Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 201234 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
425 AM PST Fri Jan 20 2017

Updated AVIATION Discussion

.SHORT TERM...Today through Saturday Night...An upper level trough
off the coast will begin to move inland today which will push a band
of precipitation across the forecast area. Precipitation will begin
in central Oregon this morning and then slowly lift north and east
during the day and evening before exiting overnight. Precipitation
type will be mainly snow but with some rain in the lower elevations
by afternoon and evening. There will be a slight chance of some
freezing rain at the onset of precipitation in the Columbia Gorge
and the lower Columbia Basin but expecting minimal ice
accumulations. Have added the Yakima and Kittitas Valleys to the
list of Winter Weather Advisories with around 2 inches of new snow
possible. There will be a brief break in the precipitation late
Friday night and early Saturday before another surge of moisture
brings a chance of precipitation but in a less organized manner so
just expecting showers. The onset of another better organized surge
of moisture will begin late saturday night and persist into Sunday
which will be discussed in the long term section.

.LONG TERM...Sunday morning through Thursday...A vertically stacked
low pressure system remains quasi-stationary near 45N/133W while
sweeping a warm front northward across forecast area on Sunday for
precipitation likely Sunday morning. Snow levels Sunday will be
1000-2000 feet along the east slopes of WA Cascades, 2000-3000 feet
along the east slopes of OR Cascades and the Ochoco-John Day
Highlands ans 400-1800 feet in north central OR, SE WA and NE OR.
The warm front lifts northward into the Lower Columbia Basin of SE
WA Sunday afternoon resulting in central and north central Oregon
being in the warm and dry sector of the aforementioned low pressure
offshore. The low drifts slowly southeastward toward the northern
California coast Sunday night and Monday, thus taking dynamic lift
associated with the low away from central and NE Oregon and SE WA
for dry forecast at lower elevations through Monday afternoon.
Monday night through Thursday night a large amplitude mid/upper
level ridge of high pressure builds just offshore thus putting the
interior Pacific Northwest on the eastern flank of the ridge for a
dry northerly flow aloft yielding dry conditions from Monday night
through Thursday night.  Polan

&&

.AVIATION...12Z TAFs...Moisture trapped under low level inversions
over the Yakima Valley and the Lower Columbia Basin of WA continues
to produce areas of dense freezing fog and low stratus deck. Thus
LIFR and VLIFR conditions are expected to persist at KYKM and KPSC
until around 16Z this morning. Vis/cigs at KYKM and KPSC should
improve to IFR with the onset of light snow during this morning.
Fog/stratus will continue at KDLS as well until -SN arrives followed
by -RASN with the boundary layer becoming more mixed, though -SN/-
RASN at KDLS will keep IFR/MVFR cigs/vis. Downslope southeast winds
at KPDT and KALW will yield VFR conditions for the next 24 hours. -
SN expected at KRDM and KBDN will lower cigs/vis to MVFR in the
morning. Snow or rain showers will linger in the vicinity of KRDM
and KBDN in the afternoon, but cigs/vis should be generally VFR.
Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  31  41  34 /  40  40  20  20
ALW  43  33  42  36 /  20  30  20  20
PSC  36  30  35  29 /  50  70  20  20
YKM  34  29  35  29 /  90  80  20  30
HRI  36  30  36  29 /  50  70  20  20
ELN  34  29  34  27 /  80  80  30  40
RDM  39  25  38  29 /  90  50  60  40
LGD  35  25  34  30 /  30  50  30  20
GCD  37  22  36  26 /  80  60  30  10
DLS  35  31  35  31 /  90  80  70  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freezing Fog Advisory until 10 AM PST this morning for ORZ041-
     044.

     Winter Weather Advisory from 7 AM this morning to 4 AM PST
     Saturday for ORZ041-510.

WA...Freezing Fog Advisory until 10 AM PST this morning for WAZ024-
     026>028.

     Winter Weather Advisory from 7 AM this morning to 4 AM PST
     Saturday for WAZ024-521.

     Winter Weather Advisory from 10 AM this morning to 4 AM PST
     Saturday for WAZ026-027.

&&

$$

91/99/99


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