Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 300348

National Weather Service Eureka CA
848 PM PDT Thu Jul 29 2021

.UPDATE...Patchy fog with varying density has set onto the North
Coast. Visibility will be reduced which could effect
transportation and create hazardous conditions.


.PREV DISCUSSION... /issued 245 PM PDT Thu Jul 29 2021/

SYNOPSIS...Temperatures across interior portions of northwest
California will peak from 100 to 110 Friday afternoon. Conditions
will then cool during the weekend into early next week.
Otherwise, isolated to scattered thunderstorms will be possible
across the interior mountains through Monday.

DISCUSSION...Relatively moist mid/upper-level southerlies persist
over NRN CA between an anticyclone to the east and troughing to
the west. That regime combined with strong afternoon surface
heating and steepening lapse rates is aiding in the development of
deepening surface based cumulus over the Yolla Bolly Mountains
and Trinity Alps. A few thunderstorms will likely evolve out of
that cumulus field through the evening. Thereafter, a plume of
monsoon moisture collocated with a pseudo elevated mixed layer
emanating from the northern Sierra Nevada Mountains is forecast to
spread northwest toward the EKA CWA during Friday morning.
Elevated showers and thunderstorms may spread across the area as a
result. However, cloudiness with that activity may also inhibit
strong surface heating going into Friday afternoon and
subsequently preclude robust surface based destabilization. Thus,
additional storm development during peak portions of the diurnal
heating cycle is uncertain at this time.

Beyond Friday...model guidance supports additional mountain
thunderstorm development on a daily afternoon basis through
Monday, though activity is expected to become increasingly
confined to northern Trinity County. Otherwise, upper ridging and
the most intense summer heat is forecast to shift east across the
Rockies, with south-southwesterly flow aloft persisting through
mid week. Warm, but not excessively hot temperatures will be
probable across interior portions of NWRN CA as a result.


AVIATION...The marine layer remains very shallow along the coast
this afternoon. As of 1pm it is hugging the coast from Trinidad
all the way south past Pt Arena. Currently it is remaining off the
land. HREF ceiling probabilities show it surging onshore this
evening by 02Z or 03Z to KACV and KCEC and bringing in very low
CIGS and VIS. Kept this idea in the TAFS, although brought it in
later than the models show as it has been slow to come in the last
several days. However, with it so close to shore it may come in
sooner than expected. When it does come in expect it will be LIFR
conditions with vis a half or a quarter mile. Friday models show
it clearing out again by mid to late morning with a shallow marine
layer. Inland areas are seeing some mid level clouds in
association with some monsoon moisture moving north. This is
expected to bring a few thunderstorms over Trinity county this
afternoon, but these are not expected to impact KUKI. Late tonight
into Friday there is the potential for a few thunderstorms to
move across the area. These are expected to remain away from the
coast and KUKI, but there is a small chance they will make impact
the TAF sites Friday. MKK

MARINE...Winds and seas remain fairly calm this afternoon.
Currently a small northwest wave that is a combination wind wave
and fresh swell is around 3 to 5 feet at 6 to 8 seconds. In the
southern waters there is also a lingering 1 to 2 foot southerly
swell around 14 seconds. Tonight into Friday models are showing a
subtle strengthening in the northerly winds to around 15 to 25 kt
and seas to building to around 5 to 7 feet. The small craft
advisories starting tonight remain on track. The southerly swell
is expected to diminish tonight. Friday afternoon winds are
expected to drop slightly in the outer waters and this should be
enough to allow the small craft advisories to expire. Late Friday
night and into the weekend winds and seas will likely flirt with
small craft advisory conditions for much of the time and
additional advisories may be needed to highlight this. Conditions
are expected to remain fairly similar into early next week. MKK

FIRE WEATHER...Afternoon and evening thunderstorm development
will be possible across the interior mountains through Monday,
though storm development will become increasingly confined to
northern Trinity County by early next week. In addition, lightning
coverage may be sufficient for a Red Flag Warning from Friday
morning through Friday evening across Trinity, northeast
Mendocino, northern Lake, eastern Humboldt, and eastern Del Norte
Counties. However, it is uncertain whether high based morning
shower and storm development will reduce instability during Friday
afternoon and subsequently inhibit redevelopment of storms during
the hottest part of the day. Otherwise, interior valley
temperatures will peak from 100 to 110 during Friday afternoon.
That will be followed by a cooling trend this weekend into early
next week.



CA...Fire Weather Watch from 8 AM PDT Friday through Friday evening
     for CAZ201-203-204-211-212-277-283.

     Heat Advisory from 10 AM to 8 PM PDT Friday for CAZ107-108-

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 3 AM to 3 PM PDT Friday for PZZ470.

     Small Craft Advisory until 3 PM PDT Friday for PZZ475.



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