Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 161210

Area Forecast Discussion
National Weather Service Medford OR
410 AM PST Wed Jan 16 2019

Updated AVIATION Section

.DISCUSSION...A relatively weak trough is moving through the
forecast area this morning. South to southeast winds remain
breezy, including in the Rogue and Shasta Valleys, as this initial
trough continues through. Radar shows some light precipitation
stretching from around Crater Lake southeast to Lakeview/Adel with
snow levels hovering around 4500 feet. This band will continue
moving from southwest to northeast, bringing some light snow to
the northeastern portions of the forecast area. Amounts should
remain below advisory criteria, but if you are traveling through
these areas this morning be prepared for wintry travel. Additional
precipitation is moving into Siskiyou and Modoc counties, and
snow levels are hovering around 3500 to 4000 feet, so expect some
wintry travel there this morning as well. All in all we`re only
expecting around 1 to 2 inches through late this morning with this
initial trough, with up to 3 inches possible in higher elevations.

The main event moves in later this morning/early afternoon, and
winds and precipitation will increase as this next stronger system
moves towards the Oregon Coast today. Strong southerly flow will
bring ample amounts of moisture to portions of Northern California
and the Coast/Coast Range, while other areas will remain relatively
dry. Valleys both west and east of the Cascades will see
significantly less precipitation as strong winds bring the drying
effect of downsloping off the surrounding higher terrain. Winds will
increase late this morning and peak this afternoon and evening. Wind
advisories and High Wind warnings remain in effect for these strong
winds, and details can be found at NPWMFR.

Snow levels will hover around 4000 to 4500 feet through this
morning, then rise to around 4500 to 5000 feet. Periods of moderate
to heavy snow are expected later this morning into Thursday morning,
especially for the higher terrain of Siskiyou County. Winter weather
products have been issued for this, and details can be found at
WSWMFR. The heaviest precipitation is expected Wednesday afternoon
and evening, and rainfall rates will approach 0.50" per hour in the
South Central Siskiyou County area. We`re not expecting the highest
rainfall rates to impact burn scars, and we don`t expect significant
snowmelt given the moderate-height snow levels, so we haven`t issued
any flood products at this time. The main rainfall impacts will be
some ponding on water on roadways below 4500 feet and some rises in
local streams and creeks.

Although conditions will improve some Thursday, breezy conditions
and showers will continue through at least Thursday evening. A warm
front will nudge into the area Friday into Saturday as upper level
ridging builds. Saturday into Sunday is looking like it could be
quite a wet period for the area. Models are showing an atmospheric
river taking aim at the coast Saturday morning and continuing into
Sunday night. Details will change as we get closer to the time, but
current indications show around 3 to 4 inches possible in the
coastal range of Curry County during this time. Beyond this event,
models show high pressure building off the Pacific Coast early next
week with dry conditions persisting through next week. /BR-y


.AVIATION...For the 16/12Z TAFs...LIFR fog/low cloud is impacting
Roseburg again this morning. This should lift faster than it has
though the last few mornings as winds aloft increase in advance of a
frontal system moving in from the Pacific. While still mainly VFR
elsewhere today, there will be increasing areas of mountain
obscuration and lowering ceilings. Steadiy precipitation will be
focused in the Mount Shasta region, western Siskiyou County and the
SW Oregon coast ranges, where MVFR to IFR will prevail with terrain

Gusty south to southeast winds, perhaps exceeding 30 knots, will
affect the Rogue and Shasta Valleys as well as the east side.
Strongest gusts will be this afternoon and evening prior to the
front moving inland. Expect plenty of turbulence on
departures/arrivals for all terminals. Offshore flow in advance of
the front will block the strongest winds from surfacing at North
Bend much of the TAF period, but this may result in a period of low-
level wind shear this evening. -Spilde


.MARINE...Updated 200 AM PST Wednesday 16 January 2019...South winds
and seas will increase today as a front moves in with gales are
expected to develop this afternoon. Seas then rapidly and
substantially increase tonight into Thursday ahead of a much
stronger front with gales and a very high long period southwest
swell. Seas will likely peak in excess of 30 feet Thursday. These
very hazardous conditions are being driven by deep low pressure
located near 40N 141W that will move east-northeastward well
offshore, but close enough to bring the strong front through
Wednesday night into Thursday. After the peak in seas Thursday, seas
remain very high with dangerous bar conditions into Friday. Yet
another front is likely to bring additional gales and very steep
seas Friday night into Saturday. The active pattern will persist
through the weekend.

Seas will remain very high Thursday night through Friday morning as
weak high pressure briefly builds into the area. With a long period
and very high swell, there will be hazardous surf conditions
Thursday through Friday. Please see the Coastal Hazard Message
/PDXCFWMFR/ for more information on the impacts and timing.

Improving conditions are expected with high pressure building in
from the southwest early next week. -Spilde


OR...Wind Advisory from 7 PM this evening to 4 PM PST Thursday for
     High Wind Warning from 1 AM to 4 PM PST Thursday for ORZ021-022.
     High Surf Warning from 7 AM Thursday to 4 PM PST Friday for
     Wind Advisory from 10 AM this morning to 1 AM PST Thursday for

CA...Wind Advisory from 7 PM this evening to 4 PM PST Thursday for
     Winter Weather Advisory until 10 PM PST Thursday for CAZ080>083.
     Winter Storm Warning until 10 PM PST Thursday above 5500 feet in
     the for CAZ082.
     High Wind Warning from 10 AM this morning to 1 AM PST Thursday
     for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 1 PM PST this afternoon for
     Gale Warning from 1 PM this afternoon to 4 PM PST Thursday for
     Hazardous Seas Warning from 4 PM Thursday to 10 AM PST Friday
     for PZZ350-356-370-376.


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