077
FXUS66 KEKA 092009
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
109 PM PDT Sun Aug 9 2026

.KEY MESSAGES...
* Moderate to major heat risk continues for much of the interior
  areas today.

* Stronger afternoon valley winds and low relative humidity will
  elevate fire danger this weekend.

* Temperatures diminish slightly next week, but most areas remain
  the upper 90s to around 100 through mid-week.

* Heavy smoke is expected within the Trinity River Valley due low
  mixing heights at to the MP 18 fire.

&&

.SYNOPSIS...High pressure aloft remains through the daytime before
finally weakening to start the coming work week. Inland areas continue
to see above normal temperatures with moderate to locally major heat
risk and afternoon gusty winds near channeled terrain. Coastal areas
will remain mostly overcast with brief clearing possible this
afternoon and breezy northwest winds.


&&

.DISCUSSION...The seemingly immovable upper level ridge that has
dominated the weather for the past week or so will finally begin to
give way to more zonal flow aloft this evening. However, through
today, NW CA can expect continued warm to VERY hot temperatures for
the inland areas. Most inland valleys and Lake County can expect
high temperatures between at or near 100F today.The ongoing heat
will be dangerous for anyone working outside. Everyone in the
interior portions of all of Northern California should be drinking
plenty of fluids and taking breaks in the shade to avoid heat
stroke or heat exhaustion. The coast continues to offer some
relief from this heat due to a strong marine layer and its
associated stratus blanketing much of the Californian coastline.

The aforementioned mentioned daytime interior heating will continue
to tighten the surface pressure gradient each afternoon forcing
stronger onshore (NW) sea breezes. In NW-SE situated river valleys
(Trinity River Valley, Eel River Valley, areas near Clear Lake,
etc.) these winds will have a higher chance to mix down to the
surface. These increased winds in addition to hot and dry conditions
will cause very localized critical fire weather conditions over the
region. For more details, see the fire weather section below.

Despite the increased surface winds, the smokey conditions within
the Trinity River Valley will likely remain through midweek as the
fire activity increase each afternoon. The HRRR smoke model shows
smoke moving along upvalley flow before settling into valleys
each night. This pattern is expected to remain through Wednesday
at the earliest.

Global ensemble models and 500mb clusters suggest that the midweek,
zonal flow aloft will likely evolve into weak to moderate troughing
by late next week. The troughing will force a cooling trend with
inland temperatures struggling to break 90F by Friday. Troughing
could also create an environment capable of supporting afternoon
thunderstorms over the interior mountains. A lot of variability
remains regarding this weather threat, such as moisture available,
if the air will be stable vs unstable, or if there will be enough
lift at the surface to create updrafts. Stay aware of forecast changes
as more details become available through the week.


&&

.AVIATION...Coastal stratus is continuing to dissipate
across most of the North Coast. Terminals close to the shoreline
will remain IFR/LIFR with minimal clearing expected this afternoon.
Northerly winds are expected through the afternoon with gusts up to
15kts or so at KACV and up to 20-25kts are KCEC. Model probabilities
show that more likely than not, IFR/LIFR conditions will return
around 03Z (+/- 1hr) with low ceilings and degraded visibilities due
to haze/mist.

Inland areas are expected to remain VFR with gusty afternoon winds
developing during the peak heating of the day. NW winds will likely
dominate the interior areas of NW CA. Anomalously hot surface
temperatures could lead to density altitude issues this afternoon as
well, be aware. Finally, the Trinity River Valley and its surrounding
areas will likely have IFR/IMC due to very heavy FU from the near
by MP 18 Fire. Expect extremely degraded slant and surface
visibilities as well as mountain obscuration near terrain for
those areas.


&&

.MARINE...Significant wave heights have been steadily building since
Saturday with buoys recording widespread 8ft @ 8sec. Satellite
imagery of the marine stratus and surface winds observations shows
northerly nearshore winds of around 15-20kts with gusts p to 25kts.
near the inner waters. The wind speeds are likely to increase
further away from the coastline in the outer coastal waters. Most
model data shows continued sustained winds near 30kts and gusts of
40kts possible through early this coming work week, especially for
the northern outer waters. Very steep waves are to be expected
leading to hazards such a blowing foam in addition to the very large
seas. The biggest area of concern for the strongest winds is
downwind of Cape Mendocino and Point St. George. WHile the winds
will likely continue to be lighter in the inner waters with moderate
to fresh breezes, waves will still be steep due to propagation from
the large short period seas in the outer waters heading towards
shore. These stronger northerly winds are likely to last through
most of the coming work week.


&&

.FIRE WEATHER...This afternoon, localized critical fire weather is
expected for the Trinity River Valley, interior Mendocino County,
and areas on the direct eastern shore of Clear Lake. This short
lived threat will be due to low afternoon RH values in the low teens
to single digits and increased afternoon winds with NW gusts up to
20mph or so. While winds and area coverage lack the official
criteria for a Red Flag warning, it is important to remember that
even a single spark could start a wildfire in these conditions. The
aforementioned areas have the greatest risk due to the NW-SE
oriented valleys and basins that will  enhance winds mixing down
to the surface through the channeled terrain and over Clear Lake.
The hot, dry, and windy conditions will likely cause conditions that
could fuel explosive fire growth from around 3pm - 7pm today.

A slight cooling trend is expected through the coming work week.
High pressure will move away from the area and very weak troughing
is likely to fill in its place, setting up over the area. This
troughing has the potential to funnel moisture into the area. The
moisture, if it materializes over NW CA, could cause some afternoon
thunderstorms for Friday and Saturday. Details on this set up are
minimal now as the high pressure is still over the area, yet updates
are expected through early week due to the dangerously dry fuels
over the interior.


&&

.COASTAL FLOODING...Sea levels continue to run approximately
0.8 ft above the predicted tide level in Humboldt Bay. Tides will
become more amplified early this week following the lunar cycle.
The predicted tide at the North Spit is 7.95 ft MLLW at 10:21 pm
on Monday the 10th and then 7.99 ft MLLW at 11:17 pm on Tuesday
the 11th. If the tide continues to run at around 0.8 ft above
predicted, this could result in minor coastal flooding around
Humboldt Bay with minor impacts in King Salmon and possibly a few
other locations around the bay. The tide anomaly will continue to
be watched this evening to warn of the possible hazard.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory until 10 PM PDT this evening for CAZ108-
     110>114-116>120.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PDT Tuesday for PZZ450-455.

     Gale Warning until 3 AM PDT Wednesday for PZZ470.

     Gale Warning until 10 AM PDT Monday 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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