Sherwood Valley Rancheria, California Weather Forecast Discussion

208
FXUS66 KEKA 062215
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
315 PM PDT Sat Sep 6 2025
.SYNOPSIS...Showers and isolated thunderstorms in northern Trinity
County this afternoon and evening. Coastal clouds scattering out
this afternoon, before redevelop and expand tonight with more
drizzle expected. Wet weather and below normal temperatures are
expected Monday and Tuesday with a gradual warming and drying
trend later in the week. There is a slight chance of showers and
thunderstorms Wednesday and Thursday, mainly in Trinity County.
&&
.DISCUSSION...A shortwave trough embedded to the main upper level
low center near 43.5N 137.8W, is moving northeastward along the
coast. Coastal stratus have been eroding back and scattering out
this afternoon to bring a period of sunshine. Onshore flow will
push back inland the stratus later this afternoon and evening.
Meanwhile, cumulus clouds (CU) has been developing with the
daytime heating, mainly over Trinity County. Isolated showers and
thunderstorms are forecast for this afternoon and evening in
northern Trinity County. Convective Allowing Models (CAMs) suggests
isolated light to moderate returns over northern Trinity this
afternoon, especially in the Trinity Alps. With increasing PWATs
late this afternoon and evening, storms will produce some rain
(less then 0.10 inch) as well as gusty outflow winds. However,
isolated dry strikes outside the main cores may still occur.
Tonight into Sunday morning, the marine layer is expected to remain
deep and there will likely be widespread clouds along the coast and,
and expanded well up the adjacent river valleys. Coastal drizzle
is expected again.
The aforementioned main upper level trough will continue to
approaches from northwest during the next 24-36 hours, before
moves over the area on Monday. An increasing cloudiness across the
region on Sunday. Coastal stratus are expected to gradually erode
back and mix out with a weak low-level inversion. A cooling trend
is expected through Tuesday, with the with the coolest day on
Tuesday as inland highs cool down into the upper 60`s to mid 70`s.
An associated cold front will push onshore on Monday. This front will
bring light to locally moderate rainfall to the area. There is a
slight chance (10-20% chance) of isolated thunderstorms on Monday
due to the presence of steep lapse rates associated with cold air
aloft, especially along the coast Monday morning. As the event
starts to get closer we can look more at the timing and amounts of
rain for just Monday and Monday night. Rainfall amounts have been
trending lower than expected previously to Del Norte County with
around 0.50 inches. Meanwhile, the rainfall amounts forecast of 0.4
to 0.7 in Humboldt County remain. Trinity county and northern
Mendocino rainfall amounts of 0.25 to 0.40, and generally a tenth
to few hundredths inch in Lake and southern Mendocino counties.
As usual the higher amounts will be farther north, higher in
elevation and closer to the coast.
Tuesday and Tuesday night, the upper level trough settle over the
region. The potential for heavier rain starts to diminish fairly
quickly. Expect post- frontal showers moving across the area.
Rainfall total amounts forecast for Tuesday range from 0.10 to
0.20 inches across the northern counties, while a tenth to few
hundredths of an inch for Menocino and Lake counties. The NBM
50th percentile 24 hr precipitation shows a range of 0.10 to 0.30
inches over Del Norte, Humboldt and Trinity counties, while
generally few hundredths to no precipitation in Mendocino and
Lake counties. Confidences for thunderstorms remain low for
Tuesday afternoon and evening.
Another shortwave trough embedded to the upper-level trough will
dive southward along the West Coast on Wednesday. The GFS and
ECMWF are suggesting an uptick in precipitation across the
interior Wednesday afternoon and evening. The GFS and NAM sounding
models shows increasing instability and steep lapse rate during
this time period. Thus, there is a slight chance (15%) of
thunderstorms for the interior on Wednesday, especially for
Trinity County.
&&
.AVIATION...Confidence in the TAF package is medium to high. Recent
observations have shown persistent MVFR stratus at the coast and the
morning burn-off at UKI, increasing confidence in the current
forecast`s handling of the marine layer.
Coastal Terminals (KCEC & KACV): The forecast follows a high-
probability scenario of progressively worsening conditions with a
marine deep marine layer of 3-3.5 K feet in place. Current MVFR
conditions are expected to persist through the afternoon before
deteriorating overnight, a trend with strong model agreement.
Probabilistic guidance indicates the chance for IFR ceilings (below
1,000 feet) climbs steadily to over 50% after 07Z. The likelihood of
lower, LIFR conditions with ceilings and visibility near a half-mile
or less rises to 30-40% after 09Z. The TAFs` depiction of a gradual
decline reflects this model trend consensus. However, it`s worth
noting that some guidance may be too pessimistic with the lowest
LIFR conditions, especially when compared to last night`s
performance where widespread dense fog did not materialize, and LIFR
ceilings were quite brief, and remained mostly IFR.
Inland Terminal (KUKI): The VFR forecast for KUKI has high
confidence. While the forecast is primarily VFR, probabilistic
guidance indicates there is a non-zero chance, up to 30%, of IFR
ceilings developing late tonight with the relatively deep marine
layer again tonight. There is some disagreement to the gustiness of
wind today. Probabilistic data show a mean west max wind gust near
15 KTS today, with some uncertainty of how much momentum transfer
will occur to the surface./MH
&&
.MARINE...The marine forecast remains on track with recent buoy
observations confirming expected trends. Buoys south of Cape
Mendocino were already reporting the forecast shift to southerly
winds this morning, while northern buoys showed a later shift to
southerly today. Wind speeds will gradually increase into Sunday
ahead of an approaching frontal system, though winds are expected
to remain below 15 knots.
A couple of swells are worthy of mention. A mid-period west to
northwest swell and a long-period southerly swell. Combined seas
will be relatively calm, generally 3 to 4 feet. Conditions are
expected to remain well below Small Craft Advisory criteria through
the weekend. However, two primary hazards exist: patchy dense fog
may develop overnight, reducing visibility for mariners. Secondly,
the frontal passage on Monday will bring a chance (15-25%) of
thunderstorms, especially for the waters north of Cape Mendocino.
Mariners should be aware of the potential for erratic, gusty winds
and dangerous lightning with any storms that develop./MH
&&
.FIRE WEATHER...Isolated showers and thunderstorms are forecast
for the afternoon and evening hours, with the greatest chances in
Trinity County. Any storm will produce some rain (less then 0.10
inch) as well as gusty outflow winds. However, isolated dry
strikes outside the main cores may still occur with a threat for
new fires. Cooler temperatures, higher RH, and rain is likely
Monday through Wednesday. Thunderstorms are possible again Monday
through Wednesday across the area, but these will be accompanied
by mostly rain. Some areas of heavy rain are possible. Warmer and
drier weather is possible later next week. /ZVS&JB
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
None.
&&
$$
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