Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 221028
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
228 AM PST Wed Nov 22 2017

.SHORT TERM...Today through Friday Night...Widespread rain
continues to move east across the eastern OR mountains early
this morning in association with a weak shortwave in moist
SW flow aloft. Further to the west, precip is more scattered
in coverage, with little/no precip for the lowest elevations.
Patches of light fog cannot be ruled out in areas of lighter
precip coverage through the morning, but intensity of the fog
not sufficient for inclusion in the forecast. Rain will gradually
decrease in coverage for most areas by this afternoon as the
greatest forcing exits to the east. However, will keep low end
PoPs for the lowlands, and high end chance to likely PoPs for
the mountains as moist SW flow continues. Very warm conditions
exist aloft and with better deep layer mixing than yesterday,
expect today`s highs very warm for late November, with upper 50s
to lower 60s for the lower elevations and mainly 50s for the
maintains. Rain coverage will remain fairly low for most areas
tonight with a cold front still well off to the west. Will use
slight chance to chance PoPs for all but the east slopes of the
Cascades where likely and higher PoPs will prevail. Very mild
low temperatures can be expected tonight, with upper 40s to lower
50s for the lower elevations.

Thanksgiving Day/Thursday Night...The next cold front will
approach the Cascade crest in the morning, crossing the majority
of eastern OR/WA during the afternoon, then exiting Thursday
Night. With ample deep layer moisture, expect widespread rain
for the higher elevations in the afternoon/evening, with chance
to likely PoPs for the lower elevations/foothills. The other
forecast concern is the wind. Surface pressure gradients tighten
behind the front. In addition, winds at 5000-10000 feet reach
50-60 knots early Thursday evening. With a sufficiently thick
mixed layer, some of these high winds could work down toward
the surface. Will have to monitor the situation closely for a
possible wind advisory for the Columbia Basin down to the
Deschutes Plateau, but will keep winds just under criteria for
now. With a mainly afternoon frontal passage, another warm day
is expected, with highs in the lower/mid 60s for the lowlands.
Cooler air will work into the area Thursday Night, with lows in
the 30s for the lowlands and mid 20s to lower 30s mountains. Snow
levels of 8000-10000 feet Thanksgiving Day will fall to 4000-6000
feet Thursday Night, so expect precip to remain rain for all
passes.

Friday/Friday Night...Rather quiet conditions can be expected, as
the cold front is well to the southeast, and the next system is
progged to be offshore. Expect cooler temperatures than on
Thanksgiving Day, but remaining seasonably mild for late November.



.LONG TERM...Saturday through Wednesday...The unsettled weather
pattern will persist into the extended forecast period. There will
be warm and cold frontal systems moving across the forecast area
every couple of days. Models are in fairly good agreement with an
upper ridge over the region, just east of the CWA, which puts the
CWA on the warm southwest flow side of the ridge. An atmospheric
river off the Pacific will continue to feed moisture up and over
this ridge every couple of days resulting in periods of rain. Snow
levels will be quite high through about Sunday with levels between
6000-8000 feet MSL. There will be no winter weather concerns during
this time period due to the high snow levels. Then on Monday a cold
front will cause snow levels to drop to about 5000-6000 feet on
Monday, and then further dropping to around 3500 feet by Tuesday
with another cold front. Then snow levels rise back up to between
5000-6000 feet again by Wednesday. These combined with mild 850 mb
temperatures will keep conditions warmer than normal for late
November. No real drying is expected through the entire extended
forecast period...though it will become drier on Tuesday and
Wednesday with precipitation by then mainly just in the mountains.
Winds will be breezy to locally windy at times during frontal
passages, especially on ridge tops, otherwise they will be fairly
light.


&&

.HYDROLOGY...Abundant rainfall across the east slopes of the WA
Cascades will lead to rising levels on area streams and rivers.
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 tonight, peaking
Thursday evening. Have issued river statements for these two
locations. At this point it does not appear that the Naches will
reach flood stage, but the situation will continue to be monitored.

&&

.AVIATION...AVIATION...12Z TAFs...There will be periods of MVFR
and possibly IFR conditions during the next 24 hours due to low
cigs and visibility in fog, low stratus and precipitation.
Ceilings will be below 3K feet at times with visibilities down to
below 3 miles at times, especially early this morning. VFR
conditions will become more frequent by Thursday morning due to
some drying taking place...but it will still be generally
unsettled at all TAF sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  51  63  38 /  50  20  70  40
ALW  60  53  65  41 /  70  30  70  40
PSC  58  48  65  40 /  30  30  30  10
YKM  54  41  58  35 /  20  30  40  20
HRI  58  47  63  38 /  40  20  50  20
ELN  52  39  56  33 /  40  40  30  20
RDM  65  47  61  31 /  30  20  40  30
LGD  59  50  60  38 /  90  30  60  60
GCD  60  50  61  37 /  80  20  30  60
DLS  55  48  61  40 /  60  40  60  40

&&

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

$$

80/88



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