FXUS66 KSEW 091723
 AFDSEW
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SEATTLE WA          
 920 AM PST TUE MAR 9 2010
 
 .SYNOPSIS...A COOL UPPER TROUGH OVER THE CASCADES WILL SHIFT EAST 
 TODAY. PRECIPITATION ASSOCIATED WITH A SPLITTING FRONTAL SYSTEM WILL 
 MOVE ONSHORE THIS AFTERNOON AND PUSH INLAND THIS EVENING. THE AIR 
 MASS IS COOL ENOUGH THAT PRECIPITATION MAY BE LOCALLY MIXED WITH 
 SNOW THIS EVENING...MAINLY AROUND HOOD CANAL. A SERIES OF FRONTAL 
 SYSTEMS WILL BRING RAIN AND BREEZY CONDITIONS TO THE AREA THURSDAY 
 INTO FRIDAY. SHOWERS WILL TAPER OFF ON SATURDAY. A MOSTLY DRY DAY IS 
 EXPECTED ON SUNDAY. 
 
 &&
 
 .SHORT TERM...SHORTWAVE RIDGING OVER THE AREA QUICKLY SHIFTS EAST OF 
 THE CASCADES TODAY AS A SPLITTING FRONTAL SYSTEM APPROACHES FROM THE 
 WEST. THANKS TO THE SHARP COLD TROUGH THAT PASSED OVER YESTERDAY 
 LAST NIGHT OVER THE AREA...A FEW MIN TEMPERATURE RECORDS WERE BROKEN 
 OR TIED THIS MORNING INCLUDING KSEA AND KOLM.  MID AND HIGH DECK CAN 
 ALREADY BE SEEN FILLING IN OVER WESTERN WASHINGTON...WITH THE BACK 
 EDGE OF THE COLD FRONT AROUND 130W. STRONG JET CAN BE SEEN ON 
 SATELLITE PUSHING BULK OF THE ENERGY WITH THE SYSTEM TOWARD THE 
 OR/CA BORDER.   
 
 PRECIPITATION WILL BEGIN EARLY THIS AFTERNOON FOR THE COAST...WITH 
 LIGHT PRECIPITATION PUSHING INTO THE INTERIOR LATER THIS EVENING. 
 THE WEAK FRONT FINALLY PUSHES EAST OF THE CASCADES AROUND 12Z WED. 
 MEDIOCRE PRES RISES BEHIND THE FRONT WED MORNING COULD PRODUCE WEAK 
 CONVERGENCE AROUND THE NORTH/CENTRAL SOUND THROUGH AFTERNOON. COOL 
 1000-850 MB THICKNESSES SUPPORT SNOW FOR A FEW FAVORED LOCATIONS 
 LATER THIS EVENING AS PRECIPITATION PICKS UP ACROSS WESTERN WA. WITH 
 LIGHT PRECIPITATION TOTALS AND THE LOW LEVEL FLOW A LITTLE TOO 
 SOUTHERLY...THINK ONLY AREAS THAT HAVE A CHANCE AT ACCUMULATING 
 SNOWS WILL BE HOOD CANAL AND ELEVATED TERRAIN AROUND THE CHEHALIS 
 GAP THROUGH 6Z. THICKNESSES SUPPORT SNOW INITIALLY IN THE MIX DOWN 
 TO SEA LEVEL THIS EVENING FOR OTHER AREAS...BUT DON`T THINK THIS 
 WILL ACCUMULATE OR BE VERY LONG LIVED. FLOW BECOMES WESTERLY EARLY 
 WEDNESDAY MORNING TURNING EVERYTHING TO COLD RAIN SHOWERS. IT IS 
 POSSIBLE IF THAT PSCZ IS STRONGER THAN ADVERTISES WEDNESDAY POST 
 FROPA THAT THERE COULD BE SOME WET SNOW MIXING IN PAE AND NORTH.  
 ALSO SATELLITE IMAGERY AND MODEL FORECASTS SHOW CAPES OF 200-400 
 J/KG OVER THE COASTAL WATERS LATE TONIGHT BEHIND THE FRONT TO 
 SUPPORT A SLIGHT CHANCE OF TSTMS. BEHIND THE FRONT SHORT WAVE 
 RIDGING APPROACHES WED AFTERNOON FOR A DECREASING CHANCE OF SHOWERS 
 AND SOME SUNSHINE. 
 
