Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 220937

Area Forecast Discussion
National Weather Service Pendleton OR
237 AM PDT Thu Mar 22 2018

.SHORT TERM...Today through Saturday Night...Latest surface
analysis/radar loop shows a warm frontal boundary moving
north across Northern OR, with a band of showers stretching from
the Columbia Basin east to the northern Blues. With snow levels
mainly 6000-7500 feet, all precip is rain. Rainfall amounts are
not very heavy, with a few locations receiving 0.05-0.10 inch.

The warm front will continue to lift north across southern WA
early this morning, with the systems cold front moving east
of the Cascades this morning, crossing the Columbia Basin by
early this afternoon, exiting to the east of the area this
evening. Precip will decrease in coverage a bit this morning
in the warm sector, increasing once again this afternoon with
numerous/widespread precip along/in advance of the frontal
boundary. The precip will be steady at times, with areas of
convective showers given some instability, thus will use
shower wording. Sufficient instability will be present across
the eastern mountains this afternoon for an isolated thunderstorm
or two, but do not expect strong/severe storms. Snow levels
6000 feet or higher ahead of the cold front will lower this
afternoon to 3500-5000 feet behind the front across Central OR/WA
perhaps low enough for some scattered snow showers across the
lower Deschutes Plateau before precip diminishes late this
afternoon. Lingering numerous/widespread showers will prevail
from the Blues east early this evening, diminishing by the
overnight hours. Precip totals today/tonight will range from
0.10-0.25 inches for the lowest elevations to 0.25-0.50 for the
higher elevations. Snow levels will continue to lower tonight to
1000-2500 feet by the overnight hours. 1-2 inches of snow,
mainly above 4000 feet will be possible later tonight across the
eastern mountains. Wind wise, breezy/windy conditions will be
possible across the Grande Ronde Valley and the higher Blue
Mountains into this afternoon in southerly flow ahead of the
front. Behind the front, winds will increase across the Columbia
Basin/Gorge as well as the Kittitas Valley, with breezy/locally
windy conditions. There could be some gusts close to advisory
criteria along the eastern Blue Mountain foothills, but given a
small area of this potential, will handle via short term forecasts
if necessary. Highs today will range from the mid 50s to around
60 for the Columbia Basin and Blue Mountain Foothills, to the mid
40s to lower 50s for the Gorge/Yakima and Kittitas Valleys down
to Central OR, and mainly 40s for the mountains. Lows tonight will
range from the upper 20s to mid 30s for the lower elevations to
the 20s for the mountains.

Upper level low pressure of the WA/OR coast early Friday will
gradually dig to the south, moving into northern CA Saturday
night. Another rather potent shortwave will clip the area Friday
producing likely PoPs mainly across OR. With low snow levels,
1-2 inches of snow will be possible across portions of central OR
with locally higher amounts further west along the east slopes
of the OR Cascades. Will not issue any advisories at this time,
but the potential will need to be monitored closely. Precip
coverage will decrease by Saturday, with chance PoPs mainly across
Central OR and the eastern mountains, with little/no precip for
the Columbia Basin. Snow levels will remain rather low, generally
between 1500-3000 feet. Precip will be rather showery with the
cold dome aloft close to the area, briefly lowering snow levels
near the more potent showers, with rain/snow/graupel mix possible
to the lowest elevations. Temperatures will be cool, about 5-10
degrees below normal for Friday through Saturday night.

.LONG TERM...Sunday through Wednesday...The medium to long range
models are in fairly good agreement with an upper trough moving
inland to the Great Basin on Sunday. This will bring in a cold pool
of air aloft which will be conditionally unstable. As such will keep
showers mentioned for Sunday over the east and northeast mountains
as well as the Cascade east slopes. Snow levels will be around 1500-
2000 feet above sea level, so precipitation will be mainly in the
form of snow. Moisture is somewhat limited however so I do not think
there will be a need for winter weather highlights, at this time.
The upper trough will continue to move eastward on Monday with a
northerly flow developing over the region. This will cause a drying
trend. Then an upper ridge will take over control of the weather
over the CWA for the remainder of the long term period with mostly
dry conditions, except for possibly a few stray showers over the
mountains. Temperatures will be on a slight warming trend which will
cause them to become slightly above normal by Wednesday with maximum
readings in the lower 60s in the lower elevations and 40s to 50s in
the mountains. Winds will be mostly light through the period, though
there could be some breezy afternoon winds at times.


.AVIATION...12Z TAFs...Scattered to numerous rain showers and
mountain snow showers may cause brief periods of MVFR conditions
today, otherwise VFR conditions will prevail. There may be a
thunderstorm or two east of the TAF sites from the Blue Mountains
eastward. Conditions will improve with drying taking place from west
to east late this afternoon and evening. However, more snow showers
will be moving in from the west late tonight with the next weather
system. There will be breezy to windy conditions this afternoon and
evening mainly affecting TAF sites KRDM, KBDN, KDLS, KPDT and KPSC.
Elsewhere winds will be mostly light. The winds will diminish late
tonight at all TAF sites.


PDT  56  32  51  31 /  80  30  30  50
ALW  56  34  52  34 /  90  40  30  50
PSC  58  33  54  34 /  60  10  30  50
YKM  53  29  49  29 /  50  10  30  40
HRI  56  33  53  33 /  60  10  40  50
ELN  48  27  45  27 /  70  10  30  30
RDM  47  28  44  22 /  50  20  70  70
LGD  52  29  46  30 /  90  70  30  60
GCD  53  30  46  29 /  90  30  30  60
DLS  50  34  48  31 /  70  30  50  60




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