Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 212300
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
250 PM PST Tue Nov 21 2017

.SHORT TERM...Satellite water vapor imagery and the height contours
of the 400mb pressure surface indicate a longwave trough and a
mid/upper level high pressure ridge couplet over the NE Pacific and
the interior Pacific Northwest. The trough is between 140-150W and
the ridge axis has pushed into Idaho this afternoon. This pressure
pattern yields southwest flow aloft on the eastern flank of the
trough, which is steering an atmospheric river of moisture into the
Pacific Northwest. This has brought a warm front and attendant rain
to the forecast area today. The warm front will continue moving
north tonight and a chance of rain through tonight to the forecast.
Snow levels will be well above normal tonight through Thursday
afternoon. A such precipitation will occur as rain in the mountains
through Thursday morning ahead of a cold front that begins to move
into the western sections of the forecast area after daybreak on
Thursday. The cold front will sweep across the region during the day
on Thursday with snow levels lowering to 4500-5500 feet along the
east slopes of the Washington Cascades by sundown Thursday, lowering
to around 5500-6500 feet along the east slopes of the Oregon
Cascades by late Thursday afternoon, and lowering to 6500-7500 feet
in the eastern Oregon mountains.  very fast moving mid/upper level
shortwave then pushes the cold front into Idaho Thursday evening
resulting in rain showers tapering off and ending in the evening,
first in central Oregon and then in the Blue Mountains by around
midnight with overnight being dry as a flat mid/upper level ridge
moves into the forecast area.  Polan

.LONG TERM....LONG TERM...Friday through Tuesday...On Friday, a
front will have moved off to the east and weak ridging will be over
the area. Most of the area will be dry Friday and Friday night
though a moist westerly flow will keep a chance of upslope rain and
snow showers in the Cascades. Snow levels will be around 3500-4000
feet. On Saturday a trough will approach the coast and push the
ridge off to the east. A front ahead of the trough will bring a
chance of rain in central Oregon in the morning and over the rest of
the area in the afternoon and Saturday night. The front will be
accompanied by breezy winds in the afternoon and early evening. On
Sunday the trough will progress to the coast as a upper low arrives
and deepens the trough. The trough will move overhead Sunday night.
This will keep a chance of rain over the area as well as another
round of breezy winds. Monday will see the trough move off to the
east and rain will be tapering off to showers. A ridge will be
building off the coast Monday night and Tuesday. This will allow the
lower elevations to dry out and keep just a slight chance of rain in
the mountains. Temperatures will be in the mid 40s to mid 50s Friday
and again on Saturday though the Yakima and Kittitas valleys will be
under the trough Saturday with temperatures in the lower to mid 40s.
Temperatures will return to the mid 40s to mid 50s on Sunday then
cool a couple of degrees on Monday and Tuesday, ending up in the 40s
and lower 50s on Tuesday. Perry

&&

.AVIATION...18Z TAFs...VFR conditions will generally prevail for the
next 24 hours with mainly mid level OVC expected. Prevailing rain
with periods of lighter showers is expected for the next 24 hours
though KBDN and KRDM may not see much rain after 12Z. With the
heavier rain, MVFR ceilings and visibility will be possible,
especially at KYKM after 12Z and KALW after 06Z. Rain will begin
decreasing after 15Z. winds will generally remain below 12 kts
though KBDN and KRDM will have gusts to 20 kts this afternoon and
early evening. Perry

&&

.HYDROLOGY...Abundant rain over the next few days will lead to
rising levels on area streams and rivers. Most will handle the
increased flow without a problem. The main concern will be in the
Yakima River basin, mainly along the Naches River. The Naches River
at the Cliffdell and Naches gauges are forecast to rise above
bankfull tomorrow evening and peak Thursday evening. At this point
it does not appear that the Naches will reach flood stage, but the
situation will need to be monitored. Perry

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  64  48  62 /  80  40  10  50
ALW  49  63  51  63 /  90  60  20  50
PSC  45  61  47  64 /  80  50  10  20
YKM  41  56  42  57 /  40  60  10  30
HRI  45  60  45  63 /  80  30  10  30
ELN  38  54  39  55 /  40  70  20  30
RDM  49  63  46  60 /  70  10  10  20
LGD  48  58  49  58 /  90  70  10  50
GCD  48  60  48  60 /  70  10  10  30
DLS  47  60  47  59 / 100  40  20  50

&&

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

$$

99/83/83


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