Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 191212
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
412 AM PST Fri Jan 19 2018

.SYNOPSIS...Showers will persist across the region through
Friday. These showers combined with cold air aloft will yield
mountain snow and possibly coastal hail. A brief period of drier
weather is expected to occur during Saturday, followed by another
round of rain on Sunday.

&&

.DISCUSSION...A cold upper trough (500 mb temperatures below -30C)
was approaching NWRN CA Friday morning. Increasing ascent and
destabilization occurring with the approaching trough was
yielding widespread shower development (as well as offshore
thunderstorms). These showers are expected to produce several
inches of snow for elevations above 2500 feet, as well as sporadic
instances of accumulating hail across coastal roadways. Showers
are forecast to dissipate tonight into Saturday as midlevel
heights rise and temperatures warm aloft. However, this period of
dry weather will be short-lived as another trough enters the
region Saturday night and Sunday.

A zone of augmented WSWLY moisture flux will subsequently impact
the coast of NWRN CA south of the previously mentioned trough. A
robust zone of precipitation will occur as a result, with highest
precipitation rates occurring along WSW facing terrain. In
addition, a subfreezing airmass will be in place over ERN Del
Norte and Humboldt counties, and much of Trinity county. Thus,
accumulating snow appears probable for elevations above ~3000
feet. Snowfall totals may be headline worthy along highway 3 from
roughly Trinity Center to Scott Mountain Summit, as well as
portions of highway 36 in southern Trinity county.

Beyond Sunday, an active/wet pattern is anticipated as another
frontal system moves across the region Monday night/Tuesday,
followed by a second disturbance on Wednesday. By the end of the
forecast period (day 7/day 8), model guidance hints at a long wave
pattern that may support the development of an atmospheric river
tapping into subtropical moisture. However, the details with that
evolution are far from certain.

&&

.AVIATION...Scattered convective showers will continue to impact
most terminals through the next 24 hours, particularly at coastal
terminals like CEC and ACV. Brief periods of heavy rain and low
ceilings will likely result in periodic reductions to MVFR
categories, with prevailing VFR conditions expected otherwise.
Occasional bouts of IFR visibilities and ceilings will be
possible for very brief periods in the vicinity of the strongest
showers, as will brief periods of small hail and minor
accumulations on runways. Showers will be less frequent at UKI,
but periodic MVFR ceilings and occasional scattered IFR low clouds
will be possible here as well. /BRC

&&

.MARINE...Westerly swell continues to dominate the waters early
this morning, although wave heights have largely dropped to 16 to
18 feet, 15 seconds at all local buoys. Meanwhile, moderate
westerly breezes continue to blow generally in the same direction
as the swell, perhaps with a few wind gusts to 25 or 30 kt in the
vicinity of stronger convective showers. This will more or less
continue through Saturday, although winds will gradually veer to
the northwest early Saturday. As a result, wave heights will very
slowly decrease in height through early Saturday, then decrease
more noticeably late Saturday as winds weaken to around 5 or 10
kt. Still, Wave heights are not expected to drop below 10 feet at
any point over the weekend. Hazardous seas warnings will continue
through Saturday morning for now, although this may be downgraded
to a Small Craft Advisory a little bit ahead of schedule if wave
heights continue to fall at their current rate.

On Sunday, an approaching cold front will bring another round of
strong southerly winds, perhaps reaching Gale Force across the
outer waters. At the same time, a reinforcing surge of westerly
swell will arrive, resulting in a chaotic and hazardous sea state
that will last through at least early Monday morning. Decreasing
winds will allow seas to settle through early Tuesday, but this
active pattern will continue with another cold front later
Tuesday. /BRC

&&

.HIGH SURF...While westerly swell continues to result in large
breakers along area beaches, breaking wave heights continue to
steadily fall. The High Surf Advisory will be allowed to expire at
11 AM today, but beachgoers are urged to continue to exercise
caution as breaking waves will remain relatively large through early
Saturday. /BRC

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 11 AM PST this morning for CAZ101-103-
     104-109.

     Winter Weather Advisory until 7 PM PST this evening for CAZ102-
     105>108.

NORTHWEST CALIFORNIA COASTAL WATERS...Hazardous Seas Warning
     until 10 AM PST Saturday for PZZ450-455- 470-475.

&&

$$

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