High Wind in Oregon, December 27, 2016

Area Forecast Discussion
National Weather Service Medford OR
317 AM PST Tue Dec 27 2016

.DISCUSSION...A cold front is approaching the coast and will
support valley rain and mountain snow mainly in areas along and
west of the Cascades. The heaviest precipitation is expected in
the Cascades and the Coast Range with significantly less
precipitation in valleys.

There are some valley locations in Josephine and Jackson Counties
with temperatures at or near freezing this morning, so we have
included a mix of rain and snow for portions of the Rogue, Bear
Creek, Applegate, and Illinois Valleys through the early morning
hours. Travelers should be cautious and on the lookout for some
slick spots, especially on bridges or highly-shaded areas where
road temperatures could be near freezing. Observations suggest
that most major roadway temperatures in these valleys are above
freezing this morning.

Strong upslope westerly flow, peaking this morning and afternoon
with 60 kt 700mb winds, will support periods of moderate to heavy
snow in the Cascades mainly north of Highway 140. The consensus of
models suggest the heaviest snow will occur this morning and early
afternoon then taper off tonight. A Winter Weather Advisory has been
issued for this expected snowfall and impacts to travel in the
passes. Gusty to strong west winds will accompany this snowfall
in exposed locations of the Cascades. Strong winds will also
impact portions of the East Side to include mainly Highway 31 from
Paisley to Summer Lake. A High Wind Warning and Wind Advisory at
NPWMFR has been issued to highlight these winds.

As the front moves away from the area, morning fog and freezing fog
chances will increase by Wednesday morning but moreso on Thursday
morning with clearer skies and some ridging aloft.

The next front, a fast-moving one, will arrive on Friday bringing
with it some generally light precipitation and a sharply colder
air mass. This front sets the stage for a cold low and moisture
moving in from the north late in the weekend, and the potential
for low elevation snowfall. We have nudged snow levels down early
next week based on good model agreement on a very cold pattern.
Please see a shortened version of the previous extended discussion
below for more details on this potentially high-impact cold
system.

Friday Night through Monday...The upper trough will follow on a
south to southeastward track Friday night...generally along shore
with the axis of the trough. The ECMWF forecast snow levels are
not as low as the GFS, but it does catch up a bit to the
GFS...around 6 hours slower with the center of what is forecast to
become a closed low. Forecast snow levels were lowered to around
2000 to 2500 feet with isolated to scattered post-frontal showers
and snow showers...with accumulations likely in the ballpark of 1
to 3 inches.

The models have been consistent in timing a break between systems
during the day on Saturday. The main weather item of interest on
Saturday would be the possibility of areas of morning valley
low clouds and freezing fog.

A second cold upper trough is expected during the latter portion of
the weekend and may produce a more significant accumulation of
low elevation snow Sunday into Monday. The highest probability is
for a frontal passage on Sunday then lingering post-frontal
showers and snow showers Sunday night into Monday. As is common,
model differences increase for day 6 and 7 of the forecast.
Compared to the Friday/Friday night trough, it may take a more
southeast rather than southward track and the trough may linger
longer over the region. There is a potential for snow levels
around 2000 feet on Sunday falling to as low as 1000 feet msl
early Monday. -DW/SK

&&

.AVIATION...27/06Z TAF CYCLE...There is a slight chance for some
mixed rain and snow in portions of West Side valleys this morning
due to temperatures hovering around freezing and light
precipitation possible. Instability and increasing clouds
associated with a front will preclude any stratus/fog, but MVFR
and local IFR conditions are expected over the area as the
precipitation increases in the morning and continues through the
day. MVFR will be most widespread along the coast and in the
Umpqua with areas of MVFR elsewhere from the Cascades west. The
east side should remain VFR through early tonight, but some snow
with MVFR conditions will be possible late in the night and
through the morning at KLMT. -CC/SK

&&

.MARINE...Updated 830 PM PST Monday 26 December 2016...A frontal
system will bring moderate south winds and steep to very steep wind
driven seas early this morning. The worst conditions will be
observed from Gold Beach north early this morning as the front
nears the shore. The front moves onshore later this morning, and
winds turn more westerly and diminish. However, a large, long
period west swell will follow quickly behind the front, and this
swell will keep seas elevated and dangerous to small craft for the
remainder of the week. Models are indicating the potential for
additional strong frontal systems next weekend and early next week
along with the possibility of a very large swell. Confidence in
unsettled weather in the extended period is increasing, but
mariners should monitor forecasts for updates the weekend
approaches. -CC/SK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 AM PST Wednesday for ORZ030-031.
     Wind Advisory until 4 AM PST Wednesday for ORZ030-031.
     Winter Weather Advisory until 4 AM PST Wednesday for ORZ027-028.

CA...High Wind Warning until 4 AM PST Wednesday for CAZ085.
     Wind Advisory until 4 AM PST Wednesday for CAZ085.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 4 PM PST Saturday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 7 AM PST this morning for
     PZZ350-356-370-376.

NSK/DW/CC