
cold trough will continue to descend in, bringing waves of
embedded disturbances and fronts which will steadily drive down
snow levels. The impressive size of the trough and expansiveness
of cold air advection has helped maintain consistency in projected
snowfall amounts. Probabilities are unyieldingly high for 2 to 3
feet of snow total over interior passes at Berry Summit and
Collier Tunnel Friday through Saturday. 1 to 5 inches of snow
should be expected on valley bottoms in Trinity County with 1 to 3
inches currently most likely along Highway 101 in northern
Mendocino County. Snow amounts are much more uncertain closer to
the coast. NBM places a 10 to 20% chance of trace amounts of snow
as low as 100 feet in Humboldt and Del Norte. Even if impactful
snow is unlikely, such cold air will bring a real threat of
accumulating small hail. This magnitude of snowfall combined with
lingering gusty winds through Friday will amplify the potential
for widespread power outages. JJW

&&

.AVIATION...MVFR conditions have largely prevailed at all the
terminals this morning, largely from low ceilings with some brief
visibility impacts. An incoming system bringing rain later this
morning will continue MVFR ceilings and visibilities, with IFR
conditions possible during heavier rain. Ceilings at UKI will
gradually rise through the day into VFR by the afternoon and will
have little to no precipitation. JDB

&&

.MARINE...Light northerlies will begin to increase late morning as a
system moves through the area. Seas will increase behind the front,
increasing to 10 to 13 feet at 13 seconds and will be accompanied by
steep wind waves. Winds will ease by Tuesday, and seas will
gradually subside below 10 feet by Tuesday night. This will be a
brief lull as another system approaches Wednesday night, with winds
increasing and shifting southerly. Gale force gusts look likely
across most the waters Thursday, bringing steep wind waves. A large,
steep W swell will build in late week elevating wave heights to up
to 19 feet. JDB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Beach Hazards Statement until 10 AM PST this morning for
     CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 3 PM this afternoon to 9 AM PST
     Tuesday for PZZ450.

     Small Craft Advisory from 3 PM this afternoon to midnight
     PST Tuesday night for PZZ455-475.

     Small Craft Advisory from noon today to 6 PM PST Tuesday
     for PZZ470.

&&

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