Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 212203
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
303 PM PDT Thu Mar 21 2024

.SYNOPSIS...Low pressure will continue to approach shore Friday.
This system will bring gusty south wind and consistent rain during
the day Friday. Showers and isolated thunderstorms will then
continue through Saturday.


&&

.DISCUSSION...A weak upper level shortwave moved across the area
last night. This wave brought a burst of clouds and coastal drizzle.
Skies have mostly cleared this afternoon, but the next round of
clouds is already evident about 50 miles offshore. A much stronger
cold front is associated with these clouds and will approach the
area over the next 24 hours.

ECMWF EFI indicates the strongest rain will stall offshore, but a
burst of precipitation remains on track early and then through the
day on Friday. Rain will be strongest as a surface cold front sweeps
across the area. 1 to 2 inches of rain is most likely along high
terrain of the north coast with 0.5 to 1.0 inches at lower
elevations. Lower elevations include the Humboldt Bay area where the
pattern will favor a moderate downsloping effect. NBM shows a 60 to
80% chance of southerly gusts along the front in excess of 35 mph,
but only a 20 to 30% chance of gusts over 45 mph even along high
terrain. This generally moderate wind will limit the risk of any
wind impacts.

Cold air aloft behind the front will increase instability with
marginal instability of 50 to 100 J/Kg of CAPE. This instability
will be sufficient to maintain rainshowers through Saturday. Rain
showers will be less bound to the terrain than the initial wave of
stratiform rain with an additional 1 to 2 inches of rain across
Humboldt and Del Norte Counties with closer to 0.5 inches most
likely elsewhere. Instability could allow for some isolated
thunderstorms (10 to 20% chance) over the waters and right along
shore, but any storms will be weak and short lived with minimal hail
risk. That said, broken skies and increasingly strong March sunshine
could allow for thunderstorms even over parts of the interior
mountains.

Warm air advection will help keep snow levels above 5000 feet with
the first round of rain Friday with any snowfall restricted only to
high mountain peaks. Snow levels will begin to fall early Saturday
morning especially in areas of upslope wind in Trinity County. NBM
shows a most likely snow level range of 3500 to 4000 feet. This
could help bring 4 to 10 inches of wet snow to the highest
elevations of Highway 3 in Trinity County with 1 to 2 inches
possible along Highway 36. Any snow will be inconsistent with mostly
limited impacts.

Essentially all ensemble models show a break in rain early next weak
with a quick hitting but weak trough mid next week. This would bring
another round of mostly light rain. ECMWF EFI does not highlight any
really anomalous weather through mid next week. /JHW


&&

.AVIATION...Southerly winds will gradually decrease through today,
providing some clearing into early this afternoon. However,
cloudiness will increase later this evening as another front moves
into the area overnight. Rain will begin moving into the region
early to mid morning tomorrow with ceilings approaching MVFR
conditions at the same time. Gusty southerly winds will also affect
the coastal terminals. Gusts to 25 knots could be possible. Later in
the morning visibilities could reach MVFR conditions at all
terminals as light rain persist.


&&

.MARINE...Southerly winds will gradually increase throughout the day
from north to south as another front, associated with a larger
parent low pressure system to our north, approaches the coastal
waters. Models indicate that gusts will reach small craft criteria
by very late tonight. As the front moves through the waters early to
mid tomorrow morning, gusts will reach near gale force in the
northern outer zone and around Cape Mendocino. A new westerly swell
built into the coastal waters this morning and will increase
slightly throughout the day.

Tomorrow evening and into the overnight hours, models are showing
another frontal boundary associated with the low bringing an
additional surge of winds. The main low remains north of the area,
but near gale or gale force winds are expected with the next frontal
boundary. A number of the models show gale force southerlies at
least in the northern waters. Saturday and into Sunday moderate to
fresh northerly winds are expected to return to the waters as high
pressure builds in behind the low. In addition on Saturday afternoon
a fresh westerly swell is anticipated to build quickly to around 11
feet at 12 seconds by Saturday night. Additional mid period swells
are expected in the new week.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 7 PM this evening to 6 PM PDT
     Saturday for PZZ450-455-470-475.

&&

$$

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