Gale Watch 25, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
331 PM PST Sun Nov 17 2019

.SYNOPSIS...Some light rain will be possible in Humboldt and Del
Norte counties late Monday and early Tuesday, and will be followed
by gusty north and northeast winds Tuesday through early
Thursday. A period of elevated to critical fire weather conditions
will be possible early Wednesday through early Thursday.

&&

.DISCUSSION...
.Short Term...High pressure remains in place over northern
California this afternoon. This is keeping the marine layer thin,
but is brought dense fog to the Humboldt and Del Norte coast this
morning. Most of this has diminished, but some remains about
Humboldt Bay. This dense fog is expected to return this evening.

Monday morning a shortwave moving into the Pacific Northwest and
the trailing cold frontal boundary start to approach the area.
This should help to lift the fog and deepen the marine layer.
Current models show the rain starting late Monday afternoon in
Del Norte county and quickly moving south into Humboldt county.
These areas are expected to see a tenth to a quarter of an inch.
It looks like Mendocino and Trinity counties will only a trace to
a few hundredths. Models are now showing a second shortwave early
Tuesday morning bring additional clouds and there could be a few
sprinkles with it.

Tuesday afternoon the winds will rapidly increase along the coast
and spread inland over the ridges. The airmass will dry out
fairly quickly as well as the wind becomes more northeast Tuesday
night. This should also help clear skies at the coast. This dry
and chilly airmass will allow temperatures to fall quickly
Tuesday night in the valleys that manage to remain calm. Frost is
possible at the coast, but confidence is low on how widespread it
will be due to the winds.

Wednesday is expected to see winds of 15 to 25 mph across the
area with some gusts to 40 mph over the ridges. Wednesday night the
winds will diminish in the valleys, but confidence is low on the
ridges. There is still quite a bit of disagreement in the details
of these strong winds. Wednesday night the winds remain strong
aloft, but it is unclear how much of this, if any, will mix to the
surface. For more details see the fire weather discussion.

Confidence is higher that winds will diminish Thursday afternoon
and Friday as high pressure moves over the area. Friday night and
Saturday an upper level low starts to approach the area, but at
this point models have it just undercutting the ridge and not
impacting the area. MKK

&&

.AVIATION...Conditions were slightly better today at KACV with
less persistent visibility down to 1/4SM in fog. Visible satellite
imagery showed a mass of stratus and fog still just offshore KACV
this afternoon. Therefore, expect IFR/LIFR conditions to fill back
in this evening and for any improvement this afternoon to be short
lived. The primary forecast problem continues to be how quickly
vsby's drop to 1/4sm. Also, the duration of these low vsby's remains
problematic. For now the forecast for the coastal terminals has been
largely based on persistence and current satellite trends. The other
forecast terminals have been VFR today except for KCEC which briefly
dropped to LIFR early this mornings. Once again it is probable that
fog and low cloud will redevelop at KCEC overnight under light
northerly flow. LIFR conditions at KCEC should be less persistent
due to weak offshore there. KUKI will remain VFR through the
forecast period, though patches of fog and low cloud will form in
the valleys to the north overnight.

&&

.MARINE...A localized region of northerly winds from 20 to 25 knots
with elevated wind waves is expected to continue downwind of Cape
Mendocino through tonight. An advisory for this remains in effect.
This localized region of stronger winds and higher seas should die
off on Monday as a trough approaches from the NW and gradients relax.

The primary issue going into Tuesday and Wednesday of next week will
be the potential for GALE FORCE northerlies and large steep seas on
top of an incoming WNW swell group. The models were all over the
place with how quickly winds will ramp up during the day on Tuesday.
The NAM was the fastest while the global models have a slower rate
of increase. There is high confidence winds will eventually reach a
full blown gale in outer waters Tuesday night. Tuesday evening is
still just outside the window for a gale watch at this point.

Steep seas are expected to build Tuesday night and reach 18 to 20
feet by early Wed, in the outer waters. That is where northerly
winds are expected to reach 35 to 40kt. The primary hazard for the
inner waters will most likely be large steep seas. Current
indications are for steep seas to hit 13 ft or so. How strong the
winds become inside 10NM and right at the coastline is still a big
unknown. Northerly winds may briefly reach gale force inside 10nm,
especially around the wind prone headlands such as PT ST GEORGE and
CAPE MENDOCINO Tuesday evening and overnight. Winds may need to be
beefed up when the high resolution models come in hot and heavy.
On Wednesday, conditions will remain elevated and hazardous, though
guidance continues to indicates winds falling off nearshore. Steep
seas are expected to be close to 20 ft in the western fringes of our
outer waters through at least mid day Wednesday.

Conditions are forecast to settle down THU and FRI, though the NWPS
indicates lingering short period wind waves around 6 feet which may
warrant an advisory for small craft on Thu. Also, ENP has a long
period westerly swell building to around 10 ft at 17 seconds on
Friday which will also warrant an advisory for small craft and a
hazardous beaches statement.

&&

.FIRE WEATHER...Confidence is growing that we will see a period of
strong winds starting Tuesday afternoon and potentially lasting
through Thursday morning. The strongest winds will be on the
ridges of eastern Mendocino county and southeastern Trinity county
with sustained winds of 35 mph and gusts to 45 mph. Most of the
other ridges will see winds to 25 mph with gusts of 30 to 35 mph.
The valleys are only expected to see of 10 to 15 mph. There is
still some fairly significant model differences on the timing the
strongest winds and how long they will last. Also, Wednesday
evening and overnight the models are suggesting winds at 850MB
will remain quite strong, but are not indicating a lot of that
mixing down. So it might mainly impact the very highest peaks.

The dry air is expected to move into the area on Wednesday and
afternoon RH may drop as low as 15 to 25 percent in the valleys of
Mendocino county, but will remain higher farther north. Wednesday
night into Thursday RH recoveries are expected to be over 70
percent in the valleys, but may remain around 40 percent on the
ridges of Mendocino county.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 AM PST Monday for PZZ475.

&&

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Hazardous Weather Outlook
National Weather Service Eureka CA
336 AM PST Sun Nov 17 2019

CAZ101>113-181145-
Coastal Del Norte-Del Norte Interior-Northern Humboldt Coast-
Southwestern Humboldt-Northern Humboldt Interior-
Southern Humboldt Interior-Northern Trinity-Southern Trinity-
Mendocino Coast-Northwestern Mendocino Interior-
Northeastern Mendocino Interior-Southwestern Mendocino Interior-
Southeastern Mendocino Interior-
336 AM PST Sun Nov 17 2019

This hazardous weather outlook is for northwest California.

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Gusty north and northeast winds are expected late Tuesday through
potentially Thursday morning, particularly along the coast and along
exposed high elevation ridges. As a result of this and lowering
humidity, elevated to perhaps locally critical fire weather
conditions will be possible across interior areas Wednesday and
Wednesday night, although uncertainty remains somewhat high
regarding the fire weather threat.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.