Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 152258

Area Forecast Discussion
National Weather Service Medford OR
258 PM PST Fri Dec 15 2017

.SHORT TERM...Tonight through Monday night...Current observations
show a band of light precipitation running across the Umpqua
Basin and diving southward. This will work to lower temperatures
and snow levels through evaporative cooling. That being said, snow
levels will stay above the valley floors, but elevations above
2500 feet may see a few snow flakes in post-frontal showers
tonight. All of the passes will pick up some snow, but it appears
as if the snow will be pretty light. In addition, the west-side
valleys reached above freezing before the rain began, so the
threat of freezing rain which was advertised yesterday has

The post frontal showers will continue through tonight before a
weak ridge of high pressure sets back up. A very weak inversion
may set up, but it`s more likely that west side valleys will see
low clouds instead of any fog tonight. For the rest of the
weekend, however, the high pressure will continue to build and the
inversions may become somewhat stronger, particularly south of the
Umpqua Basin. Fog and low clouds will be possible for both Sunday
and Monday morning. Despite the building high pressure system, the
frontal system today will preclude the necessity for another air
stagnation advisory for the weekend.

A more active weather pattern appears as if it will stay to the
north of our forecast area this weekend. This means that the
Umpqua Basin may see cloudiness not associated with valley
inversions, but overall rain chances will remain minimal. -Schaaf

.LONG TERM...Coming soon.


.AVIATION...15/18Z TAF CYCLE...Conditions have dropped to LIFR in
west side valleys. A front is slowly making its way into the
area, which will bring precipitation to the coast and west side
valleys. The front will shift winds to north or northwesterly, and
will cause enough mixing to bring cigs to MVFR in west side
valleys. The main challenge is timing the frontal passage.
Observations show the front progressing slightly slower than
expected... current thinking is the front will pass over the west
side mid afternoon. Freezing levels will drop several 1000 feet
behind the front. Late this evening, snow levels will drop to 4000
to 4500 feet east of the Cascades, which could mean some snow at
KLMT...any accumulation will be less than half an inch. However
snow showers will diminish visibility. A ridge of high pressure
will begin building early Saturday morning, and ample available
moisture should cause conditions in west side valleys to drop to
IFR... possibly LIFR. Uncertainty comes from the fact that there
may still be some low level mixing to stave off fog. -MSC


.MARINE...Updated 330 PM PST Friday 15 Dec 2017...Moderate to
strong north winds will continue into this evening, strongest
winds and steepest seas south of Cape Blanco. Winds will weaken
slightly overnight. High pressure offshore and a coastal thermal
trough will develop Saturday, bringing gusty north winds south of
Cape Blanco. Winds will be strongest south of Gold Beach into
Sunday morning. A stronger low pressure system will approach the
marine area Tuesday... ramping up south winds and wind waves, with
heavy west swell. -MSC




Pacific Coastal Waters...Small Craft Advisory until 4 AM PST Sunday for PZZ356-376.


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