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fxus66 kpdt 271749 aab 

Area forecast discussion...update
National Weather Service Pendleton or
1045 am PDT Mon Mar 27 2017

Updated short term discussion

Short term negatively tilted mid/upper level
trough currently moving across interior Pacific northwest. The
trough axis at 8 am was along a line from Ephrata to the Tri-
Cities to just east of John Day and moving east. Trough will exit
eastern Oregon and southeast Washington by around midday. Fair
amount of sunshine today thanks to thin, scattered mid/upper level
clouds, which will allow surface heating combined with cold pool
aloft associated with the upper trough to produce marginal
instability this afternoon, which will trigger scattered rain
showers over mountains of central and NE Oregon as well as along
the crests of the Oregon and Washington Cascades through this
afternoon. Aforementioned instability will occur in a shallow
layer so thunderstorms are not expected through this afternoon.
Snow level today will be around 3000-3700 feet along the east
slopes of the Washington Cascades, and around 3600-4600 feet in
the mountains of eastern Oregon and the Oregon Cascades. Current
forecast looks on target so no significant changes are planned for
today. Made minor adjustments to Max temperatures for today. Also
decreased pops below 15 percent to yield a dry forecast through
this afternoon in the "lower terrain" forecast zones immediately
east of the Cascades, including the lower Columbia Basin, since a
dearth of moisture in lower and mid levels does not support
convective showers today at lower elevations this afternoon. Polan

Aviation...18z tafs...remnant low clouds from this morning's fog
will quickly scatter out and lift in vicinity of kykm and kdls. Expect sct to
bkn mid level cumulus clouds this afternoon as the atmosphere
becomes marginally unstable. A few pop up rain showers will be
possible this afternoon and early evening, mainly in vicinity of kpdt and
kalw...and perhaps in vicinity of kbdn and krdm. Kdls, kykm and kpsc are
expected to remain dry through the next 24 hours. After some
clearing in the mid evening hours, additional high and mid clouds
will push into the area from the west later tonight and especially
Tuesday morning. Cloud bases will start between 15-25k ft agl
tonight, then a cloud layer between 6-10k ft agl will develop
Tuesday morning. There is a low chance that some patchy fog/mist may
develop again tomorrow morning...mainly in vicinity of kykm.

Winds are expected to shift more westerly and increase this
afternoon as a front moves through the area. Sustained winds between
8 to 15 kts, with gusts up to 25 kts will be possible at most
locations this afternoon. The winds will quickly diminish to mainly
under 12 kts after 28/03z and remain lighter through the overnight
period and into Tuesday morning. 77


Previous discussion... /issued 508 am PDT Mon Mar 27 2017/

Short through Wednesday...upper level trough will move
across the inland northwest today. Overnight band of showers is exiting
northeast Oregon and southeast Washington this morning. Short wave
within the trough combined with upper level cooling and daytime
heating will produce scattered showers over mainly the mountains
this afternoon and early evening. Upper level ridge to return with
drier conditions for later this evening and Tuesday. Next band of
moisture crosses the Cascades late Tuesday night and give widespread
light to moderate rain on Wednesday. Drainages coming out of the
east slopes of the Washington Cascades will need to be watched for
rising water levels due to wednesday's batch of rainfall between 1/2
and one inch in that area. In addition, snow levels in the
Washington Cascades will be rising to between 3500 and 4500 feet for
additional snow melt potential. Rainfall amounts in other areas will
be up to 1/2 inch in the northeast mountains and less than a quarter
inch in the valleys.

Long term...Wednesday night through Monday...Wednesday night and
Thursday a system will be moving through the area with rain likely
across most of the area though there will be just a chance of rain
in the Columbia Basin. Snow levels will start out at around 7000
feet and lower to around 4000 feet by Thursday afternoon. A trough
will be following the system Thursday afternoon and night. Rain will
taper off in the lower elevations Thursday evening but there will
continue to be a chance of rain and snow in the mountains through
the night. Late Thursday night and Friday a ridge will build over
the area through at least Saturday night and this will give US dry
and fair weather. By Sunday models have diverged greatly with the
GFS having a strong upper low and trough bringing rain and mountain
snow Sunday night and Monday while the European model (ecmwf) has a weak trough
crossing the area Sunday and Sunday night with light rain followed
by a ridge for dry weather on Monday. With low confidence in the
models have a chance of mainly rain in the mountains Sunday through
Monday with the rest of the area dry. Temperatures will be in the
mid 50s to lower 60s with 50s in the mountains Thursday and Friday
then warm to the mid 50s to mid 60s Saturday through Monday. Perry


Preliminary point temps/pops...
PDT 54 38 56 43 / 30 10 10 20
alw 56 42 57 46 / 30 20 10 20
psc 59 41 59 45 / 20 10 10 20
ykm 60 37 59 44 / 20 10 20 40
hri 56 40 57 43 / 20 10 10 20
eln 51 35 53 38 / 20 10 20 50
rdm 53 32 58 41 / 30 10 10 20
lgd 53 35 55 39 / 50 20 10 20
gcd 53 32 56 39 / 50 20 10 20
dls 55 42 58 45 / 30 10 20 50


PDT watches/warnings/advisories...

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