000 FXUS66 KSEW 231131 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 300 AM PST MON NOV 23 2009 .SYNOPSIS...A WARM FRONT WILL BRING SOME RAIN TO WESTERN WASHINGTON TODAY...MAINLY ALONG THE COAST AND IN THE NORTH. A WEAK COLD FRONT WILL MOVE INLAND TONIGHT. WEAK HIGH PRESSURE WILL MOVE ACROSS THE AREA TUESDAY. A WEAK WARM FRONT WILL MOVE THROUGH THE AREA TUESDAY NIGHT...FOLLOWED BY ANOTHER WEAK COLD FRONT WEDNESDAY NIGHT AND THANKSGIVING DAY....FOLLOWED BY AN UPPER TROUGH ON FRIDAY. && .SHORT TERM...THE VIGOROUS SYSTEM THAT WAS MOVING INTO THE PACIFIC NORTHWEST 24 HOURS AGO IS NOW LONG GONE...MAKING ITS WAY EAST OF THE NORTHERN ROCKIES. AN UPPER LEVEL RIDGE HAS MOVED OVER THE PACIFIC NORTHWEST OVERNIGHT -- THE BEGINNING OF A TREND TOWARD A HIGH AMPLITUDE...LESS PROGRESSIVE...AND MUCH LESS EVENTFUL WEATHER PATTERN THAT WILL CONTINUE THROUGH THE NEXT WEEK. SKIES ACROSS WESTERN WASHINGTON ARE GENERALLY CLOUDY THIS MORNING WITH VERY SPOTTY LIGHT PRECIPITATION...AS THE WARM FRONT OF A SYSTEM IMMEDIATELY UPSTREAM OF THE RIDGE IS MOVING INTO THE FORECAST AREA. TEMPERATURES ARE IN THE LOWER TO MID 40S. THE UPPER RIDGE WILL PROGRESS EASTWARD TODAY ACROSS THE CASCADES AND ALMOST TO THE EASTERN BORDER OF THE STATE. THIS WILL ALLOW THE FRONTAL SYSTEM JUST OFFSHORE TO MOVE SLOWLY INLAND TODAY. IT WILL BRING FAIRLY SIGNIFICANT PRECIPITATION AMOUNTS -- IN THE .50 TO 1.25 INCH RANGE -- TO THE COAST AND OLYMPIC PENINSULA...WITH SOMEWHAT LESS OVER THE NORTH CASCADES. BUT THE FRONT WILL WEAKEN AS IT MOVES THROUGH THE AREA TONIGHT...AND PRECIPITATION TOTALS FOR THE INTERIOR LOWLANDS WILL MOSTLY BE LESS THAN 0.25 INCH. THE SNOW LEVEL...WHICH IS STARTING OUT AROUND 2500 FT...WILL CLIMB TO AROUND 6000 FT TONIGHT. AS THE FRONT FALLS APART AND MOVES EAST OF THE CASCADES TUESDAY... ANOTHER STRONGER UPPER RIDGE WILL MOVE OVER THE PACIFIC NORTHWEST. THE RIDGE WILL SEND 500 MB HEIGHTS TO AROUND 5700 METERS. THE WARM FRONT OF ANOTHER FRONTAL SYSTEM JUST UPSTREAM OF THIS RIDGE WILL KEEP A CHANCE OF LIGHT RAIN IN THE FORECAST TUESDAY. BY TUESDAY NIGHT THE UPPER RIDGE AXIS WILL BE EAST OF THE CASCADES AND IT WILL MOVE SLOWLY EASTWARD TO THE ROCKIES ON WEDNESDAY NIGHT. MODELS SHOW THE FRONTAL BAND TRANSLATING VERY SLOWLY EASTWARD AS IT STRETCHES SOUTH-SOUTHWEST FROM VANCOUVER ISLAND. IT WILL KEEP A CHANCE OF RAIN IN THE FORECAST FOR WESTERN WASHINGTON...BUT PRECIPITATION WILL BE GENERALLY VERY LIGHT WHERE WE GET ANY...AND THE MAIN THREAT OF PRECIPITATION WILL BE ALONG THE COAST AND OVER THE OLYMPIC PENINSULA. THE SNOW LEVEL WILL BE 7000-8000 FT. MCDONNAL .LONG TERM...THE MODELS DISAGREE ON HOW THE PATTERN WILL CHANGE IN THE LONGER RANGE. THE GFS SHOWS A MUCH DRIER SOLUTION WHILE THE EUROPEAN MODEL IS WETTER. SO CONFIDENCE IN THE EXTENDED FORECAST THANKSGIVING DAY THROUGH SUNDAY IS RATHER LOW AND THE APPROACH IS A BROAD BRUSH. IN A VERY GENERAL SENSE THEY AGREE THAT THANKSGIVING DAY THROUGH FRIDAY NIGHT WILL BE WETTER AS THE FRONTAL SYSTEM SITTING OFFSHORE WEDNESDAY MOVES