Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 211801 AAA
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1100 AM PDT THU AUG 21 2014

UPDATED AVIATION...18Z TAFS. VFR WITH SCT250 TIL 02Z.


.SHORT TERM...TODAY THROUGH FRIDAY...FORECAST AREA WILL BE UNDER THE
INFLUENCE OF A COOL NORTHWEST FLOW TODAY AS A LONG WAVE TROUGH
CONTINUES. HOWEVER...A SHORTWAVE DROPPING DOWN THE CANADIAN COAST
WILL MOVE INTO THE PACIFIC NORTHWEST LATE TODAY AND OVERNIGHT
FORMING A CLOSED LOW OVER THE REGION ON FRIDAY. EXPECT TO SEE SOME
INCREASED SHOWER ACTIVITY ACROSS NORTHERN WASHINGTON TODAY WITH SOME
OF THAT WORKING ITS WAY SOUTH ALONG THE EAST SLOPES OF THE CASCADES
LATE TODAY AND OVERNIGHT. SOME WEAK INSTABILITY NEAR THE IDAHO
BORDER WILL ALSO PROVIDE THE SLIGHT CHANCE OF SHOWERS OVER THE
WALLOWA AND NORTHERN BLUE MOUNTAIN REGIONS. FRIDAY LOOKS TO BE THE
COOL AND UNSETTLED DAY WITH THE UPPER LEVEL LOW OVER THE REGION THE
COLD AIR ALOFT WILL DESTABILIZE THE ATMOSPHERE LEADING TO INCREASING
SHOWERS AND THUNDERSTORM POTENTIAL.

&&

.PREV DISC... /ISSUED 420 AM PDT THU AUG 21 2014/

SHORT TERM...TODAY THROUGH SATURDAY...A BENIGN WEATHER PATTERN IS
IN STORE FOR TODAY WITH A DRY AND STABLE NORTHWEST FLOW ALOFT
PERSISTING OVER THE CWA. THERE MAY BE A FEW HIGH THIN CLOUDS AND/OR
HIGH BASED FAIR WEATHER CUMULUS BUT NO THUNDERSTORMS OR SHOWERS ARE
EXPECTED. TONIGHT A TROUGH WILL DIG SOUTHWARD INTO THE PACIFIC
NORTHWEST BRINGING SOME LIMITED MOISTURE WITH IT. THERE MAY BE SOME
LIGHT RAIN SHOWERS OVER THE WASHINGTON CASCADE EAST SLOPES BUT
ELSEWHERE IT WILL BE DRY. A CLOSED UPPER LOW PRESSURE SYSTEM WILL
DEVELOP OVER THE CWA ON FRIDAY. SOME WRAP AROUND MOISTURE AND
INSTABILITY MAY CAUSE ISOLATED TO SCATTERED THUNDERSTORMS OVER MOST
OF THE CWA EXCEPT FOR CENTRAL OREGON AND THE SOUTHERN PORTIONS OF
THE JOHN DAY HIGHLANDS. THUNDERSTORMS ARE NOT EXPECTED TO BE STRONG
OR SEVERE AT THIS TIME. THEY WILL MAINLY BE CAUSED BY A COLD POOL OF
AIR ALOFT WITH THE UPPER TROUGH OVERHEAD CAUSING STEEP TEMPERATURE
LAPSE RATES. AS THE ATMOSPHERE BECOMES STABLE AGAIN LATE FRIDAY
NIGHT AND SATURDAY MORNING THUNDERSTORMS WILL DISSIPATE TO JUST A
FEW SHOWERS OVER THE NORTHEAST MOUNTAINS DUE TO UPSLOPE WINDS. THERE
MAY ALSO BE SOME SHOWERS OVER THE WASHINGTON CASCADE EAST SLOPES. BY
SATURDAY AFTERNOON INSTABILITY WILL INCREASE AND THEN THERE WILL BE
A SLIGHT CHANCE OF THUNDERSTORMS AGAIN IN THE AFOREMENTIONED AREAS.
WINDS THROUGH THE SHORT TERM PERIOD WILL BE MOSTLY LIGHT AT 15 KTS
OR LESS. HOWEVER THERE WILL BE LOCALLY BREEZY WINDS OF 15 TO 25 MPH
AT TIMES IN THE LOWER COLUMBIA BASIN AND ADJACENT VALLEYS AND THE
EASTERN COLUMBIA RIVER GORGE. TEMPERATURES WILL BE COOLER THAN
NORMAL FOR THE NEXT COUPLE OF DAYS AND THEN THEY WILL BEGIN TO
REBOUND UPWARD AGAIN ON SATURDAY. 88

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...AN UPPER LEVEL RIDGE
WILL BUILD OFF THE PACIFIC COAST SATURDAY AND SUNDAY. THIS WILL KEEP
EASTERN WASHINGTON AND OREGON UNDER NORTH TO NORTHWEST FLOW UNTIL
WEDNESDAY. SATURDAY AND SUNDAY A SERIES OF WEAK WAVES WILL MOVE DOWN
THE BACKSIDE OF THE RIDGE. DAYTIME HEATING...INSTABILITY...AND
LINGERING MOISTURE MAY COMBINE TO TRIGGER A FEW SHOWERS OVER THE
BLUE MOUNTAINS AND EAST SLOPES OF THE WASHINGTON CASCADES DURING THE
AFTERNOON AND EVENING. SUNDAY NIGHT AND MONDAY A STRONGER WAVE
MOVING DOWN THE RIDGE WILL DEVELOP INTO AN UPPER LOW IN MONTANA.
INSTABILITY ROTATING AROUND THE LOW AND STEEP LAPSE RATES MAY
TRIGGER A FEW SHOWERS AND THUNDERSTORMS OVER THE NORTHEAST OREGON
MOUNTAINS. TUESDAY THE RIDGE WILL MOVE INLAND. SUBSIDENCE ASSOCIATED
WITH THE RIDGE WILL BRING DRY AND WARMER CONDITIONS TO THE PACIFIC
NORTHWEST TUESDAY AND WEDNESDAY.  COONFIELD

AVIATION...12Z TAFS. MAINLY CLEAR SKIES THIS MORNING THEN SCT-BKN
CIRRUS BY AFTERNOON. 76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  82  54  79  56 /   0  10  20  30
ALW  83  60  80  59 /   0  10  20  40
PSC  84  58  82  59 /   0  10  20  30
YKM  81  56  79  54 /   0  10  40  30
HRI  84  57  82  56 /   0  10  20  30
ELN  80  56  78  55 /  10  20  50  30
RDM  77  43  73  43 /   0   0  10  10
LGD  78  49  73  49 /   0  10  30  40
GCD  78  47  72  50 /  10  10  10  20
DLS  81  59  80  58 /   0  10  20  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

$$

91/79/79





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