Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 211201
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
501 AM PDT Thu Mar 21 2024

.SYNOPSIS...Quiet weather condition for the rest of the day,
before rain and moderate south wind builds across the area
tonight through Friday. Rain showers will then persist through
Saturday mostly along the North Coast. Periods of rain will
continue through mid next week. .

&&

.DISCUSSION...Latest GOES-West satellite imagery and surface
weather observations depicted low level moisture across much of
the forecast area this morning, with occasional light showers or
sprinkles been reported. Any lingering light or shower drizzle is
expected to dissipate as a weak 500mb shortwave ridge moves over
the area and bring dry conditions through this evening. Otherwise,
mostly cloudy day is expected as mid to high level moisture
stream across the region. In addition, temperatures will be at or
slightly above normal with highs forecast in the 60s for interior
valleys, and upper 50s to low 60s along the coastal areas.

Unsettled weather pattern returns on Friday and this weekend as a
much deeper, cutoff trough will slowly approach shore with a
broad surface low over the NEPAC. An associated frontal system,
along with a plume of subtropical moisture ingested in the
southwesterly flow, will move onshore early Friday morning. A low-
level jet in advance of the approaching front will bring warm air
advection in from the southwest and aid in rising snow levels
above 5000-6000 feet along with stratiform precipitation. Rain is
expected to become moderate to locally heavy as a surface cold
front sweeps across the area. The peak rainfall rates from 0.25
to 0.35 inches per hour possible. 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. In addition, a 40-50 kts jet streak around 925-850 mb
will promote strong southerly winds along the north coast. Gusts
from 25 to 40 MPH late tonight through Friday afternoon, with up
to 50 mph possible over the higher terrain in Del Norte and
Humboldt counties.

A colder air aloft will subsequently spread across the West Coast
late on Friday. As result, instability will increase to around
100-200 J/kg of CAPE late Friday into Saturday monring. 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. The surface low will swing
toward Oregon on Friday evening, and bring a second waves of
precipitation across the area. 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, and northern Mendocino with closer to 0.5 inches most
likely elsewhere. Southern Lake County will see the lowest amounts
around 0.2 inches.

The broad upper level trough will move over the region through the
weekend. Snow levels will come down as the upper level trough passes
overhead and brings cold air aloft, generally dropping snow down to
around 3,500 to 4,500 feet MSL. Scott Mountain Pass on Hwy 3 will
see some snow, up to around 4 inches. Any snow will be inconsistent
with mostly limited impacts.Showery precipitation will continue
Sunday, then trails off Sunday night as shortwave ridging builds
aloft.

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.


&&

.AVIATION...The weak trough that moved through yesterday continues
to bring some occasional drizzle or light showers and clouds across
the area. These have mainly stayed VFR at KCEC, KACV and KUKI with
only occasional MVFR conditions. Occasional MVFR conditions may
persist through this morning, but ceilings will gradually lift as
some shortwave ridging builds in today. Southerly winds of 5 to 15
kt are expected this afternoon along the coast with generally
lighter winds inland. Tonight an approaching frontal boundary will
increase southerly winds. This will bring rain and MVFR ceilings
early Friday morning to the coast. Southerly winds to 15 to 20 kt
with gusts to 30 kt are possible along the coast. This rain is
expected to quickly spread inland later Friday morning. MKK


&&

.MARINE...Winds have diminished slightly and are now around 10 to 15
kt behind the weak system that moved through Wednesday evening.
These winds will start to pick up through the day as a frontal
boundary and upper level low approach the area. In addition, this
morning a new westerly swell is building in and is currently around
3 feet at 19 seconds. This is only expected to build slightly
through the day. Tonight as the front approaches the area winds will
increase to around 25 to 30 kt early Friday morning. A few gusts to
35 kt can`t be ruled out, but coverage doesn`t look to be enough to
warrant issuing a gale watch at this point. Friday evening and
overnight the 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 next frontal boundary. A number of the models show
gale force southerlies at least in the northern waters.

Saturday afternoon moderate to fresh northerly winds are expected to
return to the waters as high pressure builds in. In addition on
Saturday afternoon a fresh westerly swell starts to build and
quickly builds to around 11 feet at 12 seconds Saturday night.
Additional mid period swells are expected next week.

The northerly winds will diminish on Sunday with more southerly
winds and another system on Monday and again Tuesday. MKK


&&

.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.

     Small Craft Advisory until 3 AM PDT early this morning for
     PZZ470.

&&

$$

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