Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 221616 CCA

National Weather Service Eureka CA
816 AM PST Wed Nov 22 2017

.SYNOPSIS...A disintegrating frontal boundary has been moving
onshore this morning. Light rain will be possible across Humboldt
and Del Norte counties today. Widespread light rain is expected
tonight with occasional showers Thursday. Friday looks mainly dry
before another system brings rain for the weekend.


.UPDATE...Based on current radar trends updated weather and
precipitation grids to reflect the precipitation across Humboldt
county. Rain showers will remain possible for the rest of the day
across Del Norte and Humboldt counties. Newest high resolution
guidance shows the plume of moisture staying over our area rather
than across our coastal waters as was previously thought.


.PREV DISCUSSION... /issued 419 AM PST Wed Nov 22 2017/

DISCUSSION...The weakening frontal boundary remains off the CA
coast this morning. Models show this continuing to weaken and
eventually move onshore at some point tonight. The HRRR simulated
radar shows Del Norte county seeing occasional light rain through
much of the day. Late in the afternoon/evening it shows some light
rain moving onshore in Humboldt county. The warm temperatures are
expected to continue today due to southerly winds and high
pressure to the east of the area.

Tonight the front finally moves inland, although only light rain
is expected with it. This may linger into Thursday in Trinity and
Mendocino counties. Another wave will bring additional rain to
Del Norte county Thursday morning and a few showers may spread
into Humboldt county in the afternoon and evening. Temperatures
will start to cool on Thursday, although will remain above
seasonal normals.

Thursday night the rain and clouds will start to move off to the
east of the area. Cooler overnight temperatures expected and
valley fog is likely. This fog may be dense at times, especially
in the interior valleys. Friday is expected to see partial
clearing in the morning in areas without low clouds and fog.

Friday afternoon the next system starts to approach the area. The
GFS and ECMWF show significant differences in the timing of the
warm frontal boundary that moves onshore Friday night from the
southwest. The GFS has moderate rain across much of the area,
while the ECMWF keeps the systems slightly farther offshore with
much lighter rain. Generally favored the GFS in the forecast as
it may have a better handle on warm front due to higher

This spread in the models continues on Saturday with the ECMWF
continuing with a much drier solution. There is some agreement
that a frontal boundary will move through Sunday bring some rain
to much of the area. Sunday night and Monday the upper level
trough behind the front brings much colder air and showers to the
area. This could bring snow levels down to near 3,000 feet, near
highway pass levels. Drier weather is expected behind this trough
on Tuesday and Wednesday. MKK

AVIATION...VFR conditions will persist along the coast through
at least the remainder of the morning. Rain associated with a weak
cold front will slowly move onto the coast during the day, initially
impacting CEC during the late morning and eventually working its way
into ACV during the evening and overnight. Ceilings will lower as
rain begins, initially to MVFR during daylight hours and perhaps to
IFR overnight. Ceiling and visibility reductions are likely to occur
at CEC first, and will be more prolonged here than at ACV.  Some low
level wind shear is possible at CEC and ACV early this morning
before surface winds increase after sunrise. At UKI, LIFR fog will
dissipate by late morning, and VFR conditions are expected the
remainder of the day. Rain and lowering ceilings will arrive
tomorrow morning. /BRC

MARINE...Moderate to strong southerlies will continue to blow
across the waters today and tonight, with the strongest winds
located outside of 10nm from shore and north of Cape Mendocino.
These winds will continue to drive steep southerly seas across the
outer waters, which will combine with both southwest and northwest
swells to create a mixed and uncomfortable sea state. Winds will
begin to weaken Thursday and turn to the north on Friday, allowing
the steep southerly seas to settle. However, the previously
mentioned swells will continue to maintain elevated seas throughout
the waters through the end of the work week.

On Saturday, southerly winds will increase yet again as another cold
front approaches, perhaps briefly reaching Gale force. This will
bring the return of steep southerly waves, in addition to both a fresh
westerly swell and a long period northwesterly swell. In a nutshell,
seas will be large, mixed in both period and direction, and
hazardous to mariners late in the weekend. /BRC


NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 4 AM PST Thursday for PZZ470.



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