Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 182238

National Weather Service Eureka CA
338 PM PDT Thu Oct 18 2018

.SYNOPSIS...High pressure will result in dry and warm afternoons
accompanied by chilly nights persisting into the weekend across
interior northwest California. Meanwhile, periods of low clouds
and cool temperatures are expected along the coast. Rain chances
will increase later on Tuesday as a cold front approaches.


.DISCUSSION...A blocked upper-level pattern will keep stagnant
weather across northwest California through Sunday. The center of
an upper-level high will drift eastward across Oregon on Friday
and Saturday, resulting in warm air aloft above a steep subsidence
inversion. Easterly, offshore flow will be present over inland
areas, while a shallow marine layer keeps persistent cloudiness
along much of the coast. The dry air and clear skies will mean
another frosty night for the colder interior valleys, where a
Frost Advisory is in effect. Expect low temperatures Friday
morning to be very similar to this morning`s readings.

The stratus has actually peeled back away from inland areas, but
many locations within a half mile of the Pacific continue to have
fog and low clouds this afternoon. With warming aloft under the
building upper high, would expect the marine layer to even be a
bit shallower tonight, with perhaps a bit less inland extent.
Friday there may be a little more sunshine away from the immediate
coast, while many beach locations remain cloudy. Northerly winds
may be a touch stronger at exposed coastal locations, but light
elsewhere once again. Friday night into Saturday morning will see
some locally enhanced easterly winds over upper slopes and ridges.
Heading into the weekend, the upper-level high will weaken,
resulting in cooling temperatures aloft, and inland high temps
slipping back closer to normal readings. Coastal clouds will
continue to be present this weekend, and while right now we are
forecasting some afternoon clearing, do not have much confidence
in that given the light wind flow both at the surface and aloft.

Model guidance continues to show a pattern change taking place
heading into next week. A cold upper trough is forecast to deepen
over the Gulf of Alaska, which will aid in breaking down the
upper ridge and kicking out a cut-off low to our south. A
shortwave trough and associated surface front are then forecast
to move east across the PAC NW during Tuesday. This wave appears
to weaken considerably, though may yield some light rain for
Del Norte and Humboldt Counties later on Tuesday or Tuesday night.
An upper-level high to the west of California will try to build a
bit, keep the bulk of the moisture directed near or north of Cape
Mendocino. Details regarding the strength of this high as will as
strength and timing of waves of low pressure tracking eastward
into the Pacific Northwest are yet to be resolved by the models,
and thus while the sensible weather looks damp mid to late next
week, just how damp remains uncertain. /AAD


.AVIATION...Coast side a firmly entrenched stratus deck is
providing mainly mvfr cigs to near coast terminals this afternoon.
Only brief and local improvement is expected over the next few
hours before cigs and vsbys drop back to near ifr conditions which
should persist through the night. Interior sites should remain
vfr for much of the taf cycle with some localized mvfr or ifr vsby
and cigs during the hours just before sunrise across local
interior and coastal interior valleys.


.MARINE...Light northerly winds will continue through the end of
the weekend as weak high pressure remains over the eastern Pacific.
A long period northwesterly swell, long period southerly swell, and
northerly wind chop will create the total sea state through the end
of the weekend. The dominant wave group will be the westerly swell
which will peak at 7 feet at around 15 seconds tonight and then
gradually subside through the weekend. Next week as a system
approaches the coast, southerly winds will develop and another
northwesterly swell will begin to impact the waters. /WCI/JT


.FIRE WEATHER...Warm temperatures and low humidity values will
persist across the interior through the weekend. Winds will be
largely light and terrain-driven, but will tend east-northeasterly
over the exposed ridges and upper slopes in the thermal belt. This
will be especially true Friday night into Saturday morning, with
some local gusts up to 25 mph. Do not anticipate Red Flag
conditions, but will headline in the FWF. In the extended range,
rain chances will increase later Tuesday, especially north of
Mendocino county.


CA...Frost Advisory from 1 AM to 9 AM PDT Friday for CAZ102-104-106-




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