118
FXUS66 KEKA 242319
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
319 PM PST Sun Nov 24 2024

.SYNOPSIS...Wet and unsettled weather with occasional rain,
isolated coastal thunderstorms and periods of gusty winds are
expected through Monday night. Showers will taper off through
the day on Tuesday, followed by drier weather and colder
temperatures for the remainder of the week.

&&

.DISCUSSION...A wave developed along an approaching frontal
boundary this morning and has delayed the arrival of widespread
moderate rain and high mountain snow for much of the forecast
area. Radar reflectivity data has been showing returns spreading
over Humboldt County this afternoon. Rain gauge network indicated
6-hourly rates around 0.10in in the King Range and across NE
Trinity. Downslope south-southeast winds has resulted in a rain
shadow for the greater Humboldt Bay area with only sprinkles so
far.

Looking at the HREF and NBM guidance, moderate to locally heavy
precip rates are still forecast to increase late this afternoon
into this evening. Highest precip rate up of 0.25in/hr are
forecast over SW Humboldt for an hour or two before the convective
activity shifts SE in NW Mendo for a few hours. Precip rates will
also increase over the mountains of NE Trinity County with heavy
snowfall expected over Scott Mtn Pass through this evening.
Snowfall rates appear to diminish overnight into Monday per the
HREF guidance. According to surface observations in NE Trinity,
dewpoints were in the mid to upper 30s this afternoon. Precip
rates are not forecast to be very intense to drive snow levels
down for major impacts in lower elevations and passes. A dusting
or slushy snow will be possible, but certainly not a repeat of the
heavy snow event we had on Wed when major highways were closed. A
Winter Storm Warning remains in effect through Monday afternoon
for elevations above 4500 ft in NE Trinity County. Travel on
highway 3 over Scott Mountain Pass will be impacted.

South-southeast winds have been gusting to 45-55 mph in the usual
wind prone locations this afternoon. Mattole Rd in SW Humboldt as
usual has been howling with gusts of 59-65 mph. In the lower
elevations, winds have been generally gusting to 25-35 mph with a
few coastal headland sites near 40 mph. Due to the slower arrival
of the occluded front, the wind advisory has been extended a
couple hours longer - til 7PM. It will still remain breezy/windy
overnight into Monday, especially across Del Norte, as the surface
low slowly meanders southward and another trough approaches the
North Coast.

Colder air aloft and surface southerlies will continue to create
sufficient instability for low-topped isolated thunderstorms,
mostly over the coastal waters and near the coast tonight. Based
on what we have seen with isolated 50-60bBZ spiking up over the
coastal waters, expect storm duration to be short with weak
updrafts with no organization. The greatest risk from thunderstorms
will be lightning strikes and perhaps brief heavy rain. Progressive
storm motions will also preclude any major concerns for flash
flooding or debris flow.

Convective activity is expected to continue into Monday as another
trough approaches from the NW. The greatest activity appears to be
mostly north of Cape Mendocino along and offshore the North Coast.
Some small hail is possible, however freezing levels look too
high for any accumulations. Once again, the main threat will be
lightning strikes and perhaps very brief heavy downpours. The
convective activity (showers and isolated tstms) is forecast to
continue Monday night into early Tue morning as the upper trough
complex offshore the Pac NW edges southeastward toward NW California.
Showers are forecast to diminish through the day on Tuesday as
the northern branch of the splitting upper trough traverses over
the area during the day on Tue.

Cooler air and northerly winds will follow after trough passage
by Wed. Frost and freezing early morning temperature are probable
for the interior and even over coastal areas, especially the North
Coast. Expect interior valleys will have abundant low clouds and
fog after multiple days of rain. It may take an additional day of
drying northerlies and offshore flow for skies to remain sufficiently
clear and for overnight temperatures to plummet into the lower to
mid 30s. Now coastal areas will be different, specifically the
North Coast. NBM QMD minimum temperatures indicate a 80-100%
probability for 36F or less and 40-60% for 32F or less for the
Humboldt Bay area. Mckinleyville has a 70-90% chance for 32F or
less each morning Wed-Fri. Thus, the North Coast will probably be
frosty with freezing or near freezing temps each morning Wed-Fri.
The Mendo coast has a much lower chance (10-20%) for 36F or less.
36F is the upper threshold we use to forecast frost.

Generally dry weather is expected with no significant rain impacts
as upper ridging builds toward the west coast mid to late this week.
The southern branch of a split trough will most likely head well
to the south of the area and remain well offshore. As we head into
the Thanksgiving holiday weekend, a rex block pattern will begin
to unfold with a major 500mb height anomaly setting up over the
Pac NW. Dry weather is expected to continue for NW CA for the
Thanksgiving holiday weekend. Fog will no doubt continue to form
in the interior valleys each and every night once we get into a
more stable regime. The warming aloft will most likely not be
realized in most interior valleys, though mountainous areas may
warm up. This large scale rex-block pattern will be a rather
topsy-turvy in terms of temperatures with high mountain sites
warmer than the valleys as we head into the weekend. DB

&&

.AVIATION...Mostly VFR has persisted today with gusty south winds
ahead of an approaching cold front. Gusts of around 30 kts have
been observed so far, and these will continue for a few more hours
until this boundary moves onshore. A brief period of LLWS is
possible with this feature as well. MVFR ceilings are possible as
this feature approaches, but most guidance keeps ceilings above
3kft for the Redwood coast. MVFR cigs remain possible overnight
with stray showers on the coast, and are likely at KUKI later this
evening and overnight. /TDJ

&&

.MARINE...Convective showers should intermittently mix down gale
force gusts for the next couple of hours, especially as the boundary
of the front sweeps overhead. Southwesterlies develop behind this
passing front this evening and overnight, persisting around 15 to 20
kts through Monday then decaying Tuesday. Northerlies, at least for
the outer zones, may return Wednesday as a rex blocking pattern
develops offshore...with the associated low centered to our south
and offshore of the Central CA Coast. This may bring a prolonged
period of relatively light winds and low seas late next week. TDJ

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Wind Advisory until 7 PM PST this afternoon for CAZ101-102-
     104>106.

     Winter Storm Warning until 4 PM PST Monday for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Warning until 5 PM PST this afternoon for PZZ450-455-
     470-475.

&&

$$

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