Weather Service Report


144 
FXUS66 KPDT 290542
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1014 PM PDT Fri Apr 28 2017

.SHORT TERM...upper ridge offshore with dry northwest flow over
the area. Daytime cumulus is dissipating and expect mainly clear
skies overnight. Temperatures will be cool with lows in the 20s to
mid 30s. An upper level trough and frontal boundary will be 
approaching the Pacific northwest Saturday with increasing mid and
high level clouds. This system will move through Sat night and 
Sunday morning with mostly cloudy skies and a chance of rain. 
Decreasing precipitation and clouds by Sunday afternoon with 
surface high pressure building back in. Westerly winds increasing 
with breezy to windy conditions developing. 94

.AVIATION...06z tafs. Mainly clear skies overnight. Increasing mid 
and high level clouds Saturday with ceilings 100-200. Front moving 
into the area Saturday night with showers developing and ceilings 
lowering to 030-060. 

&&

.PREV DISCUSSION... /issued 226 PM PDT Fri Apr 28 2017/ 

SHORT TERM...Tonight through Monday...An upper level ridge centered 
offshore has expanded over the area as an upper low over the Rockies 
has moved south and further away from our area. A dry north to 
northwest flow is over the area and skies have been clearing this 
afternoon. While the mountains will remain partly cloudy this 
evening, skies will be generally mostly clear with little chance of 
precipitation. Breezy winds this afternoon will die down this 
evening and become light overnight. This will set up good conditions 
for radiative cooling but the increasing influence of the ridge will 
keep temperatures from falling too far, perhaps a couple of degrees 
cooler than last night with mid to upper 30s in the lower elevations 
and mid 20s to lower 30s in the mountains. Tomorrow the ridge will 
move overhead by the afternoon but it will be flattening as a system 
rides over the ridge. Saturday should see clouds increasing in the 
afternoon. A chance of showers should hold off until the evening 
along the Cascades and then over much of the area overnight and 
Sunday morning though the Columbia basin should be mainly dry. Snow 
levels will be around 6000 feet so rain will be the main form of 
precipitation. Rain amounts will be light with less than a tenth of 
an inch in the lower elevations and up to two tenths of an inch in 
the mountains. As the system clears the area Sunday afternoon, 
pressure gradients will strengthen and winds will increase. Thus far 
it looks like winds will be 15 to 25 mph in Central Oregon, 20 to 30 
mph in the Columbia Basin and 25 to 35 mph in the Columbia Gorge and 
Kittitas Valley. May need to issue a wind advisory or two for then 
but will keep evaluating for now. Sunday night and Monday, the ridge 
will be rebuilding offshore and the forecast area will be dry aside 
from a few showers along the Cascade Crest. Monday afternoon, 
another shortwave will move into the area with very light rain 
showers mainly in the mountains. Snow levels will be at 4500-5500 
feet. Temperatures Saturday through Monday will be in the mid to 
upper 60s with 50s and lower 60s in the mountains. Lows Saturday 
night will be in the mid 40s to lower 50s with mid 30s to lower 40s 
in the mountains. Sunday night will cool to the upper 30s to mid 40s 
with upper 20s to mid 30s in the mountains. Perry 

LONG TERM...Monday night through Wednesday night...On Monday 
evening a low amplitude shortwave trough will move quickly across 
the area in NW flow aloft and may produce a few mountain rain 
showers. It should be dry overnight. Tuesday through Wednesday night 
a rather pronounced ridge of high pressure will build over the 
western U.S. This will result in dry and warming conditions. Highs 
will be around 70 lower elevations Tuesday and well into the 70s 
Wednesday...with 50s/60s mountains both days. 78

Thursday morning through Saturday...There is substantial uncertainty 
in the position/strength of the of the trough approaching the coast 
on Thursday night. Have opted away from the operational GFS and more 
toward the ECMWF/Canadian solution...which is also more in line with 
the GFS ensemble mean. Instability will increase ahead of the 
approaching trough as lapse rates steepen Thursday night into Friday 
morning with a chance of showers and perhaps a couple of 
thunderstorms especially across the eastern slopes of the Oregon 
Cascades and southern Blue Mountains.  On Saturday, showers will 
clear the area from west to east as the trough clears the forecast 
area. 74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  35  63  49  63 /   0   0  30  30 
ALW  39  64  50  66 /   0   0  40  40 
PSC  35  67  50  68 /   0   0  20  10 
YKM  34  63  43  64 /   0   0  20  10 
HRI  33  66  49  66 /   0   0  20  10 
ELN  35  58  42  57 /   0   0  30  10 
RDM  23  63  42  59 /   0   0  20  20 
LGD  30  60  44  58 /  10   0  30  40 
GCD  28  61  42  61 /   0   0  20  30 
DLS  38  65  47  61 /   0   0  30  20 

&&

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

$$

94

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Western Regional Climate Center, wrcc@dri.edu