657
FXUS66 KEKA 152303
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
403 PM PDT Sun Sep 15 2024

.SYNOPSIS...Showers and isolated thunderstorm across the eastern
portion of the forecast area through tonight, with lingering
showers into Monday. Breezy west to northwest winds through
tonight, followed by breezy offshore flow over the higher terrain
into Monday. Another upper level disturbances will bring
widespread rainfall Tuesday through Wednesday. A drying and
warming trend is expected late in the week.


&&

.DISCUSSION...IR satellite imagery depict an amplified upper
level trough over the West Coast this afternoon. Showers and
isolated thunderstorms have developed over the the higher terrain
in northeastern Trinity County this afternoon, where several
lightning strikes have been detected. This will continue to
evolve into a closed low over the western half portion of Oregon
and Northern California this evening. This will bring continued
chances of showers and isolated thunderstorms over the interior
mountains into Monday morning. This upper trough will continue
digging southward toward Southern California through Monday. In
addition, breezy west to northwest winds has been observed this
afternoon with gusts from 25 to 40 mph across the coastal
headlands and exposed ridges.

An amplification of the upper level trough is expected tonight and
into Monday as the cold core upper level trough moves toward the
Great Basin and high pressure builds back into the northeastern
Pacific. This will allow dry north-northeasterly flow development
across the interior as the surface pressure gradient builds near
the coast. Gusty northeasterly winds from around 30 to 40 mph are
expected to develop this evening in response, mainly over the
highest elevations of Del Norte County.

Instability and limited moisture in the mid level will aided another
chance for isolated showers over southeastern Trinity, eastern
Mendocino and northern Lake counties Monday afternoon. Although
there is a low chance (5-10%) of isolated thunderstorms, this is
not ruled out. High temperatures are expected to be near to below
normal, with inland highs in the mid 60s to upper 70s. Meanwhile,
coastal temperatures are expected to be in the upper 50`s to low
60s. ECMWF Extreme Forecast Index (EFI) indicated a below normal
normal temperatures across the interior through Wednesday.
Interior valley lows are forecast to dipping into upper 30`s to
lower 40`s, especially for cold spots such as Hayfork and Ruth
Valley Monday and Tuesday mornings. However, frost is unlikely to
form at valley floors.

A weak ridging will build in the wake of the upper level trough
Monday night into Tuesday, followed by another upper level trough
that is forecast to move onshore Tuesday night and Wednesday,
bringing widespread rainfall. Rainfall total amounts are forecast
to range from over 0.5" in Del Norte County to a 0.10" in SE Lake
County. In addition, a weakly unstable post-frontal airmass will
aid in a slight chance (15-20%) of isolated thunderstorms
development Wednesday afternoon and evening across the eastern
portion of the forecast area, including interior Mendocino,
Trinity and Lake counties

Ensemble clusters show ridging building in from the west late
this week, possibly bringing dry weather from late this week into
the weekend. Temperatures are expected to warm up, but will remain
mainly seasonably.

VELEZ


&&

.AVIATION...Satellite early this afternoon shows mid and high level
cloud cover across most the region. Gusty NNW winds are being
reported at all terminals. LLWS is possible at the coastal terminals
this afternoon and evening. The threat of LLWS and gusty wind will
diminish overnight. Stratus development tonight is uncertain as
offshore winds and a weak marine inversion will inhibit stratus. If
any does form, it will likely be around sunrise and close to the
ground, with brief LIFR/IFR ceilings and visibilities possible.
Otherwise, VFR conditions are expected for all terminals by mid-
morning. JB


&&

.MARINE...Northerly winds have begun to ramp up behind an upper
level low. These are expected to peak tonight with gale force gusts
possible in the outer waters, and steep to hazardous seas with
significant wave heights of up to 11 ft are expected. Gradual
improvement is expected Monday night into Tuesday. A front moving
through Tuesday will shift winds southerly at around 5-15 kts and a
chance for light rain. Northerlies are forecast to ramp up again
Thursday behind this low, with 75-90% chances of small craft
advisory conditions Thursday afternoon in the outer waters. JB


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 AM PDT Tuesday for PZZ450-455.

     Small Craft Advisory until 4 PM PDT this afternoon for
     PZZ470.

     Gale Warning until 9 AM PDT Monday for PZZ470.

     Small Craft Advisory until 9 PM PDT this evening for PZZ475.

     Gale Warning from 9 PM this evening to 9 AM PDT Monday for
     PZZ475.

&&

$$

Visit us at https://www.weather.gov/eureka

Follow us on Facebook and Twitter at:
https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png