547
FXUS66 KPDT 211702
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1002 AM PDT Sat Sep 21 2024

Updated Aviation Discussion

.AVIATION...18z TAFs...VFR conditions expected. High sct-bkn clouds
will move through the area during the day as light, terrain-driven
winds prevail at all sites. Evans/74

&&

.PREV DISCUSSION... /issued 248 AM PDT Sat Sep 21 2024/

SHORT TERM...Today through Monday...A flat ridge of high pressure
will be over the region today providing generally clear skies, light
winds and near normal high temperatures.

Another weak upper level trough will pass through western Canada
Sunday clipping the Pacific Northwest similar to the one that
occurred on Friday. This will once again produce some locally breezy
conditions along portions of the east slopes of the Cascades.
Primarily the Kittitas Valley and eastern Columbia River Gorge
where winds will be 15-25 mph with gusts into the 30s. Fire weather
concerns will be elevated due to these locally breezy winds but
humidities remain high enough that no Red Flag conditions exist. A
low chance (15-20%) of some showers remain possible along the crest
of the central Washington Cascades but otherwise the forecast area
will remain free of precipitation with this trough passage.

This will be followed Monday by another ridge of high pressure
building into the region from the eastern Pacific but showing a
little more amplitude than todays flat ridge. This amplitude will
allow the ridge to persist over the region through the first of the
week before the next stronger trough arrives on Wednesday.

LONG TERM...Tuesday through Saturday...The long term forecast
remains mostly benign as high pressure ridging brings warm
conditions to the front half of the forecast, with growing
uncertainty in the later part of the period but should include a
likely cool down alongside at least Cascade rain.

The long term begins under high pressure ridging which will control
the CWA through Wednesday morning. This will allow for mostly quiet
conditions with Tuesday itself now expected to be the warmest day of
the period. Highs for our population centers are expected to range
in the mid to upper 80`s, with a chance at 90 degrees not out of the
question for portions of Central Oregon, the Columbia Basin, and the
foothills of the Blue Mountains. The NBM presents a probability of
20-50% at temperatures 90+ for Central Oregon on Tuesday, with the
other aforementioned regions at generally less than 10% for the day;
on Wednesday, those probabilities shift to the Columbia Basin and
foothills of the Blues, where a 20-40% chance at 90+ will exist.
That being said, Wednesday is when we begin to see a general cooling
pattern that will stay with us through the end of the forecast
period, as widespread highs come back down into the low to mid 80`s
for the most part. In fact, only the Columbia Basin should be as
warm as the previous day, with all other locations at least a few
degrees cooler.

This cooling trend will be activated by a pattern change in the form
of the deep ridge shifting eastwards while several systems begin to
spin down into the PacNW, but generally only grazing our area and
keeping us in a cooler, zonal flow. The first system moves in on
Wednesday during the afternoon and evening, and the second on
Friday; in both instances, moisture should be locked on the lee side
of the Cascades, with any showers that do make it over the peaks
quickly falling apart before they can make it past the foothills.
Meanwhile highs drop around 3-6 degrees on Thursday, and should
continue to descend a few degrees each day, swinging us from above
normal to back below normal by next Saturday. The end of the
forecast period is a bit more uncertain however, as ensemble
guidance begins to separate by that time.
The majority of the ensembles though are either zonal with troughing
both over Canada or offshore, or more trough-like in nature with
Friday`s system causing our flow to shift more northwesterly, either
of which would be cooler than any of the more ridge dominant
ensembles which only account for roughly 20% of overall guidance.
Therefore, there is moderate to high confidence in the overall
forecast (60-70%), with our warm mid-week and cool weekend looking
fairly likely. Each of these systems may also bring us gusty winds
on Wednesday/Friday, but nothing out of the ordinary and below wind
advisory criteria, breeziest through where else - the Cascade Gaps.
Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  70  44  77  50 /   0   0   0   0
ALW  73  48  79  54 /   0   0   0   0
PSC  75  51  81  57 /   0   0   0   0
YKM  75  47  81  52 /   0   0   0   0
HRI  74  48  81  54 /   0   0   0   0
ELN  75  47  77  52 /   0   0   0   0
RDM  71  40  78  45 /   0   0   0   0
LGD  70  42  75  47 /   0   0   0   0
GCD  70  40  76  46 /   0   0   0   0
DLS  79  50  82  56 /   0   0   0   0

&&

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

$$

SHORT TERM...91
LONG TERM....87
AVIATION...74