Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 091202 AAA

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
402 AM PST Fri Dec 9 2016

Updated aviation discussion

.SHORT TERM...Today through Sunday...A Pacific storm continues to
move across the region and CWA this morning. The main area of the
first round of steady precipitation has moved off well to the
northeast but there are still some upslope showers over the Blue
Mountains and Foothills as well as spill over precip over the
Cascades this morning. These are only producing light snowfall with
little or now accumulation. Steady snowfall will increase again as a
cold front with this system moves across the area today. However
this cold front will actually bring in warmer Pacific air rather
than colder arctic air. As a result snow levels will rise...
especially in central Oregon and over the eastern mountains. Cold
air will remain trapped in the Lower Columbia Basin and adjacent
valleys...though some warm air could nudge northward in a southwest
flow aloft over the Blue Mountain Foothills where the snow could mix
with or change to sleet or freezing rain this afternoon and tonight.
There will be a steady but slow increase in snow levels and
temperatures through Sunday which will cause precipitation in these
warmer areas to become mixed rain and snow...with mainly snow
showers at night and rain showers during the day. There will be
another cold snap moving into the region in the extended period.
Will leave current Winter Storm Warning in place over the Washington
Cascade east slopes (WA zone 520, and the Winter Weather Advisory
for the Blue Mountains. Do not believe there will be enough snow for
warning criteria for the Blues. Winds will be gusty with blowing and
drifting snow in the Grande Ronde Valley but wind speeds will stay
below wind advisory criteria. 88

.LONG TERM...Sunday night through Friday...A moist northwest flow
and a couple of shortwaves will bring a chance of snow Sunday night
and Monday with perhaps a slight chance of rain in the Columbia
Basin Sunday evening. It looks like an inch or two of snow in the
lower elevations and 2 to 4 inches in the mountains. Monday night and
Tuesday the flow turns more northerly and the lower elevations will
see an end to the snow with a slight chance continuing in the
eastern mountains. The northerly flow will bring colder air in the
area and temperatures will drop from the lower to mid 30s Monday to
the 20s and lower 30s in Central Oregon Tuesday and Wednesday. The
area will be mostly dry though there will be a chance of light snow
showers in Central Oregon and the Ochoco-John Day Highlands. The
ECMWF has changed from having a trough over the area Wednesday night
through Friday to having a ridge while the GFS maintains a northerly
flow with a chance of snow showers in the mountains. Have kept the
current forecast which leans towards the GFS and the previous ECMWF
for now. A chance of snow showers will continue in the mountains
with the lower elevations dry. Temperatures will remain cold
Thursday through Friday with highs in the mid 20s to lower 30s and
lows in the teens and lower 20s. Perry


.AVIATION...12Z TAFs...Scattered light snow showers expected this
morning with the best chance at KDLS and in upslope showers at KPDT
and KALW. Have used -SHSN at those sites and VCSH at other sites.
Low stratus and fog have developed at KPDT and KALW with LIFR
conditions. Expect this will continue through 18Z. Another round of
snow will arrive this afternoon around 20Z with generally IFR/MVFR
conditions through 06Z-09Z. KRDM and KBDN may warm up enough for the
snow to turn to rain with MVFR/VFR conditions. If cold air remains
in place longer than anticipated, KRDM and KBDN may see a period of
freezing rain. While possible, chances of freezing rain are lower at
other TAF sites. Due to the low probability, left -FZRA out of the
TAFs and will add if warranted. Snow showers will taper down after
08Z. Winds will remain below 10 kts for the next 24 hours. Perry


PDT  27  27  35  32 /  60  80  30  20
ALW  30  31  36  35 /  60  80  40  20
PSC  27  26  35  34 /  60  60  20  10
YKM  25  22  34  24 /  60  60  30  10
HRI  28  27  35  32 /  60  70  20  10
ELN  23  22  32  27 /  60  70  40  10
RDM  35  26  36  25 /  60  80  30  20
LGD  32  31  34  30 /  70  90  40  30
GCD  34  32  36  31 /  70  80  30  20
DLS  31  31  41  36 /  80  80  50  10


OR...Winter Weather Advisory until 4 AM PST Saturday for ORZ502-503.

WA...Winter Weather Advisory until 4 AM PST Saturday for WAZ030.

     Winter Storm Warning until 3 PM PST Saturday for WAZ520-521.




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