Issued by NWS Pendleton, OR
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000 FXUS66 KPDT 211103 AFDPDT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PENDLETON OR 300 AM PST SAT NOV 21 2009 .SHORT TERM...TODAY THROUGH SUNDAY...THE BACK SIDE OF A VERY SHARP AND DEEP UPPER TROUGH CONTINUES TO MOVE ACROSS THE REGION EARLY THIS MORNING. THE ENERGY DIGGING DOWN THE BACK SIDE OF THE TROUGH IS KEEPING A FEW SHOWERS...MOSTLY SNOW...GOING OVER PORTIONS OF THE AREA...ESPECIALLY ALONG AND JUST EAST OF THE CASCADES. AS THIS TROUGH EXITS THE AREA THIS MORNING SHOULD SEE THESE SHOWERS WIND DOWN FURTHER...TO MAINLY A FEW ALONG THE CASCADE CREST. A POTENT SYSTEM IS CURRENTLY TAKING SHAPE OUT ALONG 150W THIS MORNING. THIS SYSTEM WILL SWING ACROSS THE REGION LATE TONIGHT AND ON SUNDAY. THERE IS A CHANCE THAT A SURFACE LOW WILL FORM OFF THE NORTHWEST OREGON COAST LATE TONIGHT AND THEN MOVE EAST ACROSS WASHINGTON STATE SUNDAY. THERE IS SOME UNCERTAINTY AS TO THE TRACK OF THIS SURFACE LOW AS SOME DATA POINTS TO IT SWINGING MORE NORTHEASTWARD THROUGH WESTERN WASHINGTON INTO BRITISH COLUMBIA. THE TRACK OF THIS SURFACE LOW WILL DETERMINE THE WEATHER CONDITIONS OVER OUR AREA SUNDAY. IF THE LOW MOVES INTO THE INTERIOR NORTHWEST AS SOME DATA SUGGESTS THEN WE WOULD SEE STRONG WINDS OVER CENTRAL OREGON...THE BLUE MOUNTAIN FOOTHILLS...THE GRANDE RONDE VALLEY AND WALLOWA COUNTY. ALSO THERE WOULD BE SIGNIFICANT PRECIP OVER MANY AREAS AS THE SYSTEM MOVES THROUGH. ALSO THERE WOULD BE WESTERLY UPSLOPE FLOW BEHIND THE SYSTEM. A QUICK CUT OFF OF PRECIP IN THE LEE OF THE CASCADES DUE TO THE WEST FLOW WOULD LIMIT SNOW ALONG THE CASCADE EAST SLOPE ZONES. MEANWHILE THE UPSLOPE FLOW INTO THE BLUE MOUNTAINS WOULD ALLOW CONSIDERABLE POST SYSTEM SNOW ACCUMULATIONS. THE ALTERNATE SOLUTION REDUCES THE WIND RISK ACROSS THE AREA...AND ALTERS THE FOCUS OF PRECIP AND SNOW ACCUMULATIONS AWAY FROM THE BLUES AND TO THE WASHINGTON CASCADE EAST SLOPES. AT THIS TIME WILL SIDE WITH THE SOLUTIONS (NAM AND EUROPEAN) THAT ADVERTISE THE SURFACE LOW TRACKING EAST INTO THE INTERIOR NORTHWEST. AS SUCH WILL ISSUE WIND AND WINTER STORM WATCHES FOR THE AREAS MENTIONED ABOVE THAT WOULD BE AFFECTED BY THE EASTERLY TRACK. WILL ONLY GO WITH WATCHES THOUGH DUE TO THE CONTINUED UNCERTAINTY. 90 .LONG TERM...SUNDAY NIGHT THROUGH NEXT SATURDAY...A WEATHER SYSTEM WILL BE DEPARTING THE FORECAST AREA SUNDAY NIGHT WHILE AN UPPER RIDGE BUILDS OVER THE REGION. THIS WILL PUSH MOST OF THE MOISTURE WITH ANY NEW SYSTEMS THAT TRY TO MOVE INTO THE PACIFIC NORTHWEST UP INTO SW CANADA AND EXTREME NW WASHINGTON. AS A RESULT OUR FORECAST AREA WILL SEE MOSTLY DRY CONDITIONS WITH JUST ISOLATED TO SCATTERED SHOWERS IN THE MOUNTAINS. THIS SCENARIO WILL PERSIST THROUGH THURSDAY. THERE WILL BE PATCHY FOG DEVELOPMENT IN THE USUAL LOW AREAS OF THE LOWER COLUMBIA BASIN AND ESPECIALLY ALONG THE LARGER RIVERS SUCH AS THE COLUMBIA...YAKIMA AND SNAKE RIVERS. A PACIFIC TROUGH WILL THEN MOVE INTO THE REGION AGAIN ON FRIDAY AND FRIDAY NIGHT BRINGING ANOTHER CHANCE OF RAIN AND MOUNTAIN SNOW. THERE IS CONSIDERABLE MODEL DIFFERENCES THAT FAR OUT IN THE EXTENDED PERIOD SO WILL NOT MAKE ANY CHANGES TO THE CURRENT FORECAST WHICH IS ALREADY REPRESENTATIVE FOR THAT SYSTEM. 88 && .AVIATION...12Z TAFS...VFR CONDITIONS WILL PREVAIL IN MOST AREAS THROUGH TODAY WITH SCATTERED TO BROKEN MID LEVEL CEILINGS. ANOTHER PACIFIC WEATHER SYSTEM WILL MOVE INTO THE AREA LATE TONIGHT AND EARLY SUNDAY MORNING WITH RAIN AND MOUNTAIN SNOW INCREASING. THIS WILL CAUSE AREAS OF MVFR TO IFR CONDITIONS WITH POSSIBLY EVEN LIFR OR VLIFR CONDITIONS IN LOCAL AREAS WITH SNOW OR FOG...ESPECIALLY NEAR ANY MOUNTAIN RANGES OR OVER THE CENTRAL OREGON PLATEAUS NEAR TAF SITE KRDM. WINDS OF 10 TO 20 KTS WITH GUSTS TO 30 KTS FROM THE SOUTHWEST WILL BE COMMON IN ALL AREAS TODAY. HOWEVER THE WINDS WILL INCREASE OVERNIGHT TONIGHT AS PRESSURE GRADIENTS TIGHTEN UP AHEAD OF THE NEXT WEATHER SYSTEM. DURING THAT TIME WINDS ARE EXPECTED TO INCREASE TO AT LEAST 20 TO 30 KTS WITH GUSTS TO 40 KTS OR POSSIBLY EVEN HIGHER INTO SUNDAY. 88 && .PRELIMINARY POINT TEMPS/POPS... PDT 48 37 47 31 / 10 80 70 10 ALW 49 38 48 32 / 10 80 70 10 PSC 52 36 51 30 / 10 80 50 10 YKM 49 32 48 29 / 10 80 40 10 HRI 50 35 49 29 / 10 80 50 10 ELN 46 32 45 26 / 20 80 50 10 RDM 44 34 45 24 / 20 70 40 10 LGD 43 36 43 22 / 20 80 80 20 GCD 42 33 42 21 / 10 70 60 10 DLS 50 37 49 32 / 20 80 40 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...HIGH WIND WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR ORZ501-504. WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR ORZ502. HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR ORZ042-043. HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR ORZ049-050. WA...HIGH WIND WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR WAZ029. WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR WAZ030. && THREAT INDEX TODAY : YELLOW SUNDAY : YELLOW MONDAY : GREEN 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 $$ 90/88/88
