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Forecast Discussion:NW Oregon - SW Washington
917 AM PST SAT NOV 21 2009..UPDATED FOR HIGH WIND WATCH AND POSSIBLE WIND ADVISORY IN THE WILLAMETTE VALLEY TONIGHT...
SYNOPSIS
A WARM FRONT WILL APPROACH THE OREGON COAST THIS AFTERNOON THEN PUSH INLAND THIS EVENING. A COLD FRONT WILL QUICKLY FOLLOW TONIGHT AS A SURFACE LOW PRESSURE SYSTEM MOVES INLAND NEAR THE WA OREGON BORDER. A WEAK RIDGE OF HIGH PRESSURE WILL FOLLOW SUN AFTERNOON AND NIGHT...BEFORE THE NEXT FRONTAL SYSTEM ARRIVES MON. &&
SHORT TERM
LATEST MODEL RUNS CONTINUE TO EXHIBIT DIFFERENCES IN TRACK OF THE SURFACE LOW COMING IN TONIGHT. UPPER FEATURES APPEAR PRETTY WELL AGREED ON...WITH A STRONG SHORTWAVE MOVING ACROSS THE FORECAST AREA TONIGHT...DIGGING TO THE ESE. GIVEN THE TRACT OF THE UPPER VORT MAX AND THE NEGATIVE TILT OF THE UPPER TROUGH...CONTINUE TO PREFER A MORE SOUTHERLY TRACK OF THE SURFACE LOW...AS SUCH PREFER THE 00Z RUN OF THE ECMWF WHICH TAKES A SURFACE LOW E ROUGHLY ACROSS KKLS AT 12Z SUN. TIMING OF THE COLD FRONT IN ALL MODELS INDICATES FRONTAL PASSAGE ON THE COAST NOT UNTIL SOMETIME TONIGHT. GIVEN THE CONTINUED UNCERTAINTIES IN THE MODELS...WILL EXTEND THE HIGH WIND WATCH FOR THE N AND CENTRAL OREGON COAST TO INCLUDE THE SOUTHERN WASHINGTON COAST...AND EXTEND IT TILL 6AM. WINDS INLAND LOOK GUSTY WITH AND BEHIND THE FRONT AS THERE ARE STRONG PRESSURE RISES BEHIND THE FRONT...EXPECT AN ADVISORY FOR SOME PORTION OF THE WILLAMETTE VALLEY FOR LATE TONIGHT WILL BE NEEDED...WILL PROBABLY ISSUE WITH AFTERNOON PACKAGE. DOPPLER RADAR CONTINUES TO SHOW SHOWERS SPREADING OVER MOST OF THE FORECAST AREA THIS MORNING AS WESTERLY FLOW ALOFT FOLLOWS THE UPPER TROUGH. WITH UPPER RIDGING LATER TODAY...AND LOW LEVEL FLOW BACKING MORE TO THE S...SHOULD SEE SHOWERS DROP OFF TODAY. OVERNIGHT SNOWFALL AMOUNTS IN THE CASCADES SINCE LAST EVENING HAVE RANGED FROM ROUGHLY 4 TO 9 INCHES. FOR NOW WILL HANG ONTO THE SNOW ADVISORY FOR THE N OREGON AND S WA CASCADES TODAY...ALTHOUGH WILL LIKELY SEE A SIGNIFICANT DROPOFF IN SNOWFALL LATER THIS MORNING. WILL CONTINUE THE WINTER STORM WARNING FOR THE CASCADES AS MOISTURE...STRENGTH OF THE FRONT AND THE POST FRONTAL FLOW ALL FAVOR SIGNIFICANT SNOWFALL LATER TONIGHT AND SUN. CURRENT MODEL RUNS INDICATE BEST CHANCES FOR PRECIPITATION MONDAY WILL SHIFT N INTO WA WITH WARM FRONT OVERRUNNING. THE UPPER RIDGE HOLDS COLD FRONT AT BAY UNTIL MON NIGHT. LIKENS
LONG TERM
NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...WEAK HIGH PRES BUILDS OVER THE FORECAST AREA MON NIGHT. MODELS SHOW A WEAK SYSTEM APPROACH THE COAST EARLY TUE...BUT IT TRACKS FURTHER NORTH AND LIGHTLY BRUSHES THE FAR NORTHWEST CORNER OF THE CWA. THIS RIDGE IS MORE PERSISTENT THAN PREVIOUS MODEL RUNS SUGGESTED. IT MANAGES TO DELAY THE ARRIVAL OF A SECOND SYSTEM THROUGH THUR. BY MID NEXT WEEK...MODELS DISAGREE ON THE SOLUTION FOR THE WEEKEND. GFS MODEL RUNS ARE INCONSISTENT...THE 06Z RUN HELD BACK ON PRECIP THROUGH THURS NIGHT BUT THE CURRENT RUN SHOWS RAIN EXTENDING TO THE CASCADES THURS NIGHT. SO FAR...MODELS SUGGEST A FAIRLY NICE WEEKEND AS ANOTHER UPPER HIGH PRES TEMPORARILY SETS UP OVER THE PAC NW. LRAMIREZ &&
AVIATION
LITTLE CHANGE IN OVERALL CONDITIONS THIS MORNING. PREDOMINATELY VFR WITH SCATTERED SHOWERS...WHICH MAY BRING VERY BRIEF MVFR CIGS. CONDITIONS REMAIN VFR THROUGH TODAY...THOUGH WILL SEE INCREASING MVFR ALONG THE COAST AFTER 20Z AS WARM FRONT SWINGS ACROSS THE REGION. COLD FRONT TONIGHT WILL BRING INCREASING MVFR AFTER 04Z...AND INCREASING SOUTHERLY WINDS. KPDX AND APPROACHES...VFR CONDITIONS THROUGH 05Z...THEN INCREASING MVFR CIGS AS COLD FRONT APPROACHES. WATCH FOR POTENTIAL OF LOW LEVEL WIND SHEAR BETWEEN 00Z AND 06Z TONIGHT AS WILL SEE INCREASING SOUTH WINDS ALOFT...BLOWING OVER THE LOW LEVEL EASTERLY FLOW COMING FROM GORGE.ROCKEY/WOLFE &&
MARINE
NOT MUCH CHANGE. CONDITIONS WILL DETERIORATE LATER TODAY AS WARM FRONT LIFTS ACROSS THE REGION. THIS WILL BRING GALE FORCE SOUTH WINDS. HOWEVER...STRONG WINDS ARRIVE TONIGHT AS RATHER STRONG LOW PRES PASSES ACROSS THE N OREGON COASTAL WATERS. STORM WARNING FOR THE COASTAL WATERS FOR TONIGHT. WINDS TURN MORE W TO NW ON SUNDAY AND BEGIN EASING. SEAS TONIGHT LIKELY TO PEAK IN THE 20 TO 25 FT RANGE...BUT WILL DROP QUICKLY ON SUN. &&
PQR WATCHES/WARNINGS/ADVISORIES
WA/OR...GALE WARNING FOR COASTAL WATERS FROM CAPE SHOALWATER TO FLORENCE FOR THIS AFTERNOON. STORM WARNING FOR COASTAL WATERS FROM CAPE SHOALWATER TO FLORENCE FOR TONIGHT. SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR CONDITIONS THROUGH SUN. SNOW ADVISORY FOR THE SOUTH WASHINGTON AND NORTH OREGON CASCADES THROUGH 4 PM. WINTER STORM WARNING FOR THE S WA AND N AND CENTRAL OREGON CASCADES TONIGHT AND SUNDAY. HIGH WIND WATCH FOR THE SOUTHERN WASHINGTON/NORTHERN AND CENTRAL OREGON COAST TONIGHT. && $$ MORE WEATHER INFORMATION ONLINE AT... HTTP://WEATHER.GOV/PORTLAND THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY REFERRED TO AS THE FORECAST AREA.