Mad River, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

860
FXUS66 KEKA 281330
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
530 AM PST Sat Dec 28 2024

.SYNOPSIS...Periods of moderate to locally heavy rain will bring
a slight risk for minor flooding Sunday morning. Strong southerly
winds in advance of a cold front tonight will be followed by robust
westerlies and isolated coastal thunderstorms on Sunday. Dry
weather, colder mornings and valley fog are expected for Monday
and Tuesday.

&&

.DISCUSSION...Moist westerly flow into the coastal terrain has
been generating modest amounts of rain through the night. Frontal
boundary will stall over the northern portion of the area this
morning and generate light to moderate rainfall through the day.
Front is forecast to lift northward as a warm front by this
evening as a wave and surface low develops this evening and
overnight. Southerlies are forecast to ramp up as a 925mb 70kt
speed max develops over or just offshore the North Coast by 12z.
HREF mean surface gusts are on the order 50-60 mph and most likely
overdone for coastal areas. NBM 90th percentile gusts are less,
30-40 mph except for the Del Norte coast (CEC) where gusts from
50-60 mph are probable. Per the NBM 24-hour probability, there is
about a 50% chance for 58 mph or more for the Crescent City area.
ECMWF ensemble mean has gusts around 53 mph with 17 members in
the 54-61 mph range. Thus, will lean toward the NBM 90th
percentile and hoist a high wind warning for the Del Norte coast
tonight. The timing of the strongest winds looks to be around
midnight or shortly after by 1-2 hours. Winds will likely reach
advisory strength (45-55 mph) mid to late this evening and for
that reason will start the warning mid evening. Winds should
decrease by 12Z Sun, but will leave a 2 hour buffer as winds have
remained stronger and longer than the models indicate. Higher
elevations of Del Norte and Humboldt Counties will for sure gust
to 50-60mph, most likely higher at some Venturi-effect locations.
Greatest uncertainty is with strength of wind gusts around the
Humboldt Bay/Eel delta and along the Mendocino coast. Precip
loading and some instability with convection along the frontal
boundary should allow for higher momentum air to mix down to the
surface. Strong southwest and westerly winds should also develop
across Lake County just ahead and behind the front Sunday morning.
A wind advisory has been hoisted for gusts to 50 mph.

This will be the last IVT plume in the long series and will
crescendo with one last bout of heavy rain Sunday morning. There
is a concern for areal and small stream flooding, since soils
are saturated and the run-off response has been quick. See
hydrology section below for more details.

A break in the wet weather is expected on Monday after shortwave
trough passage. Surface high pressure will build and promote drying
offshore flow that should last into Tuesday. After multiple days
of rain, fog and low clouds will form in the interior valleys.
Probabilities for light rain returns Tue night and Wed and then
increases toward the end of the week. Exact magnitude and timing
of rain remains uncertain, though atmospheric river landfall
diagram indicates a 50% chance for IVT`s over 250 kg/m/s with a
frontal system late next week. This is on average the wettest
time of year and we are right on track for a normal season. DB

&&

.AVIATION...Biggest problem continues to be low-level wind shear
potential, but again, only for a short window of time. KCEC will be
most under the gun for wind shear potential once again with the next
axis of strong low-level jet 04Z-12Z Sunday. The low level jet will
produce speeds of near 65 KTS near 2K feet over KCEC, and perhaps
closer to 55KTS for KACV. This jet axis will not arrive over KUKI in
time to include in this forecast, but look for this feature to
arrive in KUKI within a few hours after 12Z Sunday. NBM indicates a
55-60% chance of IFR ceilings and 35-45% chance for LIFR ceiling for
KCEC through about 19Z before dropping to 25-40% and 20-30% chance
respectfully through 07Z Sunday before dropping even more for the
rest of the forecast. KACV follows a similar trend except a
secondary spike of chances for lower ceilings similar to the
beginning of the forecast, with a 55-60% chance of IFR ceilings and
40% chance of LIFR ceilings by this afternoon near 00Z Monday.
Lowest visibility arrives at KCEC earliest compared to the other
terminals, with up to a 60% chance of visibility less than 2SM miles
for KCEC through 18Z today, and 45-50% chance of visibility lower
than 1SM. For KACV, the lowest visibilities are forecast to arrive a
bit later for KACV near 20-22Z, with over a 50% chance of visibility
below 3SM. For KUKI, the probabilities for ceilings remain fairly
similar throughout the forecast, up to about 50% chance of IFR
ceilings, and 40-70% chance MVFR visibility. Median peak wind gusts
will be highest for KCEC, peaking near 08Z with a 50% chance of
reaching 38KTS or more, and a 50% chance of reaching 27KTS at
KACV. /MH


