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Area forecast discussion...updated 
National Weather Service Pendleton or
1050 am PST Thursday Dec 18 2014

Updated aviation discussion

Short term...morning update...the air mass across the basin
continues to become increasingly mixed due to the passage of weak
systems. Fog is patchy at most across the basin this morning, and
expect some patches to linger through the day. Still coverage is not
expected to become widespread in any area, thus do not expect any
new fog advisories at this time. Also will allow the air stagnation
advisory to continue to it's current expected end time tomorrow
morning. Another weak system is moving through the region and will
continue to produce spotty showers. A more vigorous system is
approaching the coast. Expect to see an increase in shower chances
over central and north-central Oregon this afternoon, and increased
probability of precipitation. This system will move across the area tonight, bringing precipitation
to most locations. Snow levels look to mainly run between 4000 and
5000 feet with this system, though they could be as low as 2500 feet
over western Kittitas County. 90

Aviation...18z tafs...MVFR conditions will occur at kykm and kdls
due to low stratus. Conditions should improve this afternoon. An
approaching weather system will start to spread rain after 03z/19th
to all taf sites. Conditions will deteriorate a few hours after
03z/19th to IFR/MVFR, with some LIFR under moderate to heavy rain.
Winds will be at or below 10 kts throughout the taf period. Polan


Long term...previous active weather pattern is
expected during the forecast period with several storm systems set
to impact the area. A 150 knots zonal jet is expected to line up with
the Pacific northwest Sunday and Monday. The right jet exit
region...synonymous with sinking presently prognosticated to be
over the County Warning Area Sunday and Monday with the potential for a Lee side
trough to setup downwind of the Cascades. Therefore...concern exists
for a high wind event but timing from recent model runs has delayed
the potential start of the event to Sunday night into Monday. Will
continue to monitor or the potential for high winds across the County Warning Area
and have changed the forecast to indicate strongest wind potential
into midday Sunday into early Monday timeframe. The other item of
note during the upcoming weekend is the potential for a steady
stream of moisture into the area with rainfall Saturday night through
Monday that can be heavy at times. Quantitative precipitation forecast totals could be in excess of
2 inches in the mountains with between a quarter to half an inch in
low lying areas. Given the strong winds and a warm front expected to
move in Sunday...temperatures will rise into the middle 40s to lower
50s in the Columbia Basin and upper 30s to middle 40s along the higher
elevations. This will translate to a mostly rain precipitation
event...though snow may still fall along the highest mountain peaks.

A longwave ridge will setup off the Pacific coast Monday night
bringing a northwest flow to the area. Shortwave troughs will still
ride over the ridge into the region bringing a chance of
precipitation favoring the higher elevations through early
Wednesday. A trough originating from the Gulf of Alaska and British
Columbia is prognosticated to move southeast into our region Wednesday with
a shot of Arctic air expected. This will drop temperatures 10
degrees on Wednesday...Christmas evening...with the possibility of snow
levels dropping down to the Columbia Basin floor.


Preliminary point temps/pops...
PDT 42 33 43 35 / 10 60 70 20
alw 43 35 44 37 / 10 60 80 20
psc 44 34 46 36 / 10 60 70 10
ykm 41 33 44 32 / 20 70 60 10
hri 43 33 45 36 / 10 60 70 20
eln 39 33 43 32 / 20 70 60 10
rdm 46 32 47 31 / 30 60 60 20
lgd 46 35 49 31 / 20 40 80 20
gcd 44 32 46 35 / 20 40 80 20
dls 45 37 48 39 / 20 70 70 30


PDT watches/warnings/advisories...
Washington...air stagnation advisory until 10 am PST Friday waz026>028.


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