Area Forecast Discussion
Issued by NWS Eureka, CA

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523
FXUS66 KEKA 201310
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
510 AM PST Mon Jan 20 2020

.SYNOPSIS...A cold front will bring widespread rain and high
elevation snow tonight and Tuesday. Episodes of light rainfall
will be possible through the weekend, mainly north of Cape
Mendocino.

&&

.DISCUSSION...A potent storm system will approach the area from
the NW late today, but most precipitation is expected to hold off
until late afternoon or evening. SSE downslope flow will delay the
onset of heavier rain along portions of the coastal plain.
However, precipitation will be widespread with this system,
ranging from just under 2 inches in the Del Norte mountains to
about half an inch over far SE Mendocino County. Snow levels with
this system will start out around 5000 ft but will drop below 4000
ft by Tuesday night across Trinity County. As a result, some
decent high elevation snow accumulations are expected, with over
one foot of snow possible in the highest terrain of N Trinity
county. The Winter Storm Watch for that area has been upgraded to
a warning.

Southerly winds will increase ahead of the approaching storm
system as well, peaking early Tuesday morning. A Wind Advisory has
been issued for portions of Del Norte and Humboldt counties.

An active but progressive weather pattern will continue to result
in frequent bouts of precipitation in the coming week, but there
are indications that an upper ridge will develop over the W coast
late in the week, possibly bringing high temperatures over 60
degrees. Highest rain totals for the weak will favor locations N
of Cape Mendocino. /SEC

&&

.AVIATION...VFR with abundant mid and high clouds is expected today.
Increasing south-southeasterly winds will severely reduce the
potential for any shallow mist or haze at the coastal terminals
today. Winds both at the surface and aloft will increase further
tonight in advance of an approaching front.  As a result, expect low
level turbulence or low level wind shear at the coast terminals as
speeds 1500 to 2000 feet above ground level reach 30-40kt. The
probability for brief (an hour or less) IFR/LIFR conditions will
increase with frontal passage early Tuesday morning as rain rates
increase. Otherwise, mostly VFR/MVFR conditions are expected in the
showery regime following frontal passage on Tuesday.

&&

.MARINE...Seas have fallen below advisory level at the nearshore
buoys overnight. The brief break will be short-lived, however. SSE
winds and short period wind waves will steadily increase today as
another frontal system approaches the offshore waters. In addition,
a long period westerly will combine forces with a shorter period
westerly swell to produce seas around 10 ft. Southerly winds will
ramp up further tonight, reaching solid gale in the northern waters
by mid to late evening. High resolution guidance has the wind
switching to the Sw and falling off quickly behind the front north
of Cape Mendo early Tue, but then ramping up again as a secondary
trough approaches in the cooler/more unstable air behind the front.
Also, gale gusts may briefly blow across the southern inner waters
Tuesday morning as the front heads southward. After the strong winds
(gales) die down on Tuesday, the main hazard will be a WNW swell
which is forecast to hit 15 ft at 15 seconds. An active storm track
across the NE Pacific will ensure hazardous seas through the
remainder of the week. Toward the end of the week, Friday in
particular, a long period westerly swell will build and pose a
significant threat to mariners traversing harbor entrances as well
as beachgoers.  A statement for hazardous beaches and/or a weather
story graphic will need to be considered to increase awareness of
this threat.

&&

.BEACH HAZARDS...Large W swell is forecast to build across the
waters late Tuesday. As a result, dangerous surf conditions are
possible with surf heights over 20 ft. /SEC

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 10 PM this evening to 6 AM Tuesday
      for CAZ101-102-104>106.
     Winter Storm Warning from this evening through Tuesday afternoon
     for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 10 AM this morning to 8 PM this
      evening for PZZ450-475.
     Gale Warning from 8 PM this evening to 7 AM Tuesday
      for PZZ450-475.
     Small Craft Advisory from 10 AM this morning to 6 PM this
      evening for PZZ470.
     Gale Warning from 6 PM this evening to 7 AM Tuesday for PZZ470.
     Small Craft Advisory from noon today to 7 AM Tuesday for PZZ455.

$$

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