Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...corrected 
National Weather Service Eureka California
627 am PST Sat Dec 3 2016

Synopsis...high pressure will continue to dominate today resulting
in dry weather conditions through tonight. A weak front will drop
down from the north on Sunday and bring a chance of rain by evening.
Cooler air and a chance of showers will follow Monday into Monday


Discussion...a ridge aloft will dominate and provide dry weather
conditions for northwest California today and tonight. Early
morning satellite imagery clearly showed a massive dome of warm
air aloft shunting storms to our north. The strong and dominating
ridge will flatten out on Sunday as a large scale trough in the
Gulf of Alaska slides southeastward toward the Washington coast.
The tail end of a shorter wavelength trough will clip the far
northern portion of the forecast area by Sunday afternoon and
evening. The highest chances and greatest rain amounts will be in
del Norte County. Up to half an inch is expected. This short-wave
will rapidly exit to our east Sunday night into Monday morning and
precip will wind down.

Another short-wave is expected Monday or Monday night. The latest
models have trended slower and drier with this next trough. Precip
potential has been adjusted accordingly, downward that is. This
short wave will not have much moisture and do not expect prolific
rain production. It will be colder with lower snow levels. There
is a chance for a mix bag of wintery weather over the mountain
passes Monday night. An inch or less may occur around 3000 feet on
the side of the Road on Highway 299 over Berry and BUckhorn
summits. Travelers over the mountain passes should stay alert.
Shallow instability and scattered showers will probably linger
into the early morning hours on Tuesday...mainly out toward the
coast. Ridging aloft and offshore flow will develop Tuesday night
and produce drying. Dry weather will hold through Wednesday.

GFS and European model (ecmwf) indicate broad flat ridging developing around mid
week in advance of a potentially wetter front. Both the GFS and
European model (ecmwf) indicate overrunning precip developing Wed night. This is
likely overdone. The models were in better agreement with a
surface front approaching on Thursday...with the bulk of rain
arriving Thursday night. There are still subtle variations and
timing difference. For one, the front may slow down or worse stall
and dissipate offshore. There is still plenty of time to ramp up
the precipitation potential as the event grows closer. Rain
amounts look run of the mill for December.


Aviation...VFR conditions are expected to persist through the
next 24 hours, with the exception of brief periods of MVFR ceilings
at cec and acv this morning as a weak cold front passes. Low clouds
are expected to scatter out before noon. Ceilings will gradually
lower along the Redwood coast overnight tonight as a cold front
approaches from the north. /Brc


Marine...a decaying northwest swell continues to maintain an
elevated sea state throughout the waters this morning, with some
steeper northerly wind waves south of Cape Mendocino where wind
speeds continue to hover at around 15 to 25 kt. Elsewhere, winds
remain generally light, and the sea state remains dominated by
swell. While local buoys indicate that the combined wave height
has remained relatively consistent through the night at around 9
to 11 feet, the forerunners of an approaching large swell are
beginning to appear as the dominant wave period has shifted to 20
seconds in some of the latest observations. This trend will
continue through the morning as this swell builds into the waters,
resulting in combined seas of around 14 to 17 feet with a dominant
period of 16 to 18 seconds by mid afternoon. This swell will
persist through the evening and subside slowly through the night,
settling back to around 10 feet 14 seconds by Sunday afternoon.

Late Sunday through early Tuesday, a series of passing cold fronts
will result in bursts of stronger northerlies throughout the waters.
While the northwest swell will continue to slowly decay, these
stronger winds will maintain an elevated and steeper sea state
through Tuesday. Winds will weaken considerably late Tuesday and
Wednesday and allow seas to settle.

An approaching cold front will result in strong to potentially gale
force winds late in the week. /Brc


Beach hazards...a large northwest swell will build into the waters
through the day today, resulting in large breaking waves in the surf
zone. Northwest facing beaches can expect to see breaking waves of
between 20 to 23 feet from late morning through late afternoon/early
evening. Wave heights will fall below 20 feet late this evening, but
will remain elevated through the night. /Brc


Eka watches/warnings/advisories...
California...high surf advisory from noon today to 10 PM PST this
evening for caz104-109. High surf advisory from 9 am this morning
to 7 PM PST this evening for caz101-103.

Northwest California coastal waters...Small Craft Advisory until
3 am PST Tue for pzz450-455-470- 475.



Visit US at http://www.Weather.Gov/Eureka

Follow US on facebook and twitter at:

For forecast zone information
see the forecast zone map online:

National Weather Service Glossary of Abbreviations