Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 081159
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
359 AM PST Thu Dec 8 2016
.SYNOPSIS...A broad upper trough was located over the Gulf of
Alaska Thursday morning, with shortwave ridging occurring
downstream over coastal OR/WA/BC. An occluded low-level cyclone
was positioned beneath the upper trough, with its associated
frontal wave/warm front progressing east to northwestern CA early
this morning. Moderate precipitation associated with 850 mb WAA
has subsequently moved E away from the EKA CWA. However, moist
zonal flow remains focused over the region, and will maintain
elevated precipitation chances throughout the short and long term
.DISCUSSION...Temperatures are currently moderating across NWRN CA
Thursday morning...most quickly in the 850-700 mb layer (and
immediate surface coastal locations)...and more slowly for inland
surface locations. In addition, dry midlevel air has spread
across the region, which has aided in shutting off snowfall (due
to warming cloud tops/lack of ice production), with precipitation
now falling as light rain and/or drizzle. However, chain
requirements continue across Trinity County for highways 36, 3,
and 299. Thus, a winter weather advisory remains in effect until
18Z. In addition, a SLY 40-45 kt 925 mb speed max is in the
process of spreading north along the coast. This speed max will
transition to a broad area of 30-40 kt SWLY flow by midday.
Between this period of transition, gusts to 50 mph will be
possible for ridges above 2000 feet.
Friday and Saturday...rain remains in the forecast due to a
quasi-stationary fetch of subtropical moisture spreading east
across the Pacific and NRN CA. Preferred the GFS and ECMWF during
this time period due to good consensus with the stream of
moisture. Going into Saturday afternoon, model guidance indicates
850 mb temperatures will cool to around 0 to -3 C over the
northern half of the CWA. As a result, snow levels will fall to
3500-4500 feet, yielding several inches of snow over the high
terrain of Trinity, Humboldt, and Del Norte Counties.
.LONG TERM...(Saturday night through Wednesday)...Periods of rain
will continue at times Saturday night through Wednesday as a
series of cold fronts and low pressure troughs impact northwestern
California increasing the atmospheric moisture across the region.
A brief break in rain showers will occur on Sunday. However a
wetter system will traverse the region early next week. Rainfall
will be greater on Tuesday with rain mixed with snow occurring
over the higher terrain across some inland areas. Temperatures
will remain cool with mostly cloudy skies and periods of rain
.AVIATION...A front offshore will continue to generate periods
of light rain today and tonight. MVFR ceilings and visibilities will
be the rule, however light rain and misty air will occasionally
produce IFR conditions. Moist conditions will persist overnight and
no improvement is expected.
.MARINE...Southerly winds and short period seas have been slowly
increasing north of Cape Mendo through the night. Meanwhile winds
have been diminishing south of the Cape. Seas have been up to 15 ft
at 10 seconds at the CDIP buoy anchored WSW of Cape Mendo. The North
Spit buoy on the other hand has been shielded from the southerly
waves and was only up to 7 ft at 9 seconds as of 3AM. Expect near
GALE conditions with gusts to 35-40kt and building steep wind waves
north of the Cape Mendocino through the morning hours. Gales for the
northern inner waters still does look probable except around the
Cape. As the surface low tracks northward today, expect to see a
ramp up in winds around Pt St George where gusts to 35 kt are
possible into the afternoon hours.
After the low lifts out to the north tonight, winds and seas will
decline. Seas will probably be rough and uncomfortable and an
advisory may be necessary for hazardous seas. Current indications
are for the short period waves to decay rapidly with the demise of
the strong southerly winds.
A westerly swell will build on Fri and spread into the inner waters
Fri Night and Sat. It does look squared with heights of 12-15 ft at
13-15 seconds. An advisory for hazardous seas will be necessary.
The wave model continues to indicate a sharp and unrealistic drop in
seas for the latter portion of the weekend into early next week. The
wave model has been too low with these westerly swell groups and
hazardous seas may persist through the weekend. Confidence is low.
CA...Winter Weather Advisory until 10 AM PST this morning for CAZ107-
Wind Advisory until noon PST today for CAZ102-105.
Wind Advisory until 9 AM PST this morning for CAZ104-106.
NORTHWEST CALIFORNIA COASTAL WATERS...Gale Warning until 4 PM PST this afternoon for PZZ470.
Small Craft Advisory until 9 AM PST this morning for PZZ455.
Small Craft Advisory until 4 PM PST this afternoon for PZZ450.
Gale Warning until 4 AM PST early this morning for PZZ475.
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