Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 231240
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
440 AM PST Sat Jan 23 2021

.SYNOPSIS...A dry and breezy day is expected today. A cold
front will bring a period of rain and snow to the area Sunday with
showers lingering into Monday. Starting Tuesday afternoon a
significant winter storm may bring rain and heavy low elevation
snow through Thursday.

&&

.DISCUSSION...A brief period of high pressure is building into the
area this morning. Some low clouds have developed in the interior
valleys. Clearing skies are expected this afternoon, although the
sunshine may be deceptive. The northerly winds and temperatures
in the upper 40s to mid 50s will make it seem fairly cool.
Tonight lows will be in the upper 20s to upper 30s. The interior
valleys may see some fog or freezing fog.

Sunday a cold front will bring rain and snow to the area.
Precipitation is expected to start around sunrise on the Del Norte
coast and quickly spread across the rest of the area by mid to
late morning. The cold air in place combined with a fairly cold
system will bring snow levels around 1,500 in the morning. Most
areas of Humboldt and Del Norte county will see snow levels rise
to 2,000 or 2,500 before most of the snow comes. These areas are
expected to see 2 to 5 inches. Raised the winter weather advisory
to above 2,000 feet in these areas. In Trinity county the cold
air may remain trapped keeping snow levels around 1,500 feet.
Confidence is low on this, but left the winter weather advisory
above 1,500 feet in northern Trinity county and raised it to above
2,000 feet in southern Trinity. Behind the front may be a break
in the rain late in the afternoon. Brisk northerly winds are
expected behind the front.

Sunday night into Monday morning the upper level trough moves
overhead and there is the potential for small hail and
thunderstorms. The airmass is cold with H850 temperatures dropping
to -5 to -6 C and there is a fairly strong vort max moving
through. The models are not showing a low of showers so will hold
off on highlighting this too much, but suspect they may be
underdoing this. Have added a slight chance for thunderstorms
with small hail to the forecast over the waters and on the
Humboldt and Del Norte coasts. The models are still struggling
with the evolution of this, but the NBM and SREF thunder probs
have trended higher these last few runs.

Monday afternoon the trough starts to pull out of the area,
although with daytime heating there may be slight uptick in
showers over the inland areas in the afternoon. Mainly dry
weather is expected Monday night and some valley fog may develop
again.

The next cold front is expected to move into the area on Tuesday
and has the potential to bring significant snow to the inland
areas in the north. Models are now generally showing the front
move through Tuesday late in the afternoon and overnight bringing
heavy rain and low elevation snow. This front is also bringing a
period of strong winds Tuesday evening. The big question is how
low the snow levels will be. The NBM and many of the ensemble
members show snow levels of 1,500 to 2,000 feet. If these are
correct there is the potential for over a foot snow in
Weaverville. There is tight temperature gradient in the models so
despite the good agreement in the ensemble members confidence is
low on the snow levels for the period of heaviest precipitation
Tuesday evening and overnight. Snow levels could easily end up
above 2,500 or 3,000 feet and the impacts would be much lower.
There is good agreement in the moderate to heavy rain and
confidence is higher this. The relatively cold system makes
flooding fairly unlikely.

An upper level low associated with this system moves down the
coast and as it does shortwaves rotate around it bringing
additional periods of rain and snow Wednesday night and Thursday.
Generally snow levels will be higher by this time, although they
still may only be 3000 feet. Additional showers will be possible
on Friday. MKK

&&

.AVIATION...Valley fog has formed across numerous inland valleys
overnight, and once these low clouds mix out later this morning,
widespread VFR conditions are expected to prevail today across the
region. Gusty north winds develop again along the coast today,
strongest in Del Norte county and along the Mendocino coast. A weak
front approaches the coast tonight, bringing increasing high clouds
and slowly dropping ceilings by early tomorrow morning. MVFR stratus
may form along the north coast this evening ahead of this front,
particularly in the Humboldt bay region, before more widespread
stratus approaches early Sunday morning. Inland valley fog is
possible once again this evening as well. /TDJ

&&

.MARINE...Northerly winds and seas continue today before weakening
late tonight as a weak front approaches the coast. A brief break is
then expected late tonight through Sunday morning before northerlies
quickly rebuild Sunday afternoon and evening, possibly reaching gale
force in the southern waters. A gale watch has been hoisted to cover
this threat. Winds may stay sub-gale for the northern inners during
this time, however seas will quickly build from the stronger winds
just offshore, so have issued a haz seas watch for zone 450 as well
for now.

Seas see a slow decreasing trend for the next 24 hours before
quickly ramping back up Sunday afternoon, bolstered by local wave
generation, a mid-period NW swell moving in behind Sunday`s front,
and a smaller, long-period west swell sliding under the shorter
period energy. This mix should bring combined seas up to 18 to 20 ft
Sunday night and Monday morning, which then slowly decrease through
the first half of next week. /TDJ

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 8 AM to 7 PM PST Sunday for CAZ102-
     105>108.

NORTHWEST CALIFORNIA COASTAL WATERS...
Hazardous Seas Warning until 9 AM PST this morning for PZZ470.

     Gale Watch from Sunday morning through Monday morning for PZZ455-
     475.

     Small Craft Advisory until 3 AM PST Sunday for PZZ450-455.

     Hazardous Seas Watch from Sunday afternoon through late Sunday
     night for PZZ450.

     Hazardous Seas Warning until 10 PM PST this evening for PZZ475.

&&

$$

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