Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 260412 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
910 PM PDT THU AUG 25 2016

.UPDATE...The latest satellite was showing some high level clouds to
move into the eastern portion of our area later tonight and the
forecast was updated to reflect this. Meanwhile the clouds should
slow the decent of the temperatures and this too was updated.
Otherwise the dry conditions will persist for the remainder of the
night and the present short term forecast appears on track for now.

&&

.AVIATION...vfr conditions will persist for the next 24 hours at all
taf sites.

&&

.PREV DISCUSSION... /issued 240 PM PDT THU AUG 25 2016/

SHORT TERM...Tonight through Sunday afternoon...A basically dry
forecast through Sunday afternoon. Saturday will bring breezy
conditions coupled with an extremely dry airmass and dry grassy
fuels that are ready to ignite, which creates a potential for fire
weather concerns Saturday afternoon through Saturday evening.

During the past 24 hours, a mid/upper level trough has moved east
across the Bering Strait and has entered Alaska this morning with an
attendant baroclinic frontal zone and moisture plume starting to
move into the Gulf of Alaska. Downstream from the trough a high
amplitude mid/upper level ridge of high pressure is in the Gulf of
of Alaska and the NE Pacific. The Pacific Northwest is on the
eastern flank of the ridge so a dry northerly flow aloft will
continue across the forecast area through tonight. The trough in
Alaska will move over the ridge over the next couple of days,
tracking across the Yukon, and then digging SE into NW British
Columbia during the day on Friday. This will produce falling 500mb
heights in the Gulf of Alaska and a flattening of the ridge, which
backs flow aloft to the NW across the region on Friday. Friday night
the trough amplifies and digs southward into central British
Columbia. Saturday the trough moves eastward through British
Columbia resulting in flow aloft backing to the west over the
interior Pacific Northwest. This westerly flow aloft will introduce
sinking motion east of the Cascades which will aid in transfer of
higher winds aloft associated with a low level jet down to the
surface. The jet will usher in winds of 30-40 mph at 5000 ft above
MSL. Saturday afternoon through Saturday evening, sustained surface
winds will be 15 to 25 mph from the west, with instantaneous wind
gusts to 30 to 35 mph in the Lower Columbia Basin and the Foothills
of the Blue Mountains, the eastern Columbia River Gorge as well as
Sherman and Gilliam Counties. There may be some patchy blowing dust
Saturday afternoon/evening across most of the Lower Columbia Basin as
well as the Foothills of the Blue Mountains. Sunday another
amplifying mid/upper level trough enters the Gulf of Alaska, which
causes the longwave trough to retrograde westward yielding flow
aloft over the region to back to the SW with a strong westerly
component to the winds aloft producing sinking air motion east of
the Cascades on Sunday for a continuation of dry conditions.
Polan

LONG TERM...Sunday night through Thursday...Forecast area will be
under a westerly flow Sunday night and into Monday with an upper
level trough positioned along the Canadian coast. There could be
some light rain in the central Washington Cascades and northward in
this pattern but overall remaining dry. The flow will begin to turn
more southwesterly late Monday and into Tuesday as the trough closes
off into a closed low off the Canadian coast and begins dropping
southward. Models are indicating that a piece of energy coming
around the bottom of the trough could lead to some increasing
instability but exactly where is still unknown due to model
differences and timing. Best thinking at this time is that the
better instability and chance of showers would be south and east of
the forecast area for late Tuesday. Wed and Thursday the models drop
the closed low southward placing it off the Pacific Northwest coast
but with different placement. Either way we will see increasing
southerly flow and the potential for some showers. Again, at this
point the differences keep me from placing showers in the forecast
other than along the Cascade crest.

FIRE WEATHER...No major fire weather concerns are expected through
Friday. The inverted surface thermal trough will remain west of the
Cascades...and a northerly flow aloft will keep temperatures and the
relative humidity (RH) from reaching critically hot and dry values.
However...on Saturday...the thermal trough will shift eastward and a
cold front will sweep across northern Washington.  This will cause
breezy conditions over the Columbia Basin and the Eastern Columbia
River Gorge.  I do not expect this system to be as substantial as
the dry cold front last Sunday that brought 20-30G40 mph winds in
the afternoon when the humidity was 5-15 pct.  On Saturday...the RH
will be 15-25 pct and the winds will be 15-25 mph gusting to 30-35
mph. Nevertheless...the winds will be enough to easily carry a fire
through the dry grassy areas and fire weather watches will be
issued.  Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  88  61  91 /   0   0   0   0
ALW  63  88  67  91 /   0   0   0   0
PSC  60  91  62  94 /   0   0   0   0
YKM  60  93  62  93 /   0   0   0   0
HRI  56  90  60  92 /   0   0   0   0
ELN  58  92  61  88 /   0   0   0  10
RDM  46  89  50  89 /   0   0   0   0
LGD  49  85  52  89 /   0   0   0   0
GCD  49  86  53  89 /   0   0   0   0
DLS  62  95  64  90 /   0   0   0   0

&&

.PDT Watches/Warnings/Advisories...
OR...Fire Weather Watch from Saturday afternoon through Saturday
     evening for ORZ639-641.

WA...Fire Weather Watch from Saturday afternoon through Saturday
     evening for WAZ639-641-675.

&&

$$

97/97



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