154
FXUS66 KEKA 301255
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
555 AM PDT Sun Jun 30 2024

.SYNOPSIS...Dry and seasonable conditions will continue through
weekend along with gusty northwest wind in the afternoon. A strong
heatwave will build early this week.


&&

.DISCUSSION...An upper level trough is continuing to sweep across
the area aiding in consistent onshore flow and the formation of a
widespread stratus deck overnight. Marine influence has lifted far
inland this morning bringing more widespread fog than previous
nights, at least to the northern half of the area.

Seasonable weather will close out the weekend with most likely highs
just below 90 for most interior valleys. The coastal marine layer
has been bolstered by onshore flow despite a weakened marine
inversions, making clearing along the coast more sporadic and
inconsistent compared to yesterday. The along shore pressure
gradient will remain strong this afternoon as the trough moves east
and high pressure quickly builds on its heals. This will bring gusty
northwest wind this afternoon gusting between 20 and 30 mph on
exposed ridges and in channeled terrain. Instability aloft will most
likely aid in enhanced cumulus build up over high terrain today, but
the chances for any lightning are very low (less than 5%).

There is high confidence that very strong high pressure will build
early this week, generating significantly warmer than normal
temperatures by Tuesday. By Wednesday, NBM shows a 90 to 100% chance
of highs in excess of 100 throughout inland valleys of Lake,
Mendocino, and Trinity Counties. Focused on the Russian River
Valley, there is even a 60 to 80% chance of highs above 110 just in
time for the 4th of July holiday. Such values will rival the daily
high record for Ukiah. Overnight lows will bring little relief,
especially along midslope areas of Mendocino and Lake counties where
lows are likely to stay above 70.

Such high temperatures are expected to bring Major to isolated
Extreme HeatRisk around Clear Lake and in the Russian River Valley.
With steady confidence, the existing excessive heat watch has be
upgraded to a warning. Widespread Moderate to Major HeatRisk is
expected throughout the rest of the interior. Despite similar high
temperatures, much cooler overnight lows in the 50s for Trinity and
northern Mendocino County will help lower the overall HeatRisk.
Though there are flagged areas of Extreme HeatRisk beyond Lake and
southern Mendocino, the vast majority of the populated areas show
only Moderate HeatRisk. At the moment, a heat advisory has been
hoisted for the remained of interior Mendocino County where heat is
most confident and will start the soonest.

Above average temperatures are most likely to persist late into the
week. That said, the presence of a surface low pressure off the
coast late in the week may disrupt the heat depending on how
efficiently it can break up larger scale high pressure and pull in
marine influence. It is possible its impact will be negligible, with
about 50% of model ensemble members showing Major to Extreme
HeatRisk continuing even late into the week. Still, Thursday will
most likely bring at least a brief mild  relief to the heat. As such,
no heat products have been extended beyond Thursday at the moment.
/JHW


&&

.AVIATION...A widespread marine layer and stratus are affecting the
coastal terminal early this morning. The profilers are showing a
deep marine layer up to around 2,00 feet. LIFR conditions with OVC
layer at FL002 and visibility in mist/fog are currently impacting
ACV and CEC as result. Low clouds will burn off with the daytime
heating, however stratus are expected to be stubborn to scatter out
along the immediate coast this afternoon. KACV and KCEC may have a
period MVFR/VFR category during the afternoon, before IFR to LIFR
ceilings redevelop. Meanwhile, VFR conditions and breezy NW at 10 kt
and strongest gusts continues at UKI overnight. Winds are expected
to continue breezy throughout the day at UKI, with strongest gusts
after 20Z. Surface winds from NW at 5-10 kt are forecasted for the
coastal terminals.


&&

.MARINE...Northerly winds and seas will gradually subside across the
waters this morning. However, the southern waters will continue to
see strong breezes, with localized near gale force gusts possible
south of Cape Mendocino. Wind wave driven seas around 6-8 ft will
continue promoting hazardous conditions for small crafts across the
southern waters. A mid period WNW swell is moving across the waters,
bringing an additional wave group of 4-5 ft @ 12s to the sea state.


Monday, winds are forecast to strengthen again as a high pressure
offshore begin to builds in quickly in the wake of the trough. A
thermal trough is then expected to develop near the coast Monday
afternoon and favor moderate to strong pressure gradient. Widespread
strong to gale force winds and very steep, hazardous seas through
Wednesday. Gusty northerly winds up to around 40 kt and seas around
12-16 feet @ 9-10 seconds are expected for the outer waters. Have to
hoisted a Gale Watch for the outer zones from Monday through
Wednesday in response. Winds are expected to gradually diminish on
Thursday as a southerly wind reversal move north toward
Mendocino Coast and relax the pressure gradient.


&&

.FIRE WEATHER...A strong pressure gradient along shore will continue
to promoted enhanced northwest wind in the afternoon today,
particularly in Mendocino and Lake Counties with gusts up to 30 mph
along exposed ridges. This will lead to elevated fire danger,
especially in fine fuels. That said, northwest flow will also
increase marine influence, prevent RH from dropping much below 25%
except in the driest valleys. This influence and the short lived
nature of the wind will limit the over extent of fire weather
concerns.

As a strong heat wave builds in, critically dry conditions will
impact the interior. By Tuesday, afternoon RH will drop into the
single digits with very poor overnight recoveries below 40%,
especially within midslope thermal belts.  Even in the absence of
wind, such conditions will rapidly increase fire danger. RH and
temperatures aren`t the only concerns, however. As the heat builds
in, strong northeast winds of 10 to 20 mph will impact the rim of
the Sacramento Valley. In combination, these two forces will create
localized critical fire weather conditions for southeast Lake County
on Tuesday. A Red Flag warning has been raised to highlight this
hazard. Borderline critical conditions will be present as the
heatwave wears on, especially in areas where terrain wind may be
enhanced such as the Trinity River Valley. /JHW


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory from 11 AM Tuesday to 5 AM PDT Thursday for
     CAZ110-111.

     Excessive Heat Warning from 11 AM Tuesday to 5 AM PDT
     Thursday for CAZ113>115.

     Red Flag Warning from 2 AM to 8 PM PDT Tuesday for CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 5 AM PDT Tuesday for PZZ455.

     Small Craft Advisory from 9 AM to 5 PM PDT Monday for
     PZZ470.

     Gale Watch from Monday afternoon through late Wednesday
     night for PZZ470.

     Small Craft Advisory until 2 PM PDT Monday for PZZ475.

     Gale Watch from Monday afternoon through Wednesday
     afternoon for PZZ475.

&&

$$

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