Hayfork, California Weather Forecast Discussion

073
FXUS66 KEKA 302037
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
137 PM PDT Tue Sep 30 2025
.SYNOPSIS...A front will generate strong gusty southerly winds
and periods of light to moderate rain through tonight. Showers on
Wednesday are forecast to decrease on Thursday. Dry weather is
then expected to return on Friday and hold through the weekend.
&&
.DISCUSSION...
An upper level low is sitting well off the Washington coast and
has several shortwaves and associated frontal systems moving
around it. The first front moved through on Monday, bringing rain
to much of NW CA. The next front will move through the area this
afternoon into tonight. This second frontal system looks to have
much less potential for heavy rain and poses a much greater risk
strong winds. The greatest threat for strong winds (>40mph)
capable of blowing loose objects around and causing power outages
will be in Humboldt and Del Norte counties this afternoon and
evening.
This next shortwave trough is showing up well on water vapor this
afternoon. Most all of the models (and NBM) are showing a tenth
to a quarter of an inch of rain as this front moves onshore
tonight. With stronger south-southeast winds and terrain effects,
rain amounts around Humboldt bay region will probably be limited.
Favorable southerly upslope regions, such as the King Range and
mountains of Del Norte County, will likely get much more (over one
inch). This falls well within the category of beneficial rain,
considering the dry antecedent conditions. Latest HREF guidance
also shows redevelopment on the front south of Cape Mendocino with
increased potential for higher rain rates and amounts for
Mendocino and Lake Counties tonight compared to the Monday
rainstorm. We will post a graphic on our Facebook page of
estimated 6-hourly rainfall amounts for select locations.
A low level 925mb speed max around 50kt in advance of the front
will intersect the coastal terrain this afternoon and evening.
HREF guidance and ECMWF ensemble continues to indicate high
probabilities (>60%) for gusts from 35-40 mph for the coastal low
lands and higher gusts > 45 mph for the headlands and wind prone
ridges. Remote automated stations such as Ship Mtn, Mattole Rd and
Kneeland RAWS have already gusted to 40-53 mph as 1 PM. Deep
mixing near the frontal boundary will allow the higher momentum
aloft to transport down to the surface surface, at least over the
higher terrain. Thus gust around 50-55 mph seem possible. There is
much greater uncertainty for strong winds to mix down to mean sea
level. Crescent City or Pt St George stands the best chance for
gusts to 50 mph. Wind gusts to 50 mph or more are also probable
around Cape Mendocino. Thus the wind advisory remains on track.
This is the first strong southerly winds of fall and impacts
generally tend to be greater.
Upper trough and cooler air aloft will lag behind the front on
Wed. Shallow instability and onshore westerly flow will likely
result in continued shower activity into Wed night. Upper trough
passage occurs on Thu and precip coverage to generally wind down.
Showers may spike up again with daytime heating in the interior,
Trinity. Soundings show unfavorable lapse rates for storms, however.
Friday through the weekend and into early next week dry weather is
expected to return. Strong high pressure builds over the eastern
Pacific. The uncertainty lies in exactly how far east this makes
it. It also looks like there will be some weather systems moving
down the east side of the ridge in an inside slider pattern. This
may create offshore flow bringing clear skies and dry conditions.
These clear and dry conditions will also bring the potential for
frost or freezing temperatures in the valleys. This will be highly
dependent on how much drying there is, but it is starting to look
like we will see frost at least in the colder areas. MKK
&&
.AVIATION...18z TAFs...Cloud density steadily filling in ahead of
the incoming front as baroclinic swaths arrive. Light rain and
gusty southerly winds were just arriving at KCEC as of 19z,
expected to continue into the early morning hours Wednesday with
VFR/MVFR conditions and low level wind shear around 2000ft or so
at 35-40kts. Winds could be sporadic at times, changing bearing
and gusting in pulses. KACV is also showing the effects of the
incoming frontogenesis as of 19z with gusty southerly winds with
wind shear around 2000ft at 30-40kts. Rain is due anytime as TAFS
indicate a later start time for KACV (21-22Z), and just a few
hours lagging behind KCEC as the bands land north initially.
Temperature gradients are also highlighting the thermal
differential of the airmass as temperatures and wind directions
fluctuate. Frontolysis on the backside of this process will have
dissipating effects. Stratiform rain will follow. KUKI will get
the same fate to a lesser degree with conditions setting in later
in this afternoon. VFR/MVFR through the TAF period. /EYS
&&
.MARINE...As frontal passages increase wind wave response, northwesterly
swell has combined to bring 7-9ft seas with 11-13 second periods
as of 20z. Seas will continue to be hazardous through the evening,
even after the front passes. Gale force winds are also likely to
continue and so a Gale Warning has been hoisted through 11pm
tonight for the northern inner and outer waters. The southern
waters will see near gale force conditions around Cape Mendocino
but weaker gusts only around 24 kts further south, small craft
advisories for the southern inner and outer waters into Wednesday.
Short period seas will build as much as 8-10 feet but will not have
time to grow further as southerly wind quickly fall off tonight,
replaced by more gentle southerly breezes at least through Thursday.
Despite calming winds and short period seas, a mid period swell will
build up to 12 feet at 14 seconds by early Wednesday, maintaining
generally steep seas in all waters through at least early Thursday
morning. Wind will turn northerly late in the week and begin to
increase mostly south of Cape Mendocino. A resurgence of near gale
conditions are possible lee of the Cape by Saturday. /JHW /EYS
&&
.BEACH HAZARDS...A steep, mid period northwest swell may bring
some hazardous conditions to area beaches during the day Wednesday
and Thursday. While the swell will only be around 14 feet at 14
seconds (producing a beach run up no more than about 18 feet),
this will be one of the first swells of the season. This means
most areas beaches have a shallower grade that has formed over the
summer, which may make waves especially dangerous and unexpected.
Take extra care if on local beaches this week. /JHW
&&
.FIRE WEATHER...Moist conditions, breezy winds with periods of
rain expected into mid week. Drier conditions with lower humidity
is expected to build this weekend and persist into early next
week. Potential for gusty north and northeast winds will increase
over the weekend and early next week. There is a low possibility
for a back door cold front and interior precip on Monday, but
this is an outlier scenario. ERC`s climb during the weekend and
early next week but remain well below average. Thus very little or
no major risk into early next week.
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory until 1 AM PDT Wednesday for CAZ101-102-
     104>106.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Warning until 11 PM PDT this evening for PZZ450.
Small Craft Advisory until 11 PM PDT this evening for
     PZZ455.
Gale Warning until 11 PM PDT this evening for PZZ470.
Small Craft Advisory until 11 PM PDT this evening 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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NWS EKA Office Area Forecast Discussion