High Wind in Oregon, November 15, 2021

Area Forecast Discussion
National Weather Service Pendleton OR
933 AM PST Mon Nov 15 2021

.UPDATE...An upper ridge has moved out of the area this morning
and a vigorous cold front approaching the coast is very apparent
on satellite imagery. This cold front is moving quickly and will
be crossing the Cascades into our area this afternoon and evening.
The main concern with this system will be winds. Current wind
advisories look good and are in agreement with just about every
model. Expect southwest winds peaking at 20 to 35 mph with gusts
to 50 mph from mid afternoon through early evening before
diminishing through the night. One concern is that the
experimental NBM version 4.1 is showing strong wind gusts to 70
mph along the base of the Blue Mountain Foothills from Pendleton
to Walla Walla from about 3 PM to 7 PM this evening. This would be
similar to a wind event there a week ago but other models
(including the operational version of the NBM) are not showing
gusts stronger than 50 to 55 mph. The wind event last week was
from south to southeast winds and today will see southwest winds
which is a less favorable direction for downsloping off the Blue
Mountains. So, will keep the wind advisory for the Blue Mountain
Foothills but if winds start looking stronger than expected, may
upgrade those zones to a High Wind Warning. The front will also
bring a shot of rain mainly in the mountains with just a few
hundredths of an inch in the lower elevations. Snow levels are at
around 6500 feet and will rise to 7500 feet this afternoon ahead
of the front so that is why the mountains will see rain. Behind
the front, colder air will drop the snow levels to 1500 to 2500
feet overnight, but little precipitation is expected after
midnight. Warm air advection continues today so highs will once
again be in the 60s and lower 70s over most of the area. The
colder air tonight will drop lows into the lower to mid 30s in the
lower elevations with 20s in the mountains. Current forecast was
in good shape and made some minor adjustments to temperatures,
cloud cover and pops. Forecast update already out. Perry/83

&&

.AVIATION...18z TAFs...Main impact today will be strong winds
across all sites, with SW/W gusts 40 kts and higher possible this
afternoon as a front moves through the area. Slight chance of rain
ahead of this front, however impacts from precip should be minimal,
although cannot rule out brief MVFR conditions should a rain shower
coincide with strong gusts. Winds expected to pick up around 20z,
peaking around 00z, before falling off overnight, but remaining
breezy across most sites through Tuesday morning. bkn-ovc cigs
around 5-10 kft this afternoon, becoming mostly clear later in the
evening. 74

&&

.PREV DISCUSSION... /issued 245 AM PST Mon Nov 15 2021/

SHORT TERM...Today through Wednesday...Forecast area is under an
upper level ridge this morning providing warm dry conditions.
However, conditions will be changing today as a cold front
approaches from the northwest. The front will reach the Washington
Cascades this afternoon then quickly pass over the rest of the
forecast area late this afternoon and evening. There will be some
brief precipitation associated with the frontal passage but the main
concern will be the winds. South to southwest winds will increase
ahead of the front then switch to west to northwest behind the
front. Peak winds will be associated with and after the frontal
passage and continue windy overnight. Wind advisories have been
issued for sustained winds of 25 to 35 mph and gusts around 50 mph
likely. By Tuesday the front will be well east of the area leaving
the forecast area under a much cooler and breezy northwest flow with
some lingering showers over the mountains. A ridge over the eastern
Pacific will begin to move inland Tuesday night ending all showers.
The ridge will be over the region on Wednesday for a return of light
winds but temperatures will remain cool.

LONG TERM...THURSDAY THROUGH SUNDAY...The extended period is
characterized by an upper level trough that will approach from the
west on Thursday and early Friday, which is followed by an upper
level ridge that builds in from the southwest later into the
beginning part of the weekend. This pattern will bring a return to
showers along the Cascades and Northern Blues Thursday morning
before spilling across the Basin and lower elevations by late
afternoon. Rain chances begin to drop through the afternoon hours on
Friday as the trough and associated frontal system dissipates as it
ejects to our east. This will also result in breezy conditions along
the east slopes of the Cascades, Lower Columbia Basin, and through
the Southern Blues. Gusts of 20-30 mph will be possible Friday
afternoon and evening associated with the passing system. Rain
amounts of .5-1.5 inches for the Cascades and Blues, .1-.35 inch
along the east slopes of the Cascades, and .05-.20 inch for lower
elevations of the Basin and Central Oregon are expected Thursday
through Friday afternoon. Quick ridging behind the system will
attribute to drying Friday evening and into Saturday morning. Since
the origin of the trough and its associated moisture is from the
west-southwest, snow levels will be increasing as the trough pushes
into our area. Snow levels are likely to rise from the 500-2500 feet
range Thursday morning to 3000-5000 feet by Friday morning. Snow
levels should stay consistent through Saturday before increasing
again to between 5000-7000 feet by Sunday afternoon. Temperatures
should also stay near average through the period with highs in the
upper 40s to low 50s and lows in the low to mid 30s across the Lower
Columbia Basin. The ridge's orientation should allow for northwest
flow aloft to occur on Sunday to provide more mountain rain and high
elevation snow to occur, but should stay confined along the
Cascades.

Guidance has a good handle on the overall pattern through the
period, although differences do arise regarding trough and ridge
strength. The GFS incurs a stronger trough and subsequent weaker
ridge than the ECMWF. This highlights a breezier and wetter scenario
with the GFS. In fact, the EFI shows limited wind concerns reaching
above normal values as expected with the ECMWF ensembles. The 500mb
EOF patterns show the main discrepancy with the trough and ridge
strength, which is mirrored in the 500mb height clusters. Confidence
seems to lean slightly more in the ECMWF outcome with regards to the
incoming trough, but the GEFS seems to incur more confidence in
relation to the building ridge when observing the ensembles within
the cluster phase space. Thus, the current forecast reflects this
outcome. 75

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  69  35  47  26 /  20  30  10   0
ALW  68  36  47  29 /  20  40  10  10
PSC  67  39  53  29 /  20  10   0   0
YKM  62  33  51  26 /  40  10   0   0
HRI  71  38  51  27 /  20  10   0   0
ELN  58  32  45  23 /  50  10  10   0
RDM  66  29  44  23 /  10  40   0   0
LGD  60  29  41  22 /  10  70  20  20
GCD  63  29  40  22 /  10  40  10   0
DLS  64  39  51  32 /  60  20  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 1 PM this afternoon to 10 PM PST this evening
     for ORZ041-044-507-508.

     Wind Advisory until 7 PM PST this evening for ORZ510-511.

WA...Wind Advisory from 1 PM this afternoon to 10 PM PST this evening
     for WAZ024-026>029-521.

&&

MORNING UPDATE...83
SHORT TERM...91
LONG TERM....75
AVIATION...74