576
FXUS66 KEKA 210715
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
1215 AM 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 4 corner region on Wednesday and will only
continue to build Thursday and 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 late 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% 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...21/06Z TAFs...VFR conditions have been observed across
all TAF terminals. Low clouds and patchy fog are expected to
developed overnight around Humboldt Bay and vicinity overnight.
Light reversal southerly winds nearshore should push this low clouds
northward along the coast into Thursday morning. NBM indicates there
is a 35 to 50% of LIFR/IFR conditions along the north coast by early
Thursday morning. However, stratus should clear out quickly with a
weak low level inversion. Low clouds are expected to redeveloped
after 22/05Z on Thursday night into Friday.


For inland areas: VFR conditions persist at UKI through the period.
Surface winds very light and variable, after 21Z becoming NW at
around 5-10kts with higher occasional gusts./ZVS


&&

.MARINE...Moderate to strong northerly winds will continue
across the outer waters and around Cape Mendocino through Friday.
Winds are forecast to increase slightly Thursday afternoon leeward
Cape Mendocino, which has prompted a short-fused Gale Warning in the
southern outer waters for Thursday afternoon. 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 afternoon.

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. /ZVS


&&

.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 late in the week and this weekend. 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 5%
thunder chance here). There is a very slight indication of nocturnal
thunderstorms early Sunday morning (5%), as a weak shortwave move
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 (20% chance of some storms). Storms
this weekend are more likely to be dry than storms next. 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 from 11 AM this morning to 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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