Issued by NWS Pendleton, OR
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000 FXUS66 KPDT 160326 AFDPDT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PENDLETON OR 825 PM PDT SUN MAR 15 2009 .UPDATE...RADAR IMAGERY SHOWS A BAND OF RAIN AND SNOW ACROSS THE BLUE MOUNTAINS AND EASTWARD...AS WELL AS SHOWERS WEST OF THE CASCADES. THE FRONT ACROSS THE BLUE MOUNTAINS WILL CONTINUE TO MOVE EAST TONIGHT. WITH A MORE WESTERLY WIND BEHIND THE FRONT...THE COLUMBIA BASIN AND SURROUNDING VALLEYS WILL BE RAIN SHADOWED TONIGHT...WITH ONLY SCATTERED SHOWERS FOR THE HIGHER TERRAIN. WINDS ARE ALSO ON THE DECREASE ACROSS THE REGION...THOUGH THERE ARE POCKETS OF 20 TO 30 MPH WINDS ACROSS PORTIONS OF THE YAKIMA VALLEY AND NORTHERN BENTON COUNTY. BUT OVERALL...WINDS ARE ON THE DOWNWARD TREND...THUS LET THE WIND ADVISORIES AND WARNING EXPIRE AT 8 PM PDT. HAVE UPDATED THE FORECAST TO REFLECT DECREASING WINDS AND PLAN TO UPDATE LATER TONIGHT TO REMOVE EVENING WORDING. OTHERWISE FORECAST LOOKS TO BE ON TRACK. DMH && .PREV DISCUSSION... /ISSUED 350 PM PDT SUN MAR 15 2009/ SHORT TERM...TONIGHT THROUGH TUESDAY...MAIN CONCERN CONTINUES TO BE A STRONG UPPER LEVEL JET STREAM AND AN ASSOCIATED LOW LEVEL JET STREAK OVER THE FORECAST AREA THROUGH MONDAY. SURFACE PRESSURE GRADIENTS WILL INCREASE THIS AFTERNOON IN THE LOWER COLUMBIA BASIN AND THE FOOTHILLS OF THE BLUE MOUNTAINS AND WILL CONTINUE VERY TIGHT THROUGH THIS EVENING WITH ONGOING 6-HOUR PRESSURE RISES ON THE ORDER OF 10 MB FROM 2 PM ONWARDS UNTIL AROUND MIDNIGHT. A WIND ADVISORY IS IN EFFECT UNTIL 8 PM PDT THIS EVENING FOR THE LOWER COLUMBIA BASIN... THE FOOTHILLS OF THE BLUE MOUNTAINS AND PORTIONS OF GILLIAM AND WHEELER COUNTIES. A HIGH WIND WARNING REMAINS IN EFFECT FOR CENTRAL AND NORTH CENTRAL OREGON AND THE EAST SLOPES OF THE SOUTHERN WASHINGTON CASCADES UNTIL 8 PM PDT THIS EVENING. BLOWING DUST IN THE LOWER YAKIMA VALLEY OF YAKIMA COUNTY...IN BENTON COUNTY AND IN THE LOWER COLUMBIA BASIN WILL CONTINUE INTO THIS EVENING. LOCAL VISIBILITIES WILL BE REDUCED TO 1/4 MILE THIS AFTERNOON IN THE WIND ADVISORY AREA. THE UPPER LEVEL JET STREAM BEGINS MOVING NORTH MONDAY NIGHT AND EXITS THE FORECAST AREA LATE MONDAY NIGHT. BREEZY WILL BE POSSIBLE ON MONDAY WITH WINDY CONDITIONS IN THE MOUNTAINS. OTHERWISE...MOISTURE ASSOCIATED WITH THE JET WILL KEEP A CHANCE OF RAIN AND MOUNTAIN SNOW IN THE FORECAST AREA THROUGH MONDAY AS ANOTHER UPPER LEVEL SHORT WAVE MOVES INTO THE PACIFIC NORTHWEST. ON TUESDAY A MID/UPPER LEVEL SPLIT FLOW DEVELOPS OVER THE PACIFIC NORTHWEST WITH WESTERLY FLOW ALOFT EAST OF THE CASCADES THUS GIVING THE FORECAST AREA DOWNSLOPE WINDS AND SUBSIDENCE IMMEDIATELY EAST OF THE CASCADES. POLAN LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...PERIODS OF RAIN...AS WELL AS HIGHER ELEVATION SNOW...WILL BE POSSIBLE ON TUESDAY NIGHT AND WEDNESDAY AS ZONAL FLOW BRINGS PACIFIC MOISTURE INTO THE REGION. ALTHOUGH THE MEDIUM RANGE MODELS ARE IN GENERAL AGREEMENT DURING THIS PERIOD...DETAIL DIFFERENCES DO EXIST. THE 12Z GFS IS MUCH WETTER THAN THE 12Z ECMWF...ESPECIALLY OVER EASTERN OREGON. HOWEVER...SOUTHERLY LOW LEVEL WILL ALLOW SNOW LEVELS TO RISE TO 5000+ FEET...DIMINISHING THE CHANCES FOR SIGNIFICANT SNOW ACCUMULATIONS SHOULD THE GFS VERIFY. YET ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES...SNOW LEVELS WILL REMAIN BELOW 3000 FEET...AND SEVERAL INCHES OF SNOW CAN BE EXPECTED. ON THURSDAY AND FRIDAY...DRIER CONDITIONS CAN BE EXPECTED...ALTHOUGH MOUNTAIN SHOWERS WILL STILL BE POSSIBLE. THEN ON SATURDAY...A DEEP TROUGH WILL MOVE INTO THE REGION...BRINGING WIDESPREAD PRECIPITATION THAT IS LIKELY TO PERSIST THROUGH SUNDAY. 82 AVIATION...00Z TAFS...VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES FOR THE NEXT 24 HOURS. HOWEVER...OCCASIONAL MVFR WILL BE POSSIBLE IN RAIN SHOWERS AT KPSC...KALW AND KPDT THROUGH THIS EVENING. VERY STRONG SOUTHWEST WINDS WILL PERSIST THROUGH AT LEAST 03Z...DIMINISHING OVERNIGHT. SKIES WILL REMAIN PARTLY CLOUDY UNDER SCATTERED AND BROKEN MID LEVEL CLOUDS. 82 && .PRELIMINARY POINT TEMPS/POPS... PDT 33 50 32 48 / 40 20 10 30 ALW 34 51 33 50 / 40 40 20 30 PSC 35 51 34 52 / 10 10 10 20 YKM 31 49 30 50 / 10 10 10 20 HRI 33 52 32 52 / 20 10 10 20 ELN 25 42 24 46 / 10 20 20 30 RDM 29 44 28 47 / 30 30 10 30 LGD 34 44 33 47 / 30 30 20 40 GCD 32 46 31 47 / 30 40 30 40 DLS 33 46 32 48 / 20 20 20 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...NONE. WA...NONE. && $$ TI:GGG FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT... WWW.WEATHER.GOV/PENDLETON 84