Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 202316
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
316 PM PST Fri Jan 20 2017

.DISCUSSION...We`ll have a relative break in the action tonight into
Saturday in terms of strong winds and heavy precipitation. An upper
low off the Washington coast will continue to bring a moist onshore
flow over our area. Showers this evening into Saturday will be
mainly focused along the south coast, coastal mountains and western
Siskiyou county, but were not expecting excess rainfall totals.

A strong storm will affect southern Oregon and northern California
Saturday night through at least Sunday afternoon. The models are in
pretty good agreement with a surface low deepening near or just
inside of 130 W Saturday night then moving north along 130 W on
Sunday. There seems to be general agreement that we`ll see strong
winds over the waters, Shasta Valley, and east side. Some solutions
also show very strong winds along the coast and Shasta Valley. Given
the agreement in these aspects, the high wind watch has been
upgraded to a warning. Depending on the strength of the low, strong
winds may also develop in the Rogue Valley (Medford area) as well,
but confidence is much lower in that. Also the same applies to the
eastside, so we`ll leave the watched up for now in these areas. See
NPWMFR for more details.

This storm is also likely to bring another round of heavy snow to
most of Siksyou County, including Mount Shasta City. Heavy snow is
expected to arrive Saturday night and continue into Sunday
afternoon. In fact snowfall rates could range between 1-2 inches per
hour Saturday night through Sunday morning. Could not rule out
moderate to heavy snow in the Siskiyous and southern oregon
Cascades, including I-5 near Siksyou Summit, Mount Ashland Ski
area, Highways 66 and 140 near Lake of the Woods. Confidence is high
most of Siksyou County will get the brunt of the snow and have
upgraded the winter storm watch to a warning. Also winter weather
advisories have been issued for portions of the Siskiyous, Cascades
and Modoc County. Please see WSWMFR for more details.

The upper and surface low will gradually move south Sunday night
with continued showers. However the worst of the weather in terms of
rain, snow and wind should be over with. -Petrucelli

LONG TERM...Monday through Thursday Night...The long term period
begins with showers after the aforementioned system from the short-
term forecast discussion. These showers are expected to be much
lighter, but models are prolonging the showers to continue with wrap
around moisture as the low is now forecast to weaken and dip
southward into central California. Confidence is still relatively
low on this scenario as models are sowing wide disagreements on how
close the low will come to the coast and where it will make
landfall, with the GFS and NAM being the more progressive solutions
moving the low quickly into Central California. However, have
blended the previous forecast with the ECMWF which has held more
constant in run to run solutions (and generally performs better in
the long-term anyway).

There will be a break from the more active weather beginning as
early as Tuesday, and things should dry out. The cool weather is
expected to remain as a ridge builds in. This dry pattern is
expected to continue through the rest of the week despite the ECMWF
and the Canadian models showing a dying front approaching the Oregon
coast by Wednesday night into Thursday. Have bumped up pops
slightly, as per the ECMWF; but still show the silent 10% chances
for the coast and coastal range.

The tricky part of the forecast regards the possibility for air
stagnation. Easterly winds are expected to be light across the
entirety of the forecast area after Tuesday, but this front could
help mixing just enough to prevent air quality problems. This dying
front will need to be monitored in

&&

.AVIATION...20/18Z TAF Cycle...CIGS will occasionally lower to MVFR
today as showers move across the area with partial mountains
obscuration. MVFR cigs are expected to be widespread tonight in low
clouds. Another front will move inland Saturday morning, and will
lead to gusty south winds at the coast and SE winds up to 30 knots
in the Shasta Valley and the Klamath Basin. The front will also
bring widespread MVFR cigs/vis to the Klamath Basin and
Siskiyou/Modoc Counties with occasional IFR conditions in moderate
snow. /FB


&&

.MARINE...VERY HIGH AND VERY STEEP SEAS WILL PERSIST OVER MUCH OF
THE WATERS THROUGH THE WEEKEND. LONG PERIOD WEST SWELL WILL BUILD
SEAS TO A PEAK NEAR 30 FEET LATE TONIGHT INTO SATURDAY. ANOTHER
STRONG STORM WILL DEEPEN AND MOVE NORTH ALONG 130 WEST SATURDAY
NIGHT INTO SUNDAY BRINGING STORM FORCE WINDS AND DANGEROUS SEAS.
WINDS WILL GRADUALLY EASE BY MONDAY. THE HIGH SEAS WILL GRADUALLY
SUBSIDE BY TUESDAY.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ029>031.
     High Wind Warning from 1 AM to 1 PM PST Sunday for ORZ021-022.
     High Surf Advisory until 10 PM PST this evening for ORZ021-022.
     High Surf Warning from 10 PM this evening to 10 PM PST Saturday
     for ORZ021-022.
     Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ028.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for ORZ028.
     High Wind Watch from Saturday evening through Sunday afternoon
     for ORZ026.

CA...High Wind Watch from late Saturday night through Sunday
     afternoon for CAZ084-085.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for CAZ080-081.
     Winter Storm Warning until 4 PM PST this afternoon for
     CAZ080>083.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday for
     CAZ082-083.
     Winter Weather Advisory until 4 PM PST this afternoon for
     CAZ080-081-083.
     High Wind Warning from 10 PM Saturday to 4 PM PST Sunday for
     CAZ081.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for CAZ083.
     Winter Weather Advisory until 4 PM PST this afternoon for
     CAZ085.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for CAZ085.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday for
     CAZ085.

Pacific Coastal Waters...Storm Warning from 7 PM Saturday to 1 PM PST Sunday for
     PZZ350-356-370-376.
     Gale Warning from 7 PM Saturday to 10 PM PST Sunday for
     PZZ350-356.
     Hazardous Seas Warning until 7 PM PST Saturday for
     PZZ350-356-370-376.
     Gale Warning from 1 PM to 10 PM PST Sunday for PZZ370-376.

$$



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