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Area forecast discussion 
National Weather Service Medford or
329 PM PST Thursday Dec 25 2014

Short term...tonight through Sunday night. The main item of
interest in the short term is a light snowfall expected between
Saturday evening and Sunday night with the snow level falling from
around 4000 feet to around 2000 feet.

A shallow moist layer is producing a mainly broken cover of middle-
level clouds this afternoon with a few snow flurries lingering on
northwest facing slopes of southwest Oregon. These flurries will
not produce more than a dusting of snow above 2500 feet. Through
tonight there will be little change in the pattern with our area
between a strong ridge offshore and low pressure well to the east.
Overnight valley low clouds will increase...especially in
southwest Oregon with a few patches of early morning fog possible.

The valley low clouds will gradually dissipate during Friday morning
with skies becoming mostly sunny. The air mass will stabilize
Friday night and produce a more widespread and lower ceiling of
valley stratus with areas of fog and freezing fog into Saturday

A low pressure trough tracking over the top of the Pacific Ridge
will reach Vancouver Island early Saturday and move relatively
quickly across Washington and eastern Oregon during the day. The
trough will then slow down on Sunday and settle over the Great
Basin. This trough will swing a cold front across the area as well
as trailing shortwave disturbances to produce a light snowfall.
Totals look to be around 1 to 4 inches during the 36 hour period
from Saturday evening through Sunday night on the area of
focus...eastern Douglas County, northern Klamath County, and
extreme northern Jackson County. Also, up to 2 inches of
accumulation is likely elsewhere east of the Cascades. The snow
level will begin around 4000 feet Saturday evening then it is
forecast to fall to around 2500 feet overnight and settle around
2000 feet for Sunday. There is good model consistency regarding
the front on Saturday night but less so regarding the timing and
position of individual shortwave disturbances that will produce
additional snow showers on Sunday through Sunday night. All in
all, snowfall looks to be highest in the Oregon Cascades from near
Diamond Lake Junction northward.

Long term...Monday through Thursday. Models are in remarkably good
agreement through the extended. The extended starts with a back door
slider moving down the the Great Basin bringing precipitation to mostly the
east side as it digs to the south. By Tuesday morning the upper low
is in central California with an upper ridge nudging over the top an
offshore flow spilling the very cold air mass in the Great Basin
over the Cascades. This pattern remains in place through most of the
extended. This is a typical freezing fog pattern for the west
side...especially with the abundant ground moisture and relatively
warm soil temperatures...but with the cooler air mass aloft there
may be sufficient mixing to clear things out briefly in the
afternoons. Models are indicating that the upper low then shifts
east with the ridge weakening ahead of a front that comes in late
Thursday. But with the pattern almost setting up as a Rex block
prior to that...confidence is low on this pattern change for the
tail end of the extended period. Sven


Aviation...for the 25/18z taf cycle...VFR ceilings with mountain
obscurations prevail across the region with cumulus building as we
approach maximum heating. This deck will lower and spread Post sunset
with widespread MVFR ceiling with mountain obscurations west of the
Cascades. Flow becomes offshore by late tomorrow afternoon brining
clearing to the ridges with west side valleys seeing widespread MVFR
to IFR ceilings and fog likely. Sven


Marine...updated 1000 am PST Thursday Dec 25 2014...northerly winds
will continue to diminish into Friday. Moderate wind waves will
combine with a westerly swell to produce high and steep seas into
this evening. Offshore high pressure is rebuilding and will
persist into the weekend. Winds and seas reach a minimum on Friday
then northerly winds will increase again during the weekend. Seas
may become steep early next week. Sven


Mfr watches/warnings/advisories...


Pacific coastal waters...Small Craft Advisory for hazardous seas until
8 PM PST this evening for pzz350-356-370-376.



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