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Area forecast discussion 
National Weather Service Medford or
353 am PST Monday Dec 29 2014

Discussion...have been watching satellite and radar imagery
early this morning, and have noted a large area of showers
streaming off the Pacific. As expected, this precipitation is
beginning to push south into Douglas County, and will be the major
producers of snow along the Cascades and foothills today. Given a
jump in the expected liquid precipitation amounts in the latest
model runs, have bumped up the forecast accordingly, and this has
resulted in a forecast of generally 1 to 3 inches for locations
above 2000 feet in elevation. Snow levels will be dropping
throughout the day, but much of the precipitation should be over
before those levels fall to the valley floors west of the
Cascades. However, that does not rule out the possibility of some
flakes of snow within the higher valleys of the west side. To
account for possible travel issues, have issued a Winter Weather
Advisory for today to stress the possible impacts over foothills
of the Cascades and the Umpqua Divide, where an inch or two of
snow could stick to area roads. Have continued the Special Weather
Statement for the remainder of the area, whee snow amounts will be
less than an inch and Road temperatures are likely to prevent
sticking. There is still a good bit of uncertainty regarding
snowfall amounts, but given current observations to the north,
felt erring on the wetter/snowier side was the best course of

One thing about this system is for sure, and that is the very
cold temperatures expected to arrive behind the front. This Arctic
airmass will overspread our entire area on Tuesday and remain in
place through early Thursday. Temperatures will be well below
normal through middle to late week, and with some gusty winds, we
will also see cold wind chills, especially over the mountains and
east side. We are not quite expected to meet wind chill criteria
either, so have continued to cover this in the Special Weather Statement as well, as it
seems sufficient at this point. See pdxspsmfr for details. Have
also upgraded the freeze watch at the coast to a freeze warning
for overnight and into tomorrow morning, and left the freeze watch
in place for the next few nights.

The same pattern also has a tendency to produce strong valley
inversion overnight, and of course, freezing fog as well. This
will be an ongoing concern through the week, especially for inland
west side valleys. Fog could become dense at times, and may not
completely clear out during the day.

Beyond Thursday, there have been some major changes to the
forecast models. As mentioned during previous forecast cycles,
models have had considerable trouble dealing with the blocking
pattern upstream. While model spread still remains quite wide,
there has been a trend towards a much drier forecast, at least
until the weekend. Would not be surprised if pattern progression
is not further delayed with successive model runs. This shift to a
more stable pattern under ridging aloft suggests that valley
inversions will not completely mix clear, and while temperatures
should moderate overall, colder air will likely stick around in
the valleys for at least a few days longer than previously
thought. Air stagnation could become an issue through the latter
half of the week. -Bpn


Aviation...for the 29/06z taf cycle...expect MVFR ceilings with local
IFR and widespread mountain obscuration this morning. Isolated
to scattered rain and snow showers will become more numerous this
morning into early this afternoon and may locally lower ceilings/visible
as they pass through. The cold front responsible for the showers
will move south of the area this evening and showers will
end with gradually improving ceilings. But gusty north to northeast
winds will commence over portions of the east side. Spilde


Marine...updated 800 PM PST December 28, 2014... northwest 10 to
12 foot combined seas are present primarily in areas north of Cape
Blanco. Another cold front will move in from the north on Monday
bringing showers and gusty northwest to northeast winds. Freezing
temperatures are expected near the shore north of Cape Blanco
Monday...Tuesday and Wednesday nights and near the shore from Cape
Blanco south on Tuesday night. Moderate north to northeast winds
and steep seas are expected Monday night through Wednesday. Sven


Mfr watches/warnings/advisories...
or...freeze watch from Tuesday evening through Thursday morning for
Freeze warning from 10 PM this evening to 10 am PST Tuesday for
Winter Weather Advisory until 4 PM PST this afternoon for


Pacific coastal waters...Small Craft Advisory for hazardous seas until 10 PM PST Tuesday
for pzz350-356-370-376.
Small Craft Advisory for winds from 7 PM this evening to 10 PM
PST Tuesday for pzz370-376.



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