Hazardous Seas Warning 36, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
344 PM PST Fri Nov 17 2023

.SYNOPSIS...Showers and isolated thunderstorms are forecast this
evening through Saturday night. Showers activity will diminish on
Sunday as a colder and stable airmass settles over the region.
Dry weather is forecast to prevail into early next week.

&&

.DISCUSSION...Composite reflectivity radar imagery shows isolated
showers moving northwestward across Mendocino and Lake counties
this afternoon as a shortwave pin-wheeling around the closed
upper-level low positioned west of Central California over the
offshore waters. Precipitation is expected to increase in coverage
and intensity this evening as the aforementioned upper low
gradually move toward northern California tonight and Saturday
morning. Moisture and showers will spread northwestward into
Humboldt and Trinity Counties late this afternoon and evening with
the southeasterly flow aloft. The boundary layer will increase
with CAPE values around 100-250 J/kg across Southern Humboldt,
Mendocino and Lake counties. Isolated thunderstorms, brief heavy
downpours and small hail will be possible.

Farther northwest over the Gulf of Alaska, an upstream trough will
driven a cold front across the northern portion of the area on
Saturday evening. Convective allowing models indicate moderate to
strong showers moving across the area early Saturday afternoon
north of Cape Mendocino. With 500 mb temperatures dropping to
-25C and boundary layer Cape around 100-300 J/kg, isolated
 thunderstorms, brief heavy downpours and small hail will be
 possible with it. Rainfall total amounts of a half to an inch is
 expected across the region, with up to two inches over isolated
 higher elevations. Southerly winds increase to around 25-35 mph
 ahead of an advancing front Saturday evening.

Snow level will be around 7000-8000 feet today into Saturday
afternoon, before lower to around 3500-4000 feet Saturday night
into early Sunday morning behind of the front. Forecast snow
amounts are too low, less than an inch in 12 hours, to warrant a
winter advisory even for Scott Mtn Pass at 5400 feet.

The airmass will become colder on Sunday and then drier Sunday
night and Monday as a ridge builds. Offshore flow should result in
slow drying, however suspect there will be fog and low clouds in
the interior valleys. Frost and freezing temperatures will be
distinct possibility for the North Coast and adjacent valleys
early Monday morning.

Beyond Monday, an upper ridge and dry weather will dominate early
to mid next week. A shortwave trough will move over the ridge and
may bring some light showers or rain or drizzle around mid week.

&&

.AVIATION...Increasing cloud cover and shower activity will occur
through the remainder of the day as a lower pressure system off
the California coast approaches the region. Possible heavy showers
and some isolated thunderstorm will develop into the afternoon
hours, with highest confidence further south in Mendocino and Lake
counties. Ceilings will lower over the Ukiah valley tonight. Low-
level wind shear will also impact UKI this evening into Saturday
with southeasterly winds aloft at around 30 kts. Outside of any
productive showers, prevailing offshore winds will generally
maintain VFR conditions at ACV and CEC through tonight.

&&

.MARINE...Southeasterly winds will increase tonight, with winds
strongest over the southern outer waters. A compact area of low
pressure will generate locally stronger winds, heavy rain showers
and possibly a stray thunderstorm over the southern waters this
through tonight. Localized gusts up to 30 kts are possible with
these storms. A front approaches the area Saturday afternoon, and
northerlies will increase sharply behind this front, especially in
the northern outer waters. Gale force winds are expected in the
northern outer waters with gusts up to 40 kts possible. Small craft
conditions are expected in the other zones. A large northwesterly
swell will build in behind the front on Sunday, peaking at about 15
feet at 12 seconds.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 2 PM Saturday to 9 AM PST Sunday
     for PZZ450.

     Small Craft Advisory from 4 AM Saturday to 9 AM PST Sunday
     for PZZ455.

     Gale Watch from Saturday afternoon through Saturday evening
     for PZZ470.

     Small Craft Advisory until 9 AM PST Sunday for PZZ475.

&&

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