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fxus66 kpdt 110534 aaa 

Area forecast discussion...updated
National Weather Service Pendleton or
934 PM PST Tue Dec 10 2019

..updated aviation discussion

Aviation...06z tafs...fog is being replaced by light precip
across the area. Conditions are most austere at kpdt and kalw
where 200-500ft ceilings and some br/fog persist. IFR conditions
are common at many other locations as well due mostly to low
ceilings and some obscuration by light rain or snow. Kykm in
particular has experienced some snow accumulation. As usual,
current conditions at kbdn and krdm are VFR but are expected to
drop into MVFR territory with some lower ceilings. Precipitation
over the area will trail off over the next few hours but isolated
showers remain possible through Wednesday. Low stratus/fog are
likely to persist as precipitation clears out due to ample
moisture and a quick but strong ridge between the exiting weak
front and the next approaching system. Have reflected shifting
ceilings as rain exits through early morning before returning
again in the evening but ceilings will likely remain a forecast
challenge through the day.


Previous discussion... /issued 638 PM PST Tue Dec 10 2019/

Update...a weather system was moving into the region with snow
showers developing along the WA Cascades crest and is expected to
spill over into our east slopes of the WA Cascades. Temperatures
remain at or slightly below freezing and have increased some of
the pops and snow totals across this area. Further east into the
ykm and Kittitas Valley temps remain around freezing and have
added a mix of rain and snow tonight. Elsewhere temps again are
hovering around the freezing mark and may add slight chance of
fzra along the foothills of the Blue Mountains. Otherwise the
remainder of the short term forecast appears on track.

Previous discussion... /issued 152 PM PST Tue Dec 10 2019/

Short term...tonight through Thursday...a weak cold front will move
into and across the forecast area tonight and early Wednesday with
some light lower elevation rain and high elevation snow.
Precipitation amounts will be light and well below any highlight
criteria for this first system. However, the mid and higher clouds
will prevent widespread fog tonight with only light patchy fog
expected (perhaps very local dense fog in spots of the lower
elevations overnight). Wednesday night, a stronger weather system
with deep moisture content will move through the region through
Friday. This next system will possibly bring a significant amount of
rain to the forecast area and snow to the higher mountains. Snow
levels will mainly be above 5000 feet in the northeast mountains and
around 4000 feet in the central Washington Cascades. Expected snow amounts
from this system is expected to be below highlight criteria and is
marginal and will hold off on issuing any advisories or watches at
this time. However, near term future shifts will need to monitor
future model runs for trends of higher precipitation amounts which
will create greater snowfall amounts. Also, any highlights that may
be issued will likely need to be elevation based if any is needed.
Precipitation amounts look to be between a half inch to an inch in
the higher mountains and mainly a quarter to a half inch in the
lower elevations. With the atmosphere bring mild and the high snow
levels, and marginal temperatures, any snow will be wet which will
keep snow amounts down.

It will become breezy to windy in the Grande Ronde Valley Wednesday
night and Thursday, but pressure gradients do not suggest advisory
or warning criteria for wind. Pressure differences from Ono to meh
are only expected to be around 6 mb at the peak, so may see breezy
to windy conditions in the Grande Ronde Valley, but not advisory or
warning wind speeds. 88

Long term...Thursday night through Sunday afternoon. A series of
systems will be moving through the region into the weekend, bringing
chances of precipitation, mainly in the mountains.
Starting Thursday night into Friday, snow levels will start out
between 3500-4000 feet, keeping snow chances confined to the
Cascade, blue, and Wallowa Mountains. West to southwest breezy
conditions will be likely over Thursday night, and calming as we get
into Friday afternoon. As the first system starts to make its way
out of the area Friday evening, the lower Columbia Basin will start
to see a drying trend while mountain and high elevation areas will
still see snow. In central or, the best chance of snow will be
Friday night, as snow levels will have dropped to between 2500-3000
feet. By Saturday afternoon, precipitation chances will recede to
the Cascade peaks and higher elevation areas of the blue and Wallowa
Mountains, and will signal the start of a dry period into Tuesday.

Sunday night through Tuesday...models in fairly good agreement
building in an upper level ridge by Monday afternoon into the day
Tuesday. This ridge will briefly bring drier conditions to most of
the forecast area outside of a few lingering light rain/snow showers
for the Cascade crests and higher elevations of the blue/Wallowa
Mountains. If any precipitation does occur, amounts will remain very
light. Weak, onshore flow returns Tuesday night. With snow levels
between 1000-2500 feet, light snow showers will be possible in the
Cascades and mountains of northeast Oregon. Near normal temperatures
for this time of the year are expected with afternoon highs in the
30s/40s and overnight lows in the 20s to near 30. Richards


Preliminary point temps/pops...
PDT 30 45 37 50 / 60 20 70 70
alw 32 45 38 49 / 60 20 80 70
psc 33 42 38 50 / 50 10 70 60
ykm 29 40 32 46 / 60 10 70 60
hri 32 44 37 51 / 50 10 70 70
eln 26 38 29 42 / 60 10 80 60
rdm 29 47 36 49 / 60 10 70 80
lgd 32 42 35 45 / 60 30 80 90
gcd 29 47 35 49 / 60 20 70 80
dls 36 46 40 50 / 60 10 90 80


PDT watches/warnings/advisories...

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