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FXUS66 KPDT 180928

Area Forecast Discussion
National Weather Service Pendleton OR
230 AM PDT Wed Sep 18 2019

.SHORT TERM...Today through Friday...Closed upper low centered north 
of Astoria pushed a frontal band across the region last night and is 
currently positioned from Wallowa County southwest to Klamath 
County.  The weak cold front will track to the southeast and over 
southwest Idaho this morning. There will be additional waves of 
moisture and energy rotating across WA/OR over the next 24 hours 
that will bring scattered to numerous showers.  WSR-88D is showing 
40-50 dBZ returns associated with one mid level wave traveling 
across north central OR at this time.  All zones will have at least 
a chance of showers and a slight chance of thunderstorms today as 
the closed low weakens into an open trough and migrates across the 
region. Precipitation amounts will vary from a few hundredths to 
around a quarter of an inch.  There will likely be small hail or 
graupel with some thunderstorms. Additional light snow can be 
expected above 7500 feet.  The locally breezy winds observed 
yesterday are decreasing, and winds today will be relatively light.

The upper level trough will be in no hurry to leave the region and 
will remain east of the Cascades tonight and most of Thursday. 
Showers will taper off from the west overnight, and precipitation on 
Thursday will mainly be in the eastern zones from the Blue Mountain 
Foothills down to John Day east to the Idaho border.  This area may 
also observe isolated thunderstorms Thursday afternoon.  The NAM was 
particularly bullish with QPF on Thursday with more enhanced wrap-
around moisture, and believe the GFS is more realistic with the 
heaviest precipitation amounts around 0.1-0.2 inch in Wallowa County 
with lesser amounts elsewhere. 

The trough will finally travel into Idaho Thursday night, and 
showers will taper off in the eastern zones by early Friday morning.
There will be isolated to scattered showers over Wallowa county late 
Thursday night and Friday, but dry conditions elsewhere.  The 
forecast area will be on the east side of a shortwave ridge and 
under a northerly flow aloft on Friday.  Skies will be party to 
mostly cloudy with locally breezy winds as surface high pressure 
builds with a fairly tight pressure gradient.  Friday will be a 
little warmer compared to today and Thursday but still below 
seasonal averages with highs in the upper 50s to upper 60s in the 
mountains and mid 60s to mid 70s elsewhere. Wister

.LONG TERM...Friday night through Wednesday...A northerly flow 
followed by an upper ridge will move into the region and the 
forecast area Friday night into Saturday. This will bring fair 
weather with dry conditions and warmer temperatures. However, the 
warmer temperatures will only be by a few degrees, but becoming near 
normal. Then on Sunday another upper trough and cold front will move 
down from the northwest into the Pacific NW bringing a chance of 
showers into the Cascades Saturday night and then across the rest of 
the forecast area on Sunday. Temperatures will cool down again on 
Sunday due to the clouds and precipitation. However, it will only be 
a few degrees below normal as the flow will generally be from the 
southwest. However, the upper trough axis will be over the CWA by 
late Sunday evening and the atmosphere will be more unstable. 
However, due to the timing of the trough axis late at night am not 
expecting any thunderstorm activity this time of year. Cannot rule 
it out, but will leave any mention of thunderstorms out of the 
forecast for now. Models are still in fair agreement at this point 
in time in the future. Then on Monday through Wednesday the models 
begin to diverge from each other, become greater with time. Most of 
them show another upper ridge building over the region. However, 
cannot rule out some showers due to the uncertainty in the models 
solutions through the latter extended period, especially over the 
Cascades and northeast mountains. Most areas will remain dry though. 
Temperatures will rise back to near normal again for Tuesday and 
Wednesday. Winds will be mostly light through the extended period. 88


.AVIATION...12Z TAFs...Radar is showing an area of rain moving in 
from the west. This is mostly affecting TAF sites KDLS, and 
occasionally KPDT and KALW. It is not a solid coverage of rain and 
so the precipitation will be intermittent. CIGs could drop to MVFR 
times in the precipitation along with the visibility. However, most 
of the time all TAF sites will remain VFR. Winds will be light 
through the next 24 hours at all TAF sites. 88


PDT  67  49  67  50 /  50  40  30  10 
ALW  70  52  70  53 /  50  40  40  10 
PSC  72  53  74  54 /  20  30  10   0 
YKM  68  47  72  51 /  40  30   0   0 
HRI  73  52  73  55 /  30  30  20   0 
ELN  66  46  70  52 /  60  30   0  10 
RDM  61  41  64  43 /  80  50  10  10 
LGD  60  45  61  46 /  90  70  50  10 
GCD  59  44  62  45 /  90  70  60  20 
DLS  68  51  72  55 /  70  20  10  10 



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