Whitethorn, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

186
FXUS66 KEKA 220000
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
400 PM PST Sat Dec 21 2024

.SYNOPSIS...Lingering showers tapering off this afternoon. A
similar AR storm system will arrive late Sunday morning, followed
quickly by a more impactful system Monday night into Tuesday.
Increasing hydrologic impacts are expected by midweek.


&&

.DISCUSSION...A warm occluded frontal system brought moderate to
localize heavy rainfall overnight and early this morning, and
strong gusty southeast winds for the coastal headlands and exposed
ridges. Lingering showers will continue to taper off this
afternoon, with a brief shortwave ridge building in the wake of
the upper-level shortwave trough moving northeast toward the
Cascades. This will bring a brief break of rainfall into Sunday.

Tonight, mid to high level moisture will increase ahead of the
next system approaching the area on Sunday. Overnight
temperatures are forecast to remain above normal, with lows in the
mid 40`s to low 50`s across much of the area...but Trinity County
in the mid 30`s.

Another upper-level trough embedded to a broad trough located in
the Alaska Gulf is expected to dig southward this evening and
tonight. An associated fast- moving frontal system, along with a
plume of subtropical moisture ingested in the southwesterly flow,
will move onshore Sunday afternoon. A low-level jet in advance of the
approaching front will bring warm air advection from the
southwest and aid in rising snow levels to 8000 feet along with
stratiform precipitation. HREF indicated the start time of rain
for Del Norte and Humboldt counties after midday, while areas
farther east and south after 3PM local time. This system will
bring a period of moderate to locally heavy rainfall across the
area. Shower activity is expected in the wake of the main front.
Increasing instability will promote a slight chance of isolated
thunderstorm along the coast late Sunday afternoon and evening,
especially along the Mendocino Coast and Del Norte Coast.

The surface pressure gradient is forecast to tighten late Sunday
morning as a low level jet (925mb) around 65 kts develops over
the North Coast. Gusts from 40 to 55 mph is forecast over the
coastal headlands and higher terrain of interior Del Norte and
Humboldt...although up to around 60 mph is possible over the
highest terrain. HREF ensemble means indicated gusts of 30-40 mph
for the lower elevations. A Wind Advisory is in effect from 7 AM
PST Sunday morning to 4 PM Sunday afternoon for Del Norte and
Humboldt counties. /ZVS

.FROM PREVIOUS DISCUSSION...
After another brief break late Sunday night into Monday morning,
a more impactful AR system is expected to arrive Monday afternoon
into Tuesday morning. Both WPC and GFS are forecasting widespread
2 inches to nearly 4 inches in portions of interior Del Norte and
the King Range, with the heaviest rainfall likely overnight into
Tuesday. NBM probabilities are trending a bit lower for winds
exceeding 40 mph. CNRFC ensembles are showing several rivers
(including the Eel River at Fernbridge, the Russian River at
Hopland and the Navarro River) have a 50 to 75% chance of reaching
minor flood stage by Wednesday. There is still a decent amount of
uncertainty surrounding the following AR storm system expected to
arrive late Wednesday into Thursday. Lower snow levels Christmas
Day will quickly rise in time for this additional precipitation,
but may still hover around 4000 to 5000 feet by Thursday morning.


&&

.AVIATION...VFR conditions are forecasted, yet spotty showers
arriving at coastal terminals can briefly turn into MVFR conditions,
especially at KCEC. These showers have the potential to bring
gusty, sporadic winds and degraded visibilities due to increased
rainfall. Southerly winds are forecasted to remain through the day
before increasing tonight along the coast. Another burst of
strong winds from another passing front will reach us tomorrow
midday with possible bouts of rain showers and chaotic winds. Low-
level wind shear is possible along the coast during this passover
with strong 40kt winds at 1500-2000ft AGL tomorrow.

&&

.MARINE...In the wake of last night`s frontal passage, seas remain
chaotic due to leftover wind waves and multiple large westerly
swells entering the waters. Winds are forecasted to increase again
tomorrow morning leading to gale force gusts up to 50kts over the
waters. After the passage winds will calm significantly before
strengthening again Monday midday as yet another front passes over
the coastal waters. These passages will continue to send large long
period swell into the waters that in conjunction to the strong winds
and associated wind waves will keep seas chaotic.


&&

.HYDROLOGY...A series of Atmospheric Rivers are forecast to
impact Northwest California into next weekend. Periods of moderate
to locally heavy rainfall will bring the potential for rapid
rises on rivers, streams and creeks across the region. The next
system on Sunday afternoon is expected to have a fast-moving
progression, resulting in total rainfall amounts from 0.25 to 0.50
inches...locally up to 1.50 over the southwest facing higher
terrain. After a brief break, the next stronger system will move
onshore Monday afternoon through Tuesday afternoon. Up to around 2
inches is forecasted with this system, with locally up to around 3
inches for the southwest facing terrain. Rainfall is expected to
last closer to 30 hours with this third system. This one may
bring some flooding of small streams. WPC continues to have
portions of our area in a "Marginal Risk" for excessive rainfall
Monday through Tuesday. The Russian River at Hopland currently has
around a 30 percent chance of exceeding flood stage Tuesday
morning. The Eel River at Fernbridge and Mad River near Arcata are
expected to reach/exceed action/monitor stage. These will need to
be watched as it gets closer. -ZVS


&&

.BEACH HAZARDS...A long period, westerly swell will continue to
impact the coastal waters of Northwest California during next week.
The current swell is currently entering waters according to buoy
observations at 14ft@15s. This is expected to bring breakers between
20 to 22 feet all day into the early hours of Sunday. Hazardous surf
conditions due to the breaking waves will be possible along west-
northwest facing beaches. More hazardous surf is forecasted for the
morning of Monday, December 23rd as a larger westerly swell of 19-
21ft@20s is sent into our waters. Breakers are expected to be
between 23-28ft depending on beach orientation.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     High Surf Advisory until 9 AM PST Sunday for CAZ101-103-104-
     109.

     Wind Advisory from 7 AM to 4 PM PST Sunday for CAZ102-
     104>106.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 AM PST Sunday for PZZ450.

     Gale Warning from 9 AM to 3 PM PST Sunday for PZZ450-475.

     Hazardous Seas Warning until 3 PM PST Sunday for PZZ455.

     Hazardous Seas Warning until 3 AM PST Sunday for PZZ470.

     Gale Warning from 3 AM to 3 PM PST Sunday for PZZ470.

     Hazardous Seas Warning until 9 AM PST Sunday for PZZ475.

&&

$$

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