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AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
921 PM PST THU DEC 18 2014

UPDATED FOR AVIATION DISCUSSION

.SHORT TERM...FRONTAL BOUNDARY MOVING INTO THE PACIFIC NORTHWEST 
THIS EVENING. SOME LIGHT RAIN AND HIGHER ELEVATION SNOW HAS BEEN 
MOVING THROUGH THE REGION OVER THE PAST SEVERAL HOURS. SATELLITE 
ENHANCEMENT ALONG THE COAST AND RADAR SUGGEST MORE WIDESPREAD 
PRECIPITATION WILL OCCUR LATER TONIGHT INTO FRIDAY MORNING. LOW 
CLOUDS AND FOG LIKELY IN THE COLUMBIA BASIN TONIGHT AS WELL. AS THE 
FRONT MOVES EAST OF THE FORECAST AREA FRIDAY THE PRECIPITATION WILL 
QUICKLY DIMINISH WITH SKIES REMAINING MOSTLY CLOUDY. NEXT SYSTEM TO 
IMPACT THE PAC NW WILL BE A WARM FRONT FRIDAY NIGHT INTO SATURDAY. 
THIS FRONT HAS FAIRLY SIGNIFICANT MOISTURE ASSOCIATED WITH IT AND A 
PERIOD OF STEADY RAIN, POSSIBLY HEAVY AT TIMES IS LIKELY. SOUTHERLY 
SURFACE GRADIENTS AND WINDS ALOFT WILL BE INCREASING SATURDAY 
RESULTING IN BREEZY TO WINDY CONDITIONS BY AFTERNOON AND EVENING. 94

&&

.AVIATION...06Z TAFS...EXPECT CATEGORIES TO VARY FROM VFR TO LIFR 
OVER THE NEXT 24 HOURS...AS THE NEXT SYSTEM MOVES INTO THE PACIFIC 
NORTHWEST.  OVERNIGHT TONIGHT...EXPECT RAIN SHOWERS TO TRANSITION 
OVER TO STRATIFORM RAIN WITH MOSTLY MVFR CIGS AND VIS...BUT 
LOCALIZED IFR/LIFR CONDITIONS ARE POSSIBLE.  DO NOT ANTICIPATE THAT 
LIFR CONDITIONS WOULD PERSIST FOR MORE THAN AN HOUR...BUT PROLONGED 
LIFR CONDITIONS CAN'T BE RULED OUT DUE TO LOW CLOUDS AND FOG THAT 
CONTINUES TO MIX AROUND THE VALLEY LOCATIONS.  THESE LOW CLOUDS 
COULD LINGER AROUND UNTIL THE NEXT PUSH OF WIND ON SATURDAY EVENING 
INTO SUNDAY SHOULD MIX IT OUT OF THE VALLEY AREAS.  WEBER  

&&

.PREV DISC... /ISSUED 454 PM PST THU DEC 18 2014/ 

SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...PATCHY FOG LINGERS AT A 
FEW LOCATIONS WITHIN THE COLUMBIA BASIN. DO NOT EXPECT THE FOG TO 
EXPAND THIS EVENING DUE TO APPROACH AND PASSAGE OF THE NEXT PACIFIC 
SYSTEM. THIS NEXT SYSTEM WILL BRING A GOOD SHOT OF PRECIP TO MOST OF 
THE REGION TONIGHT INTO FRIDAY MORNING. GENERALLY SNOW LEVELS WILL 
RUN BETWEEN 4000 AND 5000 FEET, BUT SNOW LEVELS WILL RUN AROUND 2500 
FEET ALONG THE WASHINGTON CASCADE EAST SLOPES IN YAKIMA AND KITTITAS 
COUNTIES. SNOW FALL OVERNIGHT AT AND ABOVE 2500 FEET IN THIS AREA 
WILL RUN BETWEEN 2 AND 6 INCHES, WITH THE HIGHEST AMOUNTS NEAR THE 
CREST. AS SUCH WILL ISSUE A SNOW ADVISORY. ELSEWHERE SNOW AMOUNTS 
WILL MAINLY RUN 1-3 INCHES ABOVE THE SNOW LEVELS. WILL SEE BREEZY 
CONDITIONS INCREASE TO THE 20 TO 30 MPH RANGE IN THE SOUTHERN GRANDE 
RONDE VALLEY OVERNIGHT. PRECIP WILL GRADUALLY DECREASE ACROSS THE 
AREA FROM LATE FRIDAY MORNING INTO FRIDAY EVENING. THE NEXT IN THE 
SERIES OF PACIFIC STORMS WILL BEGIN TO PUSH PRECIP INTO THE AREA 
LATE FRIDAY NIGHT. SNOW LEVELS WILL START OUT A BIT LOWER WITH THIS 
SYSTEM AND SNOW HIGHLIGHTS MAY BE NEEDED UNTIL SNOW LEVELS RISE. 90 

