970
FXUS66 KPDT 111028
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
328 AM PDT Fri Sep 11 2026

.KEY MESSAGES...

- Dry weather today and tonight.

- Isolated thunderstorms Saturday and Sunday.

- Widespread rain Saturday through early Sunday.

- Below normal temperatures through the next week.

&&

.DISCUSSION...
Westerly flow will be over the region today, which will bring
dry weather. The flow will become more southwesterly tonight in
advance of low pressure which will move south then southeast
over the Pacific and then approach the Washington and Oregon
coasts on Saturday.

The low will then move onshore in Oregon Saturday evening and
move northeast towards southern Canada during Sunday, bringing
rain. Precipitation should end from west to east during the day
on Sunday, with all rain ended by Sunday evening/night.

Rainfall amounts during the day on Saturday will not be very
much and mainly confined to the mountains. QPF amounts should
mainly be 0.10 inches or less. The more widespread rain is
expected to move in during the evening and overnight. QPF
amounts vary widely between the models with the NAM being on the
lower side and the GFS and ECMWF having some of the higher
amounts, depending on location. Current forecast values have
<=0.25 inches in central Oregon ).50 inches or less in most
lower elevation locations 0.75 to 1 inch for the Blue Mountain
Foothills. Amounts of 1 inch plus are forecast for the
Washington Cascades and Blue Mountains.

However, there is considerable uncertainty in these numbers. The
ECMWF EFI indicates that while these values are in the 90th to
95th percentile, it also shows a value of 5 for shift of tails,
which shows the high uncertainty. Looking at the ensemble QPF
clusters, the wettest pattern only has about a 25 percent chance
of occurring, though the most likely scenario still does bring
decent rains.

Another concern for Sunday, as the low moves across is gusty
winds, especially in the Cascade Gaps, Kittitas Valley, Simcoe
Highlands, Columbia Basin, Gorge and Foothills of the Blue
Mountains. Winds look to gust in the 30 to 40 mph range,
possibly as high as 45 mph. NBM wind gusts probabilities >=39
mph are >60 percent in many of these areas. Depending on how
things develop, it is possible wind headlines may be needed at
some point.

Dry northwest flow will then move in for Monday. Another low and
trough will then drop down from Canada on Tuesday. There is some
discrepancy as to how quickly this low exits the area, but it is
expected to be dry or mainly dry at this time, but bears
watching.

Temperatures will be below normal through the weekend and into
next week, with Sunday being the coolest day. Temperatures will
average 5 to 10 degrees below normal, but will probably be 15
degrees below normal on Sunday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
VFR conditions are expected through the TAF period. Winds will
mainly be 10 kts or less, except at DLS which will have some
gusty winds to around 20 kts this morning before decreasing to
10 kts or less this afternoon.


&&

.Preliminary Point Temps/PoPs...
PDT  72  46  72  45 /   0   0  10 100
ALW  74  52  74  50 /   0   0   0 100
PSC  77  49  77  46 /   0   0   0  90
YKM  74  52  73  49 /   0   0  20  90
HRI  76  47  76  45 /   0   0   0  90
ELN  70  48  69  44 /   0   0  10  90
RDM  74  39  66  35 /   0   0  40  80
LGD  73  46  76  44 /   0   0  30 100
GCD  75  46  77  43 /   0   0  30  90
DLS  76  53  74  51 /   0   0  20  80

&&

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

&&

$$

DISCUSSION...77
AVIATION...77