Coastal Flood Warning 1, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
445 AM PST Thu Jan 17 2019

.SYNOPSIS...In the wake of yesterday's cold front, showers and
isolated thunderstorms with heavy downpours and periods of gusty
winds will continue today. The offshore storm has also generated
a huge swell that will pound the beaches. Periods of rain will
continue Friday through this weekend, followed by high pressure
and dry weather next week.

&&

.DISCUSSION...Wet and windy weather continues across northwest
California today in the wake of yesterday's cold front. A
powerful area of low pressure centered offshore will gradually
weaken today while tracking northeastward toward Vancouver Island,
but shortwaves will continue to rotate around the upper-level
trough and across northwest California, enhancing shower activity
across our region. Mid-level temperatures have cooled
substantially, and will continue to do so until midday. This will
steepen lapse rates and result in sufficient instability for
thunderstorms. We have already seen quite a bit of lightning
activity around southern Humboldt and northern Mendocino county
overnight. The most likely areas to see thunderstorms will be
along the Redwood coast, but would not rule out a thunderstorm
anywhere in our area. Downpours will be common even outside of any
thunderstorms, and brief small hail will be possible. Temperatures
in the lower atmosphere are not cold enough for serious
accumulating small hail around our populated coastal plain, with
snow levels settling around 4,000 feet today, but that doesn't
mean drivers shouldn't exercise caution. Speaking of snow levels,
these will drop briefly lower at times in the heaviest showers,
and would not rule out minor accumulations below the 4,000-foot
level. Some of the Highway 36 passes may be impacted, though
accumulations should be limited to a couple inches of slush. Scott
Mountain Summit on Highway 3 will be high enough so that heavy
snow will continue to pile up there. Otherwise the rest of our
highway passes will remain just wet today.

Winds will be another continuing issue, though not as strong and
more localized than yesterday. A Wind Advisory continues for
interior Del Norte and Humboldt county elevations above 1500 feet,
and coastal Del Norte County. Southerly wind gusts since midnight
over the exposed high terrain and near Crescent City have been
topping out mainly around 40 to 45 mph, which is right on the edge
of advisory criteria. The advisory will end around 10 AM as winds
aloft, as well as surface winds, will begin to ease more
substantially.

Rainfall since Wednesday morning has amounted to 1 to 3 inches
across the majority of northwest California, with lesser amounts
along the Redwood coast where downsloping played a role. Expect
another half-inch to an inch of rain today with locally heavier
amounts near mountainous terrain. See the Hydrology section below
regarding flooding concerns.

Warmer air aloft coming in tonight will quickly diminish shower
activity later this afternoon and this evening. However, the next
system will quickly push a warm front across our area, with rain
becoming steadier across most of our area by Friday afternoon.
Rain will focus north of Cape Mendocino, especially near the
Oregon border, through Saturday, while a cold front stalls over
us. Another wave of low pressure will swing this front through
early on Sunday, with showers continuing into Sunday evening.
Models have been trending wetter with these two systems, with a
long duration of moderate rain. Totals may exceed 2 inches across
much of Humboldt, with as much as 4 to 6 inches across Del Norte
County by Sunday evening. Much lighter amounts, from a half inch
to an inch and a half will fall across eastern Trinity and
Mendocino county over the 3-day period from Friday through Sunday.
Winds will be locally gusty over the exposed high terrain and some
of the coastal headlands, but not nearly as strong as with this
past storm. Would not rule out a the need for a low-end wind
advisory with 40 to 50 mph gusts possible Friday afternoon or
evening around coastal Del Norte county and the high elevations
of Del Norte and Humboldt.

Otherwise, next week will feature a well-deserved break in the
weather, with a large ridge of high pressure expected to dominate
the patter across the eastern Pacific and the West Coast. Some
inland morning valley fog will likely be around to begin the
week...otherwise we have high confidence in dry, mild and sunny
weather all of next week into next weekend. /AAD

&&

.AVIATION...Showers and isolated thunderstorms will continue through
Thursday afternoon, and then dissipate during the evening. However,
another storm system will enter the region by Friday morning leading
to another period of moderate rain (particularly over Humboldt and
Del Norte counties), as well as gusty south winds, and possible IFR
ceilings/visibility. In addition to the gusty south winds, wind
shear appears probable along the coast by mid Friday morning.

JMG

&&

.MARINE...Gale force southerly winds will gradually weaken this
morning over the northern outer waters. However, a very large
westerly swell from 25-30 feet at 18 seconds will build across all
of the waters this morning, and then persist into Thursday evening.
Hazardous seas will be probable as a result. In addition, showers
and a few thunderstorms will be possible this morning and afternoon.
The west swell and seas will subside tonight, but south winds will
be on the increase once again Friday morning as a warm front lifts
north across the region...with gale force speeds possible over the
northern outer waters Friday morning into the evening. Unsettled
weather will continue through the weekend as a front lingers over
the area. Thereafter, high pressure will build over the NERN Pacific
early next week resulting in the development of moderate northerlies
persisting through Friday.

