Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 090429
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
829 PM PST Thu Dec 8 2016

.DISCUSSION...A relatively quiet and warm night, compared to last night,
is shaping up over the forecast area. A frontal boundary is
lingering over the forecast area tonight, and broad overrunning
will yield a good chance for precipitation over Southern Oregon
and Northern California. Snow levels are generally 5000-6000 feet
tonight, and with precipitation of light to moderate intensity, we`re
not expecting much in terms of snowfall impacts.

Winds will remain gusty through the morning in the Shasta Valley and
portions of the East Side. In fact, a solid 50kt 700mb flow
continues through Friday evening, so expect high terrain areas and
the Summer Lake area to remain breezy to windy through that time.

Weather will remain generally wet with gradually lowering snow
levels over the weekend. Please see the previous discussion below for
more details on the active weather pattern.

&&

.AVIATION...09/00Z TAF CYCLE...Moist, onshore flow will keep lots of
clouds and showers going over the west side. Cigs and vis will be a
mix of VFR and MVFR this evening but with some IFR mixed in, mainly
along the coast. On the east side there are fewer showers, but
similar cigs. Conditions are expected to worsen overnight,
especially in the valleys as the airmass cools, clouds lower, and
some fog/mist develops. Conditions will improve tomorrow afternoon
as clouds and cigs lift, but increasing showers may bring worsening
conditions again late afternoon and evening. -Wright

&&

.MARINE...Updated 230 PM PST Thursday 8 December 2016...Low pressure
has moved north of us, and winds are diminishing. As a result, the
gale warning has been canceled. Winds will ramp up again tomorrow as
another low pressure system moves by to our north, but winds are
still expected to remain below gales. Seas are also lowering this
afternoon, but the combination of continued wind wave and increasing
fresh swell will keep seas elevated through Friday, especially over
the waters north of Cape Blanco where wind waves will be higher.

Models continue to struggle with an incoming west swell Friday night
and Saturday, but all guidance still shows a large enough swell to
keep the Hazardous seas watch going. Once this shows up on buoys
further offshore, we will be able to get a better handle on it and
adjust our headlines accordingly. For now, it just bears watching.

Whatever ultimately becomes of Saturday`s swell, relatively calmer
weather is expected for Sunday through early next week. The storm
track may become active again later next week. -Wright

&&

PREV DISCUSSION... /Issued 310 PM PST Thu Dec 8 2016/

SHORT TERM...Tonight through Sunday night.
Temperatures have warmed up above freezing for most locations.
The only holdout is east of the Cascades, but even then a few
locations in the higher elevations are starting to warm up some. I
still could not rule out some light snow showers in northern
Klamath and Lake County, the bulk of the precipitation and coldest
air mass is north ofthe area. Currently we still have a winter
advisory out until 4 pm pst and given temperatures are still below
freezing in the areas that are affected and spotty precipitation,
we`ll continue to let that ride.

The high res short range models suggest we`ll catch a break in the
weather tonight. A few showers will continue to persist mainly west
of the Cascades, but this will likely be a high pop/low QPF event.
Suspect the NAM and GFS may be a bit overdone given they hint at
weak ridging tonight. So have adjusted QPF amounts down and kept the
higher amounts in the northern Cascades and south Coastal mountains.

The pattern will remain active through the weekend with a persistent
fast, moist west flow aloft. In fact 300 mb winds near or over 100
kts will remain near or over the area. Showers will be on the
increase during the day Friday, mainly west of the Cascades and this
will continue into Friday evening. Snow levels are expected to hover
between 5000 and 5500 feet, therefore snow should be mainly confined
to the higher terrain like Diamond Lake and Crater Lake.

The models show a good slug of moisture associated with a wave of
low pressure moving into Northern California and Southwest Oregon
overnight Friday into Saturday. Right now it does not look like snow
levels will stay above Mount Shasta, but there`s a chance portions
of highway 97 northeast of Weed could get some accumulating snow.

A cold front will move through Saturday as the wave of low pressure
moves east, but precipitation should be on the decrease from north
to south. Meanwhile valley rain and mountain snow showers will
persist mainly along and west of the Cascades Saturday through
Sunday. -Petrucelli

LONG TERM...Monday through Thursday.

Day-to-day model consistency regarding Monday is low to moderate.
The trend is to have a lower amplitude upper level pattern and also
a slower evolution of the pattern. There was concern yesterday for
an atmospheric river affecting our area Monday night into Tuesday.
This concern has diminished with a higher probability that our
region will instead be affected by a colder but weaker northern
stream of the upper level jet. The warmer/stronger/wetter system is
now indicated by both the GFS and ECMWF to be aimed at the San
Francisco Bay area and central Sierra Nevada early Tuesday through
Tuesday night. During that time...a cold but weak upper level trough
is likely to track across Washington and northern Oregon. That will
place a chance of light showers/snow showers across our area with
the highest probability across Douglas County and northern portions
of Klamath and Lake Counties. High temperatures and snow levels have
been adjusted a bit lower with levels most likely to be around 3000
to 4000 feet.

Uncertainty increases on Wednesday. The 12Z GFS is less aggressive
than the ECMWF with ridging over southern California and the 18Z GFS
even more so. The GFS solution would keep nearly all of the
precipitation aimed south of our area...perhaps brushing southern
Siskiyou County. Meantime, the ECMWF indicates the flow aloft to
back from west to southwest with a more progressive pattern sending
significant amounts of precipitation into our area. The air mass
would also warm in this scenario with snow levels increasing to
around 4500 to 5500 feet.

Confidence is low in the forecast for day 7/Thursday. The
aforementioned system may still be affecting our area or the area
may be in a cooler post-frontal regime of light showers/snow showers.
-DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 1 AM PST Friday for ORZ030-031.

CA...High Wind Warning until 1 AM PST Friday for CAZ085.
     Wind Advisory until 4 AM PST Friday for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 4 PM PST Friday for PZZ356-376.
     Hazardous Seas Watch from Friday afternoon through Saturday
     afternoon for PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 4 PM PST Saturday
     for PZZ356.
     Hazardous Seas Warning until 4 PM PST Friday for PZZ350-370.

$$

NSK/DW/TRW


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