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Area forecast discussion 
National Weather Service Pendleton or
300 am PST Monday Nov 30 2015

Short through Wednesday...the forecast area will be in
an area between an upper ridge that is centered over southwest
Canada and a low pressure system over the Rocky Mountains today.
Conditions will be dry and stable...except for some occasional snow
flurries under a stratus deck that stretches across the Columbia
Basin into the adjacent valleys of both Oregon and Washington. The
stratus layer extends southward to Jefferson County and includes the
city of Madras...and north to include the Yakima and Kittitas
valleys. It also stretches as far east as the grande ronde and
Wallowa valleys. There is some patchy fog under this stratus deck
where higher terrain meets the base of the stratus deck such as the
Horse Heaven Hills and the slopes of the mountains surrounding the
Columbia Basin and adjacent valleys. A low pressure system off the
coast will send a weak trough inland this afternoon and evening
while it weakens further as it encounters the upper ridge. The
result will mainly be just increasing middle and high clouds and it may
cause enough lift to squeeze out some snow flurries under the
stratus deck. Then there will be a short break with a weak upper
ridge on Tuesday morning before a stronger and wetter trough moves
into the region Tuesday night into Wednesday. This next system will
bring a mixed bag of precipitation with mainly snow in the mountains
and mainly rain with some freezing rain in the valleys and lower
Columbia Basin. Believe the winds will cause enough mixing to scour
out the cold air along the Blue Mountain foothills for mainly just
rain there. Farther north in the lower Columbia Basin there may be a
period of light freezing rain or snow before changing to rain on
Wednesday. Snow levels will increase to around 3500-4500 feet on
Wednesday in western and southern areas of the County Warning Area while it remains
fairly low over the eastern mountains for mainly snow there in the
mountains on Wednesday. Winds will increase mainly in the southern
Grande Ronde Valley around Ladd and pyles canyons and portions of
Wallowa County...otherwise winds will be light in the County Warning Area. Expect
warmer and wet weather in the extended forecast period. 88

Long term...Wednesday night through Monday...unsettled weather will
continue through the long term period. Wednesday night and Thursday
a front will move through the area with a chance of mainly rain
across the area with snow levels around 6000 feet. The rain will
taper off to a slight chance Thursday afternoon. Thursday night and
Friday the GFS shows another wave moving through the area while the
European model (ecmwf) is weaker with this wave. Current forecast leans towards the
wetter GFS so have kept a chance of mainly rain Thursday night and a
slight chance of rain Friday. This system will be colder with snow
levels around 3500 feet so the mountains will see snow with this
system. Friday night and Saturday will be a break between systems
and dry weather is expected though there will be a slight chance of
light snow in the mountains. Another system moves ashore either
Saturday or Saturday night and hangs up along the Cascades for 24
hours or so before moving into the area. Have leaned towards the
faster GFS solution and have a slight chance of rain and snow in and
near the Cascades Saturday then a chance of rain and snow across the
area Saturday night through Sunday as the system slowly moves
through the area. The European model (ecmwf) is slower so have kept a slight chance
of rain and snow for Sunday night and Monday in case the European model (ecmwf) is
right. Snow levels will vary from 4000 to 5500 feet with this system
so snow will be confined to the mountains. Temperatures will be in
the 40s in the lower elevations with middle 30s to lower 40s in the
mountains. Perry


Aviation...previous discussion...06z tafs...taf sites should expect
prevailing MVFR/IFR conditions to occur...with localized tempo LIFR
conditions possible late tonight and into early Monday morning. Low
clouds with ceilings at or below 020 feet and visibility between 2sm to 5sm in fog
overnight at sites except for krdm and kbdn. Pockets of light snow
have developed within the low stratus cloud deck mainly in vicinity of kykm
and kpsc and could cause temporary reductions is visibility and
slick runways here. Krdm and kbdn will remain mainly above the
inversion/fog layer with VFR conditions expected. Higher cirrus
clouds will spread across the region mainly after 18-21z on Monday
with little change to low clouds and ceilings in the lower basins. Added
some vcsh and light snow showers (mvfr/vfr) into the forecast at
kbdn...krdm..kdls and kykm after 01/00z as a weak storm system
approaches the area from the west. 77


Preliminary point temps/pops...
PDT 28 24 32 26 / 0 10 0 40
alw 28 27 33 31 / 0 10 0 30
psc 28 27 33 27 / 10 10 10 50
ykm 32 22 37 25 / 10 10 10 60
hri 29 25 33 27 / 10 10 10 50
eln 29 19 34 24 / 0 10 10 60
rdm 36 17 43 27 / 10 10 10 60
lgd 31 24 36 29 / 0 0 10 30
gcd 33 15 39 29 / 10 10 10 30
dls 36 31 41 33 / 10 10 10 60


PDT watches/warnings/advisories...
Washington...air stagnation advisory until noon PST Tuesday for waz026>028.


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