Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 262200
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
300 PM PDT Tue Mar 26 2024

.SYNOPSIS...A cold front will move across the area on Wednesday,
bringing rain and strong gusty southerly winds. Unstable conditions
behind the front will bring a threat for thunderstorms with locally
heavy rain, gusty winds and possibly isolated hail showers Wednesday
night through Thursday. A second storm system on Friday will most
likely bring more showers and a threat for strong southeast winds.

&&

.DISCUSSION...Upper level ridging over the area today will shift
eastward this evening. Chance of light precipitation will increase
late tonight as a frontal system moves inside 130W. Most of the
precipitation will occur with frontal passage Wednesday through
Wednesday night. Rainfall amounts (5 AM Wed-5 AM Thu) are expected
to range from one quarter of an inch in SE Lake county to over 2
inches in the mountains of Del Norte county. Snow levels are
forecast to remain relatively high, above 4500-5000 feet with
possible snow impacts for Scott Mountain pass in NE Trinity on Wed.
Snow levels fall Wed night into Thu down to about 3000-3500 feet,
however 6 hourly precipitation rates generally decrease to 0.10-0.20in
with locally higher 6 hourly rates of 0.30in to 0.50in in the Del
Norte and SW Humboldt. Snow impacts are certainly not completely
out of the question Wed night and Thu. Based on our snow level
and snow amount forecast, impacts are expected to be minor.

Coastal barrier jet will develop in advance of the surface
boundary by 12Z Wed with surface gusts from 45 to 55 mph forecast
for the higher elevations and coastal headlands of Del Norte and
Humboldt counties. A wind advisory remains in effect for Wednesday
morning. Robust southwesterly winds will likely persist into the
afternoon hours for mostly the higher elevations and ridges. A
post frontal trough in the colder air behind the front will bring
another uptick in S-SW winds Wed night. Instability will be on
the rise Wednesday night into Thu and isolated to scattered low
topped thunderstorms are expected. Locally heavy rain and gusty
winds will be the primary hazard. Progressive storm motion will
likely limit the threat for flash flooding. Small hail is not
completely out of the question either. Freezing level fall to
about 3500-4000 feet out toward the coast and small hail mixed
with rain will most likely not accumulate on roads.

Another potentially stronger storm in terms of winds will approach
on Friday. Deterministic model guidance were in better agreement
with the evolution and location of the surface low. NBM mean
southeasterly or easterly wind gusts increase to 30-40 mph with
90-95th percentile gusts around 50-60mph for the ridges and
coastal headlands. There is still a great deal of variability and
uncertainty with the track and location of the surface low and
how strong winds will get on Friday. For now will utilize the
National Blend of Models guidance and probabilities for gusts over
40 mph to message this threat via social media. Stay tuned.

Brunt of the precipitation with this next storm will most likely
be directed into Mendocino, Lake and Trinity. Thunderstorms and
locally heavy rain will also be a concern as a diffluent 500mb
trough approaches on Friday. Northern portion of the forecast
area will probably see precip as well in the wrap around.

Ensemble clusters were in general agreement with the 500mb cold
core staying offshore, tracking SE along the California coast over
the weekend. There are very subtle variations on the track, how
close it gets to the coast and where it will moves inland. There
appears to be sufficient instability and wrap around moisture for
continued precip chances (perhaps thunderstorms) for mostly the
southern and/or interior portions of the forecast area through the
weekend. Ridge aloft folding over the 500mb cold core Sunday into
Monday will most likely yield a drying/clearing trend from NW to
SE. Positive tilted ridge aloft appears to hold into Tue, before
clusters deviate in significantly in response to a transient
upstream trough. Overall, it looks like daytime highs will warm up
by early next week, though overnight lows may remain chilly with
some frost in the interior valleys under mostly clear skies if no
fog and low clouds form. DB

&&

.AVIATION...Prevailing conditions remained VFR today, except for
a few pockets of MVFR coastal clouds that briefly moved over ACV
and CEC before noonday. ACV also experienced a brief stint of IFR
Cig/Vis during mid-morning. By afternoon, extensive and diverse
cloud layers began advecting across all terminals ahead of an
advancing storm system. The Redwood Coast, including CEC and ACV
will start registering flight impacts late tonight/early morning
as pre-frontal winds increase...and the threat of low level wind
shear (LLWS) becomes a possibility. Surface winds will become
stronger after mid-night. A warm front will first affect the
coastal terminals and cause Cig/Vis to significantly decrease
around sunrise. A trailing cold front will usher in a more showery
regime at the TAF sites. /TA

&&

.MARINE...Energy from several long period swells is moderating
the sea state this afternoon. Southerly winds will rapidly increase
overnight as a low pressure system approaches the region. Gale
force gusts and responsive southerly wind waves will develop in
the northern waters as a cold front traverses the area. Even as
winds diminish behind the front, the low will continue to spin off
the coast of Oregon, keeping winds elevated in the outer waters.
A secondary large westerly swell will fill into the area early
Thursday and will generate steep 14-16 ft waves. Combined seas are
likely to exceed 18 feet in the northern outer waters through
Thursday evening. Elevated seas and hazardous conditions can be
expected as the swell slowly decays through the end of the week.
JMM


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory from 5 AM to noon PDT Wednesday for CAZ101-
     102-104>106.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Warning from 2 AM to 11 AM PDT Wednesday for PZZ450-
     470.

     Small Craft Advisory until 3 PM PDT this afternoon for
     PZZ455-475.

&&

$$

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