Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 231258
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
458 AM PST Mon Jan 23 2017
.SYNOPSIS...A cold storm sliding due south offshore the California
coast will generate scattered showers with snow showers above
2500 feet today and tonight. Dry weather will return on Tuesday as
the storm shifts to our south.
.DISCUSSION...A cold and conditionally unstable air mass will
continue to bring showers with snow above 2500 to 3000 feet today
through tonight. The shower activity overnight has been light
with the stronger and heavier showers confined to the coastal
waters. There has not been any lightning strikes since yesterday
evening, however a rumble or two of thunder will still be
possible today. Bands of showers pin-wheeling around the main
circulation center west of the Oregon coast will continue to
approach the coast the today. The GFS/ECMWF/NAM and even the HRRR
indicate an uptick in the precip activity this afternoon into this
evening as the vertically stacked low slowly sinks southward into
California offshore waters. The main thrust of precip looks to
shift south of the King Range and into coastal portions of
Mendocino county. There may be more storms this evening south of
the Cape and for now will add TSTMS only in the coastal waters.
The showers and storms have been weakening before making landfall.
The winter weather advisories have been hanging on by a thread.
The snow amounts for today and tonight do not support a
continuation of the advisory, with mostly 1 to 2 inches above
2500 to 3000 feet. With a slight uptick in precip expected this
afternoon, the advisory has been extended into the afternoon
hours. It may need to be cancelled if the strongest showers end up
staying over the coastal ranges.
The models were not in perfect harmony on the wrap around and
upslope precip late tonight as the low wobbles south of Cape
Mendocino. The coverage should decline later tonight into
Tuesday. Both the GFS and ECMWF indicate a sharp drop off in the
precip by early Tue. The NAM was wetter and has more wrap around
and upslope precip generation. Considering the differences in the
models and the wetter/wrap around precip of the 06z NAM, kept some
mention of showers into the early morning hours on Tuesday for the
eastern fringes of Trinity county and southern and eastern fringes
of Mendocino county.
Conditions will dry out through the day on Tuesday. Colder
conditions are in store for Tue night into early Wednesday before
clouds with a weak trough spread over the region.
Cloud cover will start to increase on Wed as a shortwave
trough moves over and through the upper ridge. All the models
were in good agreement with this occurring. The shortwave will
split apart and weaken considerably before reaching the area,
however some light precip will be possible as a surface front
edges closer to the coastline by Wed evening. The boundary will
probably stall and eventually dissipate offshore Wed night. With
the front stalling offshore, suspect we may still see some light
precip going into Thu morning. Ridging and drying should resume
later in the day on Thu.
The rest of the forecast period is looking quite dry as the ridge
aloft builds and an offshore wind flow dominates through the
period. With clear skies and light winds, it is very typical for
the interior valleys to cloud up and fog up during the night and
early morning hours. Another weak trough will move over the strong
ridge for the weekend, however current indications are for precip
to stay well to our north.
.AVIATION...Showers will continue to move onshore this morning into
this afternoon for all terminals. Crescent City and Arcata airports
have been reporting mostly VFR conditions overnight, while Ukiah
airport was seeing conditions fluctuating between MVFR/IFR. By this
evening, do expect the rain shower activities to diminish in
Crescent City and Arcata airports. With clearing skies and
relatively light rain, do expect low clouds and fog to form in the
area overnight. That can potentially drop them below VFR conditions.
For Ukiah, the showers will linger into tonight, and that will
keep them in MVFR/IFR conditions. /RCL
.MARINE...The most significant marine hazards today will be the
fairly high swell. Overnight, the offshore buoys have been reporting
wave heights of around 15 to 18 feet with wave periods of around 13
to 15 seconds. This is on the lower end of the Hazardous Seas
Warning. Do expect the westerly swell continue to move into the
coastal waters through tonight. Do expect the seas to build to 18 to
22 feet with wave period of around 15 seconds later today into this
evening. The seas will subside by early Tuesday morning to below the
Hazardous Seas criteria. The lower sea states will be in store from
Tuesday into Wednesday afternoon, before increasing again on
Winds won`t be as big of an issue compared to the last few days. We
will have south to southwest wind 10 to 20 kt with gusts up to 30 kt
in the coastal waters through early this evening, then the winds
will diminish and shift to the north by tomorrow morning. The north
wind will then continue into Tuesday night. After that, winds will
become light and variable as the pressure gradient over the area
become fairly weak. /RCL
.Beach Hazards/High SURF...The forecasted high surf is still on
track, in terms of the maximum surf heights of around 22 to 25
feet. However, the timing of the peak surf heights is delayed
slightly. Model guidance is now showing the highest surf will
arrive late in the afternoon into the evening hours. High surf
will subside late tonight. Kept the High Surf Advisory as is. /RCL
CA...High Surf Advisory until 4 AM PST Tuesday for CAZ101-103-104-109.
Winter Weather Advisory until 10 AM PST this morning for CAZ102-
NORTHWEST CALIFORNIA COASTAL WATERS...
Hazardous Seas Warning until 10 PM PST this evening for PZZ450-470-475.
Small Craft Advisory until 10 PM PST this evening for PZZ455.
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