000 FXUS66 KSEW 081142 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 342 AM PST SUN NOV 8 2009 .SYNOPSIS...A SMALL WEAK UPPER LEVEL TROUGH WILL BRING SHOWERS TO WESTERN WASHINGTON THIS MORNING...WITH A CHANCE OF SHOWERS CONTINUING THIS AFTERNOON IN THE UNSTABLE AIR MASS. A COLD FRONT WILL SPREAD RAIN AND WIND TO THE COAST LATE TONIGHT AND INLAND ON MONDAY. A LARGE UPPER LEVEL TROUGH WILL BRING SHOWERS TO THE AREA TUESDAY THROUGH THURSDAY AS IT CROSSES THE REGION. ANOTHER FRONTAL SYSTEM WILL REACH THE AREA FRIDAY OR SATURDAY. && .SHORT TERM...THE BROAD UPPER LEVEL TROUGH AND UNSTABLE AIR MASS CONTINUE OVER THE AREA TODAY. IR SATELLITE IMAGERY SHOWS A WEAK SHORTWAVE TROUGH EMBEDDED IN THE FLOW JUST OFFSHORE THAT SHOULD INCREASE THE SHOWER ACTIVITY THIS MORNING. SHOULD SEE SHOWERS DECREASE BY THIS AFTERNOON BEHIND THE SHORTWAVE...BUT WILL HAVE TO MAINTAIN A CHANCE OF SHOWERS DUE TO CONTINUING AIR MASS INSTABILITY. NAM BUFR SOUNDINGS LACK THE DEEPER INSTABILITY OF THE PAST FEW DAYS SO WILL LEAVE THUNDERSTORMS OUT OF THE FORECAST. WITH UPSLOPE FLOW OVER THE MOUNTAINS WEAKENING AND SHOWERS DECREASING THIS AFTERNOON...WILL LET THE WINTER WEATHER ADVISORY FOR THE CASCADES EXPIRE. BOTH GFS/ECMWF ARE STICKING WITH THEIR SOLUTION TO FORM A SOMEWHAT VIGOROUS COLD FRONT OUT OF THE WAVE CROSSING 140W THIS MORNING. THE WAVE IS QUITE WEAK LOOKING AT THIS POINT...SO THERE WILL HAVE TO BE SOME RAPID DEVELOPMENT THROUGH THIS EVENING FOR THE SYSTEM CATCH UP WITH THE MODELS SOLUTION. FURTHERMORE...LAST NIGHTS MODELS HAD SHOWN A WARM FRONT CROSSING W WA THIS EVENING...WHICH THE LATEST MODELS NOW TAKE UP OVER VANCOUVER ISLAND. DESPITE LINGERING DOUBTS WILL STICK WITH THE MODEL SOLUTION FOR A LITTLE LONGER AND BRING RAIN TO THE COAST LATE TONIGHT...THEN SPREAD IT INLAND MONDAY. WILL COUNT ON ENOUGH GRADIENT DEVELOPING TO PRODUCE WINDY CONDITIONS COAST AND ONE NOTCH BELOW INLAND. ANOTHER ROUND OF SHOWERY WEATHER SHOULD RESUME MONDAY NIGHT AND TUESDAY AS A COOLER MORE UNSTABLE AIR MASS MOVES INLAND AHEAD OF A LARGE UPPER LEVEL TROUGH. SHOULD HAVE ANOTHER SERIES OF WEAK SHORTWAVE TROUGHS ROUNDING THE MAIN TROUGH...EACH BRINGING A MORE ORGANIZED BATCH OF SHOWERS TO W WA. MODEL SOLUTIONS SEEM TO BE IN FLUX WITH THESE DETAILS. UPSLOPE FLOW OVER THE CASCADES NEVER GETS PARTICULARLY STRONG FOR VERY LONG THROUGH TUESDAY...AND THE NAM NEVER SHOWS THE 12 HOUR SNOW ACCUMULATION GETTING ABOVE 6 INCHES...EXCEPT FOR THE VOLCANOES. WILL HAVE WATCH FOR ANYTHING REACHING WINTER WEATHER ADVISORY CRITERIA...BUT ONE MAY NOT BE NEEDED OVER THE NEXT FEW DAYS. LOOKS LIKE SNOW LEVELS WILL GET DOWN TO 3500-4000 FEET AT THE LOWEST. KAM .LONG TERM...GFS AND ECMWF AGREE ON BRINGING AN UPPER LEVEL TROUGH AXIS ACROSS THE AREA WEDNESDAY NIGHT...WITH A MORE ORGANIZED BAND OF SHOWERS OR RAIN MOVING OVER THE AREA JUST AHEAD OF THE TROUGH AXIS ON WEDNESDAY. SHOWERS LIKELY FORECAST WORKS FINE FOR NOW. SNOW LEVELS SHOULD DROP DOWN BELOW PASS LEVELS WEDNESDAY NIGHT...BUT SHOWER ACTIVITY SHOULD BE DECREASING AT THAT POINT. GFS/ECMWF SOLUTIONS DIVERGE SIGNIFICANTLY AFTER THURSDAY...SO THE FRIDAY/SATURDAY SYSTEM REMAINS IN DOUBT. WILL LEAVE THE FORECASTS AS IS FOR NOW SINCE CONFIDENCE IN THE MODELS IS LOW. KAM && .HYDROLOGY...NO SIGNIFICANT FLOODING IS EXPECTED IN WESTERN WASHINGTON