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000
FXUS66 KPDT 152317
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
417 PM PDT Mon Apr 15 2024

Updated Aviation Discussion

.AVIATION...00z TAFs...VFR conditions expected, with windy
conditions continuing to be the main concern over the next 24
hours. W/SW gusts have ranged from 20 to 40 kts across all sites
thus far today. Winds will lighten heading toward the evening and
overnight hours, but gusts are expected to pick back up by Tuesday
afternoon as W/NW winds gust up to 25 kts. Expect primarily sct
mid to high level clouds. Evans/74

&&

.PREV DISCUSSION... /issued 240 PM PDT Mon Apr 15 2024/

SHORT TERM...Today through Wednesday Night...

Key Messages:

1. Breezy conditions through this evening.

2. Cold, sub-freezing low temperatures anticipated Wednesday
morning.

Current radar and visible satellite imagery showing light returns
exiting east of Wallowa county and accumulating along the west
slopes of the Cascades as mostly sunny skies hover overhead. This
is in response to a slow moving surface cold front passing
through our area today as an associated upper level trough digs
through British Columbia. These synoptic features are allowing
enhanced flow aloft from the west and a pressure gradient that has
developed along the Cascades to produce windy conditions across
the Kittitas Valley, Simcoe Highlands, Eastern Gorge, North-
Central Oregon, and the Blue Mountain foothills of Oregon through
this evening. Wind gusts of between 45 and 55 mph out of the west-
northwest will be possible, as a Wind Advisory is currently
active until 11 PM this evening for the aforementioned areas.
Confidence in these wind gusts are high (90%), as the NBM
advertises an 80-97% of wind gusts of 50 mph or greater and the
RAP, GFS, NAM, and SREF all highlight a pressure gradient of
9.5-13.8 mb between Portland and Spokane before 11 PM this evening
- which is indicative of wind gusts around 50 mph.

Temperatures behind the cold front tonight will be 6 to 10 degrees
colder than Sunday night (mid-to upper 30s), but lingering clouds
associated with the passing front will keep them above freezing -
with the exception of areas of higher elevation and across
Central Oregon. The upper level trough drops into northern
Washington tonight into Tuesday morning, advecting cold air into
the region as northwest flow aloft keeps temperatures trending
colder through Tuesday as highs will be 6 to 10 degrees colder
than today (upper 50s to low 60s). Skies will be clearing Tuesday
as surface high pressure sneaks onshore behind the departing
front to provide cold overnight temperatures into Wednesday.
Morning temperatures will drop into the mid-to upper 20s across
Central Oregon, upper 20s to low 30s over the Simcoe Highlands,
and in the low 30s through the Kittitas/Yakima Valleys and the
northern Blue Mountain foothills. This may warrant the need for
freeze highlights over the Yakima/Kittitas Valleys and portions
of the Blue Mountain foothills of Oregon due to the nature of low
temperatures, clear skies, and low winds. However, current
confidence in freezing temperatures is moderate (40-50%) as the
NBM highlights only portions of the Yakima/Kittitas Valleys and
Blue Mountain foothills having a 40-65% chance of Wednesday
morning temperatures dropping to 32 degrees or below. This will
have to be further analyzed as the current NBM forecast has both
Yakima and Ellensburg only dropping briefly to 32 degrees, with
the 25th and 75th percentile at 31 and 35 degrees for Yakima and
30 and 34 degrees for Ellensburg.

A tertiary concern will be the lingering breezy winds on Tuesday
as the upper level trough drops through Washington and isobars
stay relatively tight. Winds will be significantly lower than
today as pressure gradients slacken to 7-9 mb between Portland and
Spokane as suggested by the GFS, NAM, and the SREF. Wind gusts of
35-45 mph will be possible as the NBM shows a 70-80% chance of
wind gusts of 39 mph across the Simcoe Highlands and the Blue
Mountain foothills of Oregon. Chances drop significantly when
bumping up wind gusts to 47 mph, with isolated pockets of 30-50%
chances of reaching these values. Blowing dust may also be a
concern over the next 48 hours due to these elevated wind gusts as
conditions stay dry across the majority of the area. The only
chances (25-55%) for precipitation will occur over higher
elevations of the Cascades today and Tuesday, and across the
northern Blue Mountains and Elkhorns Wednesday afternoon and
evening. 75

LONG TERM...Thursday through Monday...On Thursday a deep upper
level low pressure system will be centered over central Canada and
the northern Plains keeping a cool northerly cyclonic flow over the
PacNW. The main threat of some showers should stay north and east of
the forecast area with a very low chance over SE WA and NE OR. On
Friday the low pressure system moves further east allowing an upper
level ridge of high pressure over the eastern Pacific to begin
moving into the PacNW. Models show a deep upper level trough in the
Gulf of Alaska sending a shortwave trough towards the PacNW over the
weekend with some differences in timing. This pushes the ridge axis
off to the east followed by a small shortwave closed low passing
along the Canadian border late Saturday through Sunday. Other than
some low precipitation chances along the Cascade crest and northern
Blue Mountains this will mostly be a dry event for the forecast area
followed by some breezy westerly winds. A ridge of high pressure
quickly builds back into the region on Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  54  31  56 /   0   0   0   0
ALW  40  57  35  59 /   0   0   0  10
PSC  43  61  38  64 /   0   0   0   0
YKM  35  57  32  62 /   0   0   0   0
HRI  39  60  34  62 /   0   0   0   0
ELN  34  52  32  59 /   0   0   0   0
RDM  31  54  25  54 /   0   0   0   0
LGD  34  51  29  52 /   0   0   0  10
GCD  31  54  28  53 /   0  10   0   0
DLS  42  57  37  63 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 11 PM PDT this evening for ORZ041-044-507-
     508-510.

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

&&

$$

SHORT TERM...75
LONG TERM....91
AVIATION...74