309
FXUS66 KPDT 070910
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
210 AM PDT Mon Sep 7 2026

.KEY MESSAGES...

- Showers will continue to diminish west to east through this
  evening as an upper low departs the region

- Breezy winds will develop through the Cascade gaps and Lower
  Columbia Basin today

- Drying and warming trend through the week will be followed by
  a potential return to unsettled weather in the mountains over
  the weekend (confidence 30-40%)

&&

.DISCUSSION...Satellite imagery tonight shows an upper level low
swinging into ID, with clear skies developing across the western
third of the forecast area. Meanwhile, regional radar shows a
line of isolated showers from La Grande due north into the WA
Columbia Basin and lighter showers over Wallowa county.

Today, the upper low will continue to swing east into the
northern Rockies, with showers and cloud cover continuing to
diminish west to east across the forecast area. Shower activity
will mainly be focused across Wallowa County through this
afternoon with a brief renewal in shower development tonight as
a secondary low quickly swings across the area.

Tuesday into Wednesday, the forecast area will mostly be under a
split flow aloft that`ll become zonal ahead of an approaching
trough. A drying and warming trend will develop, with afternoon
temperatures warming back into the 80s by Wednesday (confidence
65-80%). Thursday, breezy winds will return to the forecast area
as an upper trough approaches the region from the north. Winds
will generally be 15-25mph with strongest gusts up to 40 mph.
Relative humidities will also be low but above critical
thresholds across the Columbia Basin and Cascade Gaps during
this time, leading to elevated fire weather concerns for
Thursday (confidence 55-75%).

Friday into the weekend, ensemble guidance is in good agreement
of the upper trough slowly passing over the PacNW, with over 80%
of ensemble members (from ECMWF, GFS, Canadian) favoring
Saturday for light rain in the lower elevations and light to
moderate precipitation in the mountains. That said,
disagreement in timing of the trough exit is growing, with 22%
of members favoring dry conditions returning by Saturday night,
whereas 66% of members favor mountain showers continuing into
Sunday. While confidence is moderate (40-55%) in shower activity
over the weekend, confidence is low (20-25%) in timing and
extent. Otherwise, there is moderate confidence (50-60%) that
the upper trough passage will bring cooler conditions to the
forecast area. Lawhorn/82


&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...Ceilings near but
not over the PDT ALW terminals due to cool moist boundary layer
as the rains end and the fact that the HREF is printing low
vsbys in the adjacent foothills. Guidance, both climate and HREF
keep the terminal vicinities clear with light south to
southwest winds overnight. NO chances for impacts elsewhere.
Surface winds will increase marginally to 10 to 15 knots through
the Gorge/Blue Mt Foothills terminals (DLS/PDT/PSC/ALW) Monday
afternoon with gusts commonly in the 20 to 25 knot range).

&&

.Preliminary Point Temps/PoPs...
PDT  71  42  75  47 /  10   0   0   0
ALW  73  49  77  52 /  20   0   0   0
PSC  76  46  79  48 /   0   0   0   0
YKM  76  48  78  50 /   0   0   0   0
HRI  74  45  78  47 /   0   0   0   0
ELN  71  45  77  47 /   0   0   0   0
RDM  68  38  75  40 /   0   0   0   0
LGD  68  42  74  45 /  20  10   0   0
GCD  67  41  76  46 /  10   0   0   0
DLS  74  51  80  55 /   0   0   0   0

&&

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

&&

$$

DISCUSSION...82
AVIATION...71