Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 171202 AAA

Area Forecast Discussion...Update
National Weather Service Pendleton OR
400 AM PST Wed Jan 17 2018

Updated Aviation Discussion

.SHORT TERM...Today through Friday...An upper low and trough remains
off the Pacific Northwest coast this morning with a flat ridge over
our area. The low is sending a frontal system towards the coast. the
warm front from the system is moving ashore along the Olympic
Peninsula. The warm front will move northeast and just graze the
Washington Cascades later this morning and afternoon with a chance
of rain reaching as far as Yakima and Ellensburg with a few
hundredths of an inch in most locations. Snow levels along the
Cascades will climb from 4000 to 5500 feet by this afternoon so
little in the way of snow is expected except on the higher peaks.
There continues to be some low stratus and fog in the Columbia Basin
and surrounding valleys so will keep patchy fog in the forecast for
the morning but it should mix out with the front by this afternoon.
Warmer air with the front will keep temperatures in the 40s and
lower 50s again today though the Washington Cascades will have some
upper 30s. With the system tightening up pressure gradients, winds
will pick up in the afternoon in the southern half of the area.
Central Oregon will have southerly winds of 10 to 20 mph and the
southern Grande Ronde Valley will reach 20 to 30 mph and may
approach wind advisory levels but believe it will stay a couple of
mph below that. Tonight the cold front of the system will cross the
Cascades this evening and progress as far as the Blue Mountains
overnight and over the entire area on Thursday. Snow levels will be
over 6000-7000 feet until it drops to around 3500-5000 feet Thursday
afternoon so most locations will have a good shot of rain. The lower
elevations will get a tenth to a quarter of an inch with a half to
two thirds of an inch in the mountains. Temperatures will remain
mild with lows tonight mainly in the upper 30s and lower 40s while
Thursday will be mainly in the 40s to around 50 in the Columbia
Basin. The breezy winds of this afternoon will continue through
tonight before winding down on Thursday. The cold front will exit
the area Thursday night with a chance of rain and snow in the
mountains and central Oregon and mainly dry elsewhere. The trough
will remain offshore Friday. A weak impulse will move through the
area and this will keep a chance of light snow in the mountains and
a slight chance of rain in the Blue Mountain Foothills while the
Columbia Basin is dry. Temperatures on Friday will cool a few
degrees to upper 30s and 40s. Perry

.LONG TERM...Friday night through Tuesday...This period looks to be
unsettled with near to slightly below seasonal temperatures.
Isolated to scattered showers should linger Friday night into
Saturday. Another Pacific system still looks to push into the region
at some point Saturday night and/or Sunday. This system would spread
steadier precip across much of the area. Onshore flow then looks to
keep varying coverages of showers going Monday through Tuesday. Snow
levels look to be low, generally below 4000 feet through the period.


.AVIATION...12Z TAFs...A warm front will continue to spread mid and
high level clouds across the region this morning. A few showers from
these clouds may affect KYKM and KDLS. Fog and stratus currently
affect KDLS, KPSC and KALW. These conditions should persist through
much of the morning, though the lift associated with the mid level
clouds could cause temporary improvement. Expect the fog/stratus at
KPSC and KALW to lift/break this afternoon. KDLS may see IFR or LIFR
conditions until tonight when precip with a cold front causes the
lower deck to finally break. Elsewhere VFR conditions are expected.
Light showers are expected at most TAF sites late in this period. 90


PDT  52  41  49  34 /   0  40  70  40
ALW  51  44  50  35 /   0  50  80  40
PSC  44  40  49  35 /  10  40  50  10
YKM  44  37  47  31 /  20  70  40  20
HRI  49  42  50  34 /  10  50  60  20
ELN  41  34  44  28 /  40  80  40  20
RDM  53  38  45  26 /  10  50  60  40
LGD  46  41  46  30 /  10  10  80  70
GCD  50  42  46  28 /  10  10  80  80
DLS  48  42  49  35 /  10  70  60  40




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