Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 221146 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
345 AM PST MON DEC 22 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH WEDNESDAY...A WEATHER SYSTEM THAT
BROUGHT ABUNDANT RAINFALL AND WIND IS NOW MOVING AWAY FROM THE CWA
AND IS BEING REPLACED BY HIGH PRESSURE ALOFT. THERE ARE STILL SOME
SHOWERS OVER THE NORTHEAST OREGON/SOUTHEAST WASHINGTON MOUNTAINS AS
WELL AS THE EAST SLOPES OF THE CASCADES EARLY THIS MORNING. THESE
SHOULD DECREASE TODAY AS THE DAY PROGRESSES. HIGH PRESSURE WILL
AMPLIFY TONIGHT AND TUESDAY WITH DRY CONDITIONS AND MILD
TEMPERATURES. WINDS SHOULD ALSO BE LIGHT DURING THIS PERIOD. PATCHY
FOG WILL DEVELOP OVER THE LOWER COLUMBIA BASIN AND ADJACENT VALLEY
AREAS TONIGHT AND TUESDAY MORNING...ESPECIALLY ALONG THE COLUMBIA
AND YAKIMA RIVERS. THE NEXT WEATHER SYSTEM OF CONCERN WILL BEGIN TO
SPREAD MOISTURE INTO THE CASCADES LATE TUESDAY AND TUESDAY NIGHT. IT
WILL CONTINUE TO SPREAD EASTWARD ON WEDNESDAY WITH LIKELY POPS IN
MOST AREAS BY WEDNESDAY AFTERNOON. SNOW LEVELS WILL BE FAIRLY HIGH
ABOVE 5000 FEET IN SOUTHERN AREAS...AND NEAR 2500 FEET IN FAR
NORTHWEST KITTITAS COUNTY...ALONG THE CASCADE EAST SLOPES. THUS
THERE MAY BE SNOW ALONG THE WASHINGTON CASCADE EAST SLOPES...BUT
ELSEWHERE THIS LOOKS TO BE PRIMARILY A RAIN EVENT WITH SNOW ONLY ON
THE HIGHEST PEAKS ON CHRISTMAS EVE. MAY EVENTUALLY NEED WINTER
WEATHER HIGHLIGHTS FOR THE WASHINGTON CASCADE EAST SLOPES BUT IT IS
STILL TOO SOON FOR THAT AND THERE IS STILL TOO MUCH UNCERTAINTY OF
SNOW AMOUNTS. THIS SYSTEM WILL CONTINUE INTO THE EXTENDED PERIOD
BEGINNING OVERNIGHT CHRISTMAS EVE. AS PREVIOUSLY MENTIONED
CONDITIONS WILL BE MILD WITH MAXIMUM TEMPERATURE READINGS MOSTLY IN
THE 40S TO LOWER 50S TODAY AND TUESDAY AND THEN GRADUALLY COOLING
BEGINNING WEDNESDAY AS COOLER AIR MOVES INTO THE REGION. IT WILL
ALSO BECOME LOCALLY BREEZY WEDNESDAY AFTERNOON AND
NIGHT...ESPECIALLY IN THE MOUNTAINS. 88

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...A TROUGH WILL MOVE IN
WEDNESDAY NIGHT WITH A CHANCE OF RAIN AND MOUNTAIN SNOW ACROSS THE
AREA. THE TROUGH WILL EXIT TO THE EAST ON THURSDAY WITH JUST A
CHANCE OF RAIN AND SNOW CONFINED MAINLY TO THE MOUNTAINS. A
NORTHWESTERLY FLOW INTO THE AREA THURSDAY NIGHT THROUGH FRIDAY NIGHT
WILL KEEP THE AREA DRY ASIDE FROM A SLIGHT CHANCE OF SNOW IN THE
MOUNTAINS THURSDAY NIGHT. AFTER THAT, ANOTHER TROUGH WILL MOVE INTO
THE AREA BUT THE GFS AND ECMWF DISAGREE ABOUT THE TIMING. THE GFS
BRINGS IT THROUGH ON SATURDAY WHILE THE ECMWF BRINGS IT THROUGH ON
SATURDAY NIGHT. HAVE ADDED A SLIGHT CHANCE OF LOWER ELEVATION RAIN
AND MOUNTAIN SNOW TO BOTH PERIODS FOR NOW UNTIL MODELS COME INTO
BETTER AGREEMENT. THE GFS MOVES THE TROUGH EAST ON SUNDAY THEN HAS
OUR AREA UNDER AN OFFSHORE RIDGE SUNDAY NIGHT AND MONDAY. THE ECMWF
KEEPS THE TROUGH FURTHER WEST WITH A NORTHERLY FLOW INTO THE AREA.
THIS WILL GIVE A SLIGHT CHANCE OF RAIN AND SNOW IN THE LOWER
ELEVATIONS AND A CHANCE OF SNOW IN THE MOUNTAINS SUNDAY AND SUNDAY
NIGHT THEN TAPERING OFF ON MONDAY. FOR NOW HAVE LEANED TOWARDS THE
ECMWF SOLUTION. TEMPERATURES WILL BE IN THE MID 30S TO MID 40S
THURSDAY THROUGH SATURDAY THEN COOL A FEW DEGREES ON SUNDAY AND
MONDAY. PERRY

&&

.AVIATION...12Z TAFS...SKIES WILL BE BROKEN TO OVERCAST TODAY AND
TONIGHT WITH CEILINGS MAINLY ABOVE 5000 FEET AGL. AN EXCEPTION WILL
BE KRDM AND KBDN WHERE OCCASIONAL MVFR CEILINGS AND VCSH WILL BE
POSSIBLE THROUGH 18Z THIS MORNING. WINDS WILL REMAIN BELOW 15 KTS
FOR THE NEXT 24 HOURS. PERRY

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  32  49  35 /  10  10  10  10
ALW  48  33  47  37 /  10   0  10  10
PSC  49  32  46  36 /   0  10  10  10
YKM  45  32  43  34 /  10  10  10  30
HRI  49  34  47  37 /  10  10  10  10
ELN  42  31  41  33 /  10  10  10  30
RDM  48  32  52  34 /  20  10  10  10
LGD  43  30  43  34 /  20  10  10  10
GCD  44  35  45  34 /  30  10  10  10
DLS  51  38  48  39 /  10  10  20  20

&&

.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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