Piercy, California Weather Forecast Discussion

828
FXUS66 KEKA 230737
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
1237 AM PDT Tue Sep 23 2025
.SYNOPSIS...Warmer and drier weather will gradually build in
through late Tuesday. A troughing pattern could emerge by mid
week with a cut off low over coastal central/southern CA.
&&
.DISCUSSION...High pressure will continue to push into the region
early this week allowing interior highs to crest back into the
90s with warmer interior valleys potentially getting into the low
100s by Tuesday. The marine layer onshore will likely become more
diurnal with better clearing in the afternoon, but with shallow
fog and stratus overnight, especially in wind protected areas such
as Humboldt Bay.
A closed low pressure system is forecast to approach central and
southern California by Wednesday. Recent model guidance indicates
there is less than a 10 percent chance for wetting rain across
Northwest California as this low moves through to the south.
However, there could still be showers or a stray isolated
thunderstorm for extreme southern Mendocino and extreme southern
Lake counties.
The southern counties of our forecast region (Mendocino and Lake)
are projected to be on the extreme northern edge of the moisture
around this closed low system. As a result, impacts can still be
uncertain due to the region being on the periphery of the low.
Generally moderated temperatures and greater cloud cover are more
certain. Also, the low will still pull up moisture form the
south, but the general northeast flow around the low will not be
favorable for widespread wetting rain. Showers that do form will
most likely be around the rim of the Sacramento Valley where the
wind best aligns with topography as orographic lift will mostly be
a storm catalyst. The vast majority of models suggest a cooler
and more moist pattern through the end of the month, with long
range data showing above normal precipitation.
&&
.AVIATION...6Z TAFs...Monday satellite observation showed the entire
region devoid of cloud cover. High resolution guidance is struggling
to redevelop marine stratus through Tuesday morning. There are hints
of coverage around Humboldt Bay and in the vicinity of ACV (30%). If
this does form, it will be shallow with the potential for fog
visibilities given the building high pressure. If skies remain more
clear, patchy ground fog will develop. Overnight offshore winds will
limit fog duration, particularly at CEC (20% chance). Confidence is
very low on the coverage of the described conditions potentially
impacting ACV and CEC. VFR will prevail elsewhere. Marine stratus
will gain only slightly better coverage Tuesday afternoon, with at
least VCTY coverage for the coastal terminals. Confidence for better
stratus coverage looks to not increase until going into Wednesday
when southerly return flow strengthens along the coast. JJW
&&
.MARINE...Northerly winds peaked Monday evening, and are dropping in
speed as the pressure gradient weakens from surrounding troughing.
Steep, wind driven seas are also subsiding, and will drop below 10
ft in the outer zones (over 10 nm offshore) by late Tuesday morning.
High pressure will then nose back from the west in Thursday,
strengthening the pressure gradient against a cutoff upper low over
CEN CA. Southerly return flow will develop along the coast on
Wednesday. Northerly winds will strengthen Thursday through Friday
in response. Gale condition are looking more likely in the outer
zones. NBM now holds a 40 to 55% chance for gales late Thursday and
Friday. Steep seas are currently forecast to build to 10-13 ft in
the outer waters through that period.
&&
.FIRE WEATHER...High pressure building early this week continues
to quickly warm and dry conditions. Highs will likely peak
Tuesday with the hottest valley just shy of 100 and min RH in the
upper teens. Northeast afternoon winds will also be slightly
enhanced Tuesday afternoon around the rim of the Sacramento
Valley with some gusts in Lake County likely up to 20 mph.
Conditions will slightly ease (particularly daytime RH) Wednesday
and beyond. There is a very slight chance of thunderstorms for
extreme southern Mendocino and Lake Counties Wednesday
afternoon/evening, yet convective allowing models are uncertain
that there will be the right mix of atmospheric ingredients to
create these storms.
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PDT Tuesday for PZZ455.
Small Craft Advisory until 11 AM PDT Tuesday for PZZ470-475.
&&
$$
NOTE: The full forecast discussion is now regularly issued between
10 am/pm and 1 pm/am. Additional updates will be issued as needed.
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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png

NWS EKA Office Area Forecast Discussion