Heavy Snow and Winter Weather in Oregon, January 22 to 23, 2019

Area Forecast Discussion
National Weather Service Pendleton OR
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

&&

.AVIATION...0Z...A storm system will lower CIGs across all TAF
this evening. MFR conditions are possible in heavier RA after 0Z.
Surface wind gusts over 20 kts are possible tonight. 76

&&

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

     Winter Weather Advisory until 4 PM PST this afternoon for WAZ520.

&&

85/76/76

!--not sent--!