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000
FXUS66 KEKA 132133
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
233 PM PDT Sat Apr 13 2024

.SYNOPSIS...Light rain will continue through the night with light
snow as low as 3000 feet in Trinity County. Gusty onshore flow will
impact the coast early this week as generally summer-like weather
builds in.


&&

.DISCUSSION...The weather today has been dominated by cold air
wrapping around a cutoff low pressure system currently making
landfall along the Central California coast. Highs in protected
valleys have struggled to reach out of the 40s, especially in
Trinity County. Generally speaking, 0.5 to 1.0 inches of rain have
fallen across the area from Del Norte all the way to Lake County.
Easterly flow has concentrated the heaviest rain along the western
rim of the Sacramento Valley. Cold and dry easterly flow has also
allowed for snow to fall as low as 2500 to 3000 feet even as far
South of Cobb. That said generally light rates and warm ground
temperatures have led to little snow accumulation except at the
highest mountain peaks.

A break in showers is already evident this afternoon as only light
rain remains across the area on radar. That said, high resolution
models consistently show a weak, second round of rain late tonight
through early Monday most likely brining 0.2 to 0.5 inches of
additional precipitation across the area, with to 1.0 inch focused
in eastern Trinity County. Continued easterly flow and a day of
cooling will make low elevation snow accumulation increasingly
likely overnight. Generally light snow accumulation of 1 to 3 inches
is most likely down to to 3000 feet with up to 6 inches on high
peaks. A Winter Weather Advisory has been raised to message possible
light impacts of Highway 36 and 3 in Trinity County. Winds turning
onshore by mid morning Sunday will most likely  bring a quick end to
any low elevation snow. Otherwise, impacts will be minimal with
isolated easterly gusts up to 30 mph localized in Lake County.

High pressure will quickly build again early this week over the
eastern Pacific. By Monday and Tuesday, a strong pressure gradient
will form up along shore. This will bring a seasonable return to
gusty northwest winds all along shore with gusts up to 30 mph
pushing onshore each afternoon, especially on Tuesday. High pressure
will also bring clear skies and warming temperatures inland with NBM
showing interior valleys back in the 80s by Wednesday. Clearing
skies and lingering moisture will most likely allow for widespread
valley fog early Monday morning with fog pulling closer to the coast
each morning as high pressure builds. While gusty northwest wind
will help keep marine stratus scoured out early in the week,
stronger surface high pressure will likely bring a return to a
marine inversion and associated stratus by midweek.

Summer-like weather looks likely to continue through the end of the
month with 90% of the cluster ensembles showing little rain beyond
coastal drizzle for the next 10 days. /JHW


&&

.AVIATION...MVFR and VFR conditions have prevailed through the day
today with periods of light rain and E-SE winds. Precipitation
wrapping around a surface low west of Pt Reyes has been slowly
diminishing but some showers will linger into this afternoon and
early evening. Conditions are forecast to deteriorate to IFR for the
coastal terminals later tonight into Sunday morning as another front
pin-wheels back into the area from the north and light precipitation
increases. Conditions will probably deteriorate to IFR over the
interior valleys too, though confidence is not high at KUKI with
peak probabilities of 41% for MVFR and 18% for IFR by early Sunday
morning. DB


&&

.MARINE...A compact surface low west-southwest of Pt Arena will
drift southward and fill tonight. Meanwhile, a second front will
drop down from the north tonight into Sunday morning and once again
result in a complex wind field across NW California waters. High
resolution models as well as the coarse global models indicate a
wide range of possibilities in terms of the timing of wind shifts,
wind directions and to a lesser extent the magnitude of winds.
Settled on a blend of 25% NBM with 75% ARW/FV3. Model difference
diminish faster across the northern outer waters (PZZ470) with near
100% chance for gusts greater than 22kt with sufficient coverage for
an advisory on Sunday. Granted it will be marginal initially, but
the trend will be for northerly winds to increase through the day
and into the evening.

For the southern outer waters, E-SE winds will diminish as a compact
surface drifts southward. There will be a window of about 6-9 hours
before northerly winds start to increase again across pzz475,
depending on what model we use. Probabilities for northerly wind
gusts >22kts increase late tonight into Sunday morning. Thus, will
just extend the existing small craft advisory for ESE winds through
tonight into Sunday morning versus having two small craft advisory
headlines. Also, combined seas (mostly from a NW swell 8-10ft) have
been running a bit above the NWPS/GFS-Wave model guidance, but will
probably diminish tonight.

Northerly winds will steadily increase Sunday night through Monday
and again on Tuesday. Increasing stability (warmer air aloft) will
result in more laminar flow versus the turbulent flow from mesoscale
circulations and localized convection this weekend. Supercritical
flow with expansion fans downwind of Cape Mendo and Cape Blanco will
probably (80% chance) yield localized regions or tight corridors of
gusts to 35-40kt. For now it looks most probable downwind of Cape
Mendocino on Tue, but would not rule out the northern waters with a
seemingly weaker fan breaking off from Cape Blanco. Steep northerly
short period waves will build in response to the steady state
northerlies with combined seas reaching 10 to 12 ft, mostly just
outside 10NM from shore.

Prevailing northerlies will continue for the remainder of the week
with decreasing probabilities (40-60% chance) for gusts >35kts
downwind of Cape Mendo. With warmer air aloft and trapped flow
nearshore/along the coastal terrain, nearshore diurnal varying
southerlies are highly probable. DB


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Winter Weather Advisory from 11 PM this evening to 11 AM
     PDT Sunday for CAZ107-108.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 7 AM Sunday to 11 PM PDT Tuesday
     for PZZ470.

     Small Craft Advisory until 5 AM PDT Tuesday for PZZ475.

&&

$$

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