Lewiston, California Weather Forecast Discussion

725
FXUS66 KEKA 022109 CCA
AFDEKA
AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Eureka CA
209 PM PDT Thu Oct 2 2025
.SYNOPSIS...Isolated to scattered showers are expected to continue
tonight. Dry weather and breezier northerlies will build on
Friday and continue through the weekend.
&&
.DISCUSSION...Upper trough just inside 130W this afternoon will
continue to create sufficient instability for isolated to scattered
showers this afternoon and evening. Precip activity appears to be
primarily forced by upslope flow into the terrain. Satellite
imagery and radar data has been indicating precip bands with
higher reflectivity cores offshore over the coastal waters. These
have been largely dissipating into sprinkles for most coastal
areas.
Upper trough will track across the forecast area tonight into
early Friday. There is a greater risk for deeper/stronger interior
showers as lapse rates steepen in response to the cold air aloft,
500mb temps near -20C. Moisture depth is shallow, however. Once
again soundings show long thin CAPE profiles that are not too
favorable for thunderstorms. Convective allowing models (CAMS)
show strongest cores and heaviest rain rates east of the forecast
in the Sac Valley and foothills late tonight or early Friday
morning. This max appears to be associated with cold core/cyclonic
circulation aloft vs daytime heating destabilization.
Upper trough/cold pool aloft will progress SE into the Great Basin
on Friday, leaving our forecast area under drier and more stable
conditions. Some light showers in the wrap around will be possible
along the eastern periphery of southern Trinity, eastern Mendo,
northern Lake and perhaps over the Trinity Alps. Otherwise drier
weather and breezier north-northwesterly winds are expected Friday.
Dry weather and gustier higher terrain coastal northerlies will
follow for this weekend as a surface ridge builds offshore and
an inverted trough develops along or over the coast. Drying
offshore flow will yield clearer skies, especially for coastal
areas over the weekend. Fog and low clouds in the interior valleys
remain a distinct possiblility after multiple days of rain. If
skies remains clear all night, frost or freezing temperatures in
the colder valleys will be possible. NBM probabilities around 30-50%
for colder places like Hayfork and Larabee Valley to name a few.
Much greater forecast uncertainty crops up early next week with
offshore wind flow diminishing. A southerly wind reversal may
develop. This would likely result in coastal stratus and fog.
Otherwise dry weather is expected into mid next week. NBM 24-hour
QMD does indicate low chances of 10-20% for > 0.10 by 5 PM Thu
and 30-40% by 5 PM Fri as a series of shortwave trough heads into
the Pac NW. More rain is possible, but unlikely a major event with
24 hour probabilities for > 1 in in 24 hours no more than 20%.
&&
.AVIATION...(18z TAFs)...Showers for the region continue to diminish,
only with some lingering showers for North Coast terminals and
potentially terminals in higher elevation areas of interior Humboldt,
northern Mendocino, and Trinity counties. General cloudcover will
continue through the TAF period for most of the terminals in the
region. MVFR/VFR ceilings are most likely this afternoon and
early evening with some scattering to clearing occurring or
possible. Coastal terminals should see a return to LIFR/IFR
conditions this evening. Borderline MVFR/VFR conditions may be
possible around KUKI.
&&
.MARINE...Seas have remained steep due to a mid period westerly
swell that peaked at 14 to 16 ft (for some buoys) early this morning.
This swell is currently at 11 to 12 ft and will continue to gradually
decay through the day. Wave heights are generally expected to be
below 10 feet by late this afternoon/early evening.
Just as the swell decays, gentle southerly winds will gradually turn
northerly. Northerly winds will first increase in the southern waters
with some gusts over 25 kts south of Cape Mendocino during the
day Friday, with moderate to strong northerly winds across all
waters by Saturday generating steep short period seas over 6 feet.
There is a relatively widespread 30 to 40% potential for gale
force gusts by very late Saturday in the southern outer waters
with up to a 60% potential directly downwind of Cape Mendocino.
Gale conditions could persist into early next week.
&&
.BEACH HAZARDS...As a steep, mid period northwest swell diminishes,
it may still continue to bring some hazardous conditions to area
beaches into this evening. While the swell continues to diminish,
currently at 11 to 12 feet (producing a beach run up no more than
about 14 feet, currently), this is one of the first swells of the
season. This means most area beaches have a steeper grade that has
formed over the summer, which may make waves especially dangerous
and unexpected. Take extra care if on local beaches this week.
&&
.FIRE WEATHER...Humid conditions and mostly light-moderate shower
activity tonight will transition to a drier and cooler northerly
wind flow on Friday as an upper trough moves SE into the Great
Basin. Drier daytime RH`s are generally expected this weekend.
Coastal northerlies will also strengthen this weekend which may
result in poorer RH recoveries for exposed ridges and mountains,
especially Sunday night. Dry conditions expected to continue into
early next week.
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Beach Hazards Statement until 5 PM PDT this afternoon for
     CAZ101-103-104.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 5 PM PDT this afternoon for
     PZZ450-455-470-475.
Small Craft Advisory from 5 PM Friday to 5 AM PDT Saturday
     for PZZ455.
Small Craft Advisory from 5 PM Friday to 11 AM PDT Saturday
     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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https://www.weather.gov/images/eka/zonemap.png

NWS EKA Office Area Forecast Discussion