474 
FXUS66 KEKA 131301
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
601 AM PDT Mon Sep 13 2021

.SYNOPSIS...The interior will heat up heading into Tuesday, with 
localized triple digit readings. Sunshine will be muted in some 
areas by smoke and haze. The coast will remain cool, but with 
decreasing marine layer clouds through mid-week. Rain will be 
possible for portions of our region over the weekend. 

&&

.DISCUSSION...A weak upper-level trough passing through in west-
northwest flow aloft, along with clear and fairly calm conditions
outside of localized coastal stratus has all promoted cooler
temperatures overnight compared to the previous night. That will
keep inland temperatures from heating up much more compared to
Sunday's highs. Marine layer stratus has developed around 
Humboldt Bay and up the Eel River Valley, and to a lesser degree 
northward to Crescent City. The clouds do not appear to be well- 
established, despite a marine layer depth near 2000 feet, perhaps
due in part to some offshore winds poking in some drier air, and 
decreased stability from the passing trough along with strong 
north winds offshore. These winds will try to shift onshore this
afternoon, which will help clear the stratus, and bring some cool
and brisk conditions to the coastal headlands. 

Pacific high pressure builds to our north and thermal troughing 
shifts toward the coast, while an upper ridge builds in aloft 
tonight into Tuesday. That will promote more offshore flow 
tonight, and likely keep much stratus or fog from developing. 
Shallow marine air and light afternoon onshore breezes will remain
at the coast on Tuesday, but otherwise heat will build across the
interior and expand into the near- coastal areas. Expect plenty 
of 80s and 90s inland, with some triple-digits likely around Ukiah
and eastern Lake County. While sunshine will be plentiful, expect
some haze and wildfire smoke to drift southwest from Trinity and 
Siskiyou County across the rest of our area on Tuesday. Still, do 
not expect as expansive smoke and poor air quality as we've seen
in the past few weeks. 

As the upper ridge gradually flattens to our south on Wednesday, 
giving way to increased troughiness over the Pacific Northwest, 
temperatures will gradually cool, as the flow switches back to 
more onshore. That will probably allow areas of marine layer 
stratus to return for the nights and mornings mid to late week, 
and shift smoke and haze back more to the east of the fires. 
Heading into the weekend, upper level ridging will continue to 
split and shift to the central Pacific and the central and eastern
CONUS, while a deep upper low dives southward from the Gulf of 
Alaska toward the Pacific Northwest. Model guidance continues to 
be in good agreement on that general evolution, which will ensure 
steadily cooler inland temperatures, dropping well below seasonal 
norms by the weekend. The trough will send a cold front toward us 
around Saturday, which could bring some showers to the North Coast
as early as Friday night. The details regarding how much rain and
the southward extent will continue to remain rather uncertain, 
but confidence is increasing for at least a light rainfall to
areas north of Cape Mendocino. /AAD

&&

.AVIATION...Stratus is sparse this morning, although there is 
development from Cape Mendocino to Point St. George. Low lying 
interior valleys may see some light fog or mist as clear skies 
encourage radiative cooling overnight. The coastal terminals will 
get gusty north winds by the afternoon and will persist with MVFR 
categories or better. The marine layer is a bit deeper at KACV while 
minimal at KCEC. Subsidence will help keep skies clear. Wind shear 
could be an issue as winds pick up around late afternoon. KUKI will 
maintain prevailing VFR conditions through the TAF period. /EYS

&&

.MARINE...Gusty winds and steep seas are verifying at the buoys 
this morning. Significant wave heights around 11 feet at 8 to 9 
seconds will continue as wind waves and swell combine into a 
hazardous sea state.  Gale conditions will persist into Tuesday 
morning with hazardous seas lingering soon after. A Gale Warning is 
in place for the northern and southern outer waters for the next 24 
hours as the thermal trough continues to strengthen. Expect elevated 
seas to persist through the week with the return of larger 
significant waves early Thursday morning. /EYS

&&

.FIRE WEATHER...Went ahead and upgraded the Fire Weather Watch to
a Red Flag Warning for both zones 203 and 204, though admittedly
the conditions for most of 204 will probably be sub-critical.
Little has changed with overall expectations for winds and
humidity, but have extended the warning into Tuesday morning as
winds should stay strong enough over the east and north-facing
upper slopes and ridges, with very poor RH recoveries. The exposed
ridgetops of interior Del Norte will have the worst conditions, as
highlighted by all high-res models, with some gusts over 30 mph a
good bet along with recoveries only in the 20 percent range.
Tuesday will bring the hottest day of the week, along with
afternoon RH in the teens for much of the interior, but winds 
will become lighter. Some local offshore winds will develop again 
Tuesday night over interior Del Norte County ridges, along with 
widespread poor ridgetop recoveries, but this won't be enough for 
another Red Flag Warning. The flow will turn increasingly onshore 
from Wednesday through Friday, with gradual cooling. We are still 
optimistic for at least some light rain for the northern half of 
the area over the weekend; less so from Mendocino County 
southward. /AAD

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Red Flag Warning from 1 PM this afternoon to 10 AM PDT 
     Tuesday for Lower Middle Klamath-Upper Smith.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 6 AM PDT Wednesday for Cape 
     Mendocino to Pt Arena out 10 nm-Pt St George to Cape 
     Mendocino out 10 nm.

          Gale Warning until 6 AM PDT Tuesday for Cape Mendocino to 
     Pt Arena 10 to 60 nm-Pt St George to Cape Mendocino 10 to 
     60 nm.

&&

$$

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