Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 282258
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
358 PM PDT THU JUL 28 2016

.SYNOPSIS...Hot and dry conditions will continue through the end
of the week across the interior. Coastal areas will likely see
little change, with nocturnal and morning clouds and near normal
temperatures. A slight cooling trend is expected this weekend
through early next week.

&&

.DISCUSSION...Very few changes were made to the forecast package
for this afternoon, as hot and dry conditions continue to plague
northwest California. Temperatures across the populated low-lying
interior valleys have once again soared into the triple digits
this afternoon, although it appears that once again we will fall
slightly short of record numbers at Ukiah. Meanwhile, a shallow
but persistent marine layer has maintained near normal
temperatures along the immediate coastal plain, with an extremely
sharp temperature contrast as you travel inland and upwards in
elevation. A few examples of this: along the Mendocino Coast where
water temperatures are around 50 degrees, high temperatures have
only reached into the middle 50s, while weather stations only a
short distance inland have recorded temperatures well into the mid
90s. And farther north, Kneeland soared into the low 90s even at
2700 feet, while temperatures in Eureka remained in the low to mid
60s. Quite a temperature contrast, to say the least. Last year on
this date, offshore winds led to a record-setting day along the
coast, and Eureka set an all-time record high temperature for the
month of July at 77 degrees. Without these offshore winds today
and with cooler water temperatures offshore, the marine layer has
held strong, keeping us characteristically cool and records safe
for another year.

Hot temperatures are set to continue through tomorrow, but a
modest cool down can be expected beginning Saturday and
continuing through the middle of next week. "cool down" might be
a generous way to describe it, as high temperatures will still
reach into the 90s in most low-lying valleys. Coastal areas will
remain nearly unchanged, with continuing morning stratus and fog.
A developing weak trough will likely help to lift the marine layer
by about 500 to 1000 feet or so, bringing stratus a little bit
farther up the coastal valleys. Very little precipitation can be
expected over the next 7 days, although a few thunderstorms will
be possible Friday and Saturday afternoon/evening near the Trinity
Horn. For more details please see the fire weather discussion
below. /BRC

&&

.AVIATION...A typical summertime pattern will persist overnight,
with marine stratus developing after 04z along the coastal
terminals, with IFR ceilings around 600 feet likely. These
ceilings will drop further a few hours later, with visibilities
around 1/2SM or less likely as well. The morning stratus will burn
off by late morning. Farther south at KUKI, light winds with VFR
conditions will prevail. /PD

&&

.MARINE...The forecast is panning out pretty much as
expected. A gale warning continues for the waters from 10 to 60nm
along and north of Cape Mendocino, with a recent ship observation
reporting 35 knots sustained at 18z. Farther south and east, the
recent ASCAT pass from 1715z indicated winds were generally in the
20 to 25 knot range, which matches well with current buoy
observations. Here, seas have generally been running around 9 to
10 feet at 9 seconds. This is towards the higher end of of a small
craft advisory, and it`s not out of the question that observations
may show a few times where hazardous seas conditions were met.
Given the marginal nature/potential of this occurring, we decided
to keep the headlines as they are. Small craft advisories are in
effect for waters near the cape, and for the outer waters (beyond
10 nautical miles) south of the cape.

Heading into the weekend, the latest numerical guidance indicates
a stubborn area of high pressure residing across the eastern
Pacific, with a thermal low developing near Redding. The pressure
gradient between these two features will continue to increase,
helping the thermal trough along the coast to strengthen. The
models have caught onto this, as they show a noticeable increase
in wind speeds and wave heights for the outer waters from Cape
Mendocino north. Here, sustain winds around 35 knots with gusts
over 40 knots are likely, with waves pushing 17 feet, where a gale
warning continues.

For the outer waters south of Cape Mendocino, this is where the
forecast becomes a little more tricky. The pressure gradient will
be somewhat more relaxed with decreased wind speeds and waves
expected. The only except to this would be across the northwestern
third of marine zone 475 (basically beyond 10nm and north of
Shelter Cove) where waves near 13 feet at periods of 10 seconds
would argue for a hazardous seas warning. The models have showed
this potential for a couple of days, but have waffled somewhat in
their forecast wave heights with the lower end model runs being
marginally sufficient for this type of headline. For now, we`ve
opted to maintain the small craft advisories as most of the zone
will remain below criteria, and given the instability in the wave
height forecasts. However, this is something we`ll keep an eye on
and an upgrade to a warning isn`t out of the question.

Closer to shore for waters within 10 nautical miles from Cape
Mendcino north, winds and waves will keep a rough chop going,
where small craft advisories are in place through the weekend.
South of the cape, this area will be further removed from the
enhanced winds/waves associated with the pressure gradient,
resulting in decreased wave heights. /PD

&&

.FIRE WEATHER...Hot temperatures and low humidity can be expected
to last through at least tomorrow, and likely into Saturday,
before a slight cool down brings temperatures back to
normal...which is to say still quite warm and dry. Gusty offshore
winds and moderate humidity recoveries can be expected along
exposed ridges across Del Norte, northern Humboldt, and northern
Trinity counties overnight tonight and tomorrow night.

Tomorrow afternoon, a weakness in the upper level ridge overhead will
develop offshore, and an area of weak vorticity will slowly move
onto the coast. As this occurs, a tongue of modest mid- level
moisture will creep northwards along the western periphery of the
ridge. As a result, the combination of increased
moisture/instability and modest upper forcing may be enough to
trigger a few mostly dry thunderstorms across mainly the
mountains of west-central Siskiyou county, and perhaps a few in
extreme northeastern Trinity County. While fuels are receptive to
fire growth in most areas, given that coverage will likely be
extremely limited in this region, this event will continue to be
represented with a headline in the Fire Weather Forecast and not
with a Fire Weather Watch or Red Flag Warning. /BRC

&&

.EKA Watches/Warnings/Advisories...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 8 AM PDT Monday for PZZ450-475.

     Gale Warning until 8 AM PDT Monday for PZZ470.

&&

$$

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