Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 271600
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
900 AM PDT Mon Mar 27 2017

.SHORT TERM UPDATE...Today...A 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. Polan

&&

.PREVIOUS DISCUSSION... /issued 508 AM PDT Mon Mar 27 2017/

SHORT TERM...Today through Wednesday...Upper level trough will move
across the inland NW 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 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

AVIATION...12Z TAFs...Generally VFR conditions should prevail over
the next 24 hours. Currently low level moisture has led to IFR
ceilings at KYKM and expect that will vary between scattered and
broken for the next few hours. Will cover that with a tempo. Showers
will continue through this afternoon with broken to overcast skies
at 4000-7000 feet AGL. After a lull this morning, showers will
return from 20Z-02Z though chances are lower at some TAF sites and
have used VCSH for those. Chances are lowest for KYKM and did not
mention precipitation for that TAF site. Skies will lift and become
scattered above 6000 feet AGL after 03Z. Some higher clouds above
15K feet AGL will begin moving into the area after 06Z. Winds will
increase this morning and west to northwest winds at 10 to 20 kts
with gusts to 30 kts will be possible at most TAF sites from 18Z to
03Z. Winds will be a little lighter at KYKM. Winds will drop below
12 kts after 03Z. 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...
OR...None.
WA...None.
&&

$$

99/79/83



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