391
FXUS66 KEKA 142205
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
305 PM PDT Tue May 14 2024

.SYNOPSIS...Summer-like weather pattern will persist through the
week with hot and dry afternoons in the interior and low clouds
and fog along the coast.

&&

.DISCUSSION...Thin line of stratus and fog along or just offshore
the northern Humboldt coast has been slowly decaying this afternoon.
Fog and low clouds should continue to steadily erode into the late
afternoon with mostly clear skies into the evening north of Cape
Mendocino. It is not certain that stratus and fog will reform
later tonight as a broad flat ridge aloft builds from the west
tonight. E-NE winds above mean sea level should keep the stratus
and fog much more limited tonight. NE-E winds are forecast to be
strongest over Del Norte county where no stratus or fog is forecast
for tonight. Around Humboldt Bay and Eel delta, humidities remain
higher and HREF indicates low probabilities around 20% for 1/2SM
in fog. Granted the HREF probabilities were not very high for KCEC
and KACV with both ASOS sites reporting vsby`s to 1/4SM earlier
today. South of Cape Mendocino along the SW Humboldt and Mendocino
coastlines, confidence is much higher that stratus and fog will
persist. HREF indicates probabilities > 70% for 1/4SM or less in
fog. Fog may be dense in spots.

Otherwise, skies are forecast to remain clear for interior NW
California tonight through Wed. High temperatures are forecast to
peak on Wed, about 15F above mid May normals. This minor warm up
(highs in the upper 80`s to mid 90`s) may create a moderate heat
risk for sensitive groups, however. Interior temperatures are
forecast to trend down for the remainder of the week, but remain
above normal. A transient shortwave trough is forecast to move
into the Pac NW Thu into Fri and may induce a push of marine air
with greater coverage of low clouds into the interior valleys.
The ECMWF is much more stout with the ridge holding firm while the
GFS looks faster and slightly deeper with the trough. Some
coastal drizzle is not completely impossible, but for now will not
add any to the forecast with low probabilities for measurement.

Additional troughs will knock down the ridge over the weekend for
a continued downward trend of high temperatures. The rate of
decrease and the magnitude of "cooling" are not completely
certain. NBM probabilities for 80F or more for our warmest
interior valleys are still around 50-60% and no more than 10% for
90F or more. A deeper trough scenario would yield near or slightly
below normal temperatures for the interior valleys; lower to mid
70`s. This is a low probability outcome with only 16% of ensemble
members in this camp this weekebd. There are indications for breezier
or windier conditions with these troughs over the weekend into
early next week. Stronger NW-W breezes may help to knock down
interior temperatures below normal early to mid next week. DB

&&

.AVIATION...A slightly more compressed coastal marine layer
remained in place through much of the afternoon south of CEC.
However, conditions scoured out at CEC around 18z as coastal winds
increased. Pilot reports this morning indicated that cloud top
were between 1500 to 1700 feet. A persistent thin layer of
stratus/fog continued at EKA and ACV with conditions LIFR/IFR into
middle afternoon; partial clearing is expected by late afternoon.
At UKI, VFR prevailed although a surge of stratus moved to within
5 miles of the airport. Prognosis is that stratus will not
infiltrate Uki`s terminal on Wednesday. For Wednesday, offshore
flow will increase over Del Norte most likely preventing stratus
and fog redevelopment at CEC. Above ground (offshore)winds will
become strong enough to warrant adding LLWS to CEC`s TAF around
midnight. Some model data are differing on the coverage or amount
(if any) of stratus/fog reforming from Humboldt Bay to ACV. But,
history or persistence tends to support some amount of marine
clouds Monday morning. /TA

&&

.MARINE...Northerly gales are expected to persist over the
northern outer waters through much of week. Wind magnitudes
appear to be modulated by interior heat and a resultant thermal
trough along the CA-OR coasts. Therefore, strongest winds will
most likely occur during the afternoon and evening hours. Large
and very steep short period seas will lag behind the strongest
winds and probably persist into the late night and morning hours.
Thus, the long duration gale warning for the northern outer waters
through Thursday evening appears to be on track. The gale may
need to be extended into Friday and/or expanded southward into
zone 475 by Saturday.

Closer to shore, winds are forecast to remain much more subdued
with the usual wind-prone points like Pt St George gusting to
35-40kt during the late afternoon and evening hours. Winds have
been shifting to southerly across the southern inner waters as
multiple small scale eddies spin up in the lee of the Cape Mendo.

Also, small NW and S swells are forecast to move through the
waters through the week. Seas will remain primarily locally
generated and dominated by short-period northerlies from the wind
speed maximums in the northern outers. Short period seas look to
hit their maximum late tonight...with hazardous seas propagating
into the inner waters north of Cape Mendocino late tonight. Granted
the largest and steepest waves look to occur across the outer
fringes of the inner waters.

The northerly wind pattern with steep short period waves will
most likely persist into the latter portion of the week. There
are subtle indications for stronger N-NW winds to shift into the
inner waters over the weekend as an trough drops down from the
northwest and pressure gradients tighten up across the area. DB


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 PM PDT this afternoon for
     PZZ450-455.

     Hazardous Seas Warning until 9 AM PDT Thursday for PZZ450.

     Gale Warning until 11 PM PDT Thursday for PZZ470.

     Hazardous Seas Warning until 11 PM PDT Thursday for PZZ475.

&&

$$

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