Area Forecast Discussion
Issued by NWS Eureka, CA

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609
FXUS66 KEKA 201240
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
440 AM PST Mon Nov 20 2017

.SYNOPSIS...Periods of moderate to heavy rain area expected
across the area today. Rain will diminish tonight and become light
by Tuesday. However, the potential for wet and unsettled weather
will likely continue through late week.

&&

.DISCUSSION...A moderate atmospheric river is bringing moderate to
heavy rain to much of the area this morning. Satellite estimates
are showing a plume of moisture with origins in the tropics aimed
at the coast. PWATS in this plume are 1.5 to 2 inches. This is a
very warm airmass with freezing levels rising to over 10,000 feet.
A wave moved onshore in Del Norte and Northern humboldt county
early this morning bringing 1.25 to 1.75 inches of rain over the
higher terrain. This will slowly drift south and weaken this
morning. This is expected to bring a short break in the heavier
rain this morning along the Humboldt and Del Norte coast. This
afternoon heavier rain is expected again as the next wave moves
onshore.

Tonight models are in good agreement on the main plume of moisture
drifting to the north of the area. A very warm and moist airmass
is expected to persist over the area on Tuesday. This will keep
clouds and some occasional rain around as a couple of weak
shortwaves move through the moist southwest flow. Rainfall amounts
will be fairly light. Clouds are expected to persist and fog is
possible as well. If one of these shortwaves move slightly farther
south or is stronger than expected there could be quite a bit more
rain than currently expected.

Wednesday and Thursday the pattern looks to remain fairly
consistent with a warm moist airmass over the area. There will be
some weak shortwaves moving through. These are expected to bring
periods of light rain or drizzle to much of the area. This will
keep surface temperatures warm and there may patchy fog in some
locations.

Thursday night into Friday morning it looks like a frontal
boundary will push through. This is expected to bring an
additional round of rain, although it looks like it will mainly be
focused on Humboldt and Del Norte counties. Behind this boundary
there is decent agreement that Friday will generally dry across
the area, at least in the afternoon. There may be some sunshine as
well.

Another round of rain is expected at some point on the weekend.
The models currently have stronger system moving north into
British Columbia with only the trailing front reaching northern
CA. This would bring moderate rainfall amounts to the area.
Confidence is low on the exact evolution of this system due to
model differences. MKK

&&

.AVIATION...The storm system has arrived this morning and with it we
have seen the TAF sites report MVFR conditions with pockets of IFR
when heavier showers have rolled through. Look for these conditions
to continue through the morning and into the early afternoon hours
with chances waning slighlty for the evening and overnight hours.
There is some uncertainty as to how dry or wet we`ll be tonight and
into Tuesday as models show additional waves of moisture. Current
thinking is that if we get light to moderate rain, we`ll likely see
MVFR conditions prevail. Additionally, the TAF package will continue
to carry low level wind shear for the sites.

&&

.MARINE...Fresh to strong southerly winds are forecast for today
with near gale force gusts expected for the northern outer waters.
This will allow for steep southerly wind driven waves, which
combined with a west-northwesterly swell, will yield a confused sea
state. These southerly winds and steep seas will continue through
the middle of the week with weaker winds and lower seas expected
beyond then.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch through this evening for CAZ102-104>108.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 4 PM PST Wednesday for PZZ470.

     Small Craft Advisory from 4 AM early this morning to 4 PM PST
     this afternoon for PZZ450-455.

     Small Craft Advisory until 4 AM PST Wednesday for PZZ475.

&&

$$

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