Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 260338

Area Forecast Discussion
National Weather Service Pendleton OR
838 PM PDT SUN SEP 25 2016

.SHORT TERM...Tonight through Wednesday...Warming trend certainly
taking hold. 03z temperatures are 7-12 degrees warmer than last
night at this time. Current overnight forecast looks good.  Only
change was to make a slight increase in clouds over Washington as IR
satellite shows mid and high level clouds moving across the area.

00z NAM continues trend of past few days and in good agreement with
12z and 18z EC/GFS/NAM with ridge decreasing amplitude on Monday and
a west to southwest flow aloft taking over for Tuesday and
Wednesday. Monday will be 15 degrees above normal and temperatures
will be slightly cooler though still 5 to 10 degrees above normal
for Tuesday and Wednesday. The cooler air will manifest in breezy
west winds in the Columbia Gorge and Kittitas Valley on Tuesday.
Otherwise, impacts should be minimal.


.AVIATION...06z TAFS. High pressure ridge continuing. VFR to prevail
with SKC or SCT 15-20K and light diurnal wind pattern.


.PREV DISCUSSION... /issued 433 PM PDT SUN SEP 25 2016/

SHORT TERM...Tonight through Wednesday. Other than some high level
clouds...high pressure will dominate the areas weather with dry
conditions and above normal temperatures into the beginning of the
week. Temperatures will climb into the 80s and some locations could
approach 90 degrees on Monday. Meanwhile a weak disturbance will
push across the region Tuesday which may lower afternoon temps
several degrees. Also the cascade crest could experience an isolated
shower while breezy northwest winds are possible in the kittitas
valley. The high pressure shifts east Wednesday but the dry
conditions and above normal temps are expected to continue into the
middle of the week.

LONG TERM...Wednesday night through Sunday...An amplifying
mid/upper level longwave trough will be located between 130-140W
Wednesday night with forecast area on the eastern flank of the
trough, which brings a SW flow aloft that transports clouds into the
region, but not dynamic lift, so region will remain dry while the
trough slowly approaches the coast on Thursday. By Thursday
afternoon flow aloft east of the Cascades backs to the south
bringing increasing moisture and a slight chance of showers to
central and NE Oregon Thursday afternoon and evening and overnight
into Friday morning. During the day on Friday a strong shortwave
rounds the base of the offshore longwave trough and then moves
northeast across forecast area bringing strong dynamic lift and
elevated instability to central Oregon and the mountains of NE
Oregon and SE Washington for a chance of showers Friday afternoon
and evening. In addition, due to the elevated instability ahead of
the shortwave axis, I introduced a slight chance of thunderstorms
Friday afternoon and evening in Crook County, Grant County and the
eastern mountains of Oregon and SE Washington, including the
Foothills of the Blue Mountains in Oregon and Washington. Late
Friday night the shortwave exits the forecast area by moving into NE
Washington resulting in showers tapering off and ending by late
Friday evening in central and east central Oregon while a low chance
of orographic showers continues in the northern Blue Mountains
through Friday night and Saturday morning. Saturday afternoon and
Saturday night the forecast area will be dry due to sinking air
aloft immediately east of the Cascades. However, the east slopes of
the Cascades will still have a chance of slop over showers Saturday
night. Saturday night a strong mid/upper level low pressure system
dives southward just offshore, which transports increasing moisture
into forecast area for a chance of shower in central and NE Oregon.

Snow levels will lower to 5000-5500 ft Saturday night through Sunday
night along the east slopes of the Washington and Oregon Cascades as
well as in the eastern mountains of Oregon and the Blue Mountains in
SE Washington. Hikers and campers should be prepared for the
possibility of some snow above 5000 ft Saturday night through Sunday
night.  Polan

AVIATION...00Z TAFS...VFR conditions to prevail due to a building
mid/upper level ridge of high pressure over the Pacific Northwest.
FEW-SCT mid level clouds around 8000-15000 ft AGL for THE remainder
of this afternoon this evening will clear out by midnight with
clear skies continuing overnight through Monday afternoon.  Polan


PDT  53  85  56  80 /   0   0   0  10
ALW  56  86  59  81 /   0   0   0  10
PSC  49  88  53  85 /   0   0   0   0
YKM  46  87  55  81 /   0   0   0   0
HRI  48  87  51  83 /   0   0   0  10
ELN  43  85  57  76 /   0   0   0   0
RDM  43  89  44  81 /   0   0   0  10
LGD  44  85  48  81 /   0   0   0   0
GCD  45  87  49  83 /   0   0   0  10
DLS  50  89  61  80 /   0   0   0   0


.PDT Watches/Warnings/Advisories...


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