138
FXUS66 KEKA 212007
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
107 PM PDT Thu Aug 21 2025

.SYNOPSIS...Hot and very dry weather will build in through the week
with a shallower and stronger marine layer along the coast. There is
very slight potential for thunderstorms over the interior this
weekend into early next week.


&&

.DISCUSSION...High pressure already began to arch over the area from
the four corners region and will only continue to build into the
weekend. Interior highs will return over 100 today for many valleys
and peak between 105 and 110 by Friday and Saturday Saturday. Though
not quite record breaking, it`s getting late in the season for such
hot temperatures. Daytime heat, combined with enhanced overnight
lows in the mid 60s will combine to generate generally moderate to
localized major (in the Trinity River Valley and Russian River
Valley mostly) HeatRisk. Temperatures will very slightly ease Sunday
into early next week, though also slightly increase humidity will
help maintain a very similar overall HeatRisk through at least
Tuesday.

High pressure will generally promote a shallow but more resilient
marine layer along the coast, likely encouraging a stronger deck of
marine stratus later in the week, especially with more persistent
onshore flow. That said, a weakening in the wind may allow for some
hotter air to creep closer to the coast this weekend with slight
potential (25%-40% chance) for coastal highs near 70 on Saturday.

Most model ensembles show high pressure slowly weakening early next
week but especially by Wednesday. As high pressure pushes back east,
southerly flow up the Sacramento will help pull up some midlevel
monsoon moisture. This moisture, combined with enhanced instability
from the heat, will produce a slight chance (10 to 20%) of isolated,
mostly dry, thundertorms over high terrain early next week. /JHW


&&

.AVIATION...VFR conditions are generally expected (could be pesky
bouts with stratus at times) to prevail for KCEC and KACV through 03-
04Z, when stratus returns (patches still visible on satellite) with
probability of IFR ceiling increasing to 80% by late tonight, and at
least a 40% probability of ceilings as low as LIFR. Visibility is a
bit more of a guess as deterministic numbers vary from 1-2SM from
the NBM to 1/4-1.5 SM from GFS LAMP data. Although probabilistic
numbers indicate a 40% probability of 5SM or lower. I originally
sides with the more pessimistic LAMP data, but may amend for a more
optimistic solution for visibility based on recent observations.
/MH


&&

.MARINE...Moderate to strong northerly winds will continue across the
outer waters and around Cape Mendocino through Friday, with frequent
gale gusts south of Cape Mendocino this afternoon and evening, which
has prompted a short-fused Gale Warning in the southern outer waters
for afternoon through 06Z Friday. A gradual improvement in winds and
seas are expected on Friday and into the weekend. However,
conditions will remain hazardous for small crafts through at least
Saturday evening.

Steep short-period seas of 7-10 ft will accompany the strongest
winds. Some of the steep short period seas are expected to propagate
into the souther inner waters Thursday afternoon and for northern
inner waters Thursday night. A small southwest wave around 15
seconds is currently moving across the waters and will linger into
the weekend. /MH


&&

.FIRE WEATHER...Building hot and very dry weather over the next
several days will generally increase fire danger. RH late this week
will drop to some of the lowest of the season so far with some
single digit minimum RH possible in the far eastern interior on
Friday. Thankfully, high pressure will generally suppress wind with
only moderate terrain winds during the afternoon.

Beyond hot and dry weather, the main concerns will be for potential
thunderstorms this weekend into early next week. Heat will greatly
increase surface instability, but moisture will generally be lacking
to generate thunderstorms. By around Sunday, there is some
indication of monsoon moisture wrapping around and up into the
Central Valley, but the general pattern will be more conducive to
storms over the NE California rather than NW California (only 10%
thunder chance here). There is a very slight indication of nocturnal
thunderstorms early Sunday morning (5% or less), as a weak shortwave
moves along shore, but this potential is very weak. There is
potential for a more concerning pattern around next Monday and
Tuesday with moisture wrapping back around (15-20% chance of some
storms). Storms this weekend are more likely to be dry than storms
during the week. This potential will have to be watched closely.
/JHW


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory from 11 AM Friday to 11 PM PDT Saturday for
     CAZ105-106-110-113.

     Heat Advisory until 11 PM PDT Saturday for CAZ107-108-111-
     114-115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 3 PM this afternoon to 5 AM PDT
     Friday for PZZ450.

     Small Craft Advisory until 2 AM PDT Friday for PZZ455.

     Small Craft Advisory until 11 AM PDT Saturday for PZZ470.

     Small Craft Advisory until 3 PM PDT this afternoon for
     PZZ475.

     Small Craft Advisory from 11 PM this evening to 11 AM PDT
     Saturday for PZZ475.

     Gale Warning from 3 PM this afternoon to 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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