Small Craft Advisory 120, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
549 AM PST Tue Nov 29 2022

.SYNOPSIS...Below average afternoon temperatures and chilly overnight
temperatures are expected to continue into next week. A significant
winter storm is expected Wednesday night and throughout Thursday.
Another winter system is expected by Friday.

&&

.DISCUSSION...A strong cold front associated with a low pressure
system off the coast of Vancouver Island is expected to move through
Northwest California on Wednesday. As a result, widespread chances
for measurable rainfall and lower elevation snow are expected
Wednesday night and into Thursday. This will most likely be a
significant winter storm event for the region.

Rainfall could reach over 1 inch to up to 3 inches. Windward
facing slopes are expected to have higher amounts than other parts
of the region. An intense band of precipitation moving in with
the cold front could also cause concern for localized flooding.
Flood prone areas and burn scars will be monitored.

On Thursday, snow levels could be as low as 2000 ft MSL. Initially,
the snow level could lower even more due to precipitation falling
through the cold and dry air mass preceding the moist air influx.
Further into Thursday, snow levels could remain low due to heavy
precipitation and upslope flow. If the snow levels are 2000 ft MSL
or below, many highway passes in Trinity, Humboldt and Del Norte
Counties would be impacted by heavy snow. The high elevation
sections of Highway 101 in Mendocino county could even potentially
see an inch or two of snow which would impact travel. Due to the
highly localized nature and many factors that go into snow levels in
the mountainous areas of the region, it is hard to pin down an exact
snow level. However, areas above 2000 ft MSL in Humboldt, Del Norte
and Trinity counties will most likely be upgraded from a Winter
Storm Watch to a Warning due to a high probability of heavy snow. In
general, areas in these counties above 2000 ft MSL are expected to
have snow throughout the duration of the event.

Ensemble models indicate more possibilities of systems favorable for
periods of rain and mountain snow into next week. In particular,
another system could potentially affect the Pacific Northwest going
into the weekend. This next system moving in on Friday is expected
to be colder with more potential for low elevation snow. Ensemble
models indicate that it will head south and then east toward the
Oregon Coast by Saturday afternoon. All ensemble models indicate
that the low will lose momentum before making it to the coast, but
to what degree is still uncertain. /JLW

&&

.AVIATION...Mainly VFR conditions being observed across the region as post
frontal northerly flow and drier air filter across the region. The VFR conditions
are expected to persist for another 24 hours before high and mid cloud cover
associated with an approaching front move into NW CA Wednesday morning. Thereafter
clouds, southerly winds and precipitation is expected as a winter storm will
bring mvfr and windy conditions to the the coastal terminals and interior areas through
Friday.

&&

.MARINE...Seas are still lingering around 11 feet this morning but
winds have diminished significantly. A brief period of light northerlies
and sca seas will continue today before winds begin to shift southwesterly
and westerly tonight. The wind shift will continue in advance of a potent
frontal system approach the waters from the northwest. This feature will
continue to promote an increase in wind speeds to Gale force across the
northern outer waters but at this time other zones should remain within
small craft advisory.  The northern inner may still require a Gale too
but will wait for additional model runs. Winds will peak with frontal
passage on Wednesday around midday or early afternoon.  Winds then shift
around to the N-NW and diminish during the day on Thursday, however a large
W-NW swell will build and seas are forecast to rise above 10 feet. Another
front will approach toward the end of the week and gale force winds and
large steep seas are forecast again. Gale force winds may persist into
Saturday mornings, but winds are forecast to trend down as another large
swell builds.

&&

.HYDROLOGY...A multi-inch rainfall event is forecast to occur
across Northwest California Wednesday evening through Thursday
afternoon. Low-level moisture flux will be favorably oriented
with west-southwest facing terrain such that locally heavy
rainfall rates will be possible...particularly in the vicinity of
the coast. That could lead to some areas of urban and small
stream flooding, as well as an increased risk for mountain rock
and mud slides. In addition, there is a marginal risk that
rainfall rates may become sufficiently large for debris flow
concerns across area burn scars.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Freeze Warning until 9 AM PST this morning for CAZ101-103-
     109.

     Winter Storm Watch from Wednesday afternoon through
     Thursday afternoon for CAZ105>108.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 10 AM to 3 PM PST Wednesday for
     PZZ450.

     Small Craft Advisory until 3 PM PST this afternoon for
     PZZ455-475.

     Gale Warning from 7 AM to 3 PM PST Wednesday for PZZ470.

&&

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

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