JMG

&&

.HYDROLOGY...We continue Flood Watches for the areas near the
Carr, Delta, and Mendocino Complex burn scars through this
afternoon. Rain rates thus far have been below 0.50 inches, and it
is generally understood that 0.80 inches per hour is needed for
mud or debris flow. However, with the threat of heavy downpours
and some thunderstorms today, am airing on the side of caution. A
flood warning will be issued if any storms do develop and persist
over the burn scars.

The Garcia River crested at 12.8 feet near Point Arena this
morning. An area near where the river crosses highway one is
notorious for flooding around this level, though we have not
received reports thus far. The river is already falling below 10
feet early this morning, so any issues should be resolved quickly,
and the flood watch for this area will likely be cancelled soon.

The Navarro River at Navarro needed a Flood Warning, and the
forecast took it to Moderate flood stage this morning. However, it
appears the river may be cresting early this morning. In any case,
the flood warning will need to be continued until at least around
midday. Additionally, river Statements have been issued for the
Russian River at Hopland due to the potential of some flooding of
Highway 175 near Hopland this morning. This river has crested at
16.5 feet and will continue to lower today. Another statement is
in effect for the Eel River at Fernbridge to reach monitor stage
this afternoon, and continue to rise into Friday, before slowly
lowering this weekend. /AAD

&&

.BEACH HAZARDS/COASTAL FLOODING...A huge westerly swell will
impact NW California beaches today. Breaker heights will rapidly
build and reach 30 to 35 feet. This swell combined with brisk SW
winds may produce a 1 to 1.5 foot storm surge on top of high tide,
which could result in localized coastal flooding as well as very
large surf.

High astronomical high tides will occur on Sunday and into early
next week. Minor coastal flooding is possible during the daily late
morning and early afternoon high tides, with the highest
astronomical tides expected on Monday. /SEC

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch until noon PST today for CAZ109.

     High Surf Warning until 5 AM PST Friday for CAZ101-103-104-109.

     Wind Advisory until 10 AM PST this morning for CAZ101-102-105-
     106.

     Coastal Flood Advisory from 7 AM to 9 AM PST this morning for
     CAZ103.

     Flood Watch through this afternoon for CAZ107-110-113.

NORTHWEST CALIFORNIA COASTAL WATERS...Gale Warning until 10 AM PST
     this morning for PZZ450-470.

     Hazardous Seas Warning from 10 AM this morning to 5 AM PST
     Friday for PZZ450-470.

     Hazardous Seas Warning until 5 AM PST Friday for PZZ455-475.

&&

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For forecast zone information
see the forecast zone map online:
http://www.weather.gov/eureka/zonemap.png

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Special Weather Statement
National Weather Service Eureka CA
738 AM PST THU JAN 17 2019

CAZ101>106-171615-
Southwestern Humboldt CA-Northern Humboldt Coast CA-
Del Norte Interior CA-Southern Humboldt Interior CA-
Northern Humboldt Interior CA-Coastal Del Norte CA-
738 AM PST THU JAN 17 2019

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN HUMBOLDT AND SOUTHWESTERN
DEL NORTE COUNTIES UNTIL 815 AM PST...

At 736 AM PST, Doppler radar was tracking strong thunderstorms along
a line extending from 8 miles southwest of Klamath to 7 miles north
of Petrolia. Movement was northeast at 25 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Eureka, Arcata, Klamath, Orick, Fortuna, Rio Dell, Trinidad,
McKinleyville, Carlotta, Westhaven-Moonstone, Scotia, Petrolia,
Ferndale, Blue Lake, Myrtletown, Cutten, Hydesville, Capetown,
Humboldt Hill and Freshwater.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Small hail is expected to affect highways 101 from Fortuna to Orick.

Dark clouds ahead may signal the potential for small hail, so slow
down and ensure that your headlights are on. Small hail can
accumulate on roadways resulting in very slippery conditions.  If
driving on a hail covered road, do not slam on the brakes.  Instead
ease off the gas pedal and avoid over-correcting.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4060 12442 4102 12425 4118 12424 4120 12419
      4139 12413 4154 12422 4159 12421 4162 12399
      4140 12389 4110 12389 4062 12395 4026 12409
      4018 12433 4029 12441
TIME...MOT...LOC 1536Z 217DEG 55KT 4144 12416 4043 12425