555
FXUS66 KEKA 282217
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
317 PM PDT Sun Apr 28 2024

.SYNOPSIS...High pressure continues to build offshore as a cold
upper trough digs into the PNW. Very light precipitation in Del
Norte, coastal stratus and below normal temperatures expected
through mid week. Offshore flow and high pressure will promote
warming and drying in the interior late week.


&&

.DISCUSSION...Light stratiform drizzle has dissipated across the north
coast this afternoon following a weak cold frontal boundary.
Scattered cloud cover and broken sunshine should enhance coastal
temps slightly, although breezy NW winds will ensure highs remain in
the upper 50s. Low level moisture trapped beneath encroaching high
pressure subsidence will return low stratus to coastal Del Norte and
Humboldt counties this evening into Monday morning.

Meanwhile, conditions across the interior will be much drier beneath
mostly clear skies. After valley high temperatures in the mid to
upper 60s today, a frost advisory will go into effect beginning at 3
AM Monday morning as radiational cooling and relatively weak N winds
send temperatures plummeting into the upper 20`s and low 30`s. HREF
indicates a 50 to 75 % probability of <35 degrees early Monday
morning in lower elevations of northeastern Mendocino and Trinity
counties.

Synoptic scale zonal flow will soon be interrupted by a cold upper
low descending into the PNW Monday morning, bringing another few
rounds of light rainfall to northern Humboldt and Del Norte counties
Monday and Tuesday. Once again, limited QPF will prevent significant
accumulations - additional rainfall is unlikely to exceed 0.05
inches on the far northern Del Norte coast. Otherwise, coastal areas
will see a similar pattern each morning of low ceilings that
scatter out with daytime heating. Cool NW flow will continue to
dampen temperatures along the coast and in the interior, with
valley temperatures only likely to reach the low 60`s on Monday
and Tuesday. NBM continues to highlight Tuesday and Wednesday
morning with anomalously cold morning temperatures. A freeze watch
has been issued for Tuesday morning for Trinity County with
50-75% NBM probabilities of <32 degrees.

Strong mid to upper-level winds will remain decoupled from the
surface layer below 5,000 ft - as a result, HREF is beginning to
align with NBM to indicate that 25-30 mph winds will stay confined
the coastal headlands of Cape Mendocino and exposed ridges in
southern Humboldt, Mendocino and Lake counties late Tuesday.

As the high pressure ridge continues to build into the PNW, cloud
cover is expected to dissipate more reliably along the coast as
temperatures increase across the CWA. Late Tuesday into Wednesday,
gusty northerly winds are expected as the pressure gradient tightens
considerably along the coast. Clearing skies and increasing offshore
flow early Wednesday will promote widespread warming and drying
across the region, especially in the interior. RH values currently
forecast to drop to 30% in interior Mendocino, Trinity and Lake
Counties. Models are still without consensus on high valley
temperatures Thursday and Friday - right now NBM only has >50%
probabilities in southern Mendocino and Lake counties. Regardless,
an overall warming trend is expected with highs in the 70`s.


&&

.AVIATION...Ensembles indicate that stratus and the chance of MVFR
visibility (50-70%) or lower returns along the coast by the 03Z-05Z
time frame along the coast. By 12Z Monday, HREF ensemble mean
indicates light shower potential increases for the coast, especially
for KCEC and lasts through 18-21Z, then quickly decreasing stratus
for the rest of the afternoon. Ensembles still indicate the diurnal
gustiness for KUKI through early evening, and again the afternoon
Monday.


&&

.MARINE...A couple of persistent northwest swells for the next
several days gives us a combined wave height of 6-7 feet today, and
near 8 feet Monday, peaking at 10-11 feet by Wednesday. Wind speeds
gradually get stronger by mid-week as well. Models are still showing
potential for marginal small craft advisory potential for Monday,
but will hold off for now as the current forecast is slightly
overforecasting the steepness of waves. By mid-week, signals for
small craft potential grow stronger, especially in southern waters.



&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Frost Advisory from 3 AM to 9 AM PDT Monday for CAZ107-108-
     110-111.

     Freeze Watch from late Monday night through Tuesday morning
     for CAZ107-108.

NORTHWEST CALIFORNIA COASTAL WATERS...
None.
&&

$$

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