Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 101216

National Weather Service Eureka CA
416 AM PST Sat Dec 10 2016

Rainfall will gradually decrease in coverage this morning. Showers
will remain possible through Monday for locations mainly along and
north of highway 36. As cooler air filters into the region, snow
levels will drop with some higher elevation snowfall possible.
Another approaching storm system will bring widespread rainfall back
to the region by the middle of next week.



(Today through Sunday)

Widespread rainfall blanketed all of northern California over the
last 18 hours, courtesy of a shortwave that is crossing the
region as we speak. Rainfall amounts have been fairly impressive,
with Del Norte County receiving 2 to 4 inches of rainfall, and
widespread amounts generally in the 1.5 to 4 inch range for the
remainder of the forecast area. Although the widespread rainfall
will continue to gradually shift off to our east during the
remainder of the morning, cooling temperatures aloft, daytime
heating, and several weak disturbances continuing to cross the
area will all point to a general light showery pattern continuing
through at least mid afternoon. The numerical models show this
general theme as well, before dry air advection and increasing
subsidence behind the last of the disturbances starts to play
more of a role. Although a few showers will remain possible
tonight, mainly for locations north of highway 36 after sunset,
any additional rainfall will be light and becoming increasingly
spotty as the night progresses.

Temperatures will remain nearly steady along the coast with some
moderation for interior locations. Decreasing cloud cover and
drier air will allow lows tonight to be several degrees cooler
than this morning.

It`s not out of the question that some higher elevation snow showers
could result in some travel issues across interior Del Norte County,
as the models show snow levels around 2500 feet, with 1 to maybe 3
inches of snowfall possible. We`ll continue to monitor this for any
potential Winter Weather Advisory.

(Sunday night through Friday)

The forecast continues to remain a challenge for the upcoming week,
as the models started to converge on a solution earlier today to
some extent, but, that increasing continuity trend hit a brick
wall with the afternoon and evening numerical runs. What they do
agree on is a shower start to the week, with rainfall potential
and coverage increasing by mid week, before decreasing by the end
of the week. Seasonably cool temperatures (especially at night)
will develop for portions of the week as well. That`s the "easy
part" of the forecast. Where things become more interesting is
trying to figure out which model will win out with the correct
synoptic pattern.

Taking a closer look at the 00z model runs, while the GFS and ECMWF
had similar mid and upper-level patterns, there were some subtle
differences than were seen in their surface solutions as well.
Namely, the GFS continues to suggest a weak shortwave ridge will
develop across our part of the state for the Monday Tuesday time
frame, before a weakening shortwave trough crosses the region in a
nearly zonal flow. As a result, it never really develops a
surface low nor any frontal features that would help focus the
low-level convergence and increase precipitation coverage and
intensity. Conversely, the ECMWF was less aggressive with the
weakening shortwave trough, and it even showed a pair of troughs,
with both surface low and warm frontal development. These
differences resulted in a more widespread precipitation signature,
with a few inches of rainfall possible, compared to a general
showery signal with the GFS and rainfall amounts remaining under
an inch, if not a half inch.

Luckily the tables may be turning as we speak, as the new 06Z GFS
has trended more strongly towards it`s European counterpart, with
both of them nearly lock step in the pattern and timing of what is
now portrayed for the middle to end of next week. Both show a series
of vort maxes crossing the northern half of the state in a zonal
flow with no ridge signature, and a deep fast-moving trough crossing
all of California for the end of the week. Also of note is a warm
front that develops Tuesday morning just south of the forecast area,
with this front making it into central Mendocino County before
stalling, as a 1007mb low treks east along it. Both models now show
widespread precipitation, with the heavier precip across Mendocino
into southern Humboldt and Trinity counties, and lighter yet still
widespread rainfall farther north.

As the mid-week wave passes by, the front will retreat to the south
before stalling again as yet another wave with moderate to heavy
rainfall is seen passing by. If later runs shift both of these
systems and their associated fronts further north, it could get
quite wet pretty quickly hear, and that`ll be another thing to keep
an eye on. /PD


MVFR TO IFR conditions and light winds will continue at KCEC,
KACV, and KUKI today. The lower conditions will be due to showers
moving across the region at times which will maintain reduced
ceilings and/or visibilities across the area.


Light to moderate winds will continue across the waters through the
middle of this next week. Seas will subside slightly today. A
northwest swell will propagate across the waters today and Sunday.
Showers will continue moving across the region at times tonight.
Winds and seas may increase in or near any showers. Seas will be
higher across the northern outer waters tonight. A Small craft
advisory will be in effect across the northern outer waters this
evening through Sunday afternoon due to elevated seas.


NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 6 PM this evening to 6 PM PST Sunday
     for PZZ470.



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