FXUS66 KEKA 201243
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
443 AM PST Tue Nov 20 2018
.SYNOPSIS...Dry, mild, and hazy conditions will continue through
this evening with breezy southeasterly ridge top winds developing. Significant
rains will return to the area late this evening and persist
through Friday with breezy southerly winds.
.DISCUSSION...Poor air quality and hazy conditions will continue
for just one more day before widespread rain returns to the area
late this evening into early tomorrow morning. Ahead of this cold
front, southerly winds will begin to increase across the area. A
few RAWS sites such as Kneeland, Cooskie Mountain, and Ship
Mountain have begun reporting southeasterly winds near 20 mph
early this morning. These winds will continue to increase as we
go through the day. With the enhanced southeasterly winds some
downsloping may become evident for the Humboldt Bay area which may
warm temperatures into the low to mid 60's.
Significant precipitation will return to the North coast late
this evening and last into Wednesday. Widespread light to moderate
rain will lead to half an inch to an inch of precipitation area
wide. Once the front slides by a more convective situation will
develop as cold temperatures aloft move in. With this showery
activity a modest amount of MUCAPE along with steep lapse rates
mean that a few lightning strikes may be possible across the
waters and coastal locations. Any thunderstorm or stronger shower
that develops would be capable of producing gusty localized
winds due to the fairly strong winds aloft and unstable profile.
With the cold airmass aloft the stronger showers may also produce
some small hail.
The heaviest batch of precipitation is expected to move north to
south during the afternoon of Thanksgiving day into Friday morning.
Current indications are that a moisture plume will be oriented
perpendicular to our coastline which will help to enhance rainfall
totals on the windward (Ocean) side of coastal mountains. Latest
model guidance has increased the IVT amounts within this system as
well as the residence time over our area to approximately 24
hours which means even heavier precipitation can be expected than
originally thought. From Thursday afternoon to Friday morning
most locations can expect to see upwards of 2 inches of
precipitation. Areas with favorable topography could see totals
during this time period upwards of 6 inches. Fortunately, rivers
and streams are currently running well below normal so they will
be able to handle a lot of this rain however some urban or small
creek flooding may be possible. For mountain locations, it
appears that snow levels will remain above 5000 feet during this
event which means only Scott Mountain Pass on Hwy 3 will see
Strong southerly winds will also peak Thursday afternoon and evening
with area ridges experiencing gusts in excess of 35 mph. Since this
is the first strong southerly wind event of the season these winds
may bring some tree limbs down and cause sporadic power outages,
therefore a wind advisory may be required.
Looking into the long term the active weather pattern appears to continue
as weak disturbances continue to impact our area this weekend and
into early next week. While exact timing and strength is still a
bit in question it appears only minimal impacts will be
associated with these features. /WCI
.AVIATION...Southeast winds ahead of a cold front are keeping most
of the area VFR this morning. There is is still some lingering haze
in the Ukiah area, but farther north the vis has lifted to VFR.
Southeast winds have increased over the higher elevations this
morning and this will expand to include most areas this afternoon.
Speeds are expected to only reach around 10 kt with some gusts to 15
or possibly as high as 20 kt this evening. Rain is expected to start
at KCEC shortly before 12Z and will likely be after 12Z for KACV and
even later for KUKI. MKK
.MARINE...Currently the seas are fairly quiet across the area this
morning. There is a swell of around 2 to 3 feet at 11 seconds. An
approaching cold front has just started to increase the southerly
winds in the outer waters. The winds are expected to increase to 10
to 20 kt this afternoon. These will continue to increase tonight,
peaking Wednesday morning. A few gale force gusts are possible in
the northern outer waters, but most areas will peak at 25 to 30 kt.
The winds will generally be out of the south to southeast and this
will limit the waves building in the northern inner waters (zone
450)and it will be protected somewhat from the winds. For now have
held off on issuing a small craft advisory for the zone 450.
Late Wednesday afternoon and evening the winds will diminish for the
most part so have end the small craft advisory. There will be
showers around and these could bring down some stronger winds to the
surface. Local gusts to 30 mph are possible in the heavier showers.
The next system moves into the area Thursday afternoon and Thursday
night. Models continue to show this system as stronger than the
first. The northern outer waters (zone 470) are looking more like
there will be gales or at least gale force gusts. This may need a
gale watch, but will wait for a few more model runs to make sure the
models are consistent.
In addition to the winds a large swell is expected to build into the
waters starting Tuesday night. Initially it is expected to around 3
feet at 16 seconds on Wednesday. The current ENP run shows this
building to 7 to 9 feet at 12 seconds on Thursday afternoon.
Thursday night and Friday the winds increase and the wind driven
waves will combine with the swell for total wave heights of around
12 to 14 feet at 12 to 14 seconds. Saturday the winds will diminish
and the waves will become less steep.
Models continue to struggle with the timing of a weak system over
the weekend. The ECMWF has a weak system on Sunday bringing light
southerly winds while the 06Z GFs brings this system in on
Tuesday and has light northerly winds on the weekend. MKK
.FIRE WEATHER...A dry air mass with breezy southeasterly ridge top winds
will lead to elevated to locally critical fire weather conditions
today ahead of an approaching cold front. Humidity will increase
rapidly tonight, as the first round of significant wetting rains
return to the area. The strongest winds and heaviest rain will
occur Thursday afternoon into Friday morning.
CA...Frost Advisory until 9 AM PST this morning for CAZ102-103-109-
Flash Flood Watch from Wednesday afternoon through Friday
morning for CAZ107-110-113.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 3 PM this afternoon to 3 PM PST
Wednesday for PZZ470-475.
Small Craft Advisory from 2 AM to 3 PM PST Wednesday for PZZ455.
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