265 
FXUS66 KPDT 120357
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
857 PM PDT Fri Sep 11 2026

.KEY MESSAGES...
- Scattered rain showers and Isolated thunderstorms developing
  Saturday evening and rain showers becoming more numerous 
  though Sunday morning. 

- Widespread wetting rain Saturday Night and Sunday

- Breezy to windy across the eastern Columbia River Gorge 
  Saturday Night and Sunday Morning.

&&

.UPDATE...
The incoming system continues to trend towards a wetter
scenario, which is advertised by a 20-30% increase in
precipitable water via the AI ECMWF ensembles over the last 24
hours. This is a direct result of increased resonance time near
a closed low pressure system further offshore over the Eastern 
Pacific. The delay has also attributed to a stronger transient 
ridge of high pressure building ahead of this system, which will
allow for thunderstorm development across the Blue Mountains and 
leading to increased potential for heavy downpours in and around
fire scars of the Paradise and Hagen wildfires. The REFS 
suggests convection beginning around 6 PM and extending until 
shortly after midnight. As a result, a FLOOD WATCH has been 
issued across both burn scars from Saturday afternoon through 
Sunday evening as rain rates of around 0.5"/hour may be achieved
within a developed rain core. 75

&&

.DISCUSSION...
Regional radar was clear this afternoon with GOES satellite day
cloud phase showing thin high level clouds spreading east 
across the Upper Columbia Basin. Eastern WA Eastern OR, while 
most of central Oregon and the southern Blue Mts were 
clear/sunny. The weak zonal flow aloft across the region Today
will be disrupted as an upper low spreads onto the Oregon coast
by late Saturday Afternoon and Evening, placing the Interior NW
under a broad area of PVA advection/diffluence aloft. The 
showers that are already going on Today west of the Cascades 
will be diurnal in nature, so no rain is anticipated overnight. 
Increasingly broad scale lift and moisture transport will 
promote instability on Saturday, enough so for isolated to 
widely scattered thunderstorm and widespread wetting rains from 
few tenths of an inch to potential for over an inch in the 
Mountain zones though the day on Sunday, once the upper system 
exits the region. Initially a few showers are possible along the
Cascade crest, but everywhere farther east will be dry through 
about the end the afternoon Saturday. HREF (ensembles) show a 
ramp up in the mean 1 hourly precipitation fields between about 
5 and 9 pm, across the Eastern Slopes, the Columbia Basin and 
foothills of the Blue Mts. There is nothing all that anomalous 
with the PWATS for this system. About a 1 standard deviation in 
precipitable water shows up across the Cascades and the Eastern
Mts Saturday afternoon/Evening and spreading north into eastern
WA though Sunday morning as the cold conveyor belt lifts across
the Palouse. Trends for thunder continue to be pushed back in 
time as the 12z HREF now shows 4hr calibrated thunder (10 to 
30%) around 6z (nearing midnight Saturday) or so for the 
foothills of the Blues. The period of heaving rainfall will be 
between midnight Saturday and about noon Sunday with model 
spreads fairly large. Uncertainty at the Tri-Cities is a range 
of (using 25th to 75th percentile) anywhere form at least about 
a quarter of an inch to and inch and and quarter by late Sunday
evening. That uncertainty/spread is compressed a bit over the 
mountain zones. For instance at La Grande where at least one 
half inch can be expected with a higher outcome around an inch 
an a quarter of rainfall. Rainfalls of around an inch are fairly
likely (above about 60%) for the Paradise/Hagan fire areas. 
Westerly winds ramp up through the gaps on Saturday evening as 
well with the stronger period running from around midnight 
Saturday though late morning Sunday morning. The NBM mean shows 
potential for sustained winds in excess of 30 mph and gust in 
excess of 40 mph however these stronger winds are limited to the
higher ridge-tops along the Gorge. Most other areas look breezy
and falling under the general wind advisory criteria. The wet 
regime will hamper temperatures Sunday, where mid 60s will be 
the highest temps across the the Kittitas Valley, central Oregon
and parts of the Basin. Dry weather and pleasant temperatures, 
with not a lot of wind will finish out the balance of the week 
before NBM trends toward a warmup by the next weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
VFR conditions are forecast through the TAF period. Winds at 
all sites except RDM, BDN, and KDLS will be lower then 10 kts. 
BDN and RDM will experience gusting conditions of up to 20 kts 
from the 22Z to 00Z timeframe, with DLS reaching 15 kts. Low 
confidence (10-30%) in rain showers for YKM, DLS, BDN, and RDM 
starting around 22-00Z, with a PROB30 being issued for YKM.

&&

.Preliminary Point Temps/PoPs...
PDT  47  76  45  61 /   0   0  90  80 
ALW  52  79  49  60 /   0   0  90  90 
PSC  50  80  47  63 /   0   0  90  90 
YKM  54  76  50  63 /   0  10  90 100 
HRI  49  79  46  63 /   0   0 100  80 
ELN  48  72  44  59 /   0   0 100 100 
RDM  40  71  36  60 /   0  10  80  10 
LGD  47  81  44  59 /   0   0  90  80 
GCD  46  81  43  59 /   0   0 100  40 
DLS  54  77  51  66 /   0  20  90  60 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Flash Flood Watch from Saturday afternoon through Sunday 
     evening for WAZ030.
OR...Flash Flood Watch from Saturday afternoon through Sunday 
     evening for ORZ502.

&&

$$

UPDATE...75
DISCUSSION...71
AVIATION...86