High Wind in Oregon, January 15, 2020

Area Forecast Discussion
National Weather Service Pendleton OR
345 PM PST Wed Jan 15 2020

Corrected Aviation Discussion

.SHORT TERM...
Tonight through Friday...Latest radar imagery showed an area of
snow moving through the Washington Cascades, Simcoe Highlands and
Yakima Valley. It extended eastward to near Hermiston. Mainly
light snow is expected with this area of snow, and we have already
had some reports of light accumulations.

Otherwise, low pressure will move north into British Columbia and
bring additional moisture onshore into Oregon and Washington
tonight into Thursday. Most of the activity will remain west of
the Cascades, but winter weather advisories have been issued for
both the Oregon and Washington Cascades and Simcoe Highlands,
Yakima Valley and Kittitas Valley though Thursday morning. Further
east, there may be some light snow (mainly in the mountains), but
any accumulations should remain below advisory levels. Any
lingering precip will exit by THursday evening as weak ridging
builds in. Most of Friday looks dry, before some precip may begin
to work in the extreme western areas ahead of the next system
later Friday.

Tight pressure gradients continue to produce strong wind in the
Grand Ronde Valley and Foothills of the Blue Mountains of Oregon.
Wind Advisories remain in effect in those areas.

Guidance temperatures continue to have big discrepancies on
certain days, with the GFS looking too cold tonight and Thursday
and the NAM likely too warm. The ECMWF is in the middle and closer
to the model blend on temps and have split the difference on
temps...in the 30s. Overnight lows will be in the low to mid 20s.
Guidance is much closer on Thursday, generally in the mid to
upper 30s.

.LONG TERM...
Friday night through Wednesday...A Pacific warm front will move
onshore Friday night and east of the Cascades on Saturday. Snow
will spread as far eastward as Yakima, Madras, and Prineville
Friday night. Snow levels will gradually increase Saturday and
Saturday night. Most elevations will observe snow but the lowest
elevations below 1500 feet will have a rain/snow mix on Saturday.
A tongue of warmer air aloft will bring snow levels to 4000-4500
feet with the exception of the east slopes of the WA Cascades and
areas from the Blue Mountains east to the ID border where cold air
will reside and precipitation will fall as snow. Overnight
temperatures Saturday night through Sunday morning in the Lower
Columbia Basin and surrounding valleys will be in the lower to mid
30s, therefore there will likely be some light freezing rain
before changing to rain. Winds in the Grande Ronde Valley and the
base of the Blue Mtn Foothills of OR will have gusts 35-45 mph
Friday night through Saturday night.

The front will lift north across WA Saturday followed by a weak
shortwave ridge on Sunday for predominantly dry conditions (light
snow along the WA and northern OR Cascades). The ridge will shift
eastward, increasing a SSW flow aloft.  A strong upper low will
travel north along the coast, but there are model differences on the
position and strength.  The ECMWF is farther north-northeast than
the GFS, and the Canadian (CMC) is the weakest of all three.  The
changes do not have a significant influence on the forecast for our
area, but the ECMWF would imply a better chance of low elevation
rain and snow Monday compared to the GFS and CMC.  PoPs on Monday
and Monday night are around 20-40 pct with snow levels forecast at
2000-2500 feet.

Model inconsistencies remain Tuesday through Wednesday. An elongated
trough offshore has a few embedded lows positioned differently from
the deterministic models.  This poses a challenge in the sensible
weather elements in the forecast, and the confidence in the details
is low.  For now, will keep slight chance to chance PoPs in the
lower elevations with chance to likely PoPs in the mountains with
snow levels around 2500-3500 feet.  Wister

&&

.AVIATION...
.00z TAFs...A frontal band is bringing light snow to our northern
TAF
sites this afternoon with conditions deteriorating to IFR.  This
band should lift northward with conditions returning back to VFR but
possible MVFR if low stratus clouds remain.  The main upper level
trough will shift eastward on Thursday with increasing snow showers
across the TAF sites.  South-southeast winds 10-15 knots gusting to
25-30 knots have been observed this afternoon, creating some blowing
and drifting of snow.  However, this is not causing a significant
reduction in VSBY at the TAF sites.  Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  28  37  23  36 /   0  30  40   0
ALW  31  38  26  36 /  10  20  50   0
PSC  29  37  25  37 /  10  10  10   0
YKM  21  35  17  33 /  80  10  10  10
HRI  29  37  25  38 /  10  10  20   0
ELN  18  32  16  28 /  80  20  10  10
RDM  26  36  18  36 /  40  50  20  10
LGD  28  34  17  31 /  20  30  70  10
GCD  28  37  17  33 /  10  50  60  10
DLS  27  38  24  37 /  50  30  10  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST this evening for ORZ507.

     Wind Advisory until 4 AM PST Thursday for ORZ049.

     Winter Weather Advisory until 10 AM PST Thursday for ORZ509.

WA...Winter Weather Advisory until 10 AM PST Thursday for WAZ026-027-
     520-521.

&&

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