Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 260509
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
909 PM PST THU DEC 25 2014

.SHORT TERM...TONIGHT...WATER VAPOR LOOP SHOWS A MID/UPPER LEVEL
RIDGE OF HIGH PRESSURE IN THE NE PACIFIC, WHICH PUTS FORECAST AREA
ON THE EASTERN FLANK OF THE RIDGE AND PUTS INTERIOR PACIFIC
NORTHWEST IN A NORTHERLY FLOW ALOFT. THE NEXT UPSTREAM SYSTEM HAS A
LOT OF ENERGY AND IS ENTERING THE GULF OF ALASKA AT THIS TIME AND
WILL MOVE THROUGH THE RIDGE FRIDAY AND FRIDAY NIGHT, AND THEN DIVE
SOUTHEAST ACROSS FORECAST AREA SATURDAY, SATURDAY NIGHT AND SUNDAY
MORNING. THIS SYSTEM LOOKS TO BRING SIGNIFICANT SNOW ACCUMULATIONS
TO THE EAST SLOPES OF THE CENTRAL WASHINGTON CASCADES FROM MT ADAMS
NORTHWARD AND ALSO TO THE BLUE MOUNTAINS AND WALLOWA COUNTY ON
SATURDAY AND SUNDAY. A WINTER STORM WATCH WILL BE CONSIDERED FOR THE
BLUE MOUNTAINS, THE GRANDE RONDE VALLEY AND WALLOWA COUNTY FOR
SATURDAY AND SUNDAY BY THE MIDNIGHT SHIFT.

WILL BE ISSUING A WINTER STORM WATCH FOR THE EAST SLOPES OF THE
WASHINGTON CASCADES LATER THIS EVENING.  POLAN

&&

.PREVIOUS DISCUSSION... /ISSUED 130 PM PST THU DEC 25 2014/

SHORT TERM...TONIGHT THROUGH SUNDAY.  NORTHERLY FLOW WILL PREVAIL
OVER THE AREA THROUGH FRIDAY WITH RIDGE BUILDING PASSING OVER AREA
ON SATURDAY.  SOME ISOLATED SNOW SHOWERS REMAIN POSSIBLE OVER THE
MOUNTAINS TONIGHT WITH GENERALLY DRY AND COOL CONDITIONS ON FRIDAY.
THERE IS SOME PATCHY FOG POSSIBLE IN THE LOWER COLUMBIA BASIN
OVERNIGHT TONIGHT AND FRIDAY NIGHT.  THE NEXT SYSTEM WILL MOVE
THROUGH THE AREA STARTING SATURDAY AND CONTINUE THROUGH SUNDAY AS AN
UPPER LEVEL LOW PRESSURE SWINGS SOUTH OVER VANCOUVER ISLE INTO
WASHINGTON ON SATURDAY CARVING OUT A LARGE TROUGH OVER THE
NORTHWEST.  THERE WILL BE SEVERAL MOVE PIECES OF ENERGY DROP SOUTH
THROUGH THE TROUGH ON SUNDAY.  THIS SYSTEM WILL USHER IN COOLER AIR
WITH A MIX OF RAIN AND MOUNTAIN SNOW TO START AND TRANSITION TO
MAINLY SNOW SUNDAY. THE MODELS ARE WAVERING A BIT ON THE TIMING AND
POSITION OF HEAVY SNOW...BUT IT APPEARS THAT THE NORTH BLUE
MOUNTAINS MAY REACH WARNING CRITERIA FOR HEAVY SNOW SATURDAY NIGHT
AND SUNDAY. WILL WAIT ONE MORE MODEL RUN TO INCREASE CONFIDENCE FOR
TIMING. 93

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS IN SURPRISINGLY
GOOD AGREEMENT THROUGH THE PERIOD.  AFOREMENTIONED UPPER LEVEL LOW
MOVES SLOWLY THROUGH THE AREA FROM NORTH TO SOUTH. IT IS EXPECTED TO
EXIT THE REGION ENTIRELY BY TUESDAY MORNING.  SUNDAY NIGHT WILL HAVE
THE BEST CHANCE OF PRECIPITATION WITH CHANCES DIMINISHING TO ALMOST
NOTHING BY TUESDAY AFTERNOON.  AN UPPER LEVEL RIDGE WILL BUILD IN
ITS WAKE AND PERSIST THROUGH MUCH OF THURSDAY BEFORE BEING PUSHED
WESTWARD BY THE NEXT SYSTEM MOVING DOWN FROM THE NORTH.  ITS AFFECTS
WILL REMAIN OUTSIDE THIS FORECAST PERIOD.  TEMPERATURES WILL REMAIN
BELOW NORMAL AS COOLER AIR FILTERS INTO THE AREA FROM CANADA.  EARLE

AVIATION...00Z TAFS. WITH A MOIST GROUND AND MOSTLY CLEAR SKIES
TONIGHT...PATCHY FOG AND LOW CLOUD SHOULD DEVELOP AT MOST TAF
SITES.  AT THIS TIME...EXPECT ONLY MVFR CONDITIONS WITH VISIBILITIES
REMAINING ABOVE 4SM WHILE CEILINGS SHOULD REMAIN ABOVE 1000 FEET.
THE PATCHY FOG SHOULD LIFT BY LATE MORNING WITH CLEARING SKIES BY
AFTERNOON.  WINDS WILL BE LESS THAN 10 KTS.  EARLE

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  27  36  27  41 /  10  10  10  70
ALW  29  36  29  42 /  10  10  10  70
PSC  26  40  27  42 /   0  10  10  20
YKM  24  38  25  38 /   0  10  10  20
HRI  25  40  27  44 /   0  10  10  50
ELN  23  38  24  36 /   0  10  10  30
RDM  21  36  19  39 /  10  10  10  20
LGD  23  33  21  37 /  10  10  10  70
GCD  23  37  21  39 /  20  10  10  30
DLS  33  43  30  45 /  10  10  10  30

&&

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

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

$$

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