Flooding and Coastal Flood in California, January 2 to 7, 2023

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
534 AM PST Mon Jan 2 2023

.SYNOPSIS...Precipitation will begin during the morning commute on
the coast and spread to the east by noon in the form of light snow
at elevations above 2000 feet. Tuesday will be an even lighter event
precipitation wise with an intense system arriving Wednesday through
Thursday. This will bring high wind and Flooding.

&&

.DISCUSSION...A frontal boundary approaches the coast with light
precipitation expected. Light rain closer to the coast will be less
than a half inch and snow at elevations above 2000 feet will
accumulate 2 to 5 inches in a 12 hour span. Precipitation for the
area will end by late Monday night, just before an even weaker
shortwave passes through Tuesday morning which will barely produce
0.2 inches of precipitation in most areas.

There are indications of significant impacts from the approaching
upper level low pressure system. ECMWF EFI shows extreme categories
for wind gusts Wednesday evening. Most of the area of concern
regarding winds are offshore and near the Mendocino coast. Exposed
elevation at coastal areas of Cape Mendocino are showing 70 mph
gusts Wednesday while some ridges inland show 40 to 50 mph. A High
Wind Watch will be considered. There are also indications that deep
moisture is being sourced. We can see a warm air mass ahead of a
cold front intensifying towards occlusion. QPF categories of the
Extreme Forecast Index also show an out of ordinary occurrence of
precipitation for most of northern and central California. IVT
magnitude values are also similar to last weeks deluge of 700 kg/ms
or greater. This could require a Flood Watch as Wednesday
approaches, a Hydrologic Outlook has been issued currently to
highlight concerns and impacts. This can be viewed at
weather.gov/eka.

Otherwise, ensembles show a continued pattern of lingering low
pressure over the eastern Pacific. Bands of moisture will
continuously train towards the area towards the end of the week and
into the weekend. Continuous rounds of warm moist air entrainment and
cold air advection from the Great Basin, could keep active winter
weather possible through next week. Precipitation Probability from
the  Climate Prediction Center, has our area leaning towards
the above normal category through mid January. /EYS

&&

.Aviation...VFR conditions and light winds persist across the area
as of 3AM. An approaching front will increase south to southeast
winds this morning, especially along the coast. Some areas may see
some low level wind shear. A band of 45 kt winds looks to be only
around 2000 feet above KACV so have expanded the wind shear.  The
rain with the front is expected to start between 8 and 10 in most
areas. This is expected to be somewhat showery and should make it
through by mid afternoon at the coast and slightly later inland.
Tonight winds will remain southeast and start to pick up again late
tonight ahead of a stronger system. MVFR conditions may linger in
the north, but farther south skies are expected to clear out later
tonight. MKK

&&

.Marine...A frontal boundary is approaching the area this morning
and will move through this afternoon. The models are showing areas
of surface low pressure developing along the boundary bringing
locally stronger winds. The gale warning remains in effect for the
northern waters and this looks on track. Farther south the models
are struggling with the location of the surface low on the front.
For example some of the runs of the HRRR have gale force winds and
another low moving in down there. Considered issuing a gale warning,
but confidence isn't high enough so left the small craft advisory in
place. This will need to be monitored this morning.

Immediately behind the front Monday evening the northwest swell is
expected to increase again to around 12 feet at 15 seconds. This
swell is generally expected to persist through Wednesday.

Tonight winds will diminish behind the front, but this will only be
brief. Tuesday southerly winds increase ahead of the next system. It
looks like these will remain below gale force until Tuesday night.
Wednesday the winds are expected to really start to pick up as an
area of low pressure drops to around 960 mb as it slowly wobbles
around well off the coast. Models are in fairly good agreement on
this, but there are some small secondary areas of low pressure
rotating around it bringing locally stronger winds. Most of the
models are in fairly good agreement on these strong winds so have
have issued a storm watch for portions of the area for the first of
round on Wednesday. Wednesday night and Thursday these winds are
expected to remain very strong, although it is uncertain on if these
will be storm force so have not issued for that.

Immediately behind the front and strong winds on Thursday a very
large westerly swell rapidly builds in. Current model runs have it
peaking around 23 or 24 feet at 17 seconds. Have trimmed it back to
21 feet in case there is a small shift in the models and it ends up
smaller. This looks to be a dynamic fetch situation and small shifts
in the speed or location of the low will make a big difference in
the wave heights.

Thursday night and Friday the area of low pressure finally moves off
to the northeast and winds diminish. This looks be shortlived with
another front bringing more strong winds for Friday or Saturday.
There is still more disagreement on the timing of these winds. MKK

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Winter Weather Advisory until 10 PM PST this evening for
     CAZ105>108-111-114.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Gale Warning until 3 PM PST this afternoon for PZZ450-470.

     Small Craft Advisory until 6 AM PST Wednesday for PZZ455.

     Gale Watch from Wednesday morning through Wednesday evening
     for PZZ455.

     Storm Watch from Wednesday morning through Wednesday
     evening for PZZ470.

     Small Craft Advisory until 6 AM PST Wednesday for PZZ475.

     Storm Watch from Wednesday morning through Wednesday
     evening for PZZ475.

&&

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

Hazardous Weather Outlook
National Weather Service Eureka CA
417 AM PST Mon Jan 2 2023

CAZ101>104-109-110-112-113-115-031230-
Coastal Del Norte-Del Norte Interior-Northern Humboldt Coast-
Southwestern Humboldt-Mendocino Coast-
Northwestern Mendocino Interior-Southwestern Mendocino Interior-
Southeastern Mendocino Interior-Southern Lake-
417 AM PST Mon Jan 2 2023

This hazardous weather outlook is for northwest California.

.DAY ONE...Today and tonight.

No hazardous weather is expected through tonight.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Very strong winds are possible Wednesday and Thursday on the ridges
and coastal headlands.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.

CAZ105>108-111-114-031230-
Northern Humboldt Interior-Southern Humboldt Interior-
Northern Trinity-Southern Trinity-Northeastern Mendocino Interior-
Northern Lake-
417 AM PST Mon Jan 2 2023

...WINTER WEATHER ADVISORY IN EFFECT FROM 8 AM THIS MORNING TO 10 PM
PST THIS EVENING...

This hazardous weather outlook is for northwest California.

.DAY ONE...Today and tonight.

A Winter Weather Advisory is currently in effect.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Very strong winds are possible Wednesday and Thursday on the ridges
and exposed areas.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.