&&

.MARINE...Seas remain steep while wind speeds continue to decrease
this morning. A westerly swell continues build in today and move
through the waters at 15 to 18 feet at 17 to 18 seconds. A couple of
buoys are reporting 18 feet at 18 seconds early this morning. Expect
south winds to increase significantly this evening as yet another
weather system approaches. Gale Warnings have been launched for a
small window between 05Z and 11Z Sunday over the northern and outer
waters, as the southern inner waters remain in a small craft
advisory through Monday morning. NBM indicates an 80-100% chance of
frequent gale force gusts (greater than or equal to 34 KTS) for the
majority of northern and outer waters.

On Sunday morning the final cold front of this system will sweep
through the waters bringing an end to the active weather we have had
for the past several days. Waves will gradually subside by Monday.

Less active weather is anticipated for next week with lower seas and
lighter winds through the entire week. The only main concern is a
weak system that could enhance the southerly winds around mid week
with small craft conditions possible. /MH

&&

.HYDROLOGY...Modest rain amounts have fallen overnight with a
frontal boundary that will stall over the northern portion of
the area today. The front will then lift northward by mid evening
as a warm front in response to slight westerly flow amplification.
Frontal wave or surface low development and robust southeast to
south surface winds should put a halt on the steady widespread
heavy precip, before an upstream trough forces a cold frontal
boundary across the area Sunday morning. Sunday morning is the
most likely period of heavy rain, during frontal passage. HREF
shows highest probabilities for heavy rain rates > 0.30in/hr from
about 12Z-15Z across the northern basins, spreading southeast
into Mendo and Lake by 18Z, and then rapidly moving the front
southeast out of the area after 18Z. Granted individual CAM
members are out of phase with hourly timing differences and
depict higher deterministic rates on the order of 0.50-075in/hr.
The rapid progression will limit the potential for major flooding.
Minor flooding of low-lying areas with poor drainage and street
flooding will increase during Sunday morning. Low topped shallow
convection will follow as air aloft cools down, however PWATs will
fall off drastically and storms will not have deep layer moisture
to support a flash flood threat. Low topped storms with long thin
CAPE profiles tend to produce very brief downpours (a minute or
two) and some small hail. Main stem river ensemble hydrographs
indicate very low probabilities, generally less than 15%, for
minor flood stage exceedance this weekend. The exceptions are the
Eel River at Fernbridge, about a 23% chance of exceeding minor
flood stage of 20 ft Sunday, and the Russian River at Hopland,
about a 32% chance of exceeding minor flood stage of 15 feet. DB

&&

.BEACH HAZARDS...A westerly swell continues to move through the
waters at 15 to 18 feet at 17 to 18 seconds. A couple of buoys are
reporting 18 feet at 18 seconds early this morning resulting in
large breakers near 24 feet. Larger Breakers in the 20 to 25 foot
range are anticipated through 9 PM This evening before subsiding a
bit tonight.  Use great caution near beaches this weekend. /MH

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     High Surf Advisory until 9 PM PST this evening for CAZ101-
     103-104-109.

     Flood Watch from 3 PM PST this afternoon through Sunday
     afternoon for CAZ101-102-105.

     High Wind Warning from 9 PM this evening to 6 AM PST Sunday
     for CAZ101.

     Wind Advisory from 6 PM this evening to 6 AM PST Sunday for
     CAZ102-104>106.

     Wind Advisory from midnight tonight to 6 AM PST Sunday for
     CAZ103.

     Flood Watch from late tonight through Sunday afternoon for
     CAZ103-106.

     Wind Advisory from 1 AM to 8 AM PST Sunday for CAZ109-110.

     Wind Advisory from 6 AM to 1 PM PST Sunday for CAZ115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PST this evening for PZZ450-
     470-475.

     Gale Warning from 9 PM this evening to 3 AM PST Sunday for
     PZZ450-470-475.

     Small Craft Advisory until 3 AM PST Monday for PZZ455.

&&

$$

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