237
FXUS66 KEKA 042156
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
256 PM PDT Tue Jun 4 2024

.SYNOPSIS...Hot, dry weather will build by mid week with high
heat risk for many interior valleys, especially Lake County,
Wednesday and Thursday. Breezy north to northwesterly winds will
return Wednesday and Thursday, with the strongest gusts over the
coastal headlands and exposed ridges. Isolated thunderstorms are
forecast for the northern Trinity mountains on Thursday during the
late afternoon and evening.

&&

.DISCUSSION...Broad upper level ridging and above normal 500mb
heights will remain over NW California through Thursday. Large
scale subsidence and adiabatic warming will result in high
temperatures 10-20F above early June normals in the interior
Wednesday through Thursday. The hottest day will likely occur on
Wednesday for Lake county and on Thursday elsewhere. Model
guidance has been very consistent supporting 850 mb temperatures
of 24 to 28C over much of the interior. High temperatures in the
hottest valleys are expected to range from 95-105F degrees. The
heat risk is forecast to be moderate over the area, but a major
heat risk is expected to occur over portions of Lake County
Wednesday and Thursday. The heat will have impacts on anyone
without effective cooling and/or adequate hydration. As a result,
a Heat Advisory remains in effect for Lake County from Wednesday
morning through Thursday night. The above normal heat will also be
a concern for Trinity, interior portions of Mendocino and perhaps
NE Humboldt where temperatures are forecast to peak in the upper
90s to around 100F or hotter. Temperatures along the coast are
expected to warm some per the NBM, but with marine air and stratus
most likely returning late tonight into Wednesday morning and
increasing northerlies offshore, temperatures may actually cool
down and feel chilly due to the damp marine air.

Additionally, a thermal trough is expected to develop near the
coast Wednesday. This will promote breezy north-northwesterly
winds Wednesday and Thursday over the exposed ridges and coastal
headlands, with gusts probably (>60% chance) around 25 to 35 mph.

Sounding continue to indicate inverted-V profiles across Trinity
County on Thursday and a late day isolated thunderstorm looks
possible (less than a 15% chance). It will be hot on Thu and
buoyant energy will no doubt be sufficient, however the moisture
will be at mid and upper levels. Strong mid level capping may not
allow the "pent-up" energy to be released into vertically
accelerating parcels. Dry air entrainment will further reduce the
buoyancy. A poorly defined shortwave length trough in the strong
SW flow aloft may serve to erode the mid level stable layer. A
better defined trough will approach this weekend and once again
isolated thunderstorms will be possible (<15% chance) over the
interior mountains, primarily Trinity County. Interior temperatures
will moderate over the weekend as the marine layer deepens in
response to the trough, but it will most likely remain above
early June normals for interior Mendocino, Trinity and Lake.
Interior heat is then forecast to return early next week as 500mb
heights and anomalies increase again, though there is great
deal variability and considerable uncertainty with the evolution
of the weekend trough. Interior storms are not 100% out of the
question early next week, but at this point there are no definitive
signals for storms and for now will lean heavily toward the
National Blend of Models (NBM) guidance. DB

&&

.AVIATION...In the middle of the morning, a few pockets of IFR
stratus/fog developed along the Del Norte Coast...but was
shortlived. Before noonday, a bout of MVFR haze formed along the
North Coast but was also shortlived. Through afternoon VFR
prevailed. However, a weak disturbance pushed some (VFR) low
clouds over CEC. The afternoon pressure gradient has been weak
along the Coast but stronger inland; therefore UKI reported
breezy-gusty NW winds. A weak weather system, to the northwest
this afternoon, will push some level of mostly VFR low clouds into
the North Coast (at Cec). By Early Wednesday morning, conditions
are expected to fall into IFR, and thus impact the coastal
terminals. Light drizzle will be more prevalent over Humboldt Bay
but could possibly affect ACV also. /TA


&&

.MARINE...Northerly winds will steadily increase tonight through
Thursday. Strongest winds tonight will occur across the southern
waters and then pick up north of Cape Mendocino during the day on
Wednesday. Gale force gusts are highly probable in the lee of
Cape Mendocino on Wed and probably again on Thu. A second
expansion fan off Cape Blanco will likely extend southward into
PZZ470 and perhaps the far northern reaches of PZZ450 around Pt St
George per HREF probabilities for gusts > 30kt. The HREF has been
overdone lately and the synoptic gradient does not support gusts
that strong. Gale gusts to 40 kt are probable again on Thu, but
once again the coverage appears to be localized and confined to
narrow corridors in the outer waters. Steep short period waves
will steadily build on Wed, reaching 9 to 11 feet at 9 seconds.
This is borderline for a hazardous seas warming, but sufficient
when decaying NW swell is added. A late season NW swell of 10 to
12 feet at 16 seconds will arrive early Wednesday and then
gradually decay through Friday. The combination of the NW swell
and locally generated northerly waves will yield seas up 13 to 15
feet by late Wed afternoon and into the evening. This typical
strong northerly wind regime with very steep northerly waves will
persist into Thu before laying down on Fri. Steep northerly waves
and resurgence of northerly winds is expected for the weekend,
though exact magnitude of winds and timing remain uncertain. DB

&&

.BEACH HAZARDS...A large long period NW swell will build early
Wednesday with significant swell heights up to 11 feet at 16-17
seconds during the morning. This high energy swell has the
potential to bring a moderate risk of sneaker waves. Shorter
period NW swell of 7-9 feet at 7-9 seconds may mitigate the risk
for the Mendocino coast. However, the risk remains with an increase
of beachgoers looking for relief from the interior heat. A beach
hazard statement has been hoisted for the entire coast. /ZVS/DB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Beach Hazards Statement from late tonight through Thursday
     morning for CAZ101-103-104-109.

     Heat Advisory from 8 AM Wednesday to 8 PM PDT Thursday for
     CAZ114-115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Hazardous Seas Warning from 6 AM Wednesday to 3 PM PDT
     Thursday for PZZ450-470.

     Gale Warning from 8 AM Wednesday to 9 AM PDT Thursday for
     PZZ455-475.

&&

$$

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