 NEXT SYSTEM APPROACHES WEDNESDAY NIGHT WITH STRONG SOUTHWEST FLOW 
 AIMED AT THE OLYMPICS AND NORTH CASCADES. RAIN WILL PUSH INTO THE 
 INTERIOR OVERNIGHT...PERHAPS BRIEFLY MIXING WITH SNOW FOR THE HOOD 
 CANAL AREA. BUT FREEZING LEVELS WILL RISE WITH THIS SYSTEM...TO 
 AROUND 4000 FEET THURSDAY AFTERNOON...EXCEPT LOCALLY LOWER IN THE 
 PASSES WHERE EASTERLY FLOW WILL KEEP LEVELS COLDER. 12Z GFS NOW 
 BRINGS BULK OF THE PRECIP FURTHER SOUTH THAN PREV RUNS. BASED ON 
 WHAT 12Z ECMWF DOES WILL HAVE TO DECIDE IF A FLOOD OUTLOOK IS 
 WARRANTED FOR OLYMPICS AND NORTH CASCADES RIVERS THIS AFTERNOON FOR 
 THE THURSDAY-FRIDAY TIME FRAME. DAMICO 
 
 .LONG TERM...FROM PREV DISCUSSION...EXTENDED MODEL SOLUTIONS 
 GENERALLY AGREE WITH PREVIOUS SOLUTIONS THAT THE FRONT AND POST 
 FRONTAL TROUGH WILL MOVE EAST THROUGH THE AREA FRI NIGHT OR EARLY 
 SAT AND WILL BE FOLLOWED BY SHORT WAVE RIDGING LATER SAT INTO SUN. 
 ANOTHER WET PERIOD MAY BE IN STORE FOR EARLY NEXT WEEK...THOUGH 
 MODELS ARE NOT CONSISTENT AND THE RELIABLE ECMWF SHOWS THE SYSTEM 
 FOR EARLY NEXT WEEK SPLITTING. WILL NOT MAKE ANY CHANGES TO THE 
 EXTENDED FORECAST AT THIS TIME.  ALBRECHT
 
 &&
 
 .HYDROLOGY...FROM PREV DISCUSSION...A SPLITTING FRONTAL SYSTEM WILL 
 GIVE RATHER LIGHT PRECIPITATION AMOUNTS TO THE AREA TONIGHT. MORNING 
 SHOWERS WILL TAPER OFF WED. SNOW LEVELS WILL GENERALLY REMAIN 
 LOW...BELOW 2000 FT MOST AREAS...THROUGH WED NIGHT.
 
 MODELS SHOW A STRONGER AND WETTER FRONTAL SYSTEM NOW JUST EAST OF 
 THE DATELINE MOVING EAST INTO THE AREA LATE WED NIGHT OR THU...THEN 
 STALLING THROUGH ABOUT FRI AS DEVELOPING WAVES OVER THE EAST CENTRAL 
 PACIFIC WIND UP AND MOVE NE INTO SE ALASKA OR THE CHARLOTTES. 
 PERSISTENT STRONG AND MOIST SW FLOW OF 45-60 KT ABOVE ABOUT 2000 FT 
 AND FREEZING LEVELS RISING TO AROUND 6000 FT THU INTO FRI ARE NOW 
 BEING ADVERTISED BY THE VARIOUS MODELS. LOCALLY HEAVY PRECIPITATION 
 OF 3-5 INCHES IN 24-30 HOURS MAY RESULT ON THE SW FACING OLYMPICS 
 AND OVER THE NORTH CASCADES. AT THIS TIME QPF WILL BE BASED ON A 
 MODEL BLEND. IF CURRENT TRENDS PERSIST THIS MORNING...THE DAY SHIFT 
 WILL LIKELY NEED TO ISSUE A FLOOD POTENTIAL OUTLOOK FOR THE OLYMPICS 
 AND NORTH CASCADES LATER IN THE WEEK AS SOME RIVERS...PARTICULARLY 
 THE SKOKOMISH RIVER IN MASON COUNTY...COULD FLOOD WITH THIS AMOUNT 
 OF PRECIPITATION. 
 
