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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 220931

Area Forecast Discussion
National Weather Service Pendleton OR
230 AM PDT Wed May 22 2019

.SHORT TERM...Today through Friday...There is an area of showers 
moving across north central and northeast Oregon this morning in a 
wrap around flow around an upper low pressure system over the desert 
southwest. Expect this pattern to persist through tonight. There 
will be some instability this afternoon mainly along the Cascade 
east slopes where there could be a thunderstorm or two this 
afternoon and evening. Elsewhere expect isolated to scattered 
showers today over the eastern and northeast mountains. The showers 
will decrease and end by late tonight due to the loss of surface 
heating. The Lower Columbia Basin and adjacent lower elevations 
should remain dry today. Thursday will be similar to today. The 
upper low over the southwest will begin to lift to the northeast. 
There will again be enough moisture and instability again in the 
afternoon for possible thunderstorms along the Cascade east slopes. 
With the upper low departing to the northeast the eastern areas of 
the forecast area will be mostly dry and as a result did not include 
showers on Thursday in the eastern areas of the CWA. Then on Friday 
another upper low pressure system will drop southward from western 
BC into the Pacific Northwest. This system will bring a better 
chance of showers and especially afternoon thunderstorms over most 
of the forecast area. There could be a couple to a few strong 
thunderstorms on Friday, but most will not be strong. But the areal 
coverage will be much greater than today or Thursday. Temperatures 
will warm today to the upper 60s to mid 70s in the lower elevations, 
then warming further to the mid 70s to lower 80s on Thursday, but 
then cooling back down to the upper 60s to mid 70s on Friday. These 
temperature forecasts will be the result of more clouds today and 
Friday, but less on Thursday. It will be locally breezy through the 
period, mainly in the afternoons and evenings, and especially near 
any showers or thunderstorms. Winds will be mostly light by the late 
night hours each night. 88

.LONG TERM...Friday night through Tuesday...At the beginning of the 
extended period, a potent shortwave will be dropping into the 
Pacific northwest and this will cause a strong deepening of the 
longwave trough beginning Saturday and continuing into Sunday before 
the trough begins to move eastward.  The upper low will be over 
Washington and Oregon on Saturday and will drop into California by 
Sunday, and gradually push into the Great Basin by Monday.  The 
guidance has some short term ridging by Monday behind the trough 
before another low may begin to drop down Tuesday or Wednesday. 
Guidance begins to diverge after Tuesday.  With a large upper trough 
in place, expect unsettled conditions over the weekend, though it 
will not be rainy the whole time.  With the proximity of the upper 
low, there is a chance of thunder especially Saturday and into 
Sunday.  Best on the latest guidance, less confident into Tuesday. 
If guidance trends continue will likely remove thunder chances for 
Tuesday and possibly Monday in later forecasts.  Temperatures should 
begin a slow warming trend after Saturday.


.AVIATION...12Z TAFs...There has been some pesky MVFR CIGS early 
this morning, but general VFR is expected for today, with improving 
conditions later this morning into the afternoon hours.  Brief MVFR 
can not be ruled out in a passing shower for BDN or RDM but 
confidence is not high for those conditions later today.  Gusty 
northwest winds will occur this aftn and could reach as high as 30 
kts before decreasing this evening to less than 10 kts.


PDT  68  44  74  50 /  10  10   0  10 
ALW  73  49  79  55 /  10  10   0  10 
PSC  76  53  82  58 /  10  10   0  10 
YKM  75  52  80  53 /  10  10  10   0 
HRI  75  49  81  54 /  10  10   0  10 
ELN  71  50  77  53 /  10  10  20  10 
RDM  63  42  69  44 /  20  30  10  10 
LGD  62  43  69  47 /  30  20   0   0 
GCD  61  42  69  45 /  30  30  10  10 
DLS  76  53  81  54 /  10  10  10  10