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000
FXUS66 KEKA 042251
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
251 PM PST Thu Mar 4 2021

.SYNOPSIS...Gusty south winds will occur across much of the region
through Friday morning. A front will then move onshore Friday
afternoon and evening. Moderate to heavy precipitation will be
possible with the frontal passage, as well as snow for elevations
above 2000 feet. A period of relatively drier weather is expected
Saturday afternoon, followed by more rain Saturday night through
early next week.

&&

.DISCUSSION...Water vapor imagery showed a cold upper-level trough
situated over the NERN PAC Thursday afternoon. A surface frontal
boundary associated with the trough will approach the Redwood
Coast tonight, but is not expected to make landfall until Friday
morning. As the front moves onshore, precipitation intensity will
gradually increase...potentially becoming moderate to locally
heavy over portions of Del Norte and Humboldt Counties by late
afternoon. In addition, a tight pressure gradient will exist ahead
of the front, and when combined with a 40-60 kt low-level coastal
barrier jet, will favor periods of advisory level wind gusts
through Friday morning for low elevation sites such as Crescent
City, and higher elevations above 1500 feet across Del Norte and
Humboldt Counties.

Heavy precipitation rates associated with a zone of intense 925
mb frontogenesis is forecast to dynamically cool the airmass in
the 1000 to 5000 foot layer during Friday evening. Model forecast
soundings show a saturated near-freezing isothermal layer
developing as a result over Humboldt and Del Norte Counties. Snow
levels will subsequently fall to 2000 feet ASL, and possibly even
lower for a brief period of time between 4pm Friday and 4am
Saturday. Snow accumulations from 2 to 6 inches will occur as a
result across interior ridges and mountains. Reference the latest
winter weather advisory for more information.

Otherwise, model guidance indicates precipitation will become
light and scattered Saturday morning into the afternoon.
Thereafter, a second frontal boundary is forecast to move across
NWRN CA Saturday night and will aid in another period of rain.
Drier weather is forecast to redevelop during Sunday afternoon.
Then, a large upper trough accompanied by an expansive area of
500 mb temperatures from -30 to -35 C is forecast to dig over the
NERN PAC early next week. Impacts related to winter weather will
be possible with that storm system over portions of NRN CA.

Garner

&&

.AVIATION...A very broad strip of MVFR CIGS extended along the
reach of the North Coast from Trinidad and southward until mid-
morning. Over Mendocino, MVFR CIGS pushed into southern interior
areas as UKI reported MVFR CIGS in the latter morning; lasting
into early afternoon. Southerly gusty winds ramped up before
daybreak at CEC and the Del Norte Coast; then after daybreak, ACV
and the Humboldt Coast started reporting "not quite as strong"
gusty winds. Gusty winds also increased over interior Mendocino in
the late afternoon. The winds will remain gusty through
afternoon/evening/overnight ahead of Friday`s approaching cold
front. The above ground winds are really strong; there is a
potential threat for Low Level Wind Shear (LLWS) at coastal
locations. By 18z (10L), standing wave clouds were evident on VIS
Satellite Imagery along Coastal Humboldt County. Through the 00z
TAF period, upper level clouds will continue to advect into
Northern California through evening. All models are in general
agreement that VFR CIGS/VIS will prevail into Friday morning. Rain
data also indicates that rain will begin in the far north after
12z (4AM) but most likely in mid-late morning. /TA

&&

.MARINE...A front will slowly approach the coast today, bringing
a slow-moving, wide, and robust band of southerly winds. Gale
force winds will continue to spread across most of the waters
through this evening, with storm force gusts continuing to ramp up
in the N outer waters. These winds will continue to build up
short period southerly seas tonight, with heights in the lower to
mid teens expected for the outer waters. Meanwhile, another
slightly longer period 10 to 12 ft NW swell will fill in through
the evening and last through the weekend, bringing chaotic
combined seas in the high teens to lower 20s by this evening and
lasting through Friday.

Winds will significantly weaken late Friday, possibly going light
and variable Friday night before another shortwave brings
relatively light southerlies on Saturday. Southerly winds are
generally expected to continue into next week, with speeds
occasionally reaching advisory level, particularly across the N
outer waters. Seas will gradually subside Friday night and
Saturday. Then, a WNW swell is expected to fill in on Sunday,
currently forecast to peak around 18 ft at 16 seconds Sunday
night. /TJ&SEC

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 4 PM Friday to 4 AM PST Saturday
     for CAZ102-105>108.

     Wind Advisory until 10 AM PST Friday for CAZ101.

     Wind Advisory until 10 AM PST Friday for CAZ102-104>106.

NORTHWEST CALIFORNIA COASTAL WATERS...Storm Warning until 8 AM
     PST Friday for PZZ470.

     Small Craft Advisory until 9 PM PST this evening for PZZ455.

     Gale Warning from 9 PM this evening to 9 AM PST Friday for
     PZZ455.

     Small Craft Advisory until 3 PM PST this afternoon for PZZ450.

     Gale Warning until 6 AM PST Friday for PZZ450.

     Gale Warning until 9 AM PST Friday for PZZ475.

&&

$$

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