571
FXUS66 KEKA 031214
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
514 AM PDT Thu Apr 3 2025

.SYNOPSIS...Residual instability could result in isolated
showers for parts of Northwest California; however, those will
diminish completely by this evening as a cold upper low progresses
south. Clearing and drying will allow for some colder overnight
lows. A sharp warmup with building high pressure can be expected
for the end of the week, followed by a chance for rain.


&&

.DISCUSSION...As a high pressure system moves toward the region, wrap-
around moisture has generated some light showers mainly over Humboldt
and Del Norte counties. These isolated showers have diminished
greatly overnight with continued showery activity becoming less
likely through the day. As with last night, lingering moisture,
dissipating cloudcover, and some patchy fog formation will hold up
temperatures early this morning for some areas, particularly
where additional light showers occurred yesterday. Round Valley
has remained warmer than forecast overnight due to the delay in
cloud dispersal, but the valley will see cooler temperatures
before sunrise. Overall, the region has dried out even more in
the last 24 hours, and areas of frost and subfreezing temperatures
are expected in portions of areas where the agricultural growing
season has begun. Frost Advisories and Freeze Warnings are out in
Southern Mendocino and Lake counties. Interior Humboldt will be
watched closely, as the agricultural season has begun, but
confidence is low on the coverage of frost potential at this time
given the previously described conditions. Late tonight and early
tomorrow morning, there will be more clearing for the region with
offshore flow, but warmer air will begin to move in. Early morning
temperatures for tomorrow will still be chilly, but less chilly
than this morning. Frost advisories have already been issued for
Northeastern Mendocino and Northern Lake, with most other areas
having lows in the high 30s and low 40s.

Today, a ridge of high pressure will begin amplifying over the NE
Pacific and into the Western CONUS. The pressure gradient will
increase against the departing upper low and northerly winds will
increase to breezy levels, with gusts of 18 to 25 mph in the
exposed ridges and coastal headlands in response.

For Friday, the ridge progresses over W CONUS when abundant
warmth will ensue. There are indications an inverted trough may
form with favorable positioning for enhanced offshore winds and
perhaps higher temperatures than forecast. Currently, daytime
highs of around 5 degrees above climatological norms are forecast,
with low 60s at the coast and low 70s for the interior valleys.
Saturday may be the apex of warmth, with daytime highs nearing 10
degrees above average, with some mid 70s for interior valleys.
Cloud cover arriving ahead of the short wave trough may inhibit
the full potential of warmth for some.

The shortwave will be the first of two systems that will deliver
light rainfall to the region late Saturday through Monday, and maybe
into Tuesday. Snow levels look to be high, at 4500 to 5000 ft, and
snowfall does should not be an issue. The proximity of the low to
the low will determine the strength of the southerly winds, and NBM
is still struggling to resolve meaningful probabilities of wind
gusts over 25 mph through that period. There are some ensemble
solutions that portray a stronger 925mb low level jet and heavier
rainfall, and there is high uncertainty in 24 rainfall amounts
from ensemble spread (1-2 inches difference). Probabilities for
24 rainfall over 0.5 inch are currently moderate to high (46 to
75%). /JJW



&&

.AVIATION...Winds remained gusty overnight before turning offshore and
decreasing in the hours before sunrise. While most coastal cloud
cover has been scoured out by northerly flow, persistent MVFR
ceilings have inundated most of Humboldt County, including ACV,
following yesterday`s rain showers. Widespread gusty NW winds are
expected to resume late this morning/early afternoon as a high
pressure ridge builds into the eastern Pacific, tightening the
coastal pressure gradient and scattering out any remaining cloud
cover. A late afternoon diurnal push toward the coast will favor
gusts 20 to 30 knots, potentially higher at CEC - HREF probabilities
drop off quickly at 34 knots, but could definitely exceed 30 knots
by late afternoon. Winds will diminish late tonight, potentially
allowing marine stratus to develop at ACV before offshore flow dries
the coast.


&&

.MARINE...Small craft conditions with steep northerly wind waves
continue across all zones. Fresh to strong northerly breezes will
keep seas elevated today beneath building high pressure.
Probabilities for gusts 25 to 30 knots will remain highest (>75%) in
the outer waters and downwind of Port Orford and Cape Mendocino, but
diurnal surges in winds will likely push these gusts and square wind
waves into the inner waters this afternoon. A small craft advisory
for the northern inner waters will go into effect late this morning
through this evening to cover this hazard. HREF has a 20 to 40%
chance of gusts approaching low end gale gusts (34 knots) in the
northern waters, but even then it would be shortlived and lacking
proper coverage. Winds and seas diminish significantly by Friday and
Saturday beneath the ridge axis. Potential for another frontal
system to arrive Sunday as a large long period swell fills into the
waters. Previously calm conditions may pose a sneaker wave threat as
this swell arrives.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Freeze Warning until 9 AM PDT this morning for CAZ110-111-
     114.

     Frost Advisory from 2 AM to 9 AM PDT Friday for CAZ110-111-
     113>115.

     Frost Advisory until 9 AM PDT this morning for CAZ112-113-
     115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 AM PDT this morning for PZZ455.

     Small Craft Advisory until 3 AM PDT Friday for PZZ470-475.

&&

$$

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