Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 192127
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
225 PM PDT TUE AUG 19 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY...A DRY COLD FRONT CONTINUES
TO MOVE ACROSS THE FORECAST AREA TODAY FALLING APART AS IT DOES WITH
JUST A FEW HIGH CLOUDS REMAINING. OUT AHEAD OF THE FRONT THERE IS
SOME INSTABILITY STILL OVER FAR EASTERN OREGON WHICH COULD RESULT IN
SOME ISOLATED THUNDERSTORMS THIS EVENING MANLY EAST OF A LINE FROM
JOHN DAY TO LEWISTON. BEHIND THE FRONT AN INCREASING WEST TO EAST
GRADIENT IS BRING SOME COOLER AIR OVER THE CASCADES CREATING SOME
BREEZY CONDITIONS ALONG THE EAST SLOPES OF THE CASCADES. THESE
WINDS WILL MOVE OUT INTO THE COLUMBIA BASIN THIS EVENING AND THEN
WINDS WILL DECREASE SOMEWHAT OVERNIGHT. FORECAST AREA WILL BE LEFT
UNDER A COOL NORTHWESTERLY FLOW WEDNESDAY AND THURSDAY AS A WEAK
TROUGH PATTERN REMAINS IN PLACE OVER THE PACIFIC NORTHWEST. COULD
SEE A FEW LINGERING SHOWERS THURSDAY AFTERNOON NEAR THE IDAHO
BORDER. LATE THURSDAY AND INTO FRIDAY THE TROUGH WILL DIP SOUTHWARD
AND DEVELOP INTO A CLOSED LOW PRESSURE SYSTEM OVER THE INLAND
NORTHWEST. THIS WILL LEAD TO SOME INCREASED INSTABILITY FORMING
SHOWERS AND POSSIBLE THUNDERSTORMS FRIDAY AFTERNOON. FRIDAY WILL
ALSO BE THE COOLEST DAY WITH HIGHS IN THE LOWER BASIN ONLY CLIMBING
INTO THE LOWER 80S.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...SEASONABLY STRONG
MID/UPPER LEVEL LOW PRESSURE SYSTEM WILL BE MOVING SOUTHEAST ACROSS
FORECAST AREA FRIDAY NIGHT. FROM SATURDAY OVERNIGHT UNTIL NOON ON
SATURDAY WRAP AROUND MOISTURE WILL INTERACT WILL THE EASTERN
MOUNTAINS AND THE EAST SLOPES OF THE CASCADES TO PRODUCE OROGRAPHIC
LIFT FOR A SLIGHT CHANCE OF SHOWERS OVER THE THOSE AREAS. OTHERWISE,
LEEWARD TERRAIN INFLUENCES PRODUCING DOWNSLOPE WINDS AND THUS
SINKING AIR WILL YIELD DRY CONDITIONS FOR LOWER TERRAIN THROUGH
FRIDAY NIGHT. SATURDAY AFTERNOON/EVENING COLDER AIR ALOFT ASSOCIATED
WITH THE LOW COMBINED WITH DAYTIME SURFACE HEATING WILL INCREASE
VERTICAL TEMPERATURE LAPSE RATES LEADING TO AN UNSTABLE AIR MASS
OVER THE BLUE MOUNTAINS, WALLOWA COUNTY AND OVER HIGHER TERRAIN IN
GRANT COUNTY. SATURDAY AFTERNOON/EVENING WILL THE UNSTABLE AREAS IN
THE EASTERN MOUNTAINS WILL BE UNDER A NORTHERLY FLOW ALOFT AS A
RESULT OF BEING ON THE WESTERN FLANK OF THE MID/UPPER LEVEL LOW, THE
CENTER OF WHICH WILL BE OVER IDAHO/WESTERN MONTANA. THUS ANY
THUNDERSTORMS THAT DO DEVELOP SATURDAY AFTERNOON/EVENING WILL BE
STEERED BY WINDS ALOFT TO MOVE FROM NORTH TO SOUTH, WHICH IS AN
UNUSUAL DIRECTION FOR THUNDERSTORMS MOVEMENT IN OUR REGION. BY
SUNDAY THE LOW WILL HAVE MOVED EASTERN MONTANA/WYOMING WHILE THE
EAST FLANK OF A MID/UPPER LEVEL RIDGE OF HIGH PRESSURE IN THE
NORTHEAST PACIFIC PUTS FORECAST AREA IN A NORTHWEST FLOW ALOFT,
WHICH WILL CREATE DRY CONDITIONS FOR MOST OF FORECAST AREA, EXCEPT
IN THE BLUE MOUNTAINS SUNDAY AFTERNOON/EARLY EVENING WHERE DAYTIME
SURFACE HEATING WILL YIELD MARGINAL INSTABILITY FOR A SLIGHT CHANCE
OF AFTERNOON/EARLY EVENING THUNDERSTORMS OVER THE BLUE MOUNTAINS AND
EASTERN GRANT COUNTY EASTWARD INTO IDAHO. ON MONDAY I KEPT A SLIGHT
CHANCE OF AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS OVER THE
WALLOWA MOUNTAINS, THE ELKHORN MOUNTAINS, AND IN THE HIGHER
MOUNTAINS IN THE OCHOCO-JOHN DAY HIGHLANDS AS WELL AS THE STRAWBERRY
MOUNTAINS. ELSEWHERE ON MONDAY A NORTHWEST TO NORTH FLOW ALOFT WILL
PRODUCE SINKING MOTION AND DRY CONDITIONS. MONDAY NIGHT AND TUESDAY
THE PACIFIC NORTHWEST WILL BE UNDER A MID/UPPER LEVEL HIGH PRESSURE
RIDGE FOR DRY CONDITIONS.  POLAN



&&

.AVIATION...00Z TAFS...BROKEN TO OVERCAST HIGH CLOUDS ASSOCIATED
WITH AN AMORPHOUS WEAK UPPER LEVEL FRONT MOVING ACROSS THE REGION
THIS MORNING WITH CEILINGS AOA 20000 FT AGL. TIGHTER PRESSURE
GRADIENTS THROUGH THIS AFTERNOON INTO THIS EVENING WILL PRODUCE
WINDS OF 15-25 KTS INTO THIS EVENING, FOLLOWED BY WINDS DECREASING
LATE THIS EVENING AS PRESSURE GRADIENTS DECREASE WITH CLEARING SKIES
AFTER 03Z. HOWEVER, UPSLOPE WINDS ALOFT ALONG THE WEST FACING SLOPES
OF THE NORTHERN BLUE MOUNTAINS WILL GENERATE CLOUDS AT 7000-10000 FT
AGL THIS EVENING AT KPSC, KALW AND KPDT FOLLOWED BY CLEARING SKIES
BY 10Z-12Z/20TH.  POLAN


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  84  54  81 /  10   0   0  10
ALW  65  85  61  82 /  10   0   0  10
PSC  64  87  59  84 /  10   0   0  10
YKM  60  84  55  81 /  10   0   0   0
HRI  62  86  57  84 /  10   0   0   0
ELN  61  82  57  80 /  10   0   0  10
RDM  49  79  41  76 /  10   0   0   0
LGD  54  81  48  79 /  20  10  10  10
GCD  55  81  48  78 /  20  10  10  10
DLS  63  81  57  80 /  10   0   0   0

&&

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

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

$$

91/99/99







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