AREA FORECAST DISCUSSION

 
 FXUS66 KPDT 250539 AAA
 AFDPDT
 
 AREA FORECAST DISCUSSION...UPDATED
 NATIONAL WEATHER SERVICE PENDLETON OR
 939 PM PST TUE NOV 24 2009
 
 UPDATED AVIATION DISCUSSION.
 
 .UPDATE...A QUIET WEATHER NIGHT IS UNDERWAY AS WEAK RIDGING BUILDS 
 OVER THE PACIFIC NORTHWEST. THIS IS SHOVING MOISTURE AND ENERGY INTO 
 BRITISH COLUMBIA AND ONLY SOME HIGH CLOUDINESS IS GETTING INTO THE 
 WASHINGTON PORTION OF THE FORECAST AREA. HAVE CUT BACK ON CLOUD 
 COVER TONIGHT AND TOMORROW...MAINLY IN THE SOUTHERN THIRD OF THE 
 AREA. WITH REDUCED CLOUD COVER...TEMPERATURES HAVE DROPPED QUICKLY 
 TONIGHT TO WITHIN SEVERAL DEGREES OF FORECAST LOW TEMPERATURES. DEW 
 POINT TEMPERATURES SUGGEST THAT THEY WON`T DROP TOO MUCH FURTHER BUT 
 HAVE ADJUSTED SEVERAL LOCATIONS DOWN 2 OR 3 DEGREES TONIGHT. WINDS 
 REMAIN GENERALLY LIGHT ASIDE FROM THE GRANDE RONDE VALLEY. THE 
 GRANDE RONDE VALLEY HAS SEEN PRESSURE GRADIENTS RELAX TEMPORARILY 
 THIS EVENING AND WINDS HAVE DROPPED TO 15 TO 25 MPH FOR THE MOST 
 PART. PRESSURE GRADIENTS ARE FORECAST TO INCREASE AGAIN IN THE NEXT 
 FEW HOURS SO CURRENT WIND ADVISORY WILL REMAIN IN EFFECT. FORECAST 
 UPDATE FOR CLOUD COVER AND WINDS OUT SHORTLY. PERRY
 
 &&
 
 .AVIATION...VFR CONDITIONS WILL CONTINUE FOR THE NEXT 24 HOURS WITH 
 MAINLY HIGH CLOUDS ABOVE 15000 FT AGL. AN EXCEPTION MAY BE PATCHY 
 FOG TOMORROW MORNING BETWEEN 25/12Z AND 25/18Z CREATING POSSIBLE 
 MVFR VISIBILITIES ALONG RIVERS IN THE COLUMBIA BASIN AFFECTING 
 KYKM...KDLS AND KPSC. SURFACE WINDS WILL REMAIN UNDER 15 KTS AT ALL 
 TAF LOCATIONS FOR THE NEXT 24 HOURS. PERRY
 
 &&
 
 .PREV DISCUSSION... /ISSUED 230 PM PST TUE NOV 24 2009/ 
 
 SHORT TERM...TONIGHT THROUGH FRIDAY.  A WEAK UPPER LEVEL RIDGE HAS 
 MOVED OVER WA/OR KEEPING MOST OF THE AREA DRY THROUGH LATE 
 WEDNESDAY.  THE ONLY EXCEPTION WILL BE ALONG THE EAST SLOPES OF THE 
 WASHINGTON CASCADES.  A DEEP UPPER TROUGH OFF THE GULF OF ALASKA 
 WILL SAG SOUTHWARD OVER THE NEXT 24 HOURS AND SPREAD PRECIPITATION 
 OVER WESTERN WASHINGTON WITH SOME MOISTURE SPREADING JUST EAST OF 
 THE CASCADE CREST.  BELIEVE PRECIPITATION WILL FALL AS RAIN ALONG 
 THE EASTERN VALLEYS AS SNOW LEVELS ARE HIGH AND TEMPERATURES SHOULD 
 REMAIN ABOVE FREEZING.  MEANWHILE...PARTLY CLOUDY SKIES ARE EXPECTED 
 OVER THE REMAINDER OF THE REGION TONIGHT AND WEDNESDAY. ONE CHANGE 
 IN THE FORECAST WAS TO DOWNPLAY THE FOG FOR TONIGHT AND WEDNESDAY 
 NIGHT.  FOR TONIGHT...THE INVERSION WILL STRENGTHEN YET THE LOW 
 LEVEL MOISTURE IS LACKING FOR ANY FOG DEVELOPMENT EXCEPT FOR PATCHY 
 GROUND FOG ALONG THE RIVERS.  I ALSO FEEL THAT SUNDAY`S WIND EVENT 
 HAS KEPT THE AIR MASS FAIRLY WELL MIXED.  ON WEDNESDAY NIGHT...MID 
 LEVEL CLOUDS WILL INCREASE AND SURFACE WINDS WILL INCREASE ALONG THE 
 BLUE MTN FOOTHILLS...SO THE THREAT OF FOG IS MINIMAL.
 
