608
FXUS66 KEKA 192142
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
242 PM PDT Tue Aug 19 2025

.SYNOPSIS...A gradual warming and drying trend will continue with
intensification Thursday and Friday. Inland temperatures warming
from 100 to 110 late this week and through the weekend will create
fire weather concerns and a Moderate to locally Major HeatRisk.
Hot temperatures will continue into next week.


&&

.DISCUSSION...A very weak low level inversion has been allowing the
shallow marine stratus to remain quite disrupted and fully cleared
out from the land through some periods. Models have been overly
zealous with the return of the stratus, particularly by the
statistical variety. Some of the coastal temperatures have reached
higher values than guidance for this reason.

A shortwave perturbation will clip the northern region Wednesday,
but is expected to have little impacts other than suppressing the
greater inevitable warmup. Beyond the passing of the shortwave,
temperatures will indeed continue warming with a strengthening Four
Corners Region high. 500 mb heights of this high are are forecast
to reach 597 dm. This setup has strong reliability and high
forecast confidence for hot temperatures through our region.

Inland temperatures will make a substantial jump upward Thursday
when the once displaced high fills back in. This will be in sharp
contrast to the recent trend of below to much below average
inland high temperatures. This means less time for acclimation.
For this reason, and the hot temperatures of 100 to 110 combined
with warm overnight lows, there is a Moderate to some areas of
Major HeatRisk. There will be some troughing that will attempt to
dig south over the ridge Sunday, but any weakening of the strong
high will be a slow process. Heat Advisories are out starting
Thursday and lasting through Saturday evening. Extensions may be
required with later model guidance. Please exercise caution with
outdoor activity and learn the signs of heat exhaustion or stroke.

The Four Corners region high will tap into monsoonal moisture at the
end of the week. Monsoonal moisture will begin clipping the eastern
region starting Friday. There is a small but impactful chance (5-
10%) for isolated dry thunderstorms starting Saturday for Trinity
County. Chances for thunderstorms look to then trend higher through
weekend and especially early or even mid next week with
additional monsoonal moisture. The environment will attempt to
moisten through that period. There will eventually be higher
precipitable water values and a better chance for precipitation in
any shower or thunderstorm the reach the ground, but how fast
that can happen is uncertain given the amount of drying expected
ahead of it. JJW



&&

.AVIATION...(18Z TAFs)...Shallow stratus has formed right off the
Humboldt and Del Norte coasts. Daytime heating has brought
temperatures up and should keep stratus from being impactful to the
terminals, but some brief periods of IFR are not out of the question
into the afternoon. Model guidance suggests stratus returning to the
Humboldt and Del Norte coasts tonight, but confidence remains low.
The marine inversion remains weak, and while model confidence is
fairly high, it was also high last night and conditions remained
VFR. If stratus does develop, ceilings and visibilities are likely
to be IFR to LIFR. Inland, VFR conditions with mostly clear skies
are expected with afternoon breezes easing overnight. JB


&&

.MARINE...Northerly winds remain fairly light today outside the lee
of Cape Mendocino. Gusts of 20-30 kts are possible this evening in
the lee of the Cape, but otherwise, winds gusts peak around 10-15
kts this afternoon. Seas remain dominated by a 3-5 ft northwesterly
mid-period swell. This swell will gradually subside over the coming
days. Northerly winds increase this evening through the rest of the
week, with near-gale to localized gale force gusts forecast in the
lee of Cape Mendocino and Cape Blanco. The strongest winds remain 5-
10 nm or farther off the coast, with much lighter winds, peak gusts
of 5-15 kts, expected nearshore into the weekend. Steep seas of 8-10
ft are forecast to be associated with the strongest winds.
Nearshore, seas of 4-6 ft at 7 s are forecast, with the highest seas
found 5-10 nm offshore. JB


&&

.FIRE WEATHER...A warming and drying trend will continue. Northeast
winds will develop Wednesday night and this will cause an
accelerated drop in Minimum RH for Thursday, with values down to the
low teens to some single digits for zones 283, 277 and 264. Inland
heating will intensify Thursday, with a further increase Friday. The
heat and low RH will remain through the weekend. Afternoon westerly
wind surges will also bring fire weather concerns, particularly in
zones 264 and 276. Monsoonal moisture will begin clipping the
eastern zones starting Friday. There is a small but impactful chance
(5-10%) for isolated dry thunderstorms starting Saturday for Trinity
County.

Chances for thunderstorms look to then trend higher through
Sunday and early or even mid next week with additional monsoonal
moisture. The environment will attempt to moisten through that
period. There will eventually be higher precipitable water values
and a better chance for precipitation in any shower or thunderstorm
the reach the ground, but how fast that can happen is uncertain
given the amount of drying expected ahead of it. JJW



&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory from 11 AM Friday to 11 PM PDT Saturday for
     CAZ105-106-110-113.

     Heat Advisory from 11 AM Thursday to 11 PM PDT Saturday for
     CAZ107-108-111-114-115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 11 PM Wednesday to 11 PM PDT
     Thursday for PZZ470.

     Small Craft Advisory from 11 PM this evening to 11 PM PDT
     Thursday 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