FXUS66 KEKA 171243
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
443 AM PST Wed Jan 17 2018
.SYNOPSIS...Southerly winds will strengthen ahead of a storm
system during Wednesday afternoon. This will be followed by an
extended period of precipitation Wednesday evening into Saturday.
In addition, snow levels will fall to 2500 feet Thursday night and
.DISCUSSION...A strong cyclone located approx 700 NM west of
Vancouver Island BC was in the process of occluding early Wednesday
morning. A cold front extending SWD from the cyclone is forecast
to advance EWD toward NWRN CA during the day. A tightening surface
pressure gradient ahead of the front, combined with a 50 kt SLY
coastal jet, will aid in winds gusting to 45 mph in the vicinity
of Crescent City this afternoon and evening (refer to the latest
wind advisory product for more information). In addition,
strengthening SELY winds will yield enhanced downslope warming
across the Eureka metro area this afternoon...with resultant highs
expected to reach the low to possibly mid 60s.
The previously mentioned front is forecast to move inland across
the region during Wednesday night. Ascent and moistening along the
front will yield rain across much of the CWA, with the highest
rainfall totals in the 1-2 inch range occurring tonight over
interior Del Norte and northern Humboldt counties. Behind the
front, showers will continue through Thursday afternoon.
Thereafter, a much colder midlevel airmass (around -30C at 500 mb,
and -12C at 700 mb) will spread east across the area Thursday
night. This will yield steep lapse rates favorable for heavy
showers and possible isolated thunderstorms Thursday night into
Friday. Some of this activity could produce accumulating hail
across coastal roadways. Furthermore, the cold airmass will aid in
lowering snow levels to around 2500 feet. The low snow levels
combined with convective precipitation rates will favor snowfall
totals at or above 6 inches across the high terrain of interior Del
Norte, Humboldt, Trinity, and Mendocino counties. A winter storm
watch remains in effect Thursday night through Friday night.
Showers are forecast to dissipate during Saturday afternoon, but
will quickly be followed by a strong front Saturday night into
Sunday. A 6 to 12 hour period of moderate rain appears probable
with that front, with another round of rain possible next Tuesday.
.AVIATION...Fairly complex forecast for aviation. Overnight,
conditions were bouncing up and down between VFR to LIFR for Ukiah
due to low clouds and fog. For Arcata, conditions were bouncing
between VFR/MVFR/IFR due to patches of fog. Crescent City mostly
stayed in VFR.
As the weather front moves towards NW California, winds will be
on the increase for coastal terminals including Crescent City and
Arcata airports. Do expect up to 55 kt of low level wind shear
from the south for Crescent City from this morning through late
tonight. There will be some wind shear to 45 kt for Arcata airport
from this morning through this evening. Rain will move into
Crescent City and Arcata this afternoon, dropping the conditions
to MVFR. Rain will move into Ukiah this evening, lowering
conditions for them down to MVFR. Rain will continue through the
rest of the forecast period.
.MARINE...Very active marine weather will be in store for NW
California waters. We will be dealing with significant seas
through this weekend. We will also be dealing with gale force wind
gusts today into early this evening.
A strong weather front is making its way towards NW CA waters
today. Ahead of it, there will be gale force wind gusts in the
area. The strongest winds will be found in the northern outside
waters, as most of the forcing of this weather front will remain
to the northwest of the area. Do expect the winds to subside this
evening and turn southwesterly with the frontal passage. Winds
will remain westerly for the rest of the work week into the first
part of the weekend. Looks like there will be another weather
front on Sunday, bringing in another round of strong south wind.
Seas will be significant through Saturday. For today, combined
seas will be around 12 to 15 feet as we are still impacted by a
middle period decaying swell group. After the frontal passage,
there will be a significant westerly swell moving into NW
California waters this evening. Do expect combined seas to 25
feet, with the worst conditions found near Oregon waters. Seas
will start to subside on Saturday. Due to the significant swell,
Hazardous Seas Warning remains in effect from late tonight through
.HIGH SURF...With the significant westerly swell, there is high
confidence that west and northwest facing beaches will see high
surf conditions. Expect breakers of 25 to 30 feet from tonight
through Thursday evening. The most severe conditions will be found
in locations further north, as the majority of the energy is
focused to the north in the Oregon waters. The High Surf Warning
remains in effect. Please refer to the statement for more details.
CA...High Surf Warning from 10 PM this evening to 10 PM PST Thursday
Winter Storm Watch from Thursday evening through Friday evening
Wind Advisory from 11 AM this morning to 8 PM PST this evening
Winter Storm Watch from Thursday afternoon through Friday
evening for CAZ102.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until
7 AM PST this morning for PZZ470.
Gale Warning from 7 AM this morning to 10 PM PST this evening
Hazardous Seas Warning from 10 PM this evening to 10 AM PST
Saturday for PZZ470.
Small Craft Advisory until 3 PM PST this afternoon for PZZ455.
Hazardous Seas Warning from 4 AM Thursday to 10 AM PST Saturday
Small Craft Advisory until 4 AM PST Thursday for PZZ450-475.
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