LONG TERM...SATURDAY THROUGH MONDAY NIGHT...A VERY STRONG UPPER 
LEVEL JET STREAM WILL BRING ABOVE NORMAL MOISTURE AND STRONG DYNAMIC 
LIFT TO FORECAST AREA SATURDAY THROUGH MONDAY. THE JET STREAM WILL 
USHER IN A WARM FRONT WITH DRAMATICALLY RISING SNOW LEVELS DURING 
THE DAY ON SATURDAY RESULTING IN COPIOUS AMOUNTS OF RAIN FALLING ON 
THE SNOWPACK IN THE MOUNTAINS. AS SUCH AREA RIVERS, STREAMS AND 
CREEKS WILL RISE TO OR ABOVE BANKFULL IN SOME AREAS. AT A MINIMUM 
2.00 INCHES OF RAIN ARE EXPECTED IN THE BLUE MOUNTAINS FOR THE 48 
HOUR PERIOD FROM SUNUP ON SATURDAY THROUGH SUNUP ON MONDAY. LOWER 
ELEVATIONS CAN EXPECT TO RECEIVE ANYWHERE FROM 0.40 TO 1.00 INCH OF 
RAIN. SNOW LEVELS START EARLY SATURDAY MORNING AROUND 3500-4000 FEET 
AND THEN RISE DRAMATICALLY TO AROUND 4500-5000 SATURDAY AFTERNOON. 
SNOW LEVELS CONTINUE TO RISE IN RESPONSE TO THE WARM FRONT TO AROUND 
6000 FEET ALONG THE EAST SLOPES IF THE WASHINGTON CASCADES BY 
DAYBREAK ON SUNDAY, AND RISE TO AROUND 7000-8500 FEET IN THE 
MOUNTAINS OF CENTRAL AND NORTHEAST OREGON. SNOW LEVELS REMAIN HIGH 
PERSISTING AT THE AFOREMENTIONED LEVELS THROUGH SUNDAY NIGHT, AND 
THEN LOWER TO 4500-6500 FEET DURING THE DAY ON MONDAY.  POLAN

TUESDAY THROUGH THURSDAY...A RIDGE OF HIGH PRESSURE OVER THE AREA 
WILL BEGIN TO BREAK DOWN ON TUESDAY. DAYTIME HIGHS WILL BE IN THE 
40S TO LOWER 50S AS A WEAK DISTURBANCE BRINGS A CHANCE OF RAIN AND 
HIGH MOUNTAIN SNOW. A STRONGER SHORTWAVE WILL THEN SWING THROUGH THE 
AREA ON WEDNESDAY BRINGING MORE PRECIPITATION ALONG WITH A COLD 
FRONT. SNOW LEVELS SUBSEQUENTLY WILL LOWER TO THE BASIN FLOOR ON 
WEDNESDAY NIGHT. HOWEVER, BY THE TIME THE COLDER AIR ARRIVES, 
PRECIPITATION WILL BE DIMINISHING AND ONLY LIGHT SNOW SHOWERS ARE 
EXPECTED ON CHRISTMAS MORNING. ON THURSDAY, NORTHWESTERLY FLOW ALOFT 
WILL KEEP CONDITIONS COOL WITH DAYTIME TEMPERATURES IN THE 30S, AND 
CLEARING SKIES THURSDAY NIGHT WILL ALLOW TEMPERATURES TO DROP INTO 
THE TEENS AND LOW 20S.  COBB 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  35  46  35  47 /  70  70  20  80 
ALW  37  46  37  47 /  70  70  20  80 
PSC  36  49  36  47 /  70  50  10  80 
YKM  35  43  32  43 /  70  30  20  80 
HRI  35  48  35  48 /  70  50  20  80 
ELN  33  42  31  43 /  70  40  20  80 
RDM  34  46  33  47 /  70  50  30  80 
LGD  37  44  34  46 /  70  80  20  90 
GCD  34  45  33  46 /  80  70  20  80 
DLS  37  48  36  48 /  80  60  30  90 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...AIR STAGNATION ADVISORY UNTIL 10 AM PST FRIDAY WAZ026>028.

     WINTER WEATHER ADVISORY UNTIL 7 AM PST FRIDAY ABOVE 2500 FEET 
     FOR THE WAZ520.

&&

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

$$

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