Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 091218
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
416 AM PST Fri Dec 9 2016

.SYNOPSIS...
A wet and cloudy pattern will persist over the next several days,
with periods of widespread rainfall keeping things moist and rather
fall-like. Onshore flow will and waves of energy passing by in the
atmosphere will also help maintain seasonal temperatures and
abundant cloud cover through much of the period.

&&

.DISCUSSION...

.SHORT TERM...
(Today through Tomorrow)

Light drizzle and rainfall has been fairly widespread across
northwestern California this morning. We expect this trend to
continue through at least lunchtime, before rain chances begin to
increase as a vort max crosses the region. By late afternoon,
widespread rainfall is expected to overspread the region from west
to east, with some of the rainfall becoming moderate to locally
heavy in intensity at times. In fact the model consensus shows
rainfall totals should range from near 3 inches across most of Del
Norte County, dropping to near 2 inches for Humboldt and Trinity
counties,and about 1.25 to 2 inches for most (if not all) of
Mendocino County. At this time, it looks like the "steadier period"
of rainfall will occur between 6 PM today and noon on Saturday.

The widespread rainfall will will keep temperatures in check, with
highs ranging from the mid 40s across the interior, to the mid 50s
along the coast. Lows tonight should cool into the upper 30s
(interior) to mid 40s (along the coast). Slightly cooler highs are
expected on Saturday, as somewhat cooler air filters into the region
behind the departing wave. Snow levels through Saturday afternoon
should remain at or above 5000 feet, with only Scott Mountain Pass
possible being affected by some wintry precipitation.

.LONG TERM...
(Saturday night through next Thursday)

A wet and unsettled period will dominate much of the upcoming week.
Cooler air aloft will continue to filter into the region for the
remainder of the weekend, with snow levels dropping to near 3000
feet for locations along and north of highway 36. Showers are
expected to develop. However, precipitation coverage and amounts
remain in question, precluding the need for a winter weather
advisory at this time, especially with it being a fourth or fifth
period event as it stands right now. However, this is something
we`ll continue to keep a weary eye on, as the snow levels could be
lower since the models under-forecast both the freezing levels and
depth of wet bulb cooling with the last event.

The forecast becomes more challenging for the work week portion of
the forecast, as model discontinuity increases with time. The GFS is
faster with a shortwave trough diving south along the California
coast, before having it turn east once it reaches the Bay Area, with
a mainly flat zonal flow from central portions of the state through
the Mid Mississippi Valley. It then has a decent mid-level low and
associated trough slowly approach the region from the west for the
end of the latter half of next week. With this solution, a mainly
showery or drizzle pattern is seen in its forecast for much of the
upcoming week, with roughly 1 to 3 inches of rain possible.

Conversely, the ECMWF never really develops a shortwave trough
through mid-week, and instead hints at a series or weak to moderate
in strength vort mazes passing by in a fast zonal flow through
Wednesday morning, before a brief shortwave ridge builds over the
area, ahead of an approaching trough/mid-level low, which it has
traversing the area while de-amplifying as it crosses our neck of
the woods in the Wednesday through thursday time frame. It does this
as the wave gets "kicked" ahead of a stronger trough dropping south
along the Pacific Northwest coast for the weekend. It also shows a
couple of surface lows passing by to our northwest, sending a warm
front northward across the region on wednesday, followed by a
prefrontal trough for Thursday evening, and a weak cold front Friday
morning. All of these features serve as a low-level focus, allowing
for more widespread precipitation to develop with heavier amounts.
This results in a general 4 to 8 inches of rainfall forecast through
the end of the work week.

While it`s way too early to get excited about any rainfall amounts,
as the "needle in the haystack" gets bigger the farther out one goes
in numerical forecasting, it`s important to note how subtle these
differences could have a more significant impact on our weather.
Stay tuned everyone,a s I`m sure the models will get their acts
together in the next few days, especially as the evolving pattern
gets better sampled by the upper air (RAOB) network. /PD

&&

.AVIATION...
MVFR TO IFR conditions and light to moderate winds will
continue at KCEC and KACV today. MVFR to IFR conditions and light
winds to calm conditions will continue at KUKI today. The lower
conditions occurring today is due to a cold front in the region
producing showers at times which will maintain reduced ceilings
and/or visibilities across the area.

&&

.MARINE...
Winds will gradually decrease today and tonight. Then light to
moderate winds will persist across the marine areas this week. Seas
will subside today. However a west to northwest swell will propagate
across the waters Saturday increasing the seas.  A weak cold front
near the waters will generate showers across the waters at times
today. A small craft advisory will continue across the northern
outer waters today due to short period seas. A Small craft advisory
is likely across the northern outer waters Saturday due to the west
to northwest swell increasing the seas.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 9
PM PST this evening for PZZ470.

&&

$$

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