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Area forecast discussion 
National Weather Service Eureka California
525 am PST Thursday Dec 18 2014

Synopsis...building high pressure will result in a mostly dry
day today...although clouds will persist. An approaching cold
front will bring the next opportunity for rain Thursday evening
through Friday morning. Additional rain is expected north of cape
for the weekend with a drying trend for next week.


Short term (through sunday)...a very weak warm front moving
across the area today will bring a few sprinkles...mainly over the
higher elevations and cloudy skies to the area.

Late this afternoon into tonight a cold front will bring rain to
the area. Rain is expected to start in Crescent City around sunset
and spread south across the area through the evening. The heaviest
rain is expected overnight. Snow levels will be above 5000 feet
with most of the precipitation with this front. Rainfall amounts look to
be around one inch with local amounts up to 1.5 inches in the
higher terrain of del Norte County. Most of this rain is expected
to fall in a short period of time with the front so terrain may
not have as much impact on the rainfall amounts as with a longer
event that is more weakly forced.

Friday showers will continue across the area...although most
areas will likely see fairly low rainfall amounts. Snow levels
will be lower with these showers...dropping to around 4500 feet.
This should keep most snow above the main Highway passes. Snow
levels could be lower in some of the stronger showers...this will
need to be watched as it gets closer. Behind the front on Friday
afternoon a Post frontal swell will build rapidly and peak
overnight. Breaker heights are expected to be around 22 to 25 feet
so have issued a high surf advisory. Friday night some showers
will linger...however rainfall amounts will be fairly light.

Saturday a warm front starts to move into the area. This will
bring heavier rainfall to del Norte County. This will spread a bit
farther south Saturday afternoon. This event be more weakly forced
and southerly winds are 15 to 25 knots which makes it look to be a
situation where the terrain influences will be enhanced with much
higher amounts over the higher terrain. Increased the quantitative precipitation forecast a bit
over the rfc on Saturday to be more in line with the GFS and
wpc...but still a bit lower than the European model (ecmwf). Confidence is average
on the precipitation looks like there will be a strong plume
of moisture going into Oregon with some coming to northern California. If
the stream shifts slightly north or south the forecast will need
to be adjusted. Most of the rain in our area is expected to be in
Humboldt and del Norte County with this system with amounts lower
to the south and east. Snow levels initially with the warm front
will be around 4000 feet. These will rise fairly quickly in most
areas. The challenge will be in the Weaverville and the Trinity
Lake valleys where cold air may get trapped in these valleys and
keep snow levels lower than expected...possibly impacting Highway 299.
Precipitation amount looks to be light to moderate in Trinity
County...but this will need to be watched. Mkk

Long term (sunday night through thursday)...stronger ridging
will build over the eastern Pacific early next week bringing
warmer temperatures and drier weather through the middle of the
week. Both the GFS and European model (ecmwf) hint at another trough for late next
week but differ in the strength. Adjusted temperatures towards the
stronger and colder European model (ecmwf) solution.


Aviation...low clouds continue to linger across northwest
California with areas of IFR and LIFR across the interior and MVFR
near the coast. Ceilings should lift through the day as southerly
flow ahead of a frontal system increases. By later this afternoon
rain will begin to develop and then spread inland becoming heavy at
times overnight. Lower ceilings and visibilities will be possible
during the moderate to heavy rainfall. Gusty south winds are
expected near the coast north of Cape Mendocino through the day
and then will decrease overnight as the front moves inland. Rpa


Marine...a cold front will advance through the waters this
evening bringing a brief period of strong southerly winds. Some
gale force gusts are expected this evening in the outer waters
north of Cape Mendocino which required the issuance of a Gale
Warning. Otherwise winds will remain small craft or even below
small craft today such as in the southern inner waters as the
front slides through. Behind the front a very large swell is
forecast to arrive on Friday building to between 18 and 20 feet at
18 seconds Friday evening and night. This swell will bring an
enhanced risk of shoaling and hazardous bar conditions at the
entrance to harbors. Went ahead and issued a hazardous seas watch
and removed the marine weather statement since they would cover
the same hazard. Additionally...with breakers expected to be
between 22 and 25 feet as the waves hit the coast late Friday
afternoon through Saturday...a high surf advisory was issued as
well. There still has not been a good Jason-2 pass through the
core of the waves near the low in the Pacific south of Alaska to
confirm the swell magnitude but with hurricane force winds having
occurred for a while yesterday the swell magnitude in the enp
guidance seems reasonable. The swell will subside through the

Another front will bring a period of small craft or near gale
southerly winds Saturday with the strongest winds in the northern
waters. Behind the front a ridge of high pressure will build over
California allowing winds to become lighter and northerly for early
to middle next week. Rpa


Coastal flood...persistent southerly winds continue to keep
water levels above the astronomical tides by 1 to 2 feet. The
astronomical tides are nearly 8 feet in Humboldt Bay on Saturday and
8.1 feet on Sunday. Depending on how persistent the southerly winds
are...this could cause some coastal flooding in the low lying
areas around Humboldt Bay. In addition, with these high water
levels the high surf may push water up higher in exposed coastal
areas. Mkk


Eka watches/warnings/advisories...
Northwest California coastal waters...
Small Craft Advisory until 3 PM PST this afternoon
for pzz450-455.

Small Craft Advisory until 9 PM PST Sunday for pzz470-475.



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