Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 211142
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
342 AM PST Sat Jan 21 2017

.DISCUSSION...Some light to moderate precipitation will continue
this morning as an upper level trough and associated weak front
slide north through our area. Portions of western and southern
Siskiyou County will pick up a few more inches of snow
accumulation, and a Winter Weather Advisory is in effect for these
areas through this morning. For the rest of the area, only light
rain or snow is expected through today.

The big event arrives later this evening and tonight. A deep trough
will dig in along the Oregon coastline, supporting a rapidly
deepening surface low just offshore. This system will differ from
the "classic" winds storms of our area, in that pressure gradients
will be more East-to-West than Northeast-to-Southwest, and this will
produce a more southerly to southeasterly flow. While gusty winds
are expected across the East Side, the lack of alignment with the
terrain is not likely to result in strong winds there, but the flow
will be aligned well enough to produce strong winds in the Shasta
Valley, and in the Rogue valley between Ashland and Medford.
Additionally, strong winds along and ahead of the occluding front
will cross the waters and impact the shoreline, particularly
between Brookings and Cape Arago. High Wind Warnings and Wind
Advisories have been issued for tonight into Sunday, and more
details are available in the significant weather message,
PDXNPWMFR.

Also, this storm will produce significant upslope flow into
Northern California, including the Siskiyou, Trinity, and Marble
Mountains, and the Mount Shasta region. Once again, very heavy
and wet snow is expected to fall in these areas, with up to a foot
or more possible in Mount Shasta City and McCloud, and along
Interstate 5, Highway 89, Highway 97, and several other area
passes and higher elevation roads. Meanwhile, lighter snow amounts
are expected across Modoc County, and into the Siskiyou and
Cascade Mountains in Southern Oregon. Numerous Winter Weather
Warnings and Advisories remain in place, and more details are
available in the Winter Weather Message, PDXWSWMFR.

Conditions will improve Sunday afternoon as the system wraps itself
up and weakens, but showers will continue across the area through
Monday night as the low slowly meanders its way to the south. The
region should begin to dry out by Tuesday morning as high pressure
builds overhead.  All signs point to this as the beginning of an
extended dry period that should persist through the remainder of the
forecast period. Skies will therefore be mostly clear, and
temperatures should see a gradual warming trend. However, as is
normal for high presure this time of year, valley inversions will be
strong, and fog is likely to form in many of our local valleys
overnight and persist into the mornings. -BPN


&&

.AVIATION...21/12Z TAF Cycle...Areas of MVFR cigs this morning
with scattered showers. There may be some isolated IFR vsbys in snow
showers over higher terrain and the east side.  All areas will clear
to VFR this afternoon, but not for long. Another strong front will
move in tonight.  This will bring gusty winds, and low level wind
shear will develop over the area, including KOTH, KRBG, and KMFR.
MVFR cigs will move in with rain, and the higher elevations will see
IFR conditions in snow.  LIFR conditions will develop in the Mount
Shasta area.  The lower conditions will continue into Sunday
morning.

&&

.MARINE...Updated 200 AM PST Saturday 21 January 2017...Very high
and steep seas will persist over the waters through the weekend.
Long period west swell will peak later today with combined seas 25
to 28 feet at 18 seconds. Winds will be south to southwesterly at
advisory level today, but another strong storm will deepen to sub-
970 mb along 130 West and move northward Saturday night into Sunday.
Storm force winds will develop offshore Saturday night with gales
over the remainder of the area. The wind over the inner waters are
now forecast to only reach gale force, so the storm warning has been
cancelled there. The storm force winds will diminish Sunday but
gales will continue everywhere into Sunday evening. Winds will
gradually subside Monday, but it will take a bit longer for the seas
to subside, which they will do on Tuesday.  The remainder of the
week looks to be relatively quiet, except for some moderate westerly
swell Wednesday night through Thursday night.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 1 AM to 7 PM PST Sunday for ORZ021-022.
     High Surf Warning until 10 PM PST this evening for ORZ021-022.
     Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
     Sunday for ORZ028.
     Wind Advisory from 10 PM this evening to 7 AM PST Sunday for
     ORZ026.

CA...Winter Weather Advisory until 11 AM PST this morning ABOVE 3000
     FEET for for CAZ080.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Sunday
     ABOVE 3000 FEET for for CAZ080.
     Winter Weather Advisory until 11 AM PST this morning for
     CAZ082-083.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Sunday
     for CAZ082-083.
     High Wind Warning from 7 PM this evening to 9 AM PST Sunday for
     CAZ081.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Sunday
     for CAZ081.
     Wind Advisory from 7 PM this evening to 9 AM PST Sunday for
     CAZ081.
     Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
     Sunday for CAZ085.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Sunday
     for CAZ085.

Pacific Coastal Waters...Gale Warning from 10 PM this evening to 10 PM PST Sunday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 10 PM PST this evening for
     PZZ350-356-370-376.
     Storm Warning from 10 PM this evening to 4 AM PST Sunday for
     PZZ370-376.

$$

BPN/JRS



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