Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 270235
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
735 PM PDT FRI AUG 26 2016

.UPDATE...An upper trough to the east and an upper ridge off the
coast is resulting in a dry northwest flow aloft over the region
this evening. There are a few high thin cirrus clouds otherwise fair
conditions are expected overnight with slightly warmer minimum
temperatures overnight. On Saturday a change in the weather pattern
is forecast as a cool front moves south out of western Canada and
drops down into the northern portions of the forecast area. This
system will bring increasing winds but the atmosphere will remain
dry and warm. As a result there will be fire weather concerns again
with Red Flag Warnings in effect for the Lower Columbia Basin and
adjacent valleys/Blue Mountain Foothills as well as north central
Oregon and the Simcoe Highlands of southeast Washington on Saturday.
This is discussed in more detail in the fire weather section below.
The cool front will stall out along the Oregon and Washington border
Saturday night and then it will retreat back northward as the flow
aloft becomes more southwesterly by Sunday afternoon. This pattern
will keep warm but still dry conditions over the CWA for Sunday and
Monday. Some mid level moisture along with increasing instability
will be pumped northward into the CWA by Tuesday which will bring a
slight chance of showers and afternoon/evening thunderstorms on
Tuesday...mainly from the Blue Mountains southward and in Central
Oregon. The threat of afternoon and evening thunderstorms will then
persist through much of the rest of next week with cooler
temperatures due to more clouds and the chance of precipitation. 88

&&

.AVIATION...06Z TAFs...VFR conditions will prevail for the next 24
hours. There will be high thin clouds tonight through Saturday night
above 12K ft. Winds will be light and diurnally terrain driven
tonight but then they will increase to 15 to 25 kts with gusts to 30
kts at all TAF sites except KRDM and KBDN on Saturday. However, it
will remain dry and warm. 88

&&

.PREV DISCUSSION... /issued 237 PM PDT FRI AUG 26 2016/

SHORT TERM...Tonight through Monday...Pattern remains a ridge of
high pressure centered over the eastern Pacific and an upper level
trough over the northern Rockies. The shortwave riding over the top
of the ridge is beginning to move down the Canadian coast. This
shortwave will help pull the upper level trough over the northern
Rockies westward and back over western Canada this weekend. This
will place the forecast area under a dry westerly flow through the
weekend following the frontal passage on Saturday. This front will
produce some breezy conditions through the afternoon and evening
hours and be a fire weather concern. The trough will continue moving
westward and begin to form a closed low over the eastern Pacific by
Monday. This will begin to turn the flow southwesterly but continue
to be dry.

LONG TERM...Monday night through Friday...Mid/upper level longwave
trough offshore Monday night captures a mid/upper level shortwave
immediately off the northern California coast and steers it to the
northeast and across forecast area Tuesday afternoon/evening.
Dynamic lift and mid level moisture associated with the shortwave
interact with daytime surface heating yielding marginal instability
for scattered showers and a slight chance of afternoon/evening
thunderstorms in central and NE Oregon. The longwave trough remains
parked offshore on Wednesday through Friday thus giving a chance of
showers and a slight chance of afternoon/evening thunderstorms each
day through the remainder of the period.  Polan

FIRE WEATHER...A change in the weather pattern will also mean fire
weather will be more active this weekend and through the middle of
next week.  The upper level trough and its associated cold front
will track across British Columbia and northern Washington tomorrow.
The Fire Weather Watches that were in effect for the Lower Columbia
Basin, the Yakima Valley, the Eastern Columbia River Gorge, and the
Blue Mtn Foothills have been upgraded to Red Flag Warnings in effect
from 1 PM-9 PM Saturday for gusty winds and low humidity. Fire
weather concerns will shift from the wind/RH threat to a threat of
thunderstorms Tuesday-Thursday (details can be found in the long-
term discussion). The last time our forecast area observed
thunderstorms was August 10...so this is the first time in over two
weeks that new fire starts with lightning will be addressed.  There
is a possibility of wetting rain with some storms...but this does
not appear to be a big rain producer for most of our area.  Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  91  59  87 /   0   0   0   0
ALW  63  90  66  87 /   0   0   0   0
PSC  55  94  61  89 /   0   0   0   0
YKM  59  92  59  88 /   0   0   0   0
HRI  56  91  61  88 /   0   0   0   0
ELN  57  86  56  84 /   0   0   0   0
RDM  47  89  46  89 /   0   0   0   0
LGD  51  89  52  87 /   0   0   0   0
GCD  50  88  53  90 /   0   0   0   0
DLS  59  88  63  89 /   0   0   0   0

&&

.PDT Watches/Warnings/Advisories...
OR...Red Flag Warning from 1 PM to 9 PM PDT Saturday for ORZ639-641.

WA...Red Flag Warning from 1 PM to 9 PM PDT Saturday for WAZ639-641-
     675.

&&

$$

88/99/88



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