High Wind in Washington, January 23, 2019

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
954 PM PST Tue Jan 22 2019

Updated aviation discussion

.UPDATE...An upper level ridge remains offshore this evening but
a system is riding over the top of it into our area. A warm front
has moved into the area with widespread precipitation. This warm
front is bringing warmer air into the area and expect
temperatures tonight to remain steady or slowly rise. Snow levels
should rise as well but have been slow to do so. Already extended
the Winter Weather Advisory along the East Slopes of the
Washington Cascades before letting it expire at 8 PM. Light snow
continues but do not expect much additional snow in the next few
hours. A heavier band of precipitation has come ashore in
Washington but by the time it arrives, am anticipating that snow
levels will be high enough by then for the snow to switch to rain.
Elsewhere moderate rain continue in the Columbia Basin and Blue
Mountain Foothills and snow from the Blue Mountains eastward. Snow
amounts have been heavier than expected and will have to look at
the need for additional advisories, particularly in the Grande
Ronde Valley. Current Winter Weather Advisory in the Blue
Mountains looks good. Additionally, winds are starting to show
signs of increasing and expect that the current High Wind Warning
for the Simcoe Highlands and the Wind Advisory for North Central
Oregon will prove warranted. The Columbia Basin should increase to
15 to 25 mph late tonight and early tomorrow morning before
beginning to decrease. Made a few wind and temperature
adjustments. Forecast update already out. Perry

&&

.AVIATION...06Z TAFs...A storm crossing the area is bringing rain
with snow in the mountains to the area tonight though central Oregon
including KRDM and KBDN are mostly dry. Rain will end at other TAF
sites by 12Z though it may linger on through 15Z-18Z at KALW.
Ceilings and visibilities will be primarily VFR though KALW could
have MVFR ceilings and visibilities through 12Z. Winds will be
increasing in the next few hours and westerly winds of 10 to 20 kts
with gusts to 30 kts are expected through around 18Z before
decreasing below 12 kts by 00Z. Perry

&&

.PREV DISCUSSION... /issued 200 PM PST Tue Jan 22 2019/

SHORT TERM...An upper level ridge is present off the eastern
Pacific with the axis of the ridge along 130W.  A strong shortwave
is sliding down the east side of the ridge and will be over
Vancouver Island this evening then across eastern WA and northeast
OR tonight and Wednesday morning.  There are several weather
concerns expected with the shortwave.  A warm front ahead of the
shortwave is bringing widespread precipitation across western WA and
northwest OR, and precipitation is along the east slopes of the
Cascades.  Based on surface temps and dewpoints, snow levels range
from around 2500 feet in south central WA to 4000 feet in central
OR.  Current winter weather advisory for the WA Cascade east slopes
expires at 4 PM.  This looks reasonable as snow levels will continue
to climb overnight to above pass levels.  Precipitation will quickly
spread across the forecast area late this afternoon and evening, and
the northern Blue Mountains will begin to receive snow by sunset.
Winter weather advisories for snow are in effect for the northern
Blues above 4000 feet.  4-8 inches are expected with the heaviest
accumulation above 5000 feet.  Snow accumulations elsewhere will be
light, and areas south of the Blue Mountains and across central OR
will have little to no precipitation with this system.

It was a tough decision on the High Wind Watches that were issued
for areas across south central WA.  Mountain waves will develop
along the ridgetops where many of the exposed ridges and wind prone
areas of the WA and northern OR Cascades will have very strong
winds.  The question is whether the mountain waves will propagate
into the valleys with a potential for foehn winds. There is a well-
defined lee side trough, but forecast cross sections would indicate
trapped lee waves rather than propagating waves. The only exception
will be in the Simcoe Highlands where damaging winds may reach the
surface, and the watch was upgrade to a warning for this zone.  All
other watches were cancelled.  A wind advisory was also issued for
North Central Oregon (zone 510) as the Highway 97 corridor from Moro
to Mount Identifier may have gusts 45-55 mph.  Blowing snow was
added to several of the mountain zones this evening, but the impacts
will not be significant due to increasing snow levels and potential
for compacted snow.

A strong northwest flow aloft will remain over WA/OR Wednesday for
continued orographic mountain snow showers and breezy to windy
conditions. Surface winds will decouple from winds aloft Wednesday
night and will diminish.  Mountain showers will also end Wednesday
night.  Thursday and Thursday night will be dry as high pressure
rebuilds.  Another shortwave is progged to dive south across WA/OR
Thursday night but should do little except increase cloud cover.
Wister

LONG TERM...Friday through Tuesday...An upper level ridge
will build offshore and persist through the long term period. This
will create dry conditions with late night and morning fog in the
Columbia Basin and surrounding valleys. On Friday and Sunday
disturbances will dive down the backside of the ridge from NW Canada
to MT. This will increase cloud cover over the CWA but no
precipitation is expected since the trajectory is too far east.
Temperatures will be quite mild with highs in the mid 40s to lower
50s.  Coonfield

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  39  50  36  47 /  80  40  10   0
ALW  39  50  38  48 /  90  60  20   0
PSC  40  53  36  48 /  70  10   0   0
YKM  34  49  32  45 /  40  20   0   0
HRI  40  55  36  49 /  60  10  10   0
ELN  33  45  31  41 /  60  20   0   0
RDM  34  51  30  50 /  10  30  10   0
LGD  30  45  35  44 /  80  80  30   0
GCD  30  48  34  47 /  50  40  20   0
DLS  39  53  37  49 /  50  40  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from midnight tonight to 8 AM PST Wednesday for
     ORZ510.

     Winter Weather Advisory until 4 AM PST Wednesday for ORZ502.

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

     High Wind Warning from midnight tonight to 8 AM PST Wednesday
     for WAZ521.

&&

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