Alton, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

438
FXUS66 KEKA 262011
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
111 PM PDT Thu Jun 26 2025

.SYNOPSIS...
A gradual warming trend is expected over the next few days with
highs pushing into the 100s for many interior valley location on
Sunday. Moderate to locally major HeatRisk will occur this
weekend, especially on Sunday. Thunderstorm chances will return
for interior areas Monday into Tuesday.

&&

.DISCUSSION...
Stratus continues to plague the coast, as it often does this time of
year, but the afternoon breakup is bringing sunshine to most areas
this afternoon. The stratus will once again spread to many areas
along the coast overnight except for off the southern Humboldt
coastline into far northern Mendocino where offshore northerly flow
should dominate.

There are two main concerns for this week: 1) Heat for this weekend
and 2) Thunderstorm chances Monday and Tuesday.

As for the heat, models remain consistent with a ridge building over
the west cost this weekend allowing 1000-500 mb heights to increase
and 850 mb temperatures to warm. On Sunday an upper low is forecast
to strengthen off the California coast and begin to move north
toward northwest California. A shortwave ridge on the north side of
this low will nose itself over Northwest California leading to a
brief window for much above normal temperatures across the interior.
100 degree temps will be possible for many interior valley
locations, particularly on Sunday, as 850 mb temperatures reach
25- 30C. At this time the heat is expected to be brief and
overnight cooling recoveries should keep the HeatRisk from
becoming too intense. Thus, no heat advisories are anticipated at
this point. Temperatures will cool several degrees Monday into
Tuesday as the low moves overhead.

Speaking of this upper low, it is also the system that will pull
moisture toward our region bringing a chance for thunderstorms,
primarily over the mountains of Trinity County Monday and Tuesday
afternoons. There is an approximately 15% chance that storms could
form and move northwest into Humboldt and Del Norte interiors and
additionally farther south into the Mendocino National Forest in
Mendocino and northern Lake counties on Monday. The flow Tuesday
will become more southerly to southwesterly keeping storms farther
east. Storms will likely be a mix of dry and wet over this time
period with guidance showing bullseyes of QPF greater than 0.10 in
the interior but inverted V soundings near the surface. GFS
precipitable water values are currently forecast to be around
0.8-1" both days.

Dry conditions are likely to return by Wednesday as the low moves
east of the area leaving zonal flow over the west coast. /RPA

&&

.AVIATION...
18Z TAFs...The marine layer greatly deepened overnight form a
passing shortwave. A weaker, more subtle shortwave will pass
through tonight. Soundings show the marine layer compressing some
overnight, presenting higher chances for IFR CIGs tonight verses
the mostly MVFR levels observed over the previous 24 hours. There
is a chance that the weak shortwave holds the ceilings up higher
than soundings portray, to more in the MVFR levels. There is
enough model support and confidence to include IFR levels in the
18Z TAfs however, with much lower confidence on LIFR levels. A
brief window for LIFR CIGS does exist, and was included for early
Friday morning in the TAFs. Current thinking is that subsidence on
the backside of the passing shortwave after 12Z will allow for
further compression of the marine layer and lower CIGS.

Overnight weakness in the northerly winds may allow for weak stratus
intrusion around the Fort Bragg area and inland valleys south
through Mendocino, but probabilities for IFR levels are low to
moderate (35-45%). This are also has higher probabilities for low
level wind shear in this described region with 30 kt north to
northeast winds aloft through 2000 ft AGL.

Inland terminals, including UKI will remain VFR through this 18Z TAF
period with relatively light surface winds.


Forecast Confidence:

Chance for LIFR CIGS along the Humboldt coastal terminals Low:
Coastal Terminals have 20-35%, mainly from 13-15Z Friday.

Chance for IFR CIGS along the Humboldt coastal terminals Moderate to
High: 65 to 70%

Fog probability Very Low: Coastal Terminals 5-15%.  JJW

&&

.MARINE...
Fresh to strong northerly breezes will continue across the
southern waters, with isolated gusts over 30 kts downwind Cape
Mendocino. Gentle to moderate northerly winds continue for the
northern zones, ranging only up to around 15 kts through Thursday.
A building high pressure ridge and interior heating will
strengthen a thermal trough near the coast this weekend. Northerly
winds begin to strengthen in response on Friday. Gale force gusts
over 34 kts are probable in the southern zones (61 to 73%),
mainly fanning off of Cape Mendocino. A Gale Warning has been
issued for this zone with the higher confidence for the strength
and sufficient coverage of these winds Friday.

The thermal trough will strengthen and expand north Saturday. Gale
strength gusts 34, to up to 40 kts will develop in the northern
zones Saturday. A Gale Watch is now up for the Northern Outer zone
470. A narrower band of gale strength northerlies will continue to
extend off Cape Mendocino in the southern waters on Saturday.
Looking at modeled coverage of these winds, extension of the Gale
Warning in the southern waters may be considered through Saturday or
possibly further into Sunday.

There is growing indication that the northerlies will increase by
early next week, potentially significantly as the pressure gradient
tightens up from building high pressure to the west. Chances for
greater than 34kt gusts are currently moderate to high (45 to 65%)
early through at least mid next week for much of the waters. JJW

&&

.FIRE WEATHER...
Hot and dry conditions are expected over the next several days with
highs pushing back over 100 degrees on Sunday. This heat will be
followed by the potential for a mix of wet and dry thunderstorms
primarily during the afternoons both Monday and Tuesday. Highest
chances will be in Trinity and Siskiyou counties but there is a
distinct possibility storms could move farther west into Humboldt
and Del Norte counties and south into the Mendocino National
Forest on Monday. Some guidance is indicating even a slight chance
of storms early Monday morning out to coastal areas but chances
of this are too long to include in the forecast. Dry conditions
will likely return on Wednesday.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PDT Saturday for PZZ455.

     Gale Watch from Saturday afternoon through Sunday morning
     for PZZ470.

     Small Craft Advisory until 1 PM PDT Friday for PZZ475.

     Gale Warning from 1 PM Friday to 3 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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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png