Keene Summit, California Weather Forecast Discussion

900
FXUS66 KEKA 290735
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
1235 AM PDT Mon Sep 29 2025
.SYNOPSIS...Rain is expected to arrive this morning in the north,
quickly spreading south across the area through the day.
Additional rain and wind are expected Tuesday afternoon and
overnight. Lingering showers are expected Wednesday and will off
on Thursday. Dry weather is expected to return for Friday and the
weekend.
&&
.DISCUSSION...A cold front is approaching the area bringing
southerly winds to the area. These are strongest are along the
coast and over the higher terrain with gusts of 20 to 30 mph in
some areas. The winds are not expected to get much stronger, the
lower levels are fairly stable and the wind at 850 mb only peaks
around 30 to 35 kt. The models are still showing some differences
in the timing of the onset of the rain, although they do seem to
be converging on a slightly earlier solution. Crescent City is
expected to see rain start around 7 or 8am am and then it is
expected to be 1 to 2 hours later in the Humboldt Bay area. This
is expected to continue to move south and east through the day
reaching Mendocino and Trinity counties by early to mid afternoon
and Lake county mid to late afternoon. Rainfall totals are
currently expected to be around 0.75 to 1.50 inches in Humboldt
and Del Norte counties, around a half inch in Trinity and northern
Mendocino counties and around a quarter inch in southern
Mendocino and northern Lake counties. Southern and southeastern
Lake county may see only a tenth of a inch through Monday evening.
There is also the threat for thunderstorms Monday afternoon in
the interior areas. The soundings at the coast only show a shallow
layer of instability. Areas farther inland could see a few
embedded thunderstorms in the afternoon. The GFS is showing some
areas with 100 j/kg of CAPE. Lapse rates aloft are only around
6c/km so few, if any, thunderstorms are expected. Monday night is
generally expected to be dry with lighter winds between cold
fronts. Any areas that do clear out will likely see valley fog
develop.
Tuesday the next cold front is expected to move onshore bringing
more wind and rain. The rain is generally expected to hold off
until the afternoon. Overall this second system is expected to
have less rain and more wind as it moves onshore. The strongest
winds are expected to move onshore in the evening. The NAM is
showing 850 MB winds of 30 to 40 kt over Humboldt and Del Norte
counties. This will likely bring some 40 mph gusts to higher
terrain of these areas. The low levels remain fairly dry and
unstable along the coast so these areas could see a few gusts to
40 mph or even 45 mph in Crescent City. So have decided to issue a
wind advisory, for now have confined it to Del Norte county, but
it may need to be expanded. Rainfall amounts are expected to be
fairly light with this second front. This will be especially true
in areas in the lee of the mountains, notably the Humboldt Bay
area. Most areas are expected to see less than a half inch with
the exception of a few mountainous areas of Humboldt and Del Norte
counties.
Wednesday may see some lingering showers around the area, but in
general not much rain is expected. Winds are also expected to
diminish. There is still the potential for a thunderstorm or two,
but confidence is low on this with poor lapse rates aloft.
Wednesday night if there is some clearing aloft many of the
valleys are expected to see widespread low clouds and fog.
Thursday there may be a few lingering showers in the morning, but
generally dry weather is expected.
Friday and into the weekend high pressure is expected to start
building into the area. This will bring a return of high
temperatures in the 80s in the warmer inland valleys. Some of the
colder valleys of Trinity could see their first frost of the
season. This will depend on which nights manage to stay clear and
dry. Hayfork dropped to 40 degrees Saturday morning so with a
slightly cooler and drier airmass it could easily drop into the
low 30s. Sunny weather is possible along the coast with offshore
flow returning as well. MKK
&&
.AVIATION...Forecast confidence is increasing with the impacts of an
incoming upper level trough will create degraded conditions through
the TAF period. Strong southerly winds with gusts up to 20-25kts on
exposed coastal areas and ridgelines tonight through tomorrow. Wind
shear of 30-35kts at 1500 ft AGL can create turbulent conditions and
localized mountain wave conditions. Low clouds will give way to
precipitation, further degrading flight conditions early  through
tomorrow. There is a slight potential for fog, yet model data shows
cloud ceilings will be between 1-3 kft AGL along the coast. Inland,
winds will be forced by this incoming synoptic event and be
generally MVFR overnight before giving way to VFR conditions by 00Z
this afternoon. DS
&&
.MARINE...Southerly winds expand across the area waters as
a cold front approaches the area this morning. Wind waves to
increase as the front crosses the waters, mixing with the ongoing NW
Swell. There may be some localized gale force gusts as the front
passes, however the airmass is looking somewhat stable as the front
passes by and the may keep too many gusts from mixing down to
sea level.
Later in the day, the winds are expected to diminish quickly behind
the front. This lull will be brief, only about 18-24 hours or so.
Another cold front will impact the coastal waters early Tuesday
morning with more southerlies. These are expected to peak around 30-
35kts, especially in the northern waters near Cape Mendocino. A
Gale Warning has been issued for the northern outer waters
(PZZ470) from midday Tuesday until around dawn on Wednesday. More
hazards are possible as increased high resolution data becomes
available this afternoon.
Southerly winds are expected to continue on Wednesday and
Thursday with models still confirming a large NW swell entering
the coastal the waters. The NBM and GlobalWaveWatch both show this
building to 12 to 14 feet around 14 seconds. If this
materializes, this would be the first large swell of the fall. The
beaches generally still have their shallower summer slopes
allowing larger than expected breakers with it. Breakers may
exceed 16 feet Wednesday night. DS
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory from 11 AM Tuesday to 1 AM PDT Wednesday for
     CAZ101-102.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 8 PM PDT Monday for PZZ450-470.
Gale Watch from Tuesday afternoon through late Tuesday
     night for PZZ450-470.
Small Craft Advisory from 8 AM to 8 PM PDT Monday for
     PZZ455-475.
&&
$$
NOTE: The full forecast discussion is now regularly issued between
10 am/pm and 1 pm/am. Additional updates will be issued as needed.
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

NWS EKA Office Area Forecast Discussion