FXUS66 KSEW 151225 RRA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
430 AM PST TUE DEC 15 2009...CORRECTED TYPO

.SYNOPSIS...RAIN SHOWERS AND MOUNTAIN SNOW WILL PERSIST TODAY BEHIND 
A COLD FRONT THIS MORNING. ANOTHER FRONT WILL BRING MORE RAIN AND 
MOUNTAIN SNOW TO WESTERN WASHINGTON LATER TODAY AND TONIGHT. A 
SERIES OF FRONTAL SYSTEMS WILL CONTINUE TO AFFECT THE REGION THROUGH 
THE WEEKEND.

&&

.SHORT TERM...THE FRONT APPEARS TO HAVE MOVED THROUGH WRN WA EARLIER 
THIS MORNING WITH A WIND SHIFT FROM ELY TO SLY NOTED ALONG THE COAST 
AND PRECIP BECOMING MORE SHOWERY. COLD AIR OVER THE N INTERIOR IS 
SLOWLY MIXING OUT WITH TEMPS ACROSS THE SAN JUANS JUMPING UP TO 
AROUND 40 AND SNOW ENDING AT EAST SOUND. WEAK OUTFLOW CONTINUES TO 
KEEP WESTERN WHATCOM COUNTY DOWN BELOW FREEZING BUT PRECIP HAS ALSO 
ENDED HERE FOR THE MOST PART. JUST A FEW SHOWERS THIS MORNING BEFORE 
TEMPS FINALLY RISE ABOVE FREEZING. WITH VERY LITTLE PRECIP EXPECTED 
UP NORTH TODAY WILL ALLOW THE WINTER WEATHER ADVISORY TO EXPIRE. 
SNOW AMOUNTS IN THE OLYMPICS AND CASCADES ARE RUNNING LESS THAN 
EXPECTED ALTHOUGH A BURST OF HEAVIER POST FRONTAL SNOW IS OCCURING 
IN THE PASSES OF WRN KING/SNOHOMISH COUNTIES. IT IS STILL POSSIBLE 
TO VERIFY THE WARNING THERE WITH UP TO 1 FOOT THIS MORNING SO WILL 
OPT TO KEEP THE WARNING UP BUT LOWER THE AMOUNTS. THERE WILL BE A 
LULL IN SNOW SHOWERS LATE THIS MORNING AND EARLY AFTERNOON BUT WILL 
LET THE DAY SHIFT DECIDE ON WHEN TO END THE WARNING BASED ON TRENDS.

THE NEXT FRONT LIFTS INTO THE AREA FROM THE S LATE TODAY AND 
TONIGHT. THIS SYSTEM WILL BRING LIGHTER QPF AMOUNTS BUT TEMPS IN THE 
MOUNTAIN PASSES WILL STILL BE COLD ENOUGH FOR SNOW OR POSSIBLY 
SLEET/FREEZING RAIN WITH ELY DRAINAGE WINDS CONTINUING. THIS EVENT 
IS CLOSE TO THE 12 HOUR WINDOW SO I WILL ISSUE A WINTER WEATHER 
ADVISORY FOR 3 TO 6 INCHES OF SNOW FOLLOWED BY A PERIOD OF 
SLEET/FREEZING RAIN. TRAVEL THROUGH THE PASSES WILL CONTINUE TO BE 
HAZARDOUS. JUST PLAIN OLD RAIN FOR THE LOWLANDS TONIGHT EVEN ACROSS 
WESTERN WHATCOM COUNTY WHICH SHOULD BE MIXED OUT BY THIS TIME.

A LULL IN PRECIP IS EXPECTED WEDNESDAY MORNING...FOLLOWED BY ANOTHER 
TRAILING WAVE MOVING THROUGH DURING THE AFTERNOON AND EVENING. THIS 
SYSTEM APPEARS WEAKER WITH GENERALLY LIGHT QPF BUT THE CASCADE 
PASSES MAY STILL NOT BE MIXED OUT BY THIS POINT. THIS SYSTEM COULD 
REQUIRE ANOTHER ADVISORY...PROBABLY FOR FREEZING RAIN. 

THE NAM/GFS DIFFER ON TIMING OF THE NEXT SYSTEM ON THURSDAY. THE GFS 
IS MUCH FASTER BRINGING WARM FRONTAL RAIN INTO THE AREA DURING THE 
MORNING WITH THE NAM NOT WET UNTIL LATE IN THE DAY OR EVENING. THE 
ECMWF SEEMS TO BE SLOWER LIKE THE NAM SOLUTION BUT IN THIS 
PROGRESSIVE PATTERN TIMING IS PROBLEMATIC. WILL LEAVE POPS IN THE 
LIKELY CATEGORY FOR LOWLANDS AND CATEGORICAL MOUNTAINS. MERCER
    
.LONG TERM...A FLAT RIDGE BUILDS OVER THE WRN U.S. FRIDAY INTO THE 
WEEKEND. THE GFS/ECMWF BOTH AGREE THAT SYSTEMS BREAKING OVER THE TOP 
WILL BE STRONG ENOUGH TO DRAG WEAK SYSTEMS THROUGH THE AREA. EXPECT 
A CHANCE OF SOME RAIN EACH DAY BUT RAINFALL AMOUNTS DURING THE 
PERIOD ARE LIKELY TO BE ON THE LIGHT SIDE. TEMPS WILL ALSO WARM 
SLIGHTLY WITH SNOW LEVELS POSSIBLY RISING ABOVE SOME OR MOST OF THE 
PASSES. 