 THE FLOODING THREAT FOR THE GREEN RIVER IS LOW FOR THE NEXT 10 DAYS. 
 ALBRECHT
 
 &&
 
 .AVIATION...PATCHY LOW LEVEL MOISTURE OTHERWISE JUST INCREASING MID 
 AND HIGH CLOUDS AHEAD OF THE NEXT FRONT. THE FRONT SPREADS 
 RAIN...MAYBE A LITTLE WET SNOW ON THE HILLS...TO THE COAST THIS 
 AFTERNOON. PRECIP ARRIVES INLAND PORTION OF WRN WA NOT UNTIL EVENING 
 WITH RAIN AND A FEW POCKETS OF WET SNOW OVERNIGHT...AND FROPA AROUND 
 DAYBREAK WED. SNOW LEVEL WILL PROBABLY AVERAGE 1000FEET 
 TONIGHT...AREAS AROUND HOOD CANAL COULD SEE THE SNOW LEVEL LOWER 
 THAN THAT...AREAS NEAR THE WEST SLOPES OF THE CASCADES A NOTCH 
 HIGHER. THE FRONTAL PASSAGE WILL PROBABLY REACH THE COAST ARND 9PM 
 AND THE I-5 CORRIDOR AROUND 3AM. SSW FLOW ALF INCREASING THRU 
 TONIGHT WITH THE FRONT...THEN A SHIFT TO LIGHTER MORE WLY FLOW ALF 
 WED...TURNING NW ABV 700MB AS THE UPPER TROF MOVES IN. THERE IS A 
 GOOD CHANCE OF A PSCZ ACTIVITY KPAE-KAWO WED MORNING. THE NEXT 
 SYSTEM WILL BE MUCH WARMER AND WETTER AND ARRIVE ON THU. 19
 
 KSEA...CLOUDS INCREASE TODAY...PATCHY LOW CLOUDS SHOULD STAY 
 SCATTERED...AND THICKENING HIGH CLOUDS THIS MORNING. CIGS DROP LATER 
 TODAY WITH RAIN DVLPG THIS EVENING...PERHAPS MIXING WITH A LITTLE 
 WET SNOW AT TIMES OVERNIGHT...BUT A SNOW LEVEL ARND 1000FT SHOULD 
 KEEP SEA TAC FROM SEEING ANY ACCUM WHATSOEVER...AND 38 DEGREE RAIN 
 AND A SSE WIND 10-15KT TNGT IS A GOOD BET. 19 
 
 &&
 
 .MARINE...NO UPDATES EXCEPT TO SLOW DOWN THE GALE FORCE WINDS IN THE 
 NRN INLAND WATERS TIL EARLY EVENING...THE 12KM UW WRFGFS SHOWS 25KT 
 SE WIND IN THE EAST ENTRANCE TO THE STRAIT THIS AFTERNOON WITH 
 15-25KT IN ADMIRALTY AND THE NRN INLAND WATERS...THEN GALES DEVELOP 
 EARLY THIS EVENING BETWEEN DUNGENESS AND VICTORIA EXTENDING NORTH 
 THRU HARO STRAIT AND THE CANADIAN GULF ISLANDS. THE FROPA IS AT THE 
 COAST ARND 9PM W/NW 20-30KT COASTAL WATERS BHND THE FRONT AND THE 
 WESTERLIES WORKING DOWN THE STRAIT ARND MIDNIGHT. ONSHORE FLOW 
 DECREASES RAPIDLY WED AS GRADIENTS RELAX AHEAD OF THE NEXT FRONT 
 WHICH WILL BRING ANOTHER ROUND OF GALES BY THU. 19
 
 &&
 
 .SEW WATCHES/WARNINGS/ADVISORIES...
 WA...NONE.
 PZ...GALE WARNING COASTAL WATERS AND WEST AND EAST ENTRANCE JUAN DE  
      FUCA...NORTHERN INLAND WATERS.
      SMALL CRAFT ADVISORY CENTRAL STRAIT AND ADMIRALTY INLET. 
      SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR BAR. 
 
 
 
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