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000
FXUS66 KEKA 112215
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
315 PM PDT Thu Apr 11 2024

.SYNOPSIS...A weak storm system will impact the area by tomorrow
afternoon brining to light to moderate rain and gusty south wind.
Light snow is also expected above 3000 feet. Warmer conditions with
gusty coastal wind will return early next week.


&&

.DISCUSSION...A strong stream of moisture and associated midlevel
clouds is now evident several hundred miles offshore, gradually
approaching the coast. The band is accompanying the leading edge of
a cutoff low pressure system that is dipping down the west coast
forcing high pressure eastward. That said, surface conditions have
so far been slow to respond with marine stratus still entrenched
along the North Coast and interior highs still near 80.

The influence of high pressure will slowly wain through the night
with winds turning southerly by Friday morning. Southerly winds will
help scatter out any remaining marine layer. Southeast wind will be
strongest in Lake County Friday afternoon with most likely gusts of
25 to 35 mph along high terrain. There is less than a 5% chance of
any damaging wind gusts over 45 mph.

The low will very quickly push south on Friday, brining the heaviest
rain to Mendocino and Lake Counties and around the rim of the
Sacramento Valley. In these areas, 0.5 to 0.8 inches of rain is most
likely by sunrise on Saturday. Generally lighter rain of 0.3 to 0.6
inches is most likely further north in Humboldt. Rain will begin
late Friday afternoon with the heaviest rain very early Saturday
morning. Locally stronger rain rates and isolated thunder are
possible (10 to 30% chance)around the Trinity alps thanks to
orographically favored easterly wind Friday night. Models have
somewhat shifted from previous forecasts, now showing a second round
of showers Saturday night as disturbances rotate around low. That
said easterly flow at that point will limit the available moisture,
making only light rain of an additional 0.1 to 0.3 inches most
likely through early Sunday morning.

Beyond rain, some cold air is associated with the low pressure
system, though the air mass is very weak and modified. Still, high
resolution models show snow levels dropping as low as 2500 to 3000
feet during the overnight hours early Saturday and Sunday morning.
Snow elevations that low are most likely as winds turn east and pull
drier air. That said, dwindling QPF at that point will only support
1 to 3 inches of light snow along Highway 36 with less snow on other
highways. NBM shows less than a 10% chance of more than 3 inches
anywhere outside the highest peaks.

High pressure will quickly return early next week with a strong
pressure gradient along shore bringing a return to strong northwest
winds at the coast gusting up to 30 mph. A return of summer like
weather will also bring a return to sunny and warm conditions.
/JHW


&&

.AVIATION...Coastal stratus north of Cape Mendo has been breaking up
this afternoon with VFR reported at both coastal sites, CEC and ACV.
A secondary push of MVFR ceilings (possible IFR ceilings) offshore
will likely impact the terminals late today into this evening. Top
of the marine layer is forecast to lift up later tonight in response
to an approaching shortwave trough. Ceilings should lift to MVFR or
VFR at coastal terminals by early Fri morning as a surface front
disrupts the marine inversion and light offshore flow develops.
Higher and deeper humid layer overnight will bring an increased risk
for low cloud cover at KUKI by early Friday morning, although
probabilities for MVFR cigs are only 36% and for IFR cigs only 9%
for UKI. DJB


&&

.MARINE...Northerlies continued to weaken today from north to south
as a weak surface trough approached the coast. Localized gusts to 30
knots are probable this afternoon and evening in the lee of Cape
Mendocino and a small craft advisory remains in effect til 9 PM.
Winds are forecast to weaken much further on Friday as a broad
surface low tracks southeast over the offshore waters. Wind
directions will become much more variable and chaotic on Friday as
multiple small scale eddies spin up nearshore and a front stalls
offshore. Thus, wind directions are forecast to become much more
variable. For the most part, sub-advisory speeds are forecast (less
than 20kt), although brief and localized gusts up to 20 knots are
possible (<20% chance) with mesoscale circulations.

Potential (<30% chance) for localized or isolated gusts to 25 kt
will continue on Saturday as broad and diffuse low pressure remains
over the area, while the main core of the low center heads southward
into Central California. Potential (>60% chance) for widespread
northerly gusts 25-30 kt will increase on Sunday as surface high
pressure builds toward the coast from the west. Pressure gradient
tighten more by Monday and potential (>70% chance) for gusts to 35kt
will increase, mostly downwind of Cape Mendo.

A mid period WNW swell is forecast to continue to decay over the
next few days, while short period northerly wind waves trend down
over the next couple of days. A fresh NW swell is expected this
weekend, possibly filling in Saturday, although details will depend
on the track of this incoming surface low. A steady build up of
steep northerly wind waves in conjunction with stronger northerly
wind is anticipated for early next week. DJB


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PDT this evening for PZZ455-
     475.

&&

$$

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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png