Flash Flood Watch 2, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
404 AM PST Mon Nov 19 2018

.SYNOPSIS...Dry, mild, and hazy conditions will continue through
Tuesday. Significant rains and occasional breezy southeasterly
winds will return to the area late Tuesday night and persist
through the weekend.

&&

.DISCUSSION...If you have any outdoor plans or yard work you will
have 2 more good days before the rains return. The downside to
outdoor activities will be the continued degradation of air
quality and haziness from area wildfire smoke across our region.
Along the coast, stratus will continue to play peak-a-boo with the
coast. Most of the coast has remained clear so far this morning
however stratus is moving back to the south which means low clouds
and reduced visibilities may be possible around Humboldt Bay near
Sunrise. Interior locations will remain pleasant however high
level cloudiness will begin to increase as the first of several
systems approach our area.

Now for the rain...significant precipitation will return to the
Northcoast late Tuesday evening. Three systems will move across
the West Coast from Tuesday night through the weekend. The first
batch of rain should be light to moderate and last through
Wednesday morning. Once the bulk of precipitation from the first
wave moves out of the area Wednesday morning continued showers
will be possible for the remainder of Wednesday and into
Thanksgiving morning. With this showery activity a modest amount
of MUCAPE, steep lapse rates, and fairly cold 500mb temperatures
indicate that a few lightning strikes may be possible across at
least the southern waters and along the coast of Mendocino County.
Any thunderstorm that develops would be capable of producing
cloud to ground (or water) lightning, gusty localized winds, and
potentially some small hail.

The heaviest batch of precipitation is expected to move north to
south during the afternoon of Thanksgiving day into Friday
morning. Current indications are that a moisture plume will be
oriented perpendicular to our coastline which will help to enhance
rainfall totals on the windward (Ocean) side of coastal
mountains. This batch will also have the heaviest stratiform
precipitation rates of the three systems therefore this would be
the time frame of greatest threat for debris flows in the vicinity
of recent burn scars. While the overall threat for debris flows
appears to remain fairly low at this time it will need to be
watched closely as the more fine scale details are worked out
closer to the event. If you live near a recent burn scar now is
the time to start planning what you would do if debris flows
develop. For mountain locations it appears that snow levels will
remain above 5000 feet during this event which means only Scott
Mountain Pass on Hwy 3 will see some accumulating snow.

Strong southerly winds will also peak Thursday afternoon and
evening with area ridges gusting in excess of 35 mph. Since this
will be the first strong southerly wind event of the season these
winds may bring some tree limbs down and cause sporadic power
outages. For this reason, if the wind forecast remains relatively
unchanged a wind advisory may be required.

This weekend another weaker system will move across the area
leading to more widespread light to moderate rain. Confidence
continues to increase in most areas receiving 3-6 inches with
localized areas receiving even more once all is said and done.
While this rain and higher elevation snow will be primarily
beneficial to our area it will impact Thanksgiving travel plans.
Slippery roads will be possible from oil build-up and ponding of
water. Rock and mud slides may also lead to challenging driving
conditions and possibly some road closures. Lastly, snow
accumulations will be possible on roads generally above 5000 feet
Thanksgiving Day and Friday morning. /WCI

&&

.AVIATION...The stratus is more limited this morning and is mainly
just off the coast north of Cape Mendocino as the offshore flow has
increased. As of 3am there are only a few spots north of Trinidad
where it is hitting the coast. Offshore flow is expected keep it
limited and most areas seeing stratus should clear out by mid
morning. Tonight there may a few pockets of brief stratus along the
coast, but in general the southeast winds should keep it offshore.
KCEC may be one of these spots where it returns.

There is a continued haze/smoke across the area bringing MVFR
visibilities to most areas. The HRRR smoke model is showing lower
concentrations for today than yesterday, but there may still be
smoke lingering in some areas that is not accounted for. MKK

&&

.MARINE...Light south to southeast winds persist across the waters
this morning. There is also a northwest swell of 4 feet at 13
seconds. This swell will slowly diminish through Tuesday. The light
southerly winds are expected to continue through tonight.

Tuesday a strong weather system approaching the area will start to
increase the southerly winds. The newest models have generally
slowed down this system. Now it looks like winds will increase to 10
to 20 kt by mid to late afternoon on Tuesday. Winds are expected to
peak late Tuesday night or early Wednesday with some gale force
gusts are expected in the northern outer waters. At this point these
gusts are not expected to be widespread enough that a gale watch
will be needed anywhere.

There is expected to be a break in the winds Wednesday afternoon and
Wednesday night as the models have slowed the second system down as
well. The next system moves into the area Thursday afternoon and
Thursday night. Confidence is growing on the timing of this system
and current models show it slightly stronger than the first one.
Gale force gusts still look to be limited to the northern half of
the outer waters.

In addition to the winds a large swell is expected to build into the
waters starting Tuesday night. Initially it is expected to around 3
feet at 16 seconds on Wednesday. The current ENP run shows this
building to 7 to 9 feet at 12 seconds on Thursday afternoon.
Thursday night and Friday the winds increase and the wind driven
waves will combine with the swell for total wave heights of around
12 to 14 feet at 12 to 14 seconds. Saturday the winds will diminish
and the waves will become less steep. Confidence is low on the
forecast for the weekend as the GFS and the ECMWF have significant
differences int he timing of the next system. MKK

&&

.FIRE WEATHER...Mild conditions with poor humidity
recoveries will continue through Tuesday, with steadily increasing
southeasterly winds along exposed ridges. Elevated fire weather
conditions may develop Tuesday due to the combination of low
humidity and gusty southeast ridgetop winds, particularly in the
afternoon. Humidity will increase rapidly overnight Tuesday, as the
first batch of significant wetting rains return to the area.
Strongest winds and heaviest rain can be expected Thursday and
Friday.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...None.
&&

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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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