655 
FXUS66 KPDT 062348 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
448 PM PDT Mon Sep 6 2021

.Updated aviation discussion

.SHORT TERM...Tonight through Wednesday...Other than air quality
concerns, the next 48 hours is looking quiet weather-wise. High
pressure aloft is strengthening, and the surface gradients are
weakening as a result. Tuesday will be the warmest day of the
week with highs in the mid-80s to mid-90s. The relative humidity
will be in the single digits and teens, but winds will be light. 

High pressure will shift eastward Tuesday night, allowing a
southwest flow aloft to increase east of the Cascades. This will
likely impact the forecast area by increasing the instability as
well as push smoke from fires to the northeast. Upon review and
collaboration with air quality agencies tomorrow, the Air Quality
Alerts and Advisories may need to be expanded in coverage and 
into Wednesday. A shortwave trough riding north along the backside
of the ridge will clip our northwest corner of the forecast area 
early Wednesday morning with a potential for high based 
thunderstorms along the east slopes of the WA Cascades and the 
Kittitas Valley. Rainfall amounts will generally be less than 0.10
inch but any lightning will be short-lived with the fast moving 
trough. By 18Z Wednesday, it will be in NE Washington and out of 
the forecast area. An associated surface cold front will bring 
breezy winds but mainly through the Cascade gaps and eastern 
Columbia River Gorge. 

.LONG TERM...Thursday through Monday...GFS, ECMWF and Canadian all
advertise another trough off the coast Thursday and split the 
trough into two separate shortwaves Thursday night and Friday. 
However, models differ on the position and timing of the shortwave
along the southern branch. Therefore, confidence where showers or
thunderstorms occur is low but all point in the eastern mountains
and valleys. There are signs of instability Thursday night, and 
the NBM places the best potential in Wallowa County. The passage 
of the northern shortwave will increase winds aloft and at the 
surface, and breezy to windy conditions are expected. This will 
pose concerns for fire weather, and the relative humidity that 
afternoon will be in the 20s. Since there are some model 
differences and confidence isn't high in the overall pattern, 
will hold off any fire weather highlights for now.

On Friday, it seems best to have around 15-20 percent chance of 
showers covering the eastern mountains and valleys until 
confidence improves on the position of the southern shortwave
trough. Based on the individual ensemble members, a majority of 
the ECMWF has light QPF in this area...but only a few members of
the GEFS indicate the same.

This upcoming weekend is looking like a dry westerly flow with  
near to below seasonal temperatures.  Wister/85

&&

.AVIATION...00Z TAFs...Areas of smoke will continue to cause MVFR 
and possibly IFR conditions at KRDM, KBDN and KYKM. Elsewhere expect 
VFR conditions through the next 24 hours with just a few high think 
clouds. Winds will be mostly light. 88

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  90  57  90 /   0   0   0   0 
ALW  58  92  61  91 /   0   0   0   0 
PSC  58  92  60  92 /   0   0   0  10 
YKM  53  89  59  89 /   0   0   0  20 
HRI  57  93  59  93 /   0   0   0   0 
ELN  53  88  59  85 /   0   0  10  20 
RDM  52  95  55  91 /   0   0  10  10 
LGD  55  93  57  90 /   0   0   0   0 
GCD  55  98  57  95 /   0   0   0   0 
DLS  61  95  66  91 /   0   0  10  10 

&&

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

&&

$$

SHORT TERM...85
LONG TERM....85
AVIATION...88