458
FXUS66 KEKA 241147
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
447 AM PDT Tue Sep 24 2024

.SYNOPSIS...Another round of seasonably warm weather with fair
conditions and hot interior temperatures, expected today. Cooling
is expected on Wednesday, followed a warming trend Thursday and
Friday. Coastal stratus with patchy fog will likely return around
mid week.



&&

.DISCUSSION...Synoptic views of satellite imagery in the IR as well
as water vapor wavelengths, show a large synoptic scale anticyclonic
rotation over the Pacific and Mountain-West states. This clockwise
rotation is indicative of high pressure and subsidence which is also
keeping skies clear to partially cloudy over land. Modeled pressure
maps in the 500mb heights are also showing the signature 588mb
isobar over the area which is bringing high temperatures to bear
once more on the CWA. The max temperatures observed for some of the
interior hot spots yesterday, were 5-7% above normal when compared
to max temperature mean values. With similar conditions today,
absent some of the gusty winds, we expect to see inland valley
temperatures as high as 102F. Water vapor imagery also shows a
distinct boundary of dry air along the 36N-37N latitude, which is
getting entrained into the anticyclonic rotation and bringing dry
air with easterly flow.

The long wave ridging pattern aloft will begin to shift eastward
towards the Midwest tonight. An upper level trough approaches the
Pacific Northwest simultaneously. Meanwhile, a dry cutoff low
located offshore of southern California will drift northward
parallel to the coast before being absorbed by the upstream trough
by early Wednesday. The marine layer will likely develop during
this time frame. Daytime high temperatures will diminish to near
or below seasonal averages in the interior. Seasonal averages
range from 82- 88F in the interior. Chances for precipitation with
this incoming trough is quite meager, generally 10% or less. If
anything, some light drizzle may occur in coastal areas with no
impacts.

Ensemble means and deterministic guidance indicates above normal
500mb heights and above normal 850mb temperatures Thu-Sun. This will
most likely result in above normal interior high temperatures.
How much above normal is not 100% certain. Looking at the National
Blend of models (NBM), sure enough chance for 90-95F increases as
early as Friday. Dry weather and above normal interior high temps
are most probable Fri-Mon. /DB /EYS

&&

.AVIATION...Continued offshore flow has allowed VFR conditions to
prevail across the area, even along the immediate coast. An
extensive bank of marine stratus is visible about 50 miles offshore
but so far has been kept at bay thanks to offshore winds. The only
concerns early this morning would be patchy and inconsistent
radiation fog bringing MVFR conditions along the coastal plain,
which would be most likely to happen briefly this morning around
Humboldt Bay (less than 25% chance of actually impacting the
airport).

Otherwise, VFR conditions should prevail during day alongside mostly
calm wind. There is high model agreement that the stratus bank will
gradually approach the coast but the timing of impacts is highly
uncertain. Some high resolution models imply the bank should already
be at the coast while others show it hang off until early Wednesday
morning. All show any impacts occur right along the coast with very
little progress inland. All told, and impacts are very unlikely
until at least 2000 this evening. After that point, NBM is implying
a 30 to 60% chance of IFR ceilings at some point Tuesday night into
Wednesday, the the greatest chance after midnight though ceilings
at any point are likely to be inconsistent. /JHW

&&

.MARINE...High pressure moving onshore today combined with a
disrupted pressure gradient due to a closed low moving up the coast
will combine to generate mostly gentle to calm northerly wind across
the waters today. Early this morning there are still some isolated,
steep short period seas above 6 feet in the outer waters, but these
will quickly fall later this morning.

Seas won`t be totally calm, however. A mid period, northwest swell
will build in this afternoon through Thursday. This swell will most
likely peak around 8 feet at 14 seconds early Thursday morning. In
absence of meaningful short period seas, this swell will dominate
the sea state, especially in the northern waters. Also with calm
seas, the first front runners of the swell hold the potential for
some minor sneaker waves, though the generally mid period and
middling heights of the swell will limit the overall sneaker wave
risk.

Northerly winds will begin to rebuild Thursday afternoon first in
the southern waters with moderate breezes. Winds will continue to
increase and spread north by Friday. There is uncertainty as to the
exact strength of winds, but model ensembles generally show around a
30 to 50% chance of gusts reaching gale force Friday into the
weekend. Regardless of exact strength, steep short period seas over
8 feet should be expected, especially in the outer waters and
fanning south of both Cape Mendocino and Pt. St. George. /JHW


&&


.FIRE WEATHER...Elevated conditions with low daytime RH`s and
locally gusty winds are forecast to continue. Temperatures will
remain hot today with daytime RH`s from 10-20%. Offshore flow
will continue, however ridge level winds will become
southeasterly by early morning, and then turn westerly to
southwesterly in the afternoon. A trough will move across the area
on Wed and daytime temperatures will cool down. RH`s should also
increase on Wed-Thu, but minimum RH`s will still be low, around
20-30% in the interior. Warmer and drier conditions with stronger
N-NE winds expected Fri-Sat. Elevated to locally critical
conditions will be possible. DB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 8 AM PDT this morning for PZZ470.

&&

$$

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