588
FXUS66 KEKA 312235
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
335 PM PDT Sun Aug 31 2025

.SYNOPSIS...A warming trend will increase the HeatRisk and fire
weather threat as low RH and hot temperatures build across the
interior on Monday and then peak on Tuesday. The coast is expected
to see night and morning clouds with some afternoon clearing most
days. There is a slight chance of isolated dry thunderstorms on
Tuesday in the interior.


&&

.DISCUSSION...Another day with quiet weather conditions across
Northwest California. Satellite pictures show plenty of sunshine
skies in the interior with cirrus (high-level) clouds streaming
northeast this afternoon. Coastal stratus persist along the North
Coast, while sunny sky south of Cape Mendocino. Low clouds are
still expected to scattered out briefly this afternoon, before
onshore flow push back inland the stratus late this afternoon and
evening. A deep marine layer around 2000 feet is expected to
redeveloped again tonight and into Monday.

Monday, 850mb will begin to increase as the upper-level heights
rises across the Pacific Northwest, while the upper-level trough
move north toward the Gulf of Alaska. This will warm inland
temperatures by around 5 degrees, with high temperatures in the
upper 90`s across the hottest valleys. Interior heat is expected
to peak on Tuesday. High temperatures are forecasted to reach or
exceed the 100F degrees across the warmer locations of interior
Humboldt, interior Mendocino, Trinity and Lake counties on
Tuesday. Expect widespread Moderate HeatRisk across the interior.
The heat will have impacts on some individuals sensitive to heat,
especially those without effective cooling and/or adequate
hydration. This will also strengthen the marine inversion and
coastal clouds may be a bit more stubborn to clear out. NBM
probability indicated there is a 60% chance for Big Bar reaching
or exceeding 105F degrees on Tuesday.

A weak upper level trough still forecast to move up across the
west periphery of the ridge Tuesday through Thursday. This may
bring some moisture and instability. Latest (18Z run) GFS and NAM
models suggest PWAT values between 0.60 to 0.80 inches. The
combination of a "moderate" instability around 200-300 J/kg and
very dry atmosphere (low PWAT) will bring a slight chance
(10-20%) of isolated thunderstorms development on Tuesday
afternoon and evening across the high terrain in Trinity County
and portions of northeastern Mendocino and northern Lake
counties. See Fire Weather Section.

Wednesday the shortwave is expected to be north of the area. Even
the slower solution of the ECMWF has pushed the instability north
of the area by the afternoon ending the threat for thunderstorms.
Temperatures are expected to be similar to Tuesday. Thursday and
Friday a gradual cooling trend is expected, although temperatures
are expected to remain hot. /ZVS



&&

.AVIATION...(18Z TAFs)...Satellite imagery is showing stratus
hugging the Humboldt and Del Norte coasts late this morning. Some
further eroding to the coastline and lifting is expected this
afternoon, before stratus returns to the coastal terminals this
evening, returning LIFR/IFR ceilings. There is some variation in the
models on the depth of the marine layer, where a deeper marine layer
may support IFR ceilings and little restriction in visibility, like
the previous few days. The low pressure to the north supports this
idea, but there is still the possibility ceilings and visibilities
end up lower. Interior areas, including UKI, remain VFR today with
only a few high clouds. Breezy northwest winds up to 15-20 kts are
possible at UKI this afternoon. JB


&&

.MARINE...Northerly winds continue to increase in the lee of Cape
Mendocino, with gusts of 25-35 kts forecast this afternoon into the
evening. Stronger winds and steep seas may reach nearshore Mendocino
this afternoon and Monday afternoon, with gusts peaking around 25-30
kts. Elsewhere, winds and seas remain mild with combined seas of 2-3
ft. A small long-period southerly swell continues and will persist
trough the weekend. Models are beginning to resolve a fetch of
northerly winds in the northern outer waters, likely to build and
fill in Monday, with steep seas of up to 6-7 ft possible by Monday
night. This general pattern continues into mid next week. /JB /EYS



&&

.FIRE WEATHER...Low daytime RH in the single digits to teen`s
percent and breezy westerly winds are promoting elevated to
locally critical fire weather conditions over the higher terrain
in zones 277, 283 & 264 this afternoon. Winds are expected to ease
this evening. Poor overnight RH recoveries around 25 to 35
percent over the higher terrain, while good to moderate recoveries
for areas below the inversion (<2000 feet).

A warming and drying trend is expected with high temperatures
forecasted to peak in the upper 90s to near 105 across the
interior valleys on Tuesday. A weak upper level trough will bring
some moisture and moderate instability across the area on Tuesday.
The combination of these factors, "moderate" instability and very
dry atmosphere (low PWAT), will bring a slight chance (10-20%) of
dry thunderstorms on Tuesday afternoon and early evening across
the high terrain in Trinity County and portions of northeastern
Mendocino and northern Lake counties. In addition, gusty winds
combined with hot temperatures and low relative humidity will
produce critical fire weather conditions. Existing fires and any
new fire will have the potential to spread rapidly.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for CAZ204-277-283.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 11 PM PDT Monday for PZZ455.

     Small Craft Advisory from 11 PM Monday to 3 PM PDT Tuesday
     for PZZ470.

     Small Craft Advisory until 3 PM PDT Tuesday for PZZ475.

&&

$$

NOTE: The full forecast discussion is now regularly issued between
10 am/pm and 1 pm/am. Additional updates will be issued as needed.

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