358
FXUS66 KPDT 140527
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1027 PM PDT Mon May 13 2024

Updated Aviation Discussion

.AVIATION...06Z TAFs...VFR conditions to prevail through the
period. Breezy winds 12-17kts at sites DLS/YKM/PSC will continue
through the next couple of hours, then decreasing to less than
12kts. Otherwise, light winds, less than 12kts, will prevail at
most sites through the period. Site DLS is expected to see winds
12-15kts with gusts around 20kts redevelop after 21Z tomorrow.
Lawhorn/82

&&

.PREV DISCUSSION... /issued 448 PM PDT Mon May 13 2024/

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

Key Messages:

1. Windy conditions across the Kittitas Valley through Tonight.

2. Elevated river levels on the Naches River.

An upper level shortwave will continue to pass through the area
this evening, which will allow a slight increase in cloud cover
and a pressure gradient to develop along the Cascades to promote
elevated winds over the Kittitas Valley, Simcoe Highlands, Eastern
Gorge, and the northern Blue Mountain foothills. Maximum wind
gusts of 44 mph have already been observed at the Ellensburg
Airport, with the pressure gradient and winds expected to peak
between 5 PM and 11 PM this evening. This has warranted the
issuance of a Wind Advisory for the Kittitas Valley through 11 PM
as gusts of up to 50 mph will be possible. The 44 mph gusts
occurred during an observed pressure gradient of 8.7 mb between
Portland and Spokane, and the pressure gradient is expected to top
out just shy of 11 mb via GFS guidance. Confidence in wind gusts
reaching 50 mph is moderate to high (70-80%), as the NBM suggests
a 75% chance at Ellensburg, increasing to an 86% chance of gusts
reaching 47 mph or greater.

The consistent above normal temperatures coupled with the mountain
snow event preceding the warm temperatures last weekend have
allowed for some elevated river levels - primarily for the Naches
River. The currently level of the Naches River at Cliffdell is
28.86 feet, as action stage is forecast to be reached Tuesday
evening and peak Friday morning at 29.76 feet. Confidence is high
(>95%) in this reach breaking into action stage, but low (<5%) in
reaching minor flood stage (31 feet). The Naches River at Naches
is currently at 15.38 feet, and is also expected to reach action
stage (16 feet) Thursday morning. This reach is forecast to peak
Friday morning at a level of 16.3 feet before dropping below
action stage Saturday morning. Confidence in reaching action stage
is moderate (62%), as reaching minor flood stage is low (<5%).
All other area rivers are currently forecast to stay well below
action stage.

An upper level ridge will build offshore as high pressure
infiltrates into the region from the west. This will keep skies
mostly sunny and conditions dry. Northwest flow aloft will set up
in the wake of the passing shortwave tonight into Tuesday,
dropping high temperatures slightly by 1-3 degrees from today.
Flow will incur more of a westerly component to keep temperatures
above normal and increasing high temperatures 5 to 9 degrees
Tuesday to Wednesday. Afternoon humidities will be on the decline,
dropping about 5% Monday to Tuesday and another 3% to 6% on
Wednesday. 75

LONG TERM...Thursday through Monday...Dry, northwesterly flow
continues through Thursday afternoon as high pressure remains
anchored off the Pacific Coast. A shortwave will begin to move
through the northern reaches of the forecast area Thursday night,
producing a slight chance (10-20%) for showers over the Washington
Cascades. The shortwave will dig further south through Friday,
bringing cooler air with it, though leaving showers generally
confined to the Washington Cascades.

Temperatures across the area will cool 10 to 15 degrees under the
influence of this shortwave, though values still generally remain 5
degrees above seasonal averages. The other impact related to this
system will be an increase of gusty to breezy wind both late
Thursday and again Friday afternoon. The strongest winds are
expected across the Columbia Basin and into the Yakima and Kittitas
Valleys where wind gusts of around 35 kts are highly favored (75-
95%).

Beyond Friday, model disagreements become more apparent, with the
clusters showing variations in both placement of the next area of
low pressure, as well as the intensity of it. Current forecast
indicates a slightly stronger lean towards a solution with moisture
across the Pacific Northwest, though mostly west of the Cascades.
The Oregon and Washington Cascades present in this forecast area
will see a slight chance (15-30%) for mountain showers into early
next week.

A slightly better agreement is demonstrated for Monday as low
pressure is favored to impact the Pacific Northwest.  Cooler
temperatures will return, along with a larger coverage area for
shower activity. In addition to the Oregon and Washington Cascades,
guidance demonstrates the potential (10-20%) for showers to develop
across the Blue Mountains on Monday. This system will again create
increased winds across the region, with a 50-70% chance for gusts of
30 to 35 kts. Branham/76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  74  47  80 /   0   0   0   0
ALW  50  76  52  82 /   0   0   0   0
PSC  53  81  54  87 /  10   0   0   0
YKM  46  81  49  87 /   0   0   0   0
HRI  50  80  50  86 /   0   0   0   0
ELN  46  75  49  82 /   0   0   0   0
RDM  41  73  43  80 /   0   0   0   0
LGD  44  72  44  77 /   0   0   0   0
GCD  42  73  44  79 /   0   0   0   0
DLS  50  80  53  85 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 11 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...75
LONG TERM....76
AVIATION...82