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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 231603

Area Forecast Discussion
National Weather Service Pendleton OR
900 AM PDT Thu May 23 2019

.UPDATE...Upper low to the south of the region will keep a NELY
upper flow over the area today into tonight. There will be 
sufficient moisture for a few mountain showers during the late 
afternoon and evening. Added a slight chance of showers for the 
eastern/northeastern mountains based on the latest model 
guidance. It appears that there may be enough instability during 
peak heating for a few weak thunderstorms and this is supported 
by the SREF thunder probabilities. Otherwise it will be clear to 
partly cloudy and warm with a north breeze that will be gusty at 
times especially in Oregon. 

.AVIATION...18z tafs. Clear skies through early afternoon then 
developing cumulus with sct 060-090. Scattered showers over the 
mountains mid afternoon through evening. Winds 10-20kt. Sct-bkn
070-120 tonight. Winds 5-15kt. 


.PREV DISCUSSION... /issued 240 AM PDT Thu May 23 2019/ 

SHORT TERM...Today through Saturday...An upper low pressure system 
that is currently over the Great Basin will begin to swing to the 
northeast today. There will still be some wrap around flow around 
this low into the forecast area which will cause some upslope 
showers along the Cascade east slopes. There may also be enough 
instability this afternoon for possible thunderstorms along the 
Cascades as well. Then overnight tonight it will become stable and 
the showers will taper off and end temporarily. On Friday that low 
pressure system will move off to the northeast, however another 
upper low will drop down from western Canada and bring more showers 
to the forecast area, especially in the afternoon. There will also 
be more widespread instability and have included a slight chance of 
afternoon thunderstorms in all areas of the forecast area. Some 
storms could be strong with small hail and gusty winds, but most 
storms will be weak. Then another upper low will drop down again 
from western Canada along the coast on Saturday for another chance 
of showers and possible afternoon thunderstorms. However, the 
thunderstorm coverage will not be as great and will mainly just be 
over the Blue Mountain Foothills southeastward. There could be a 
strong thunderstorm or two again, but most will be weak. 
Temperatures will be a little above normal today with highs mainly 
in the 70s to lower 80s in the lower elevations, with 50s and 60s in 
the mountains. Then cooling will take place on Friday and Saturday, 
mainly due to more clouds and some cold air advection as the lows 
drop down from Canada. High temperatures on Friday and Saturday will 
be slightly below normal with max readings in the upper 60s to mid 
70s both days. It will be breezy to windy in mainly central and 
north central Oregon today and Friday, with the winds diminishing at 
night. Winds on Saturday will be light, except for possible gusty 
winds near any showers or thunderstorms. 88

LONG TERM...Saturday night through Wednesday...Low pressure off the 
Washington/Oregon Coasts at the start of the period will move south 
off the northern California coast on Sunday morning.  From there, it 
will move inland over central/souther California and carve out 
another deep upper trough over the western CONUS by Monday morning. 
As this low moves inland on Sunday, there will be increasing 
moisture, with southerly flow in advance of the low.  There will be 
enough instability for thunderstorms, especially over eastern 
portions of the area during the afternoon.  The low will move into 
the Great Basin on Monday, and moisture will decrease, however, 
there will still be some moisture, northerly flow and some residual 
instability that there could still be some showers.

Beyond Monday, the ECMWF keeps the low much stronger over the Great 
Basin while the GFS weakens it and ejects it to the northeast. 
Tuesday would have greater shower chances if the ECMWF were to be 
correct.  As for Wednesday, both models bring in ridging and drier 
and warmer weather, but the ECMWF has stronger ridging in response 
to the stronger downstream low than the GFS.  There are still a lot 
of differences in the models beyond midweek and the overall pattern, 
but it does look like temps will be warming up and will be closer to 


PDT  75  51  69  42 /   0  10  30  20 
ALW  79  55  73  47 /   0  10  30  20 
PSC  82  58  77  50 /   0  10  20  20 
YKM  80  54  73  47 /  10  10  20  20 
HRI  81  55  75  46 /   0  10  20  20 
ELN  77  53  69  46 /  10  10  30  20 
RDM  69  44  65  37 /  10  10  20  10 
LGD  69  47  65  41 /  10  10  60  30 
GCD  69  45  67  39 /  10  10  50  30 
DLS  82  55  69  47 /   0  10  20  10