DURING THE NEXT WEEK. THIS INCLUDES THE GREEN RIVER. NO SIGNIFICANT FRONTAL SYSTEMS ARE EXPECTED THIS WEEK. MONDAYS FRONT WILL BRING SOME BRIEF MODERATE RAIN...WITH SNOW LEVELS AROUND 4500 OR 5000 FEET. THE PRECIPITATION BAND THAT IS FORECAST TO FORM AHEAD OF THE UPPER LEVEL TROUGH ON WEDNESDAY MAY BRING SOME BRIEF MODERATE SHOWERS TO THE AREA...BUT SNOW LEVELS WILL BE DOWN TO 3000 TO 3500 FEET. MODELS ARE HAVING TROUBLE IN THE LONG TERM WITH THE FRIDAY OR SATURDAY FRONTAL SYSTEM...BUT SO FAR ALL THE SOLUTIONS INDICATE A PROGRESSIVE SYSTEM THAT ONLY BRINGS A RELATIVELY SHORT PERIOD OF MODERATE TO HEAVY PRECIPITATION. IN THE EXTENDED WAY OUT PERIOD...THE GFS HEMISPHERIC 5-WAVE CHARTS SHOW A MEAN LONG WAVE TROUGH OUT NEAR 150W OR SO WHICH WOULD MAINTAIN THE CURRENT PROGRESSIVE PATTERN OF WEATHER SYSTEMS CROSSING THE AREA...BUT NOT LINGERING TO PRODUCE LENGTHY PERIODS OF RAIN. KAM && .AVIATION...A WEAKER IMPULSE OF SHOWERS WAS MOVING INTO WRN WA EARLY THIS MORNING...PLENTY OF CLOUDS ON SATELLITE IMAGE BUT JUST SCATTERED SHOWERS ON RADAR AT 3AM. I THINK THAT BY THE MIDDLE OF THE AFTERNOON SOME OF THE LOWER TO MID LEVEL CLOUDS WILL BE DRYING UP SOMEWHAT. I DO NOT SEE ON SATELLITE IMAGERY A WARM ADVECTION DECK OF MID LEVEL CLOUDS OFFSHORE...IN FACT THE NEXT SYSTEM NEARING 135W AND THE SECONDARY FRONTAL WAVE NEAR 145W DO NOT LOOK LIKE THEY HAVE A GREAT DEAL OF MOISTURE GETTING INTO THEM. SO I THINK IT IS A GOOD BET THAT IT WILL BE DRY LATER TODAY THROUGH TONIGHT WITH IMPROVING CONDITIONS AS OFFSHORE FLOW SETS UP AHEAD OF THE NEXT FRONT. THEN AROUND DAYBREAK ON MONDAY CIGS AND VSBY COMES DOWN FAST WITH RAIN SPREADING INLAND. 19 KSEA...NOT PLANNING AND BIG CHANGES TO THE TAF...SCATTERED SHOWERS TODAY...INCREASING SE OR ELY FLOW TONIGHT AND DRIER...AND THERE MIGHT BE ENUF CROSS CASCADE GRADIENT MONDAY MORNING FOR SOME EASTERLY WIND FOR A FEW HOURS. THE RAIN AGAIN DVLPG MON MORNING WITH ANOTHER VIGOROUS FRONTAL SYS. 19 && .MARINE...I HAVE MADE NO SGFNT CHANGES TO THE FCSTS...SO THE GALE WATCH FOR THE COASTAL WATERS AND WEST ENTRANCE BECOMES A GALE WARNING FOR TONIGHT. A SMALL CRAFT FOR HAZARDOUS SEAS IS UP FOR TODAY FOR THE COAST AND WEST ENTRANCE TO THE STRAIT...COASTAL SEAS STILL 18FT EARLY THIS MORNING. THIS NEXT FNTL SYS LOOKS TO BE QUITE STRONG AND A FULL GALE UP AND DOWN THE COAST IS LIKELY BETWEEN MIDNIGHT TONIGHT TIL ARND 10 AM MONDAY WITH THE FROPA. A GOOD CHANCE OF GALES ACROSS ALL THE NRN INLAND WATERS AS WELL...BUT LEFT THAT A GALE WATCH FOR NOW. THE LATEST NAM SHOWS A 994MB LOW OVER NRN VRISL ARND DAYBREAK MON WITH THE FRONT OVER THE COASTAL WATERS AND 925MB/2500FT WINDS UP TO 60KT. THE 4KM WRFGFS HAD A GOOD PART OF THE COASTAL WATERS GETTING UP TO 45KT LATE MONDAY NIGHT...SO THERE IS A CHANCE OF REACHING STORM FORCE 50KT IN A FEW SPOTS BY DAWN MON. 19 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS COASTAL WATERS AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA TODAY. GALE WARNING COASTAL WATERS AND WEST ENTRANCE TONIGHT. SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL TIL 9AM. SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR. GALE WATCH FOR THE EAST ENTRANCE TO THE STRAIT AND NORTHERN WATERS FOR TONIGHT AND MON MORNING. $$ WWW.WEATHER.GOV/SEATTLE FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.