953
FXUS66 KEKA 151217
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
517 AM PDT Sun Sep 15 2024

.SYNOPSIS...An upper level disturbance continues to approach the
area. Unsettled weather conditions are expected today, with
lingering showers into Monday. Isolated thunderstorms are possible
for Trinity County this afternoon and evening. Another shortwave
will bring scattered showers mid week. A drying and warming trend
is expected late in the week.


&&

.DISCUSSION...An upper level disturbance continues its advance
from north to south down the West Coast. This afternoon and
evening, as the upper level low begins to pivot to the northeast around
Mendocino County and the north Bay Area, moisture will wrap around
and move into Northwest California from the Central Valley. As a
result, Trinity and eastern Mendocino counties are the most likely
to have a wetting rain today and into early tomorrow. Locations
along the coast will most likely see little to no accumulation
with this first system.

Showers are expected to develop across the interior this
afternoon, especially over Trinity County. Some light rain is
also possible across interior Humboldt, northeastern Mendocino
and portions of Lake counties as the the trough will continue to
move east-southeast. Additionally, there is a slight chance
(15-25%) of isolated thunderstorms late this afternoon and
evening. Sounding models show elevated instability with an
inverted V today over Trinity County, mostly over northeastern
Trinity. Showers will gradually diminish tonight, with lingering
showers into Monday morning.

In addition, windy to gusty north to northwest winds are expected
again this afternoon over the coastal headlands in Humboldt and
Mendocino counties, with gusts from 25 to 35 mph. Stronger winds
around 40 mph are possible over the exposed ridges in the King
Range and Crescent City.

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. Monday, lingering low
level moisture, along with the diurnal heating, will promote some
isolated showers in Trinity County during the afternoon and into
evening.

Even cooler temperatures in the mid 60`s to mid 70`s are
anticipated across the interior today as probabilities of
exceeding 75 stay low, even in the valleys. Interior valley lows
also have a high probability of dipping into upper 30`s to lower
40`s, especially for cold spots such as Hayfork and Ruth Valley
both Monday and Tuesday mornings. However, frost is unlikely to
form at valley floors.

Another low is forecast to move onshore Tuesday night and Wednesday,
bringing additional rain and keeping temperatures well below normal.
Ensemble clusters show ridging building in from the west late this
week, possibly bringing dry weather from late this week into the
weekend.

VELEZ & JLW

&&

.AVIATION...Widely varied CIGS and VIS continue this morning as an
upper level low approaches the area with an area of mid and low
clouds along with some periods of patchy dense fog. Satellite and
observations up the coast show generally clearing skies once this
boundary passes. This afternoon gusty northwest winds are expected
across the area. This combined with a non-existent marine inversion
should allow for MVFR or VFR conditions at the coast. Confidence is
low on the timing of these lifting ceilings. Tonight it looks like
there may be a return of some clouds, but they look to be generally
MVFR. The HREF is showing very low probabilities of these clouds
returning and this is a reasonable solution as well. Offshore flow
is setting up and should help keep the coastal areas clear. MKK


&&

.MARINE...An upper level low is moving onshore this morning and then
slowly moving to the south and out of the area later this afternoon
and tonight. Behind this system winds are expected to increase with
some gale force gusts and steep waves behind it this evening and
into Monday morning. The winds are expected to increase a little
early than previously expected in the northern waters so have
started the gale warning a few hours early. These winds are expected
to remain elevated through Monday evening.

Monday night and Tuesday high pressure moves overhead and allows the
winds to weaken, especially in the waters north of Cape Mendocino.
This weakening is sped up by another upper level low that is
expected to move down across the area on Wednesday. This will bring
some southerly winds and lighter winds, around 5 to 15 kt. Wednesday
night and Thursday stronger northerly winds return to the area with
speeds of 20 to 25 kt. The ensemble clusters are still showing some
differences in the timing of how quickly these winds will return. By
Thursday afternoon the clusters are all showing winds of 15 to 20
kt.

The northern Pacific basin remains generally quiet with no
significant swells expected over the next week. The only swell is
expected is a fresh swell with periods ranging 8 to 11 seconds.
This generally remains around just 3 to 6 feet. MKK


&&

.FIRE WEATHER...Temperatures will cool well below normal today for
the interior. RHs will be higher today as stronger northwesterly
winds develop with a trough. This cold trough aloft will also
create instability and showers, primarily over the interior, this
afternoon through Monday. Isolated wet thunderstorm with LAL`s of
2 are also possible for the northern zone of 283 this afternoon.
Chances for wetting rain will increase to 35 to 45% by this
evening in zone 283 and then shift into zone 277 by early Monday
morning. Cooler weather with below normal temperatures and
generally higher relative humidity is expected for Monday and
Tuesday. A secondary trough will bring another chance for wetting
rain and gusty northwesterly winds by mid week. A warming and
drying trend is forecast for the latter portion of the week.

VELEZ


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory from 9 AM this morning to 9 AM PDT
     Tuesday for PZZ450.

     Small Craft Advisory until 9 AM PDT Tuesday for PZZ455.

     Small Craft Advisory from 9 AM this morning to 4 PM PDT
     this afternoon for PZZ470.

     Gale Warning from 4 PM this afternoon to 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.

&&

$$

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