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000
FXUS66 KPDT 092318 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
200 PM PST MON DEC 9 2013

UPDATED AVIATION DISCUSSION

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...WEATHER PATTERN IS
SLOWLY UNDERGOING A CHANGE. THE COLD NORTHERLY FLOW IS BEING
REPLACED BY A NORTHWEST FLOW TONIGHT AND TUESDAY FOLLOWED BY A RIDGE
OF HIGH PRESSURE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. THIS RIDGE
WILL GIVE WAY TO A COLD FRONT SWEEPING OVER THE REGION ON THURSDAY.
AS A RESULT THERE WILL BE A GRADUAL WARMING TREND TAKING PLACE OVER
THE COMING DAYS.

UNDER THE NORTHWEST FLOW THERE COULD BE SOME SNOW SHOWERS THROUGH
TUESDAY OVER THE CASCADES AND AGAIN OVER THE EASTERN MOUNTAINS BUT
ACCUMULATIONS IF ANY WILL BE LIGHT. AS THE RIDGE SHIFTS OVER THE
REGION TUESDAY NIGHT THROUGH EARLY THURSDAY CONDITIONS LOOK DRY BUT
THEN THE COLD FRONT WILL SWEEP OVER THE REGION THURSDAY AND THURSDAY
NIGHT. SOME COLD AIR WILL REMAIN TRAPPED IN THE LOWER ELEVATIONS
THURSDAY MAKING FOR THE POSSIBILITY OF A WINTERY MIX OF
PRECIPITATION. THE MOST LIKELY AREAS TO SEE THIS WOULD BE THE EAST
SLOPES OF THE WASHINGTON CASCADES AND THE LOWER COLUMBIA BASIN OF
WASHINGTON. PORTIONS OF NORTH CENTRAL OREGON INCLUDING THE COLUMBIA
GORGE AND LOWER COLUMBIA BASIN OF OREGON COULD ALSO SEE INITIAL
WINTERY PRECIPITATION MIX AT THE ONSET OF THE PRECIPITATION THEN
CHANGE TO ALL RAIN. PRE FRONTAL SOUTHERLY WINDS WILL INCREASE
WEDNESDAY AND THURSDAY. THIS WILL MAINLY IMPACT THE GRANDE RONDE
VALLEY WHERE WINDY CONDITIONS ARE EXPECTED AND COULD BECOME
BORDERLINE WIND ADVISORY CONDITIONS. WILL CONTINUE TO MONITOR THIS.

.LONG TERM...FRIDAY THROUGH SUNDAY...A LOW PRESSURE SYSTEM WILL BE
PASSING THROUGH THE REGION ON FRIDAY, WITH AN EXPECTATION THAT
ENOUGH MIXING WILL HAVE OCCURRED TO FINALLY SCOUR OUT THE COLD
ARCTIC AIRMASS THAT HAS BEEN IN PLACE FOR THE LAST WEEK.  A CHANCE
OF RAIN SHOWERS AND MOUNTAIN SNOW ABOVE 3500 FEET IS POSSIBLE.  THE
SYSTEM IS EXPECTED TO QUICKLY MOVE OUT WITH A RIDGE BUILDING IN FOR
SATURDAY, THOUGH A SLIGHT CHANCE OF RAIN AND SNOW SHOWERS ABOVE 3500
FEET MAY STILL OCCUR. ANOTHER SYSTEM IS PROGGED TO MOVE ACROSS LATE
SATURDAY INTO EARLY SUNDAY, WITH SOME SUGGESTION THAT RAIN SHADOWING
MAY OCCUR IN THE LOWER COLUMBIA RIVER BASIN.  THEREFORE, THIS SYSTEM
MAY BRING A CHANCE OF RAIN SHOWERS AND SNOW SHOWERS ABOVE 4500 FEET
ALONG THE HIGHLANDS AND LOCAL MOUNTAINS.  BY MONDAY, THE AREA WILL
BE UNDER NORTHWESTERLY FLOW WITH INTERMITTENT SHORT WAVE TROUGHS
PASSING THROUGH IN THE FLOW ALLOWING FOR A SLIGHT CHANCE OF LIGHT
RAIN AND SNOW SHOWERS ON THE MOUNTAINS.  HIGHS FRIDAY THROUGH MONDAY
WILL BE IN THE LOWER 30S TO LOWER 40S, WITH OVERNIGHT LOWS IN THE
MID 20S TO MID 30S. BIEDA


&&

.AVIATION...PREVIOUS DISCUSSION...00Z TAFS...MARINE LAYER INFLUENCE
AT KDLS, AND UPSLOPE FLOW AT KALW AND KPDT, HAVE ALLOWED CLOUDS TO
FORM AOA 4K FT AGL. KDLS MAY HAVE CIG/VIS DROP TO MVFR AS CLOUDS
THICKEN AND POSSIBLE FOG FORMATION BTWN 10/06Z AND 10/13Z, WHILE
KPDT AND KALW WILL ALSO HAVE POTENTIAL FOR CIG DECREASES AFT
10/02Z.  HAVE REFLECTED WITH SCT DECK AS THERE IS SOME UNCERTAINTY.
ALL OTHER TAF SITES SHOULD REMAIN AT VFR, WITH CIG AOA 5K FT AGL.
WINDS WILL BE AOB 10 KTS DURING THE TAF PERIOD.  BIEDA


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  14  26  20  30 /  10  10  10   0
ALW  17  28  23  32 /  10  10  10  10
PSC  11  27  20  30 /   0  10  10   0
YKM  12  28  19  29 /   0  10  10  10
HRI  10  27  19  30 /   0  10  10   0
ELN  12  31  19  29 /  10  10  10  10
RDM   6  33  16  38 /   0   0   0   0
LGD  14  28  20  29 /  20  20  10  10
GCD  11  30  15  34 /  10  10  10   0
DLS  18  31  26  31 /  10  10  10  10

&&

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

THREAT INDEX
TUESDAY : GREEN
WEDNESDAY : GREEN
THURSDAY : YELLOW

GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.

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

$$

91/98/98