Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 242204
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
304 PM PDT Sat Oct 24 2020

.SYNOPSIS...A very dry air mass and strong northeast winds over
the ridges will spread over the area Sunday afternoon and evening.
Extremely dry conditions and robust offshore winds are expected
to persist for Monday and Tuesday. Frost and freezing temperatures
will be possible in the valleys and in coastal areas early Monday
morning.

&&

.DISCUSSION...A small scale eddy in the lee of Cape Mendocino has
kept low clouds and some fog near the SW Humboldt and Mendocino
coastlines all day again today. High resolution model guidance has
not been handling this small eddy very well and clouds and
patches of fog may linger through the night again. Increasing
northerlies offshore should wipe out the stratus on Sunday.
Clouds were also stubborn to scour out completely across Del Norte
and the western slopes of the Humboldt county this afternoon.
Higher humidities tonight should also result in good recoveries
for most all locations tonight.

A shortwave trough will drop into the Great Basin by midday
Sunday. Surface high pressure will start to build in the wake
of this shortwave by the afternoon, with a very dry airmass
spreading across NW California during the overnight hours Sunday
night. Northeast winds will also start to increase over the upper
elevations and ridges through the day on Sunday, with possible
gusts to 50 mph by late in the day. A red flag warning for
critical fire weather conditions remain in effect from late
morning through Monday afternoon. The peak in the NE winds will
likely occur Sunday evening and overnight when instantaneous speed
should reach 60 mph over the ridges. We also posted a wind
advisory for the upper elevations of Lake and southeastern
Mendocino counties above 1500 feet, and northeastern Mendocino,
southeastern Humboldt and southern Trinity counties above 2500
feet.

Even though winds will be quite robust over the ridges, many of
the valleys and wind-shelter areas will likely not see advisory
level winds. Winds may even go calm in the valleys overnight
Sunday night. Overnight temperatures are expected to plummet in
the mid 20`s to lower 30`s across the valleys of Trinity county.
The vert dry airmass, light valley winds and longwave cooling
overnight will allow many of the valleys of Humbodlt and Mendocino
counties to dip to near freezing early Monday morning. The air
mass is not exceptionally cold for NW California, so it will
depend highly on the amount of wind. Even coastal areas could see
frost and freezing temperatures early Monday morning.

Guidance indicates an upper ridge building over the forecast area
Tue and Wed as the upper trough slowly edges eastward across the
Desert SW. The warming aloft will likely promote above normal
daytime temperatures, however the dry air, light offshore flow and
clear skies will also allow temperatures to plummet each night.
Continued frost and freezing temperatures will be possible each
night in some of interior valleys.

There is a great deal variability and spread in the guidance late in
the week, around Thursday and Friday. The ECMWF and ENS have been
consistently wetter than the GFS/GEFS and CMC. WPC clusters
reflect these differences with about 25% of 100 members wetter
(over one tenth of inch of rain) than the combined ensemble mean.

&&

.AVIATION...Coastal low clouds, drizzle, and fog have given way to
partly to mostly sunny skies along the North Coast this afternoon.
However, low clouds continue over portions of the inland terrain
generally N of Cape Mendocino. Coastal stratus remains entrenched
along the coasts of S Humboldt and much of Mendocino counties.
Expect smaller areas of low clouds to develop along the North Coast
overnight, particularly from Humboldt Bay to Cape Mendocino.
However, drier air near the surface and a slowly increasing offshore
component to low-level winds should prevent significant reductions
in visibility due to fog. However, some patches of ground fog are
certainly possible around sunrise. NW-N winds will be gusty along
the coast into the evening.

For KUKI, mostly VFR conditions are expected with light winds.
However, high resolution models indicate some low clouds may develop
over the Russian River Valley. Uncertainty is high, so only a low
scattered deck has been included in the TAF. /SEC

&&

.MARINE...Northerly winds will increase tonight across the area
tonight. However, it looks like the gales over the S outer waters
may be delayed and have a shorter duration. As a result, have
adjusted the headlines over the S waters a bit. Otherwise, the
forecast remains generally unchanged. The strongest northerlies are
forecast to shift farther offshore Sunday afternoon through the day
Monday, with the strongest winds eventually residing across the NW
corner of the waters. NW swell at 3 to 4 feet is expected to build
into the area late Sunday, then slowly decay into the middle of the
coming week. /SEC

&&

.FIRE WEATHER...RH`s will generally be higher with light to
moderate winds through tonight. An exceptionally dry airmass is
forecast to spread across the region Sunday afternoon through
Tuesday. That airmass combined with very dry vegetation and east-
northeast ridgetop winds gusting from 30 to 50 mph will yield
critical to locally extremely critical fire weather conditions
from Sunday afternoon through Tuesday morning.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 11 AM Sunday to 5 PM PDT Monday for CAZ201-
     203-204-211-212-264-276-277-283.

     Freeze Warning from 4 AM to 8 AM PDT Sunday for CAZ107-108.

     Hard Freeze Watch from late Sunday night through Monday morning
     for CAZ107-108.

     Wind Advisory from 5 PM Sunday to 11 AM PDT Monday for CAZ106-
     108-111-113>115.

     Freeze Watch from late Sunday night through Monday morning for
     CAZ105-110-111.

     Frost Advisory from 4 AM to 8 AM PDT Sunday for CAZ111-114.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 9 AM PDT Monday for PZZ450.

     Small Craft Advisory until 9 PM PDT this evening for PZZ470.

     Gale Warning from 9 PM this evening to 9 PM PDT Sunday for
     PZZ470.

     Small Craft Advisory until 9 AM PDT Sunday for PZZ455.

     Small Craft Advisory until 3 PM PDT this afternoon for PZZ475.

     Gale Warning until 3 PM PDT Sunday for PZZ475.

&&

$$

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