Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 182232
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
332 PM PDT Wed Oct 18 2017

.SYNOPSIS...An approaching storm system will bring increasing south
winds and widespread rain across northwest California for Thursday.
There is another chance for rain this weekend, primarily to the
north, before building high pressure brings warm and dry weather for
early next week.

&&

.DISCUSSION...Soon we will undergo a swift change in weather
conditions as an approaching storm system brings increasing south
winds and widespread rain to northwest California for Thursday.
Southerly winds will begin to increase tonight, bringing breezy
conditions along the Humboldt and Del Norte county coasts with
stronger gusts expected across ridgetops. South winds will peak
Thursday afternoon with gusts around 45 mph above 1000 feet and 50
mph across ridge tops. A wind advisory was hoisted for areas above
1000 feet. This looks to be a lower-end advisory withs areas like
Kneeland and other exposed ridges possibly sees 45 to 50  mph wind
gusts Thursday afternoon. Other areas won`t be as strong but still
breezy ahead of the front.

Once the rain arrives, winds should quickly diminish. The front
will make first impact on Del Norte County late Thursday morning
into early afternoon. The band of rain will continue to shift
southeastward Thursday evening with parts of Trinity and Mendocino
counties observing rain later Thursday night and persisting into
Friday. Storm totals through Friday evening are amounting to 2 to
3 inches for Del Norte, 1 to 1.75 inches for Humboldt, and 0.25
to 1 inch for Trinity and Mendocino counties. Any breaks from rain
on Friday will be shortlived as another upper wave will bring
moist onshore flow for Saturday. This means light, but persistent
rain will impact northwest California bringing another 0.50-1.50
inches to primarily the north.

Snowlevels will remain near 5000 feet during the rain with colder
air moving in behind the front. 500 mb heights will fall to -28C
early Friday morning. Some convective showers will be possible but
thunderstorms potential still looks low. Looking ahead into next
week, building high pressure will bring a return of dry weather and
increasing temperatures. /KML

&&

.AVIATION...Stratus clouds and fog persisted along the North Coast
through the day. Therefore coastal airports dropped to LIFR/IFR
conditions this morning. There was partial afternoon clearing.
However, the low cloud/fog remained a threat to ACV and CEC
through afternoon as marine stratus continued to hug the immediate
coast. Onshore flow allowed for low clouds and fog to yo yo over
ACV & CEC...with these conditions to continue through the evening
and penetrate into local coastal valleys. In the morning...more
cloud advection ahead of an approaching weather system that will
bring rain to the north coast overnight and Thursday. Inland
areas remained VFR, but will also see increasing cloudiness as the
weather system advances on Thursday.

&&

.MARINE...Southerly winds are beginning to develop ahead of the
advancing cold front in the northern waters. The southern waters
will continue to have northerly winds for a few more hours before
they eventually switch around as well. Southerly winds will continue
to strengthen tonight through tomorrow afternoon. A few gale force
gusts may be possible across the northern outer waters however due
to the small area and limited time no gale warning will be issued.
As the winds begin to die down Thursday afternoon a very large and
long period west-northwest swell will build behind the front Thu
night and Friday therefore, a hazardous seas warning has been
hoisted. Another round of brisk southerly winds and steep southerly
waves will return Sat for the northern waters. Large seas will
persist through the weekend and into early next week as the westerly
swell begins to decay.
/WCI

&&

.BEACH HAZARDS AND SURF...Models remain consistent with
very large west-northwest swell building Thursday Night and Friday.
A swell of 17 to 20 feet with periods near 18 seconds will occur
late Thursday Night and peak early Friday morning. Swell of this
magnitude will result in very large breakers in the surf zone as
well as hazardous waves in the harbor entrances. Current indications
are for surf to exceed 20 feet for west and northwest oriented
locations by late Thursday afternoon and remain elevated through
Friday night and a high surf advisory has been issued. Some beaches
still have a summer profile which will allow for large wave run-up
onto beaches. This surf will slowly begin to decay through the
weekend.
/WCI

&&

.FIRE WEATHER...Increasing southerly winds will bring stronger
gusts above 1000 feet, primarily to ridgetops across Humboldt and
Del Norte counties. Breezy winds, however, should be expected
elsewhere tonight and peak Thursday afternoon. Fortunately there
will be good recoveries tonight with improving humidity Thursday
afternoon as this approaching storm system ushers in moist air.
Pretty much all of northwest California will receive a wetting
rain later Thursday afternoon through early Friday morning. As
typically, the greater rainfall totals will be farther north.
Relief from critical fire weather conditions will persist through
the weekend as another upper wave brings a chance for rain on
Saturday. Then building high pressure will bring a return of
increasing temperatures and dry conditions next week. /KML

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory from 6 PM Thursday to 6 PM PDT Friday for
     CAZ101-103-104-109.

     Wind Advisory from 11 AM to 5 PM PDT Thursday for CAZ102-104>106.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 3 AM to 3 PM PDT Thursday for PZZ470.

     Hazardous Seas Warning from 3 PM Thursday to 3 PM PDT Friday for
     PZZ450-455-470-475.

     Small Craft Advisory from 9 AM to 3 PM PDT Thursday for PZZ450-
     455-475.

&&

$$

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