Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 181147

National Weather Service Eureka CA
358 AM PDT Wed Oct 18 2017

.SYNOPSIS...Widespread rain will spread across the region
Thursday afternoon into Friday, with lighter showers persisting
through the weekend. Drier and warmer conditions are expected
next week.


.DISCUSSION...The pictures from space this morning show stratus
along Del Norte and Humboldt counties and it crawling towards the
Mendocino coast. The local profiler at KACV depicts a shallow
marine layer so there should at least be partial clearing along
the coast this afternoon. This is expected to be short lived as
high pressure will be giving way to a shortwave trough as it digs
into the PACNW. Come Thursday morning, portions of the CWA will
start to see rain and by the afternoon widespread rain is
forecast for all of NW CA which will then continue into Friday.
Storm total rainfall accumulation is forecast to be around 2
inches over Del Norte County, ranging to around a quarter inch
over southern Mendocino County.

After the frontal passage, snow levels are forecast to drop to
near 5000 feet. Snow accumulation should remain confined to
elevations above 6000 feet and near the Trinity Alps. Post frontal
thunderstorms are not expected as unfavorable convective
parameters, rising 500mb heights, and slightly warmer midlevel
temperatures will thwart development.

For the weekend, shower activity will persist but should remain
limited to areas north of Mendocino County. Models continue to
suggest drier and warmer weather for early next week as high
pressure builds over the area.


.AVIATION...A shallow layer of fog and low clouds was hugging
the coastline early this morning. As of 4am, LIFR conditions has
been occurring at KCEC and KACV. High resolution models indicate
moist boundary layer air holding through the day. Thus the stratus
may end up persisting over or nearby the coastal terminals through
the day. Any clearing will be brief. Away from the shoreline, VFR
conditions will continue through today. The marine layer will likely
deepen tonight with low clouds and IFR conditions pushing deeper
into the interior river valleys by early Thu.


.MARINE...The tail end of a robust cold front will move across
the waters on Thu. Southerly winds in advance of this cold front may
briefly gust up to 35 kt north of Cape Mendo. Steep southerly wind
waves will also be generated, primarily outside 10NM. The exception
will be around Pt St George which will be near the end of the fetch.
Large swell from 18 to 22 feet with long periods will build behind
the front Thu night. Surf is expected to build Thu Night with
breakers up to 25 ft. High surf conditions will continue through the
day on Friday. The large seas will subside this weekend, but an
active storm track will maintain hazardous seas through the weekend.


.FIRE WEATHER...West-southwesterly winds are forecast to
strengthen across area ridgetops tonight and into Thursday ahead
of a cold front. However, RH values will be increasing as winds
strengthen, which should mitigate a more significant fire weather
threat. By Thursday afternoon, widespread rain will spread across
northwest California, with storm total values near 2 inches
expected in Del Norte county, ranging to around a quarter inch
over southern Mendocino county. Lighter showers will then persist
through the weekend, primarily north of Mendocino County, before
warmer and drier conditions return next week.


.BEACH HAZARDS AND SURF...ENP and NWPS remained consistent with
large west-northwest swell building Thu Night and Fri. Swell around
18 to 20 feet with periods near 17 seconds will build Thu Night and
peak early Friday morning. Swell of this magnitude will result in
large breakers in the surf zone as well as hazardous waves in the
harbor entrances. A high surf advisory has been hoisted.


CA...High Surf Advisory from 6 PM Thursday to 6 PM PDT Friday for

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 9 AM to 3 PM PDT Thursday for PZZ450-

     Hazardous Seas Watch from Thursday afternoon through Friday
     afternoon for PZZ450-455-470-475.

     Small Craft Advisory from 3 AM to 3 PM PDT Thursday for PZZ470.



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