752
FXUS66 KEKA 292130
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
230 PM PDT Tue Jul 29 2025

.SYNOPSIS...Chance of thunderstorms is forecast for the interior
of Northwest California through Friday. Storms may produce strong
and gusty outflow winds, heavy rain and hail.

&&

.DISCUSSION...Primary hazard all this week continues to be deep
moist convection across the interior mountains. A relatively dry
upper trough remains parked offshore and will continue create
favorable thermodynamic profiles for afternoon and evening
thunderstorms over the interior mountains. Calibrated guidance
(NBM and HREF) guidance are not showing a strong signal for storms
this afternoon and evening as a weak cyclonic center meanders
about just offshore the North Coast. Individual CAMS do show
isolated activity possible around the periphery of Northern
Trinity County, along the Siskiyou border. Shallow cumulus
convection has also been building - even across Mendocino NF and
Yolla Bolla`s and a few weak cells may develop with peak daytime
heating.

A better defined cyclonic center offshore central California will
travel E-NE tonight into Wed and provide better support for
convection with greater mid layer moisture, favorable wind
directions at 700-500mb and some upward motion. New fire starts
will be possible with lightning strikes on dry fuel beds
Wednesday afternoon and evening. Greatest coverage of storms
appears to be in zone 283 or Shasta-T. Confidence for abundant
lightning for Klamath NF and Six Rivers NF is much less with a
steep drop off in HREF probabilities for storms across zones 203,
204 and 211. Deterministic models have been incongruent on the
activity outside Siskiyou county. HREF paint-balls show a few
cells > 40dBZ on the Humboldt/Del Norte side and a few strikes
seem possible. The bulls-eye appears to be over northern Trinity
and over Siskiyou. We will not rule out the possibility for storms
for Mendocino NF zone 277 either, though soundings do not look as
favorable. Legacy SREF guidance continues to show a 10-20% chance
for NE Mendo and far northern Lake on Wed.

Storms in Trinity County will probably produce precipitation, mostly
light over a large area. Directly over storm cores, hail and
locally heavy rainfall will be possible. Soundings also show
inverted-V profiles which will make strong outflow wind gusts with
micro-bursts a distinct possibility (20% chance). Storm motions
are not forecast to be very fast and locally heavy rain cannot be
ruled out. Individual HREF members indicate hourly rates over
0.50 inches which are most likely overdone. HREF probabilities
for 0.50in/hr ramp up to 40-60%.

Upper level trough will linger offshore or over the area Thu through
Fri, bringing a continued chance for diurnal convection and storms
each afternoon through Fri over northern Trinity.

Potential for interior thunderstorms should diminish over the weekend
as 500mb height increase and drier westerly flow aloft develops.
Shorter wavelength troughs in the westerly flow may keep the
ridge from building full force and interior temps may not warm
much. ECMWF ensemble also indicates higher probabilities for
stronger NW and W diurnal winds over the weekend for mostly the
persistently windy and dry areas of our forecast area; Lake,
southern Mendo and eastern Trinity. Fire weather threats may
increase especially with the passage of a 500mb trough by Sunday.
This trough could also produce some precip as well. Once again it
may be a mixed bag with precip and higher RH`s for the northern
zones and dry-windy conditions for the southern zones.

&&

.AVIATION...

18Z TAFs...Troughing kept the marine layer fairly deep this morning
with mostly MVFR ceilings for the coastal terminals. Stratus is
rapidly eroding late this morning, with mostly clear skies expected
for the afternoon. Some northwesterly breezes are possible this
afternoon, and could be gusty in Mendocino County. Interior areas
are likely to remain mostly clear, with any convection remaining
confined to northern Trinity County this afternoon. Winds ease
this evening and overnight, and stratus is likely to return this
evening and overnight to the coast. Model guidance is strongly
suggesting IFR or LIFR ceilings, but synoptic conditions are
forecast to be largely unchanged, so have hedged more toward
IFR/MVFR ceilings. NBM probabilities for IFR ceilings are about
80% and LIFR ceilings are about 40%. Reduced visibility, if any,
would likely occur briefly in the early morning hours of Wednesday.
Models are hinting at more persistent stratus for Wednesday along
the coast, with NBM showing roughly 50% probabilities for MVFR
ceilings for the whole day Wednesday. JB

&&

.MARINE...

Troughing has continued to keep strong northerly winds mostly
subdued, but some breezes of 20-25 kts are still possible downwind
of Cape Mendocino today. Seas nearshore are mild at 2-4 ft. Wind
driven seas of 5-7 ft are forecast for the outer waters into
tonight, with slightly higher and steeper waves found south of
Cape Mendocino. Winds trend upward Wednesday, with gusts up to
25-30 kts in the outer waters and gusts to 15-20 kts possible
nearshore. Steep wind waves south of the Cape may propagate
nearshore, with seas rising to 6-7 ft by Wednesday night. A
similar pattern is expected through Friday, with the potential for
slightly higher winds into the weekend. Gales force gusts are
currently unlikely, with NBM only showing 20-30% chances for gales
in the outer waters downwind of Cape Mendocino. JB

&&

.FIRE WEATHER...New fire starts will be possible with lightning
strikes on dry fuel beds Wednesday afternoon and evening.
Greatest coverage of storms appears to be in zone 283 or Shasta-T.
Confidence for abundant lightning for Klamath NF and Six Rivers NF
is much less with a steep drop off in HREF probabilities for
thunder across zones 203, 204 and 211. The bulls-eye appears to
be over northern Trinity or zone 283.

Potential also exist for strong and gusty outflow winds with dry
micro-bursts. Strong outflow winds from 30 to 50 mph could fan
exiting fires. The fire weather watch has been upgraded to a red
flag warning for abundant lightning on dry fuels and strong gusty
outflow winds.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Red Flag Warning from 2 PM to 11 PM PDT Wednesday for
     CAZ204-283.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 3 PM Wednesday to 3 PM PDT
     Thursday for PZZ455.

     Small Craft Advisory from 3 AM Wednesday to 3 AM PDT
     Thursday for PZZ470.

     Small Craft Advisory until 3 PM PDT Thursday 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