Area Forecast Discussion
Issued by NWS Eureka, CA

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718
FXUS66 KEKA 250006
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
406 PM PST Fri Feb 24 2017

.SYNOPSIS...Unsettled weather will continue for the next few days
as a series of cold low pressure systems impacts Northwest
California. Scattered showers will continue periodically through
Monday...with snow levels to as low as 1500 feet.

&&

.DISCUSSION...The first of these systems is currently centered
off the coast of Oregon at approximately 45 N and 128 W, and
slowly drifting southwards toward the California waters. While the
low center is still quite a ways away, the nose of an upper level
jet streak is currently moving onto the coast of Northwest CA,
and is providing a bit of forcing and upper level support for
shower development. This is in addition to the increasing thermal
instability, which is being driven by cold air aloft moving across
the relatively warm ocean waters. Considering that the airmass
already in place ahead of this system was somewhat cold to begin
with, the showers that have moved onto the Humboldt/Del Norte
coast this afternoon have exhibited relatively low snow levels,
with light snow falling to roughly 2000 to 2500 feet in elevation.
Given that the coldest air aloft has yet to arrive, and that
surface temperatures will naturally drop after sunset, snow levels
are expected to fall even lower overnight, possibly to as low as
around 1500 feet and periodically lower in some places. Meanwhile,
scattered to numerous showers will likely continue through the
night and tomorrow morning as the low passes along the coast,
eventually transitioning southwards into Mendocino county
tomorrow. Snow totals continue to look a bit lighter than
originally anticipated. However, light accumulations are still
expected through at least tomorrow morning at low elevations and
along many of the busier highway passes throughout the
region...particularly across Humboldt and Del Norte counties.

Showers will diminish from north to south through the day tomorrow
as the low pressure center moves south of the area and a
shortwave ridge moves overhead. However, another more potent storm
system will move in quickly behind it on Sunday, bringing with it
another round of showers and low elevation snow accumulations.
While there remains some uncertainty as to how much snow will fall
during this next round, current data indicates that this second
storm will be the stronger of the two with slightly higher
accumulations.

Showers will continue through Monday morning but gradually
diminish by Tuesday as a larger upper ridge gradually builds
across the west coast. This ridge will continue to build through
the end of the week, resulting in a gradual warming and drying
trend. /BRC

&&

.AVIATION...A cold and unstable air mass sliding southward
offshore the coast tonight will bring on and off showers to the
coastal terminals. Periods of low vsbys and ceilings are expected
in moderate to heavy showers. Conditions should improve on
Saturday as the low drifts south of the area. At UKI, conditions
will most likely remain vfr tonight, though some showers and
clouds may push over the coastal mountains late tonight and
produce brief MVFR ceilings.

&&

.MARINE...A cold and unstable air mass over Oregon offshore
waters will move southward tonight. Scattered showers and isolated
thunderstorms are expected tonight over our waters. Winds for the
most part with this low will be relatively weak. A surface trough
will develop offshore later tonight and E-SE gusts around 20-25kt
are expected. The low will drift south of Cape Mendo on Sat.
Fresh ESE breezes are possible for Mendo waters. Winds will slowly
shift around to the N-NW behind the low late on Sat before
another storm system drops down from the Northwest on Sunday.
Winds with this second storm will be slightly stronger, mainly
from the west and northwest after frontal passage. Current
indications are for winds to be borderline for an advisory.

A long period WNW swell will continue to decay through Sat. Short
period wave energy will also decay through Sat. Seas look to
remain under our criteria for an advisory. Another long period WNW
swell group will arrive Saturday night into Sunday. Even though
there will be short period wave energy present, there will be a
small risk for sneaker waves Sunday morning. Granted weather
conditions will not be great for going to the beach on Sunday,
with more rain and show knocking on our door steps. The NW swell
should intermingle with shorter period wave energy by Sunday night
and produce combined seas around 10 ft. An advisory for small
craft may be necessary.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory until 4 PM PST Saturday for CAZ102-
     104>106-108-110.

NORTHWEST CALIFORNIA COASTAL WATERS...None.
&&

$$

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