168
FXUS66 KEKA 272153
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
253 PM PDT Sat Apr 27 2024

.SYNOPSIS...Light rain or drizzle will be possible for mostly
coastal areas of Del Norte and northern Humboldt Counties tonight
through Monday. Otherwise, dry weather with slightly below normal
temperatures are expected into early next week. Offshore flow
around mid week will result in a warming and drying trend for the
interior mid to late next week.

&&

.DISCUSSION...Weakening frontal system offshore has been spreading
thick mid level clouds across the northern portion of the area
today. Radar has been showing 20-25 dBZ returns just offshore
with stations in SW Oregon reporting light rain. Amounts will not
be very much today, a trace to few hundredths based on the HREF
mean. A northwesterly push of shallow moist air later tonight
behind the warm front may result in slightly higher amounts of
light rain for coastal Del Norte and coastal Humboldt as well as
the west facing slopes of the interior where HREF indicates a
60-80% chance for a tenth or more in 6 hours. Granted the high
resolution models may be overcooked with the precip generation
and the NBM 50th/75th percentiles may prove to be superior with no
measurable rain except near the ORCA border. These amounts are
not forecast to be significant by any means, but even light
amounts will have impacts on outdoor activities and projects.

The NW influx of low level moist air will continue on Sunday and
light drizzle for mostly coastal areas of Del Norte and Humboldt
during will be possible (10-20% chance). Another front or trough
in the westerlies may generate another bout of light rain or
drizzle early Monday morning.

Forecast uncertainty increases Monday night and Tuesday regarding
light precip with global models trending drier as another shortwave
trough progresses into the PAC NW. Surface ridge and northerlies
will likely strengthen after trough passage and dry weather will
most likely prevail except for perhaps a few showers near the ORCA
border..

Overnight/early morning temperatures are forecast to remain below
late April normals with nightly occurrences of mid-upper 30`s at
the typical colder valleys that do not cloud up during the night,
mostly Trinity County. The coldest morning looks to be Tuesday
(based on the NBM) when probabilities for subfreezing temperatures
are highest (over 70% in some of the coldest valleys). It is
3 days out and too early to issue a freeze watch. For we posted
a weather story graphic and social media post to call attention
to this potential for freezing valleys temperatures early Tuesday
in Trinity County. The upshot this time of year is solar insolation
will yield mild afternoon temperatures; upper 60s to lower 70s.

Northerly winds will strengthen Tue night into Wed, followed by
robust offshore or E-NE flow as an inverted surface trough
develops along or offshore the coast. Expect temperatures to cool
down in the valleys under a drier air mass after winds decouple.
Upper elevations will warm in response to the offshore winds and
large scale subsidence (adiabatic warming). Daytime highs will
warm above normal mid to late week. Probabilities for >80F are
highest for Mendocino and southern Lake (40-60%). Mid 80`s are in
the realm of possibilities, 40% or less with the current set of
NBM ensemble members. Chance for 90F or more is no more than 10%
and highly unlikely based on the latest NBM set.

There are still subtle variations and differences between the
ensemble systems and that is why the forecast still has a slight
chance (20%) for rain Wed-Thu north of Cape Mendo. About 50% of
500mb cluster members by day 7 (Saturday May 4th) indicate yet
another trough dropping down from the NW for the start of a
cooling trend and perhaps more rain. The overall "cool" pattern
with below normal temperatures so far has been consistent. DB

&&

.AVIATION...The biggest problem will be timing of potential MVFR
ceilings as they lower tonight with an approaching cold front. HREF
indicates a clear lowering for the coastal terminals today, fairly
consistent and confident of some light rain/drizzle for at least a
few hours (20Z to 03Z, from HREF ensembles) this afternoon and
evening. Ensembles suggest a 50-70% chance of MVFR ceilings this
evening through roughly 15-18Z Sunday. MVFR visibility is less
certain, in the 20-30% range. Ensembles also indicate an overall
improvement to flight conditions after 18Z Sunday. The main problem
at KUKI will be wind gusts from the north northwest to near 20 to 25
KTS perhaps, peaking near 00Z Sunday this late afternoon, then
decreasing in speed as mean ensemble solutions would indicate. MH

&&

.MARINE...Observations indicate we are probably looking at the last
vestiges of the small craft advisory continuing through 6PM PDT with
waves at about 6-7 feet in height and 8 seconds and continuing to
decrease. Gusts to 21 KTS at the Point Arena ob trending down as
well.

Currently dealing with 3 main wave groups, all from the north
northwest. The two shorter period groups with periods near 4 seconds
and 9 seconds get partially combined in the forecast. The longest
period of around 14 seconds is the shortest height at about 3 feet.
The other groups consisting of heights of 5 to 7 feet. These groups
eventually converge upon 2 groups by Sunday, with steep waves
associated with the waves forecast to have heights near 6 feet and
period of 6 seconds for the southern waters by late Sunday into
Monday. This would be enough for another small craft advisory, along
with advisory level winds kicking in shortly afterwards behind a
cold front (especially fanning out south of Cape Mendocino), giving
us potential wind and wave conditions for small craft from late
Sunday night into late Monday night for all of our southern waters.
For now I will hold off on an advisory to avoid confusion from the
current advisory ending in a few hours. If the forecast persists, we
will likely have to hoist another small craft advisory for the
southern waters again. MH


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 6 PM PDT this evening for PZZ455-
     475.

&&

$$

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