056
FXUS66 KEKA 191141
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
441 AM PDT Sat Oct 19 2024

.SYNOPSIS...Gusty northeast winds and low humidity will continue
to promote critical fire weather conditions for southern Lake
County through Saturday. Otherwise, dry and warmer conditions are
expected this weekend. Coastal stratus will return on Sunday.


&&

.DISCUSSION...Primary concern continues to be the red flag
warning and critical fire weather conditions for southern Lake
County through late this afternoon. For more information, please
see the fire weather section below.

The upper level pattern is characterized by a ridge extended from
offshore of northern California and into southern Oregon. This is
promoting increasing subsidence aloft, breezy to light offshore
flow and abundant clear skies this morning. Surface observations
confirmed the warmer air-mass over the area with overnight low`s
running generally 5 to 15 degrees warmer compared with yesterday`s
reading. However, some colder valleys of northern Mendocino have
been reporting low temperatures in the mid to upper 30`s with the
dry air-mass and light winds. High temperatures today will warm
well above normal, into the 80s to perhaps a few warmer valleys
locales, like Ukiah, topping out around 90F.

Offshore flow will diminish over the later portion of the weekend
and temperatures will trend downward, though it will still be
pleasant with above normal highs in the interior. Coastal stratus
and fog will probably return by Sunday as a 500mb shortwave trough
approaches the Pac NW, inducing development of a shallow marine
layer. The duration and extent of the stratus remains uncertain.

Global deterministic models, particularly the GFS, NAM12 and
ECMWF, continue to depict a frontal system approaching the coast
Sunday night through Monday morning. The aforementioned trough and
associated cold front will bring increasing PWATs of 1-1.4 inch
Sunday into Monday. ECMWF ensemble and NBM 24-hour probabilities
for 0.50 over 24 hours continue to look promising for Del Norte
County. Meanwhile, ECMWF probabilities for 1.0 inch is completely
ruled out, while NBM is showing a 50% chance. Overall no impacts
from this system are expected with only light to locally moderate
rain for Del Norte, Humboldt and Trinity, and no rain for
Mendocino and Lake Counties. Dry weather with temperatures near or
above seasonal averages are forecast for the remainder of next
week.

Ensemble and deterministic guidance continues to indicate another
trough breaking through later in the week (around Friday), but
this could end up fizzling out again leaving the area with less
than a tenth in 24 hours or zilch. Once again RAW ensemble systems
and NBM indicate highest probabilities (50%) for over 0.50-1.00
of rain in 24 hours in the far northern half of the area with lower
chances (25 to 45%) in the far southern portion of the area.
/ZVS/DB

&&

.AVIATION...Offshore flow and a particularly dry airmass have
allowed for VFR conditions to prevail overnight across the whole
area once again. That said, weakening dry air has allowed for more
midlevel cloud cover as well as some very shallow MVFR marine fog
just along shore, mostly north of Trinidad Head.

VFR conditions are expected during the day today and all across the
interior , but generally weakening wind and at least brief high
pressure building along shore will most likely allow for increased
marine influence tonight. Deterministic model soundings suggest a
weak and shallow marine layer tonight north of Cape Mendocino,
likely buoyed by a weak wind reversal. NBM indicates a 20 to 40%
chance of IFR conditions at coastal terminals, most likely very
early Sunday morning. /JHW


&&

.MARINE...Moderate north winds have continued overnight in the
northern waters with a fan on stronger breezes maintaining steep
seas int he southern waters. Current model guidance was verified
well by a 0530z satellite pass. Strong winds will continue this
afternoon in the southern out waters with near gale force gusts just
south of Cape Mendocino. Otherwise more moderate winds up to 15 kts
will continue in the northern waters.

Very gentle to even calm winds will build Sunday alongside much
calmer seas. With little wind wave influence to speak of, mild mid-
period northwest swells will control the sea state by early Sunday.
A subdued sea state will most likely continue into early next week,
despite the passage of a weak frontal system. Moderate northerly
winds are most likely behind the front around next Tuesday with very
slight chance (less than 20% chance) of isolated gale force gusts.
There are strong indicators of a storm system and associated steep
seas (possibly over 15 feet) sometime late next week but the exact
timing is highly uncertain. /JHW


&&

.FIRE WEATHER...Red Flag Warning remains in effect for southern
Lake County through 5 PM today. Strong northeasterly winds have
redeveloped on the ridges overnight. Gusty winds around 35 to 45
mph are reported on the higher ridges surrounding eastern and
southern Lake County, with higher gusts over 50 mph observed by a
few mountain RAW this morning. Very poor RH`s recoveries are
observed around 15 to 25 percent in Lake County. RH recoveries
have also been poor around 20 to 30 percent over the ridges across
interior Mendocino, while elsewhere valley areas were reporting
over 45 percent. Very dry conditions are expected to continue this
afternoon with RH values in the teens. Winds are expected to
gradually diminish/weaken during the day, but breezy conditions
will linger over some of the more prominent Lake County ridgetops
through this afternoon. Tonight, onshore marine moisture will
promote a slight improve in the RH`s overnight recoveries.
However, poor RH`s recoveries from 25 to 35 percent are expected
to continue over the higher terrain in Lake and eastern Mendocino
counties. A shortwave trough will pass through the northern
portion of the forecast area early Monday with a shifting winds
becoming west to northwest, but they should remain fairly light in
most spots and accompanied by some cooling and RH improvement.
/ZVS



&&

.HYDROLOGY...No significant rainfall is expected for the next 7
days. DB


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Frost Advisory until 8 AM PDT this morning for CAZ110-111.

     Red Flag Warning until 5 PM PDT this afternoon for CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PDT this evening 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