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Area forecast discussion 
National Weather Service Pendleton or
238 am PST sun Nov 29 2015

Short through Tuesday...high pressure aloft with an
easterly flow will continue for one more day. Main forecast concern
in the short term will be the expanding fog and low clouds that will
eventually spread over all of the basin and foothills. Low cloud
cloud bases are high enough for most valley locations to have just
low clouds while the higher terrain against the mountains meets the
low cloud layer surrounding the basin and adjacent valleys. These
areas will see the most fog. The fog and low clouds will persist
through Tuesday morning and then decrease as a weather system moving
into the region Tuesday night and Wednesday brings enough mixing to
lift the stratus layer or at least the surface fog into a stratus
layer. The other concern will be the onset of precipitation which
may begin as freezing rain in the colder valleys or snow in the
mountains. Temperatures this morning are significantly warmer than
the past few days. The forecast soundings are showing air that
will be too warm for freezing rain along the foothills...but some
basin locations and areas against the Cascade east slopes may
see some snow or freezing rain to start. 88

Long term...Tuesday night through Sunday...a weather system will
continue to move inland Tuesday evening...starting with a winter mix
of precipitation. Snow will likely be the form of precipitation
over the east slopes of the Washington Cascades...the Kittitas and
Yakima valleys...and the mountains of northeast Oregon. All other
areas will likely see a rain/freezing rain mix. This is due to a
strong warm layer aloft...and cold air that has remained trapped at
the surface over the past several days. Lately models have been
mixing out the colder air fairly quick. Freezing rain looks to
start after sunset Tuesday...and may not change over to rain until
middle to late Wednesday morning. Areas that will be prone to cold air
trapped for longer periods of time include...the Washington
Basin...Yakima and Kittitas Valley.

This weather system is expected to linger over the area through the
end of the work week...providing a continued chance of rain and high
elevation snow. By Friday morning a cold front should push
through...lowering snow levels again. Keep in mind the lower
elevations will still be mild and may not notice the change as much
as some of the mountain areas. Another warm front is expected late
Saturday into Sunday. This will likely be a rain/high elevation
snow cloud cover will likely keep areas from getting
too cool at night to develop fog. Overall expect a fairly wet
extended...but temperatures turning more mild...once the cold air is
mixed out. Weber


Aviation...previous discussion...06z tafs...flight categories will
vary from VFR to LIFR over the next 24 hours. Widespread low stratus
clouds and pockets of fog are in place over the lower Columbia Basin
and into the Blue Mountain foothills at this time...and are expected
to persist through the taf period here. Therefore LIFR to low end
MVFR ceilings and visible are forecast to continue over the next 24 hours at
kpsc...kpdt and kalw...with the most likely time for lower ceilings/visible
between about 29/13-17z...then there may be some improvement during
the late morning and afternoon hours especially in regards to
visibility in vicinity of kpsc. For kdls and kykm skies are mainly clear at
this time but patchy fog and stratus is expected to develop and/or
move into the area later tonight and into Sunday morning. Once the
fog and stratus move into these terminals at least MVFR restricted
ceilings and visible should continue. At kbdn and krdm the top of the
inversion and fog layer is now between 3000 to 4000 feet mean sea level...which
means that conditions may be highly variable here. Right now the
forecast calls for occasional mist and freezing fog in IFR/LIFR
conditions at krdm through 29/18z before some gradual improvement.
Kbdn may stay just above the fog layer and therefore kept conditions
mainly VFR here...but did indicate that there is the potential for a
MVFR/IFR low stratus cloud deck to affect the terminal from 29/12-
17z...this is a low confidence forecast here. Winds will remain
light at or below 10 kts at all locations over the next 24 hours. 77


Preliminary point temps/pops...
PDT 27 23 30 23 / 0 0 0 10
alw 28 27 30 27 / 0 0 0 10
psc 29 22 31 22 / 0 0 10 10
ykm 33 16 33 16 / 0 0 10 10
hri 29 20 31 20 / 0 0 10 10
eln 32 14 31 14 / 0 0 0 10
rdm 25 8 36 13 / 0 0 10 10
lgd 33 16 32 20 / 0 0 0 0
gcd 29 7 33 11 / 0 0 10 10
dls 34 25 38 25 / 0 0 10 10


PDT watches/warnings/advisories...
Washington...air stagnation advisory until noon PST Monday for waz026>028.


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