178
FXUS66 KPDT 190519 AAC
AFDPDT

Area Forecast Discussion...UPDATED
National Weather Service Pendleton OR
1019 PM PDT Wed Sep 18 2024

Updated Aviation Discussion

.AVIATION...06Z TAFs...VFR conditions expected over the next 24
hours with skies clear. Winds generally 10-12 knots or less,
though sites DLS/PDT could see gusts around 20-25 knots.
Goatley/87


&&

PREV DISCUSSION... /issued 252 PM PDT Wed Sep 18 2024/

SHORT TERM...Today through Friday night...

Key Messages:

1. Breezy afternoon conditions each day, peaking Thursday evening.

2. Warming through Thursday, cooler through the end of the week.

Current radar and visible satellite imagery showing dry conditions
as mostly clear to partly cloudy skies extend across the area as
clouds mainly impact areas of elevation over the Blue Mountains.
These conditions are in response to our proximity to two upper
level systems, one continuing to depart through southeastern
Montana and the other dropping south along the coast. These
exiting systems will open the door to upper level ridging
infiltrating into the area from the west this evening into
Thursday. As a result, clear to mostly clear skies and dry
conditions will persist through Friday. A pressure gradient has
already developed along the Cascades as high pressure pushes
onshore, which has allowed for breezy winds to occur across the
Gorge, Kittitas Valley, and portions of the Basin today. Gusts of
20-25 mph have been recorded at the Dalles and Ellensburg this
afternoon, which will linger until between 7PM and 8PM before
slowly subsiding tonight. These elevated winds are expected to
return each afternoon, peaking late Thursday afternoon and evening
as an upper level shortwave rides along the Canadian border and
further tightens pressure gradients. Gusts of 30-35 mph will be
possible Thursday afternoon/evening and 25-30 mph Friday
afternoon/evening over the aforementioned areas. Confidence in
these wind values is moderate to high (60-80%) as the NBM
advertises a 90-95% chance of 30 mph gusts across the Kittitas
Valley and a 55-75% chance through the Gorge, Simcoe Highlands,
and portions of the Basin west of Hermiston both days. Confidence
is high (90-95%) that expected winds both days will stay below
advisory criteria (Sustained winds of 30 mph and gusts of 45 mph)
through Friday as suggested by only a 5-15% chance of 45 mph gusts
or greater via the NBM.

The upper level flow is out of the north today, and will turn more
out of the west on Thursday to allow high temperatures to increase
2 to 5 degrees and break into the low 80s across lower elevations
of the Basin. Confidence in high temperatures of 80 degrees or
greater for Yakima, Hermiston, and the Tri-Cities is moderate to
high (65-80%) per the NBM. Flow aloft turns more out of the
northwest on Friday to bring a cooler airmass across the area as
highs drop 4 to 8 degrees from Thursday. Normal high temperatures
for this time of year is around 77 degrees, so these values will
be briefly above normal on Thursday before returning to below
normal on Friday. Mostly clear skies overnight will also provide
cool morning temperatures as lows will bottom out in the upper 30s
to low 40s over Central Oregon and the Grand Ronde Valley both
Thursday and Friday night. Confidence is high (70-90%) in this
occurring as the NBM showcases a 65-85% chance of low
temperatures reaching below 40 degrees for Redmond and La Grande
Friday night. 75

LONG TERM...Saturday through Wednesday...Generally dry
northwesterly flow will start out the extended period on
Saturday, though some weak shortwave energy could potentially
touch off a shower over the Washington Cascades. Probabilities at
this time are too low to mention in the forecast.

The northwest flow will strengthen Sunday into Monday as a ridge
builds over the Pacific. However, by Sunday in to early Monday, some
moisture will move over the ridge and will bring some rain potential
to the Washington Cascades beginning Sunday and to the eastern
mountains later Sunday into Monday.  These showers should be
relatively light.  The higher elevations of the Washington Cascades
could get up to one quarter of an inch with much less elsewhere.
Most of the areas that do receive precipitation will get a few
hundredths at best.

The ridge over the pacific will then move inland for Monday and
Tuesday and bring dry weather everywhere.  Another trough will
approach the region Tuesday night and bring a return to a zonal flow
on Wednesday, with shower chances returning to the mountains.

There will be diurnal breeziness on Sunday and Tuesday and
Wednesday, but winds should generally be less than 25 mph.  The NBM
probabilities of wind gusts >=39 mph on Sunday are generally less
than 30 percent, though there are a few isolated spots tin the 30 to
40 percent range across the Columbia Basin and Simcoe Highlands.  On
Wednesday, probabilities of wind gusts >=39 mph rise to the 40 to 50
percent range across the Columbia Basin, Simcoe Highlands and
Kittitas Valley, as the westerly flow moves in.  However, this is
day 7, so we will see how this plays out across the area.

Overall, the model guidance is in very good agreement through the
period.

High temperatures will be generally near normal, rising to 5 to 10
degrees above normal by Tuesday (and into the lower 80s in some
areas) under the ridge.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  77  47  69 /   0   0   0   0
ALW  52  79  51  72 /   0   0   0   0
PSC  55  81  53  75 /   0   0   0   0
YKM  49  80  47  75 /   0   0   0   0
HRI  53  80  52  75 /   0   0   0   0
ELN  49  76  49  72 /   0   0   0   0
RDM  43  77  41  72 /   0   0   0   0
LGD  46  78  45  69 /   0   0   0   0
GCD  45  77  43  72 /   0   0   0   0
DLS  53  80  53  72 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...75
LONG TERM....77
AVIATION...87