Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 222321
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
321 PM PST Mon Jan 22 2018

.SYNOPSIS...Dry weather will continue through daytime on Tuesday for
most areas. A strong weather front will be the big weather maker
after that. Wind and heavy rain from Tuesday night through
Wednesday. Snow for higher elevation locations Wednesday, with
lowering snow level on Thursday. Lingering showers on Friday into
Saturday.

&&

.DISCUSSION...Enjoy the dry weather today and Tuesday, before the
weather turns into its active side once again. Highs today were in
the 50s in coastal locations and in Mendocino County, with 40s
reported in inland locations. With previous precipitation from
Sunday, our ground is pretty saturated. With light winds and really
stable low level airmass, do expect conditions very conducive for
fog formation. Do expect fog for wind sheltered locations overnight.
Tuesday will be another nice day, with dry conditions and highs in
the upper 50s to near 60 degrees along the coast.

However, Tuesday will be the transition day with the approach of a
strong weather front from the northwest. By late afternoon on
Tuesday, the front will make landfall over Del Norte County.
Precipitation should begin by Tuesday afternoon/evening. There will
be gusty south wind ahead of the front. Do expect southerly gusts to
50 mph for exposed locations along the coastal ridges from Tuesday
night into Wednesday morning. Overnight, precipitation will spread
south and east into the rest of NW California. Precipitation will be
heavy at times during the day on Wednesday. Precipitation should
taper off during Wednesday night as the precipitation pushes inland.
Do expect 1 to 3 inches for most areas, higher amounts to 5 inches
over the exposed windward slopes along the coast.

With the moderate to heavy rainfall over the area, the area rivers
are expect to have modest rises. However, they are expected to
remain below flood advisory criteria. We are fortunate to have two
days of dry weather on Monday and Tuesday before the heavy
precipitation comes in on Wednesday, so that the rivers have time to
drop towards the baseline flow level.

On Wednesday night, as the front pushes inland and much colder air
will filter into the area on the back side. Snow level is expected
to drop from 6000 feet down to 3500 feet by Wednesday evening. Snow
level will further drop into 2000 to 2500 feet through Friday. There
will be lingering showers over the area through Thursday night.
Precipitation over higher elevation locations in Trinity County will
be snow. Looks like mountain pass locations along roadways in
Trinity County will be the most impacted, with a few inches of snow
expected. Scott Mountain Pass may see much higher snow accumulation.
Stay tuned to more updates on this situation. Snow showers will
linger into Friday.

Forecast confidence is low starting on Saturday. There is
significant model disagreement on the placement of the atmospheric
river. GFS place the atmospheric river over NW California on
Saturday, while ECMWF has the feature further north in
Oregon/Washington states. If ECMWF solution is correct, then we will
have a dry weekend. If GFS is right, then we will have a soaking wet
weekend, at least for Humboldt and Del Norte County. Forecast
confidence is low unless models resolve their differences.



&&

.MARINE...A new storm system will impact the waters Tue through Fri.
Southerlies will start to ramp up on Tue in advance of this storm.
The strongest winds on Tue appear to remain over the northern outer
waters (PZZ470) where gale force gusts are possible in the afternoon
as a warm front clips the area. Gale force winds for the rest of the
waters will likely hold off til Tue night or Wed morning, right
before and during cold frontal passage. Robust SW and W winds will
likely follow behind the front on Wed before easing up on Thu.

Large mid period swell will continue to subside tonight and Tue.
The downside is that southerly wind waves will start to build
through the day on Tue. The highest southerly waves will likely be
across the northern outer waters (PZZ470) on Tue. Short period
southerly seas will continue to build Tue night as winds ramp up
throughout the waters. Combined seas will eventually reach 12 to 14
ft on Wed due to a combination of two short period wave groupds, one
from the west and the other from the s-sw.

The storm will also generate another fairly large westerly swell
group that should arrive on Thu and last through Fri. The swell
should peak near 17 feet at 15 seconds Thu Night or early Friday
morning. The exact magnitude and timing are still not certain,
however.

High pressure will build on Fri and wind fields should become
lighter. Seas will most likely remain elevated and hazardous,
however. Another storm will approach Fri night or Sat and robust
southerly winds may once again generate steep southerly waves.
The GFS and ECMWF were not in great agreement on the location
and evolution of this storm, so there is low confidence with
the wind and wave forecast going into Sat.

&&

.AVIATION...Rainy conditions, low clouds and fog accompanied a
frontal boundary that pushed across the region overnight. Since
then, scattered skies and dry conditions have been the result of
weak high pressure ridging that will be somewhat shortlived.
Another weather system will bring more rain to the region on
Wednesday. In the mean time, increasing cloudiness overnight
expected at the coast, but interior areas will most likely develop
fog/low CIGS again... including UKI`s airport. Afternoon at some
coastal locales today was briefly obstructed as westerly
winds/onshore flow brought hazy conditions to ACV and CEC...with
both locations briefly reporting MVFR Cigs/VIS. Wednesday as early
as middle to late morning at CEC, models have light rain
possible. /TA

&&


.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Gale Watch from Tuesday evening through Wednesday morning for
     PZZ450-455-475.

     Small Craft Advisory until 9 PM PST Tuesday for PZZ450-455-475.

     Small Craft Advisory until 1 PM PST Tuesday for PZZ470.

     Gale Warning from 1 PM Tuesday to 10 AM PST Wednesday for PZZ470.

&&

$$

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