 PREVIOUS MODEL RUNS HAD SIGNIFICANT DIFFERENCES IN THE POSITION AND 
 STRENGTH OF AN APPROACHING SYSTEM AT THE START OF THE THANKSGIVING 
 HOLIDAY.  12Z GFS AND ECMWF ARE IN MUCH BETTER AGREEMENT AND WERE 
 PREFERRED OVER THE OUTLIER NAM MODEL.  A MOIST WARM FRONT IS PROGGED 
 TO SPREAD RAIN OVER CENTRAL WASHINGTON WEDNESDAY NIGHT.  THE FRONT 
 WILL MOVE NORTH INTO CANADA BY THANKSGIVING DAY FOLLOWED BY A STRONG 
 COLD FRONT.  PRECIPITATION WILL INCREASE OVER THE FORECAST AREA 
 THURSDAY NIGHT WITH SNOW LEVELS AROUND 4500-5000 FEET EARLY IN THE 
 EVENING LOWERING TO NEAR 2500-3000 FEET THURSDAY NIGHT AND FRIDAY 
 MORNING.  BELIEVE THERE WILL BE SNOW ACCUMULATIONS IN THE MOUNTAINS 
 WITH VERY LIGHT AMOUNTS BELOW 3500 FEET BUT I DO NOT ANTICIPATE ANY 
 AMOUNTS MEETING ADVISORY AT THIS TIME.  THE BIG CONCERN WILL BE 
 WINDS.  THE TRACK AND STRENGTH OF THE SYSTEM IS COMPARABLE TO THE 
 VERY WINDY CONDITIONS THAT WERE OBSERVED LAST SUNDAY.  A WIND 
 ADVISORY IS CURRENTLY IN EFFECT FOR THE SOUTHERN PORTION OF THE 
 GRANDE RONDE VALLEY THROUGH WEDNESDAY AFTERNOON...BUT THE ADVISORY 
 MAY BE EXTENDED THROUGH THANKSGIVING FOR THE GRANDE RONDE VALLEY AND 
 OTHER LOCATIONS IN OUR FORECAST AREA.  JOHNSON
 
 LONG TERM...FRIDAY NIGHT THROUGH TUESDAY. A DEPARTING DISTURBANCE 
 WILL MOVE ACROSS THE REGION FRIDAY NIGHT BRINGING COOLER TEMPS ALONG 
 WITH CLOUDS AND SHOWERS TO THE AREA MOUNTAINS. THEN A WEAK RIDGE 
 IMPROVES THE REGIONS WEATHER SOMEWHAT SATURDAY BUT MOISTURE AGAIN IS 
 EXPECTED TO LINGER IN THE AREA MOUNTAINS WHERE SOME SHOWERS SHUD 
 CONTINUE. THEN ANOTHER STORM IS FORECAST TO TRACK THROUGH WA/OR 
 SATURDAY NIGHT WITH WARMER TEMPS AND THE CLOUDS AND SHOWERS SHOULD 
 PERSIST. THE STORM MOVES EAST AND HIGH PRESSURE SHOULD BUILD INTO 
 THE TWO STATE AREA SUNDAY AND REMAIN INTO THE BEGINNING OF NEXT 
 WEEK. PATCHY FOG MAY DEVELOP OVER THE COLUMBIA BASIN SUNDAY NIGHT 
 AND MONDAY NIGHT.
 
 &&
 
 .PRELIMINARY POINT TEMPS/POPS...
 PDT  35  48  36  51 /   0   0   0  10 
 ALW  37  46  36  51 /   0   0  10  10 
 PSC  33  48  36  46 /   0   0  10  10 
 YKM  31  45  34  45 /   0   0  30  30 
 HRI  32  48  34  49 /   0   0   0  10 
 ELN  34  45  32  43 /  10  10  40  40 
 RDM  29  51  30  50 /   0   0   0  10 
 LGD  30  44  31  42 /   0   0   0  10 
 GCD  32  51  28  49 /   0   0   0  10 
 DLS  35  51  38  48 /   0   0  10  30 
 
 &&
 
 .PDT WATCHES/WARNINGS/ADVISORIES...
 OR...WIND ADVISORY UNTIL 3 PM PST WEDNESDAY FOR ORZ049.
 
 WA...NONE.
 &&
 
 THREAT INDEX
 WEDNESDAY : GREEN
 THURSDAY : GREEN
 FRIDAY : 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
 
 

 
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