THROUGH THE AREA. AND THEY AGREE THAT AN UPPER RIDGE WILL BUILD OVER THE AREA OVER THE WEEKEND ...REDUCING THE THREAT OF WET WEATHER TO A CHANCE. MCDONNAL && .HYDROLOGY...THE SKOKOMISH RIVER REMAINS JUST ABOVE FLOOD STAGE EARLY THIS MORNING. THE CURRENT RIVER MODEL FORECAST SHOWS IT DROPPING BELOW FLOOD STAGE LATER TODAY...BUT THE ACTUAL RESULT WILL DEPEND HEAVILY UPON THE OPERATION OF CUSHMAN DAM #2 ON THE NORTH FORK OF THE RIVER. A PLANNED RELEASE OF WATER FROM THE DAM BEGAN EARLY SATURDAY AND CONTINUES EARLY THIS MORNING. TWO FRONTAL SYSTEMS WILL MOVE THROUGH THE AREA THROUGH WEDNESDAY NIGHT...AND THE SNOW LEVEL WILL GRADUALLY CLIMB TO 7000-8000 FT. THESE SYSTEMS WILL NOT BRING ENOUGH PRECIPITATION FOR FLOODING CONCERNS ON ANY WESTERN WASHINGTON RIVERS...WITH THE POSSIBLE EXCEPTION OF THE SKOKOMISH RIVER. THE FORECAST FOR THANKSGIVING AND BEYOND IS LESS CERTAIN...BUT AT THIS TIME THERE DOES NOT APPEAR TO BE ANY THREAT OF FLOOD-PRODUCING RAINS. NO FLOODING IS EXPECTED ON THE GREEN RIVER AT ANY TIME DURING THE FORECAST PERIOD. && .AVIATION...THE TAIL END OF AN UPPER TROUGH WILL BRUSH BY THIS AFTERNOON...PUSHING A WEAKENING COLD FRONT ACROSS WRN WA. FOG IS BECOMING INCREASINGLY UNLIKELY THIS MORNING GIVEN THE THICKNESS OF MID-LEVEL CLOUDS AND ENOUGH WIND TO MIX THE BOUNDARY LAYER. AN OFFSHORE COMPONENT TO THE LOW-LEVEL FLOW IN ADVANCE OF THE FRONT WILL LIMIT CLOUDS BELOW 040...EXCEPT NEAR HOOD CANAL. THE FRONT SHOULD CROSS WRN WA FROM 00Z-06Z THIS EVENING...ACCOMPANIED BY RAIN AND FOLLOWED BY INCREASING LOW-LEVEL MOISTURE OVERNIGHT TONIGHT. KSEA...CIGS SHOULD IMPROVE THIS MORNING AS AN OFFSHORE LOW-LEVEL FLOW COMPONENT STRENGTHENS IN ADVANCE OF THE APPROACHING FRONT AND INHIBITS LOWER CLOUDS. A COLD FRONT WILL PASS KSEA BTWN 00Z-03Z ON MON EVENING. WINDS ALOFT SHOULD PEAK AROUND THE TIME OF FROPA...WITH SOUTHWEST 850 MB WINDS NEAR 40 KNOTS ARND 00Z. LOW-LEVEL MOISTURE WILL INCREASE BEHIND THE FRONT WITH CIGS DETERIORATING TO IFR TONIGHT AND CONTINUING ON TUE MORNING. HANER && .MARINE...SOUTHERLY FLOW WILL INCREASE TODAY IN ADVANCE OF AN APPROACHING FRONT. THE WIND AT BUOY 46036 GUSTED TO GALE FORCE IN ADVANCE OF THE FRONT...SO AM THINKING LOW-END GALES SHOULD AFFECT THE COASTAL WATERS TODAY. THE FRONT WILL BE WEAKENING QUICKLY AS IT MOVES INLAND LATE THIS AFTN AND EVNG. AS A RESULT...NOT EXPECTING THE GALES ALONG THE COAST TO TRANSLATE TO THE NORTH INTERIOR. SMALL CRAFT WINDS OVER THE INLAND WATERS ARE THE MOST LIKELY OUTCOME AT THIS POINT...BUT WILL NEED TO BE WATCHED. HIGH PRES WILL BUILD OVER THE WATERS TONIGHT AND TUE WITH LGT TO MDT OFFSHORE FLOW DVLPG. HANER && .SEW WATCHES/WARNINGS/ADVISORIES... WA...A FLOOD WARNING REMAINS IN EFFECT FOR THE SKOKOMISH RIVER IN MASON COUNTY. PZ...GALE WARNING COAST AND WEST ENTRANCE. SMALL CRAFT ADVISORY ALL OTHER WATERS EXCEPT THE CENTRAL STRAIT. SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS AT GRAYS HARBOR ENTRANCE. $$ WWW.WEATHER.GOV/SEATTLE FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.