Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 232333
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
335 PM PST Fri Feb 23 2018

Updated Aviation Discussion

.SHORT TERM...Tonight through Saturday night...A system embedded
within the northwesterly upper level flow will move across the
Pacific Northwest tonight and Saturday morning. This system will
bring varying amounts of snow to the region tonight into Saturday
morning. Varying coverages of showers will persist into Saturday
afternoon, with the best coverages due to upslope affects into the
northern Blue mountains. Snow accumulations in the Blue mountains
are expected to run 9 to 12 inches by late Saturday above 4500 feet.
Therefore will issue a winter storm warning for locations above 4500
feet in the Blues. Will keep the winter weather advisory going for
the Blues between 3000 and 4500 feet. Elsewhere should see decent
snow accumulations along the Cascade east slopes, especially near
the crest. Thus will continue the advisory along the Washington
Cascade east slopes, and add an advisory for the Oregon Cascade east
slopes. Also, now expect 3-5 inches of snow by late Saturday morning
over the Grande Ronde valley and Wallowa county. Thus will also add
advisories for these two zones. Elsewhere snow accumulations look to
be light with only a few localized amounts near 2 inches. Winds
will be 10-20 mph overnight into Saturday morning. These winds will
allow for a slow warming and rise of snow levels at locations below
2000 feet. This slow rise in the snow levels will affect the ability
for snow to accumulate Saturday morning at the lowest elevations.
Winds will increase over portions of the area by Saturday afternoon,
reaching values of 20-30 mph sustained. Isolated to scattered
showers, mainly of snow, will persist across the area Saturday night
due to the persistent northwest upper flow. Best chances will be
over the mountains. Another system looks to change the showers to
steadier snow along the Washington Cascade east slopes late Saturday
night. 90

.LONG TERM...Sunday through Friday...Cool, wet and occasionally
windy conditions summarize the long term forecast. The forecast area
will be under a moist westerly flow aloft for most of the period.
Sunday will be the day with the strongest winds with sustained winds
15-30 mph for most of the area.  The upper level trough and its
associated cold front will move south Sunday night followed by a
moist W-NW flow aloft Monday through Wednesday.  Snow levels will be
near the Basin floor Sunday night rising to 1500-2000 feet Monday
through Wednesday. Despite the low snow levels, the westerly flow
will cause precipitation shadowing off the Cascades so that any snow
that falls in the Columbia Basin and surrounding valleys down to the
Columbia Deschutes Plateau should be light or none at all.  The
Grande Ronde Valley and the Wallowa Valley may also observe periods
of light snow but nothing significant as the Blue Mountains and the
Wallowas receive most of the snow in the westerly flow aloft.  The
John Day Basin and Ochoco Highlands will have periods of light snow
but most of the precipitation will be north.

Models are hinting at a deep low moving onshore Thursday and setting
up a large trough pattern off the eastern Pacific and the Pacific NW
Thursday through Friday.  There are some differences in the timing
and position of the parent low, but the overall story remains the
same. It will be continued wet and breezy late in the week. Wister

&&

.AVIATION...00Z TAFs...Clouds have increased across the region and
will continue to thicken this evening.  CIGS will lower to around
2500-5000 feet AGL tonight, thus MVFR CIGS are expected.  Doppler
Radar is showing a band of light precipitation over south central WA
that will approach KPDT and KALW and bring light snow over the next
several hours.  Runways may have a light dusting of snow this
evening. The best chance of snow or snow/rain mix will occur
Saturday morning between 12Z-20Z, and IFR to MVFR conditions are
possible with the exception of KPSC and KYKM where precipitation is
not expected due to the downsloping conditions off the Cascades.
Westerly winds at 5-15 knots will continue through the evening and
will increase to 10-20 knots gusting to 25-30 knots Saturday.  Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  28  42  32  44 /  30  70  20  50
ALW  30  44  35  47 /  50  70  20  70
PSC  30  48  34  50 /  20  30  10  30
YKM  22  45  30  47 /  20  30  20  50
HRI  28  47  35  48 /  20  40  10  40
ELN  23  40  29  42 /  30  40  30  60
RDM  22  38  26  42 /  20  80  20  80
LGD  24  36  29  37 /  60  80  40  90
GCD  23  35  27  39 /  40  80  40  80
DLS  28  46  36  46 /  40  60  30  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST Saturday for ORZ049-050-
     502-509.

     Winter Storm Warning until 4 PM PST Saturday for ORZ502.

WA...Winter Weather Advisory until 4 PM PST Saturday for WAZ030-520.

     Winter Storm Warning until 4 PM PST Saturday for WAZ030.

&&

$$

90/85/85



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