000
FXUS66 KEKA 192148
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
248 PM PDT Fri Apr 19 2024

.SYNOPSIS...Above normal afternoon temperatures will continue across
the interior valleys into early next week. A weak cold front will
bring a slight chance of light rain and drizzle to the North Coast
on Saturday followed by breezy northerly winds on Sunday.

&&

.DISCUSSION...Shallow layer of stratus has been swirling around
offshore and over coastal areas of Mendocino and SW Humboldt today.
Webcams have not revealed much or any dense fog, yet. The northward
extent of the stratus has reached Cape Town, but light northerlies
have been eroding the leading edge of the northward advance and even
forcing the "stratus surge" back southward. Stratus bands may form
in situ over the northern waters late tonight and spread onto the
North Coast by early Sat morning as a weakening front approaches.
Otherwise, variable high thin cirrus will drift over the area
through the night again.

A weak front associated with a transient shortwave trough will bring
a push of shallow moisture and perhaps some light rain and drizzle
to Del Norte and northern Humboldt counties during the afternoon or
early evening on Saturday. Otherwise, dry weather with some cooling
of interior high temps are expected on Saturday. Breezy west to
northwest winds are also expected across the inferior after frontal
passage late in the day and evening, especially in channeled terrain
and ridges where gusts to 30 mph are probable (75% chance per HREF)
for Lake and far southern Mendocino counties.

Surface high pressure will build in quickly over the Pacific Northwest
Saturday night and Sunday in the wake of the front. Breezy northerly
winds are forecast to redeveloped over mostly coastal areas as surface
pressure gradients tighten by early Sunday. HREF has over a 70%
probability for gusts > 40 mph over the King Range and 50% probability
for coastal SW Humboldt by 5 AM Sunday.

Coarser NBM guidance indicates northerly winds ramping up during
the day on Sunday (afternoon and evening) for lower elevations and
coastal areas. Ensemble means indicate peak gusts from 25-32 mph
with 75th to 90th percentile gusts to 40-50 mph. 75th-90th
percentile gusts may be too high, but certainly within the realm
of possibilities (50% chance) for wind prone points like around Pt
St George and Cape Mendocino based on the NBM data.

Interior high temperatures are forecast to rebound Sun through Tue
as a flat ridge aloft springs back up and offshore flow returns.
Isolated showers are possible (20% chance) over the higher terrain
of Trinity County Tue afternoon and evening as a 500mb shortwave
trough progresses eastward toward the PAC NW. Thunder chances are
much more doubtful due to dry SW flow aloft and potential for a
mid level cap. For now will add a 20% chance for showers, but hold
off on adding thunderstorms at this time.

Potential for wider coverage and more frequent precipitation will
increase mid to late next week, though probabilities for > 0.50 inch
of rain in 24-hours for the western slopes of Del Norte and northern
Humboldt Counties are about 20% or less. Afternoon high temperatures
are forecast to cool down with probabilities for 75F or more no more
than 30% for the warmest interior valleys of Mendocino and Lake. NBM
means are close to normal (high in the 60`s). Thus, it is shaping
up to be cooler compared to the recent interior warmth. How fast
it cools down and to what degree are still uncertain. Precipitation
may occur and based on the ensemble guidance, amounts are most likely
going to be light. Even light amounts may have minor impacts on
outdoor plans, but timing and duration of rain or showers remain
elusive and uncertain at this time. Stay tuned. DB

&&

.AVIATION...(18Z TAFS) Afternoon visible satellite reveals poorly
modeled stratus fully encompassing the coast from Cape Mendocino
and southward down the Mendocino coastline. The stratus surge is
attempting to squeeze around the cape on an inevitable track
northward. There is a high degree of uncertainty of the depth of
the stratus and timing of advancement. The Bodega Bay profiler
shows the depth to be shallow, in the 600-400 ft range and
lowering. Have given the best estimate for impacts at ACV and CEC,
with CIGs lowered per sounding and observational data. HREF (Prob
of Vis less than 1 mile) is indicating fog will be possible as
well (60% along or near the coast). Southerly winds will pick up
in advance of weak front on Saturday. This further complicates and
emphasizes the low confidence of the forecast with the possiblility
for deepening of the marine layer or disruption of fog conditions.
Stratus touched into the Ukiah valley this morning in the weak
southerly flow, and there is slightly better agreement of a
further north push into UKI early Saturday morning. /JJW

&&

.MARINE...Northerlies have further weakened into the afternoon to
around 12 kts over the outer zones. Light and variable flow with
areas of southerly return flow will continue in the inner zones
tonight. A stream of shallow coastal stratus, currently along and
south of Cape Mendocino, will likely surge northward to bring
opportunity for quickly dropping visibility. Seas will bottom out
early Saturday afternoon at 3 to 4 feet before a sharp increase in
northerlies from a passing front occurs into the early evening. NBM
is still indicating 80-90% probabilities of >34 kt gusts developing
downwind of Cape Mendocino early Sunday morning before expanding to
the northern and southern waters by Sunday afternoon. Gale Watches
are up beginning Sunday. Steep, wind driven waves and a mid- period
NW swell will produce seas of 12 to 14 feet from Sunday through
Monday. Uncertainty remains as to how quickly the axis of elevated
winds will retreat offshore before another trough complex approaches
the PNW and N CA Tuesday. /JJW

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Watch from Sunday afternoon through late Sunday night
     for PZZ470.

     Gale Watch from late Saturday night through late Sunday
     night for PZZ475.

&&

$$

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