Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 051155
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
355 AM PST Mon Dec 5 2016
.SYNOPSIS...NWLY upper flow is forecast to persist through
midweek, and then transition to quasi-zonal/WLY during the second
half of the week. Before the transition takes place, a relatively
cold/dry airmass will spread S across NRN CA Monday-Wednesday,
only to be replaced by a warmer airmass Wednesday night into
Thursday as a cyclone progresses E across the NERN Pacific.
.DISCUSSION (MON-WED)...Post frontal NLYS are occurring across
the region Monday morning, and will aid in ushering a cold deep-
layer airmass SWD into NRN CA...with 700 mb temperatures cooling
to -10 to -15 C by Monday night. This will support snow levels
locally falling to 1500-2500 feet. As a result, several inches of
snow accumulation are likely over the high terrain in the NRN CWA
Monday night/Tuesday morning as a reinforcing low to midlevel
frontal zone focuses vigorous shower development. Showers are then
forecast to dissipate during Tuesday afternoon, followed by
partially clearing skies Tuesday night. Resultant enhanced
radiational cooling combined with weakening boundary layer winds
will support frost for coastal locations. Will continue to
evaluate for possible frost advisory.
.EXTENDED DISCUSSION (WED-SUN)...Forecast models still intent on
bringing in rain producing front late on Wed. Prior to that happening
however a very cool morning looks on tap for Wed as skies should be
clear and while some residual cold air remains over the interior
valleys. A frost advisory or possible freeze warning may be warranted
as morning lows of the high 20`s are likely. By thursday heights and
thickness`s gradually fall as another pacific low approaches the pacnw
coast. Forecast models have diminished rain amounts expected with the
Thursday system. Initially This feature was being progged to deliver
1-2 inches of rain along the coast and higher amounts across rain prone areas
however latest runs have dropped these numbers about 50% through thurs
night. So have reduced qpf values a bit with new forecast amounts being
.5 to 1 inch or so of rain along the north coast. On friday another front
may bring an additional bout of sustained rainfall for the region. Snow
levels look a little lower for friday but still should be above pass level.
after the front goes through a few showers are possible on friday with lower
snow levels. Forecast models still in flux for how sat and sun will be. One
model shows a fair amount of shower activity while the other keeps things
somewhat dry. Have kept a minimum of climo (30-40%) pops present for this
time period until things become a little more clear.
.AVIATION...A cooler and drier air mass settled over the region
overnight. The subsiding air has resulted in VFR conditions at the
coastal terminals. Patches of low clouds and fog may affect interior
valleys through the early morning hours. A weak secondary trough in
the cooler air will bring a potential for showers by this evening
and overnight. Some of the showers may produce ceilings around 2000
to 3000 ft out toward the coastal terminals through Tue morning.
VSBY`s may also be reduced to 4SM to 6SM in and around showers.
Otherwise VFR is expected through tonight.
.MARINE...NW swell has been running around 11 ft at 15 seconds this
morning. A small craft advisory remains in effect for all coastal
waters through Tuesday afternoon for seas at or above 10 ft.
Northerly winds will ease up today, primarily north of Cape Mendo,
as a weak trough approaches Pt St George from the NW. NW winds will
probably be gusty around 25 kt tonight after this trough passes to
our north and a mini-surge develops behind it. Overall winds appear
too low for a solid advisory. We will see a break in heavy seas and
winds Tue night as an offshore flow regime develops. Lower seas and
easterly wind should hold through the early morning hours on Wed.
A warm front will approach Northern California coastal waters from
the southwest on Wed. The GFS continues to be the fastest and
strongest with southeasterly winds ramping up to GALE on Wed.
A GALE WATCH has been hoisted for the outer waters starting 10AM
Wed. It will probably take til afternoon and evening for the
strongest winds to arrive. The wave generation with this storm will
be short period dominated. Steep short period waves around 10 feet
or more are expected Wed night into Thu.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 1 PM PST Tuesday for PZZ450-455-470-
Gale Watch from Wednesday morning through late Wednesday night
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