004
FXUS66 KEKA 302149
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
249 PM 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...Seasonable weather will close out the weekend, with
highs hovering in the high 80s to low 90s for most interior valleys
this afternoon. The coastal marine layer has been bolstered by
onshore flow despite a weakened marine inversion, so while stratus
has receded this afternoon many coastal locations remain
inundated with cloud, primarily the Humboldt Bay region. The along
shore pressure gradient will remain strong this afternoon as the
trough moves east and high pressure quickly builds on its heels.
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 today. The profilers are showing a deep marine
layer up to around 1,000 feet. LIFR conditions with OVC layer at
400ft and visibility  around 3-2mi due to 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. 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 hold steady in regards to
conditions 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 along the
coast resulting in strong northerly winds. Widespread strong to gale
force winds and very steep, hazardous seas can be expected through
Wednesday evening. Gusty northerly winds up to around 40 kt and seas
around 12-16 feet @ 9-10 seconds are expected for the outer waters.
An official Gale Watch for the outer zones from Monday through
Wednesday has been enacted due to the increased coverage of these
windy conditions. Winds are expected to gradually diminish on
Thursday, a southerly wind reversal is forecasted to move north
towards the Mendocino Coast and relax the pressure gradient.


&&

.FIRE WEATHER...A strong pressure gradient along shore will continue
to promote enhanced northwest wind this afternoon, 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, 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 Warning from 5 PM Monday to 2 AM PDT Thursday for
     PZZ470.

     Small Craft Advisory until 2 PM PDT Monday for PZZ475.

     Gale Warning from 2 PM Monday to 3 PM PDT Wednesday for
     PZZ475.

&&

$$

Visit us at https://www.weather.gov/eureka

Follow us on Facebook and Twitter at:
https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png