458 FXUS66 KPDT 012346 AAA AFDPDT AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE PENDLETON OR 346 PM PST MON DEC 1 2008 UPDATED AVIATION DISCUSSION .SHORT TERM...TONIGHT THROUGH WEDNESDAY...SATELLITE IMAGERY SHOWS THE LOW PRESSURE SYSTEM APPROACHING THE PACIFIC NORTHWEST COAST. THE COLD FRONT...CURRENTLY MOVING ONSHORE...WILL CROSS THE CASCADES THIS EVENING. WITH HIGH SNOW LEVELS...THE DOMINANT PRECIPITATION TYPE WILL BE RAIN TONIGHT. RAIN WILL SPREAD ACROSS THE REST OF THE AREA TONIGHT AS THE LOW WEAKENS INTO A WAVE AND MOVES OVER OREGON. RAINFALL AMOUNTS OF 0.1 TO 0.2 ARE POSSIBLE...WHILE THE EASTERN MOUNTAINS MAY SEE AMOUNTS UP TO 0.5 FROM THIS SYSTEM. FOG AND LOW STRATUS HAS BEEN GRADUALLY DECREASING ACROSS THE BASIN AND FOOTHILLS TODAY AS UPPER LEVEL WINDS GRADUALLY ERODE AT THE TEMPERATURE INVERSIONS AND MIX OUT THE LOWER LEVELS. WINDS ARE EXPECTED TO INCREASE THIS EVENING AND OVERNIGHT WITH THE FRONT. THE ONLY EXCEPTION IS IN THE YAKIMA VALLEY WHERE TEMPERATURE INVERSIONS HOLD STRONG. SURFACE WINDS WILL REMAIN UNDER 10 MPH OVERNIGHT DESPITE THE COLD FRONT...LIMITING MIXING AT THE SURFACE. THEREFORE...THE AIR STAGNATION ADVISORY HAS BEEN EXTENDED INTO TOMORROW WHEN COOLER AIR WILL HELP AID IN WEAKENING THE INVERSION AND PROMOTE MIXING AT THE SURFACE. THE WEATHER DISTURBANCE WILL MOVE OFF TO THE EAST ON TUESDAY...AND A RIDGE OF HIGH PRESSURE WILL REBUILD IN THE EAST PACIFIC. THIS WILL LEAVE THE REGION UNDER A NORTHWESTERLY FLOW. SHOWERS WILL CONTINUE IN THE NORTHEAST MOUNTAINS IN AN UPSLOPE FLOW...AND GRADUALLY DECREASE BY TUESDAY NIGHT. WITH COOLER AIR MOVING IN BEHIND THE COLD FRONT...SNOW LEVELS WILL DECREASE ON TUESDAY. THIS WILL BRING SNOW LEVELS TO AROUND 4500 FEET TUESDAY NIGHT. THIS COOLER AIR WILL ALSO LOWER TEMPERATURES FOR MOST OF THE REGION ON WEDNESDAY...WITH HIGH TEMPERATURES IN THE 40S ACROSS THE REGION. A WEAK WAVE WILL MAINLY CLIP THE EASTERN ZONES BRINGING A SLIGHT CHANCE OF SHOWERS. DMH .LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...12Z MODELS SHOW A WEAK WAVE AXIS WILL CROSS EARLY EVENING THEN EXIT TO THE SOUTH WITH REMNANT MOISTURE BRINGING CONTINUES SHOWER CHANCES TO THE WALLOWA MOUNTAINS. A REX BLOCK THEN FORMS OVER THE EASTERN PACIFIC WITH THE INTERIOR NORTHWEST UNDER THE RIDGE PORTION AND REMAINING DRY THROUGH SATURDAY AFTERNOON. THE RIDGE FLATTENS AS A SHORT WAVE ENTERS THE EARLY STAGES OF CYCLOGENESIS BRINGING A DECENT CHANCE OF PRECIP TO THE REGION. SNOW LEVELS STILL LOOK TO REMAIN FAIRLY HIGH WITH ONLY THE HIGHEST PASSES ALONG THE EASTERN MOUNTAINS POSSIBLY SEEING A RAIN/SNOW MIX. ELEVATIONS ABOVE THAT COULD SEE A FEW INCHES OF SNOW ACCUMULATION. THERE SEEMS TO BE A FAIRLY HIGH AMOUNT OF TEMPORAL VARIABILITY HOWEVER WITH THE DEVELOPMENT OF THIS SYSTEM. ADDITIONAL WAVES LOOK TO MOVE ALONG THE NORTHERLY BRANCH OF THE JET BUT FAR TOO MUCH UNCERTAINTY REMAINS TO PIN POINT ANY ONE FEATURE AT THIS TIME. /JBONK && .AVIATION...00Z TAFS...PREVAILING LIFR CONDITIONS ARE EXPECTED TO CONTINUE AT KYKM THROUGH THE 07 TO 08Z TIME FRAME. THERE WILL LIKELY BE A SCATTERING OUT OF THE DECK OVERNIGHT WITH STRATUS BECOMING CONCENTRATED AGAIN AROUND THE 02/15Z PERIOD. ALSO EXPECT KPSC TO SLIP BACK UNDER IFR CIGS GIVEN THE PROXIMITY OF THE DECK TO THE NORTH. PRESSURE GRADIENTS DONT SUPPORT A SOUTHWEST WIND TO PUSH THE STRATUS AWAY THERE UNTIL ABOUT 09Z. OTHERWISE...EXPECT MAINLY MVFR AND VFR CONDS THROUGH THE NEXT 24 HOURS...EXCEPT POSSIBLE IFR CONDS AS A FRONT CROSSES THE REGION DURING THE EVENING AND OVERNIGHT HOURS WITH POSSIBLE VLIFR CONDS AT KYKM AFTER 15Z. /JBONK && .PRELIMINARY POINT TEMPS/POPS... PDT 42 50 35 45 / 80 30 10 0 ALW 41 52 36 45 / 80 30 10 0 PSC 42 52 33 45 / 70 20 10 0 YKM 36 49 31 46 / 40 20 10 0 HRI 42 52 33 46 / 70 30 10 0 ELN 37 48 31 44 / 50 20 0 0 RDM 36 53 24 47 / 40 20 0 10 LGD 40 48 33 45 / 70 50 20 10 GCD 40 49 31 47 / 70 50 10 0 DLS 46 54 38 49 / 60 20 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...NONE. WA...AIR STAGNATION ADVISORY UNTIL 3 PM PST TUESDAY FOR WAZ027. && $$ TI:GGG FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT... WWW.WEATHER.GOV/PENDLETON 84/87/87