891 
FXUS66 KPDT 210923
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
223 AM PDT Tue May 21 2019

.SHORT TERM...Today through Thursday...An upper level low pressure 
system along the Oregon coast this morning will move southeast 
across southwest Oregon today and then settle into the large upper 
level trough over the western United States forming a closed upper 
level low over the Great Basin. This low is currently creating a 
nearly stationary frontal boundary with precipitation across the 
forecast area stretching from southwest Idaho to western Washington. 
This boundary will persist through much of the day stretching from 
the east slopes of the Washington Cascades back into northeast 
Oregon producing a steady light rain. It will begin to weaken and 
fall apart late this afternoon and evening with the precipitation 
emphasis overnight shifting south across eastern Oregon as the flow 
aloft turns more easterly. Wednesday and Thursday the forecast area 
will be under a north to northeast flow feeding into the large upper 
level low centered over the Great Basin. Some weak instability over 
the region in this flow will result in some showers over the eastern 
mountains and the Cascades both days with showers tapering off in 
the evenings. There will be a slight chance of thunderstorms today 
over central Oregon and then along the east slopes of the Washington 
Cascades Wednesday and Thursday afternoons.

.LONG TERM...Thursday night through next Tuesday...The 
weather pattern will remain unsettled and showery through most of 
the extended period. There will be a break or two in the weather 
between systems, but overall it will remain unsettled. On Thursday 
night and Friday there will be an upper low over the northern Rocky 
Mountains and an amplified upper ridge well off the coast. This will 
put a north to northeasterly flow over the forecast area. An upper 
low pressure system will drop down from BC and bring more rain 
showers to the CWA on Friday. There will also be enough instability 
for possible afternoon thunderstorms on Friday over southeast 
portions of the forecast area. This upper low will slide southward 
along the coast into northern California by Saturday. There will 
still be some wrap around moisture into the CWA in an easterly flow 
on Saturday as this low moves southward. Once again, there will be 
enough instability Saturday afternoon and evening for possible 
thunderstorms, if there is enough surface solar heating. The upper 
low will stall over California and keep and easterly flow over the 
forecast area through Sunday. Yet again, there will be enough 
afternoon instability due to surface heating for possible 
thunderstorms as well on Sunday. By this time, the longer range 
models really begin to diverge significantly with each other, and 
therefore made little change to the forecast after Sunday as a 
result of the uncertainty. However, it will still remain unsettled 
with showers on Monday...with possible thunderstorms again in the 
afternoon in southeast areas of the CWA. On Tuesday some drying will 
take place as an upper ridge tries to build over the region. 
Temperatures will be rather cool through Saturday and then there 
will be a warming trend from Sunday onward with temperatures 
climbing up back into the 70s to lower 80s in the lower elevations 
and 60s to lower 70s in the mountains by Tuesday. It will be breezy 
on Friday, mainly in north central Oregon and the eastern Columbia 
River Gorge, but the winds will become calm Friday night. Winds will 
then remain light after that through Tuesday. 88



&&

.AVIATION...12Z TAFs...A band of rain showers has developed in a 
southeast flow over the area from northeast Oregon northwest to 
Yakima County along the Cascade east slopes in a wrap around flow 
around a low pressure system along the Oregon coast. There could be 
brief periods of MVFR conditions under this band of rain due to 
lower CIGs and visibility in the rain. However, most of the time it 
will remain VFR. The band of rain will shift southward through the 
day and tonight with KRDM and KBDN receiving the best chance of 
precipitation tonight. There could be more periods of MVFR 
conditions at KRDM and KBDN tonight as a result. Winds will be light 
through the next 24 hours. 88


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  46  71  46 /  80  30  10  10 
ALW  64  47  73  49 /  90  30  10  10 
PSC  68  51  78  53 /  70  10   0   0 
YKM  67  50  76  53 /  70  10  10  10 
HRI  66  48  76  49 /  70  20   0  10 
ELN  66  48  72  50 /  60  10  10  10 
RDM  59  41  66  42 /  60  70  40  20 
LGD  57  44  64  43 /  90  60  20  20 
GCD  56  43  62  42 /  70  60  20  20 
DLS  67  51  76  53 /  40  20  10  10 

&&

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

$$

91/88/88