853
FXUS66 KPDT 161646
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
946 AM PDT Thu May 16 2024

.UPDATE...Current radar and visible satellite imagery showing
dry conditions and clear skies as some lingering high pressure is
still present this morning. However, this will be exiting to the
east as an upper level shortwave and associated cold front will be
passing through the area this evening into Friday morning. The
approaching system has already begun to develop a pressure
gradient along the Cascades, allowing increased winds through the
Eastern Gorge, Simcoe Highlands, Kittitas Valley, and the northern
Blue Mountain foothills as a Wind Advisory is currently active
until 11 PM tonight with wind gusts between 40 and 50 mph
possible. Confidence in these wind gust values is high (80-90%) as
the NBM suggests a 75-90% chance of wind gusts of 47 mph and a
40-60% chance of wind gusts of 55 mph over the aforementioned
areas. Rain is expected to develop along the Cascades this
afternoon and evening before extending into the Blue Mountains
overnight into Friday morning. Lower elevations will stay dry as
high temperatures drop 10 to 15 degrees Thursday (upper 70s to low
80s) to Friday (upper 60s to low 70s) behind the cold front.

There is a potential for the Wind Advisory to be extended through
the overnight period as pressure gradients along the Cascades stay
tight through 10 AM Friday via GFS, NAM, and SREF guidance. The
NBM also highlights a 60-80% chance of wind gusts of 47 mph or
greater on Friday over the same areas that are included in today`s
advisory. This will be further analyzed this morning, and may be
included with the afternoon forecast package. 75


&&

.AVIATION...18Z TAFS...VFR conditions expected during this
period. Clear skies currently for all sites with some clouds
coming by for KDLS this afternoon and Friday morning at KYKM until
clearing again. The biggest concern today will be wind gusts as
they will increase to 25-35kts until decreasing overnight for
KRDM/KBDN. Feaster/97


&&

.PREV DISCUSSION... /issued 211 AM PDT Thu May 16 2024/

SHORT TERM...
Today through Saturday night...
High pressure off the coast will be suppressed to the southwest
later today and tonight by a strong shortwave and upper level
trough that will drop down from the northwest. This trough and
shortwave will move across the area tonight into Friday morning
before moving east of the region. Another shortwave will move
across mainly eastern sections of the area on Friday. Dry
northwesterly flow will return for Friday night into early
Saturday before yet another trough and shortwave move
southeastward across Washington during the day on Saturday into
Saturday night.

As the trough approaches, it will bring precipitation first to
the Washington Cascade crest, then to the Oregon Cascade crest and
Blue Mountains. QPF is expected to be light, only a few
hundredths, with the exception of the Washington Cascades which
could see over a tenth of an inch and possibly up to 0.20 inches.

Snow levels will start off over 8000 feet, but by Friday morning
will be around 3000 feet in the Washington Cascades and 4500 to
5000 feet elsewhere, so it is possible there could be some very light
snow at or above these levels.

The biggest concern continues to be gusty winds ahead of and with
the passage of the trough. Based on the latest data, a wind
advisory will be issued for the Kittitas Valley, Simcoe Highlands,
Oregon Columbia Basin, Columbia Gorge, and Oregon Foothills of the
Blue Mountains. Winds of 25 to 35 mph with gusts 40 to 50 mph are
expected. NBM probabilities of wind gusts >= 39 mph are 90 to 100%
in these areas today. NBM probabilities of wind gusts >= 47 mph
range from 60 to 80% in these areas. The ECMWF EFI has these same
areas generally in 0.6 to 0.7, with some embedded locations of 0.7
to 0.8.

Breezy conditions are expected to continue behind the trough as
well through much of Friday, and winds will increase with the
approach of the next shortwave later Friday into Friday evening.
Breezy to windy conditions will occur again on Saturday with the
approach of the next trough on Saturday. Additional precipitation,
mainly over the mountains is possible later Saturday into
Saturday night, but QPF should be less than the event tonight into
Friday.

High temperatures will be about 10 degrees above normal today,
but then will drop to near normal on Friday and Saturday.

LONG TERM...
Sunday through Thursday...Models coming into better agreement on
what looks to be a relatively active pattern through most of next
week, filled with chances for showers and potentially mountain
thunderstorms as a couple of upper-level lows look to impact the
region.

For Sunday, the forecast area will fall on the southern flank of an
ongoing low situated over western Canada, inviting a band of
amplified NW flow over the PacNW. Light orographic shower activity
is possible across the crests of our mountain zones, however chances
are on the lower end (20-30%) as the western Canada low will help
usher in a pretty dry airmass overhead through much of the weekend,
with PWATs reading in the 0.3 to 0.5 inch range. Such a pattern will
invite breezy winds across the Cascade Gaps as well, namely through
the Columbia River Gorge, Kittitas Valley, and Simcoe Highlands.

Better chances for area-wide showers look to occur later in the work
week as a well-developed upper-level low is shown dropping down into
the forecast area from the Gulf of Alaska by around Tuesday. Given
this system`s northwesterly approach, not expecting particularly
heavy rain, but lift will be much more supportive for shower
activity Tuesday into Wednesday. Some of these showers may develop
into thunderstorms across primarily the eastern mountains, should
lift prove to be suitable enough, however the pattern thus far
doesn`t look to be conducive for particularly strong storms, as
temps will be right at or just below seasonal averages under this NW
pattern, which would mean generally 50s and 60s for daytime highs
across the eastern mountains. QPF guidance isn`t particularly
precise this far out, but NBM does depict widespread PoPs in the 25-
50% range Tuesday into Wednesday, increasing across our mountain
zones.

Ensembles and deterministic guidance are a bit shaky beyond the
midweek next week, as to be expected under a relatively progressive
pattern, but ensemble clustering does hint at continued troughing
across the PacNW. Expect a continuation of persistent shower
chances, roughly seasonable temps, and breezy winds should these
ensemble members verify. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  77  44  65  40 /   0  10   0   0
ALW  80  47  68  45 /   0  20  10   0
PSC  85  51  72  45 /   0   0   0   0
YKM  80  42  70  39 /   0   0   0   0
HRI  82  48  70  44 /   0   0   0   0
ELN  71  41  63  42 /   0  10   0   0
RDM  77  42  65  34 /   0   0   0   0
LGD  77  44  60  36 /   0  30  10   0
GCD  79  45  62  36 /   0  10  10   0
DLS  74  49  67  45 /   0  10   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 11 PM PDT this evening for ORZ041-044-507.

WA...Wind Advisory until 11 PM PDT this evening for WAZ024-026-521.

&&

$$

UPDATE...75
SHORT TERM...77
LONG TERM....74
AVIATION...97