Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 202201

National Weather Service Eureka CA
201 PM PST Mon Nov 20 2017

.SYNOPSIS...Moderate to heavy rain will come to an end this
evening. A period of drier weather during Tuesday will be followed
by a wetter pattern Wednesday and Thursday. Another storm system
producing additional rain will be possible this weekend.


.DISCUSSION...A 180 kt anticyclonically curved upper jet was
positioned above a low-level baroclinic zone over the NERN Pacific
Monday afternoon. This configuration was yielding surface
cyclogenesis, with an associated warm front lifting north across
the coastal waters of NWRN CA. A zone of strong W-E oriented
moisture flux was occurring in the vicinity of the warm front,
and was aiding in the occurrence of moderate to locally heavy
rainfall from roughly Cape Mendocino north across the remainder of
Humboldt and Del Norte counties. An additional 1-3 inches of rain
will be possible over west facing mountain slopes through this
evening, particularly over Del Norte county. Thus, the areal flood
watch will be continued for the time being.

Model guidance shows the zone of strong moisture flux lifting
north away from the EKA CWA by 06Z Tuesday, which will cause rain
to decrease in coverage and intensity. This trend will continue
through much of Tuesday, with mainly dry conditions expected over
Mendocino county, and light orographic precipitation expected in
Humboldt and Del Norte counties. The occurrence of light rain
during Monday combined with partially clearing skies Tuesday night
could yield patchy valley fog in Mendocino county.

During midweek, model guidance shows remnants of an atmospheric
river spreading across NW CA, which will aid in increased
precipitation probabilities for the area. This will be followed by
the development of a surface frontal wave ejecting northeast
across the outer waters during the weekend. Moderate rain and
gusty winds will be possible with that feature.


.AVIATION...Overnight through today, a moderate at best, warm
storm system moved into Northwest California. This system brought
mostly light rain with periods of moderate-heavy rain loads.
Impacts at local air terminals/airfields included: Prevailing MVFR
cigs with CEC & UKI conditions frequently dipping and lingering
in IFR, gusty southerly winds mainly along the far North
Coast...including CEC and possible LLWS. Through the span of the
TAF period (late afternoon into Tuesday afternoon), improving
conditions as the rain extent diminishes, Cigs and VIS generally
lift, and the LLWS threat decreases. However, residual light rain,
low Cigs/Vis will persist across some local areas through early
morning. But still much of the significant weather impacting the
main air terminals will push north of the region into Tuesday
afternoon. /TA


.MARINE...Fresh to strong south-southeast winds are forecast
through mid week as a series of fronts move toward the west coast.
Models continue to indicate marginal gales (gusts to 35kt) around
and north of Cape Mendocino on Tuesday, as another warm front
lifts northward. The greatest coverage and longest duration of
gale force winds appears to be in the northern outer waters. With
seas forecast to hit 12 ft at 9 seconds by Tuesday evening, a
warning seems appropriate. Southerly winds and steep seas will
continue on Wed, before southerly conditions slacken up on Thu.
The wave models continue to indicate short period SW swell
impacting the coastal waters on Thu, however. Thus seas may still
be rough and uncomfortable. There is much more uncertainty come
Friday and Saturday regarding a longer period NW swell group. This
will need to be monitored for possible beach hazards and large
breaking waves in the surf zone.


CA...Flood Watch until 10 PM PST this evening for CAZ102-104>108.

     5 AM PST Tuesday for PZZ470.

     Gale Warning from 5 AM to 4 PM PST Tuesday for PZZ470.

     Small Craft Advisory until 4 PM PST this afternoon for PZZ455.

     Small Craft Advisory until 6 PM PST this evening for PZZ450.

     Small Craft Advisory until 4 AM PST Wednesday for PZZ475.



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