Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 242205
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
305 PM PDT Sat Jun 24 2017

.SYNOPSIS...Hot conditions will gradually cool to near normal by
Monday, and continue through much of the week. Isolated
thunderstorms will be possible across interior areas Sunday and
Monday during the afternoon and evening. Coastal clouds and
periods of fog and drizzle will increase over the next couple of
days.

&&

.DISCUSSION...The heat continues throughout the region today
thanks to a relentless upper level ridge of high pressure.
Temperatures across many of the interior valleys of NW CA have
reached well into the upper 90s and low 100s this afternoon,
particularly in Trinity county where readings have already neared
105 degrees. Near the coast, a southerly flow reversal has
steadily filled the offshore waters with marine stratus clouds,
although much of the immediate coastline remains clear as of 2:30
PM.

Fortunately for those living in or traveling to interior areas,
gradual heat relief is on the way thanks to a developing offshore
low pressure system. While still developing and located well
offshore at this point, this disturbance will slowly move onto
the coast tomorrow and Monday, effectively weakening the
persistent ridge of high pressure that has plagued the region with
oppressive heat. While temperatures by Monday will fall to more
reasonable levels, interior valleys will not fall much below
normal...likely with high temperatures in the mid 80s to low 90s
through much of the week. Meanwhile, a steadily deepening marine
layer will result in increasing cloud cover along the coast,
including periods of drizzle overnight tonight and especially
overnight Sunday and Monday night. In addition, stratus will
steadily move farther into coastal valleys each night as the
marine layer deepens. The amount of clearing that will take place
in the afternoons along the coast is a bit of a wildcard, but as
the marine layer deepens and cloud bases get higher, immediate
coastal areas will likely see clouds dissipate more rapidly in the
afternoons than places farther inland and up in the lower coastal
hills.

The other item of concern aside from the heat will be the
potential for thunderstorms over the next few days. The previously
mentioned upper low will gradually advect increasing mid-level
moisture and instability into the region tonight through Monday,
resulting in periods of isolated high-based thunderstorms. While
it wouldn`t be completely out of the question to see a flash of
dry lightning near the coast tonight or early tomorrow morning,
the best chances for thunderstorms will occur late Sunday
afternoon and evening across northeastern Mendocino, Trinity,
northeastern Humboldt, and eastern Del Norte counties. Even here
thunderstorms will likely be far flung, and are likely to produce
little precipitation in the lower elevations. Thunderstorms may
continue into the overnight hours as well, but this is most likely
farther north in Siskiyou county. Additional isolated storms will
be possible near the Trinity Horn Monday afternoon and evening as
well.  For more details see the fire weather discussion below.

Tuesday and beyond, quiet and dry weather can be expected in most
areas with warm, near-normal temperatures.

&&

.AVIATION...Early morning fog along the coast gave way to sunny
skies during the day. Conditions went down to LIFR last night for
Arcata and Crescent City, and they have both improved to VFR as the
fog burned out. However, do expect the marine stratus to come back
once again starting this evening. Have both locations going back
down to LIFR. Meanwhile, should stay VFR for the next 24 hours in
Ukiah.

&&

.MARINE...Light winds and low seas this weekend into Monday. An
area of low pressure is set up off the coast of California. This
allows the pressure gradient to relaxes. Do expect light winds for
the next couple of days. With light winds, seas will be 5 feet or
less.

We will return to a strong northerly wind regime starting on
Tuesday as the East Pacific High re-establishes itself. With tight
northerly pressure gradient, the strong northerly wind regime
will persist through most of next week. Gale force wind gusts will
be possible starting middle of the week.

Forecast is still on track. Little changes were made to the
previous forecast package. GFS is used to update the forecast
package.

&&

.COASTAL FLOODING...There will be potential for localized coastal
flooding near King Salmon in Humboldt Bay overnight tonight due to
astronomical high tide. The high tide will take place at around
midnight tonight, with a predicted high tide of 8.2 feet. For the
past few days, the tide has been running around 0.5 to 0.7 feet
above normal. Expect the actual high tide around 8.5 to 9.0 feet.
When water level is above 8.8 feet, there is potential for localized
flooding near King Salmon. More details can be found in the Coastal
Flood Advisory statement.

&&

.FIRE WEATHER...Hot and dry conditions will continue the
remainder of today, although a lack of strong nocturnal winds will
allow valleys to recover reasonably well overnight tonight.
Recoveries will continue to be moderate to poor in the higher
elevations, but this will be offset by moist fuels in these areas.
Gradually lowering temperatures can be expected Sunday through
early next week, although temperatures will continue to be warm
across the interior.

Of more pressing concern is the potential for thunderstorms over
the next two days. By late tonight and early tomorrow morning, a
plume of mid-level moisture and instability associated with an
upper level disturbance will move overhead, setting the stage for
an unstable environment later in the afternoon. While not likely,
there is an outside chance that a nocturnal dry thunderstorm or
two could develop overnight tonight and tomorrow morning as this
plume moves through the area, although best chances for this will
occur offshore. Inland areas will more likely wake up to scattered
ACCAS clouds, with isolated to scattered thunderstorms developing
across the mountains of northern Mendocino, Trinity, and eastern
Del Norte counties. Dry sub-cloud air will likely mean that very
little rain will fall from storms that do develop, meaning that
dry lightning strike are possible. However, these should be widely
scattered in nature, and mostly in the higher mountainous terrain
where fuels remain relatively moist.

Isolated thunderstorms will again be possible across the Trinity
Horn and farther north on Monday.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT this evening for CAZ102-105>108-110-
     111-113.

NORTHWEST CALIFORNIA COASTAL WATERS...None.
&&

$$

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