Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 052212

Area Forecast Discussion
National Weather Service Pendleton OR
212 PM PST Thu Dec 5 2019

.SHORT TERM...Tonight through Saturday afternoon...Most of the CWA
is currently under a deck of high clouds, while the lower
Columbia Basin, Kittitas and Yakima valleys are experiencing some
hazy conditions. The ridge overhead is still on track to extend
northward ahead of the low pressure system off the west coast.
Under this ridge, inversions will settle in overnight and allow
some freezing fog formations in the lower Columbia Basin. A
frontal passage associated with the low pressure system will move
through the area starting Friday afternoon, and help to push out
the fog by the late morning and break down the ridge. The front
will then be followed up by an offshore upper low off the coast
Saturday morning and a shortwave coming down from Alaska Saturday
afternoon. Snow levels associated with these systems will mainly
stay above 5,000 feet, which means mainly mountain snow with rain
in the lower elevation areas. On the eastern side of the WA
Cascades, snow levels are fairly lower due to a potential cold
pool in that area. Though snow levels are around 2,750 feet, still
expect rain in this area, but will keep watch for a slight
potential of freezing rain. The lower elevation rain and mountain
snow will persist through the period. A southerly wind increase
ahead of the frontal passage will start occurring tonight mainly
in the Blue Mountains, Grand Ronde Valley, and the Ochoco-John Day
Highlands. Breezy conditions will persist through Saturday, and
will decrease with the weakening of the upper low pressure system
as it marches east across OR and WA. Highs will be in the 40s both
Friday and Saturday. Lows tonight and tomorrow night will be in
the low 30s. Lawhorn

.LONG TERM...Saturday night through Tuesday. Offshore upper low
will move into the Pacific northwest Saturday night and Sunday
and merge with a short wave crossing southern BC. This will
result in rain and high elevation snow for the region. Snow levels
look to be about 4-5000 feet. Expect the precipitation to be
fairly widespread Sat night into Sunday morning then decreasing
in the afternoon. Northwest upslope flow will keep rain/snow over
the Blues through afternoon then diminish in the evening. Upper
ridge starts to build in Sunday night with gradual clearing. The
ridge will be over the area Monday and Tuesday with partly cloudy
skies. Freezing fog likely to develop in the valleys and Columbia
basin Mon night. High temps remain in the 30s to mid 40s through
the period. Lows in the 20s to mid 30s. No significant winds
expected. 94

.Tuesday Night through Thursday...Models continue to have
differences about a couple of disturbances moving through the area.
The GFS brings the first one through the area Tuesday night with a
chance of snow in the mountains and a slight chance of rain in the
lower elevations. The ECMWF brings it in at the same time but the
disturbance fizzles out and doesn`t amount to much. Have split the
difference Tuesday night with a chance of snow in the Cascades and
higher mountains of northeast Oregon while a slight chance of rain
in confined to central Oregon south of Redmond. Snow levels will be
around 3500-4000 feet. Wednesday afternoon through Thursday the
ECMWF brings in a stronger system while the GFS is much slower and
has it arriving in central Oregon Thursday afternoon. Preferred the
faster ECMWF solution so have a chance of snow in the mountains with
a slight chance to chance of rain in the lower elevations for
Wednesday through Thursday. Snow levels will be around 3500-4500
feet Wednesday and will rise to 4000-5500 feet by Thursday.
Temperatures Wednesday and Thursday will be in the upper 30s to mid
40s. Lows Tuesday night and Wednesday night will be in the 20s and
lower 30s. Perry


.AVIATION...00Z TAFs...KRDM and KBDN will continue to have VFR
conditions with clouds mostly above 12K feet AGL for the next 24
hours. Other TAF sites have partially cleared out with VFR
conditions and scattered clouds above 12K feet AGL this afternoon.
KYKM is an exception with MVFR cigs/vsby. Expect that MVFR/IFR/LIFR
conditions will return to all TAF sites besides KRDM and KBDN this
evening though fog will perhaps not as extensive as last night.
Conditions will improve from 16Z-21Z and most TAF sites will reach
VFR. However, KYKM may stay at MVFR through 00Z tomorrow afternoon.
Winds will be mainly below 10 kts though KRDM and KBDN will have
gusts to 20 kts this afternoon through 03Z and again tomorrow
afternoon after 22Z. Perry


PDT  31  46  35  49 /   0   0  40  60
ALW  32  43  35  46 /   0   0  40  60
PSC  32  39  33  42 /   0   0  40  50
YKM  28  39  30  41 /   0  10  40  50
HRI  31  40  33  43 /   0   0  40  50
ELN  29  40  30  41 /  10  10  40  50
RDM  28  48  32  49 /   0  20  60  60
LGD  32  43  34  44 /   0   0  60  70
GCD  32  45  35  46 /   0   0  70  70
DLS  33  41  35  43 /   0  20  60  70




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