&&

.HYDROLOGY...A SERIES OF PROGRESSIVE SYSTEMS WILL BRING PERIODS OF 
RAIN TO THE MOUNTAINS BELOW 4-5K FEET OVER THE NEXT FEW DAYS. SNOW 
IS EXPECTED ABOVE THIS LEVEL WHICH WILL HELP MITIGATE RIVER RISES. 
MOST BASINS ARE CURRENTLY RUNNING LOW AND THE DURATION OF PRECIP 
EVENTS SHOULD NOT BE LONG ENOUGH FOR FLOOD CONCERNS.  

HIGHER PRESSURE BUILDS LATE IN THE WEEK AND THE WEEKEND. SYSTEMS 
WILL STILL BRUSH WESTERN WASHINGTON AT TIMES BUT RAINFALL AMOUNTS 
SHOULD BE ON THE LIGHT SIDE. FLOODING IS NOT ANTICIPATED IN THE 
EXTENDED.

NO FLOODING IS EXPECTED ON THE GREEN RIVER OVER THE NEXT WEEK. MERCER

&&

.AVIATION...WARM FRONT HAS MOVED INTO THE CASCADES AT 11Z. CEILINGS 
BEHIND THE COLD FRONT GENERALLY IN THE 2000 TO 3000 FOOT RANGE WITH 
CEILINGS BELOW 1000 FEET ALONG THE COAST. STILL SOME WINDS ALOFT 
WITH THE SANDPOINT PROFILER SHOWING 20 KNOTS OUT OF THE SOUTH AT 
1000 FEET AND 30 KNOTS AT 2000 FEET. THESE WINDS WILL BE EASING THIS 
MORNING. SURFACE GRADIENTS WILL ALSO WEAKEN THIS MORNING. WITH 
PLENTY OF LOW LEVEL MOISTURE AVAILABLE EXPECT CEILINGS TO LOWER DOWN 
TO THE 1000 TO 2000 FOOT RANGE WITH LOCAL CEILINGS BELOW 1000 FEET 
AND VISIBILITIES 3-5SM IN FOG FROM MID MORNING INTO EARLY AFTERNOON. 
EASTERLY GRADIENTS WILL PICK UP AGAIN LATER THIS AFTERNOON AS THE 
NEXT FRONT APPROACHES THE AREA. THIS WILL HELP LIFT CEILINGS BACK UP 
TO NEAR 3000 FEET LATE AFTERNOON BUT AS THE PRECIPITATION INCREASES 
THIS EVENING CEILINGS WILL ONCE AGAIN LOWER BACK DOWN INTO THE 1000 
TO 2000 FOOT RANGE. LOCAL VISIBILITIES 3-5SM IN LIGHT RAIN 02Z-08Z. 
FELTON

KSEA...CEILINGS RUNNING AROUND 2000 FEET LOWERING DOWN TO NEAR 1000 
FEET MID MORNING WITH POSSIBLE CEILINGS IN THE 500 TO 900 FOOT RANGE 
16Z-20Z CEILINGS WILL LIFT BACK UP TO NEAR 3000 FEET THIS AFTERNOON 
WITH RAIN FROM THE NEXT SYSTEM BEGINNING AROUND 00Z WED. CEILINGS 
LOWERING BACK DOWN TO 1000 TO 2000 FEET THIS EVENING. SOUTHEAST 
WINDS LESS THAN 10 KNOTS THROUGH THIS EVENING. FELTON

&&

.MARINE...WINDS EASING THIS MORNING IN THE WAKE OF THE WARM FRONT. 
ANOTHER FRONT OFFSHORE WILL MOVE THROUGH THE AREA TONIGHT. THIS 
SYSTEM DOES NOT LOOK TO BE AS STRONG AS THE SYSTEM THAT MOVED 
THROUGH EARLY THIS MORNING WITH GALE FORCE WINDS CONFINED TO THE 
COASTAL WATERS. SMALL CRAFT ADVISORY WINDS DEVELOPING AHEAD OF THE 
FRONT FOR THE ENTRANCES TO THE STRAIT AND CAMANO ISLAND TO POINT 
ROBERTS. THE NEXT SYSTEM IN THIS SERIES TIMED INTO THE AREA ON 
THURSDAY. THIS SYSTEM HAS THE POTENTIAL TO BE THE STRONGER ONE OF 
THIS SERIES WITH GALES AGAIN FOR THE COAST AND POSSIBLY ENTRANCES 
TO THE STRAIT AND NORTHERN INLAND WATERS. WINDS SETTLING DOWN ON 
FRIDAY WITH THE NEXT FRONT ARRIVING DURING THE LATTER HALF OF THE 
WEEKEND. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...A WINTER STORM WARNING IS IN EFFECT FOR THE OLYMPICS AND        
     CASCADES THROUGH 6 PM TODAY. 
    .A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE OLYMPICS AND     
     CASCADES FROM 6 PM TODAY THROUGH 6 AM WEDNESDAY MORNING.
    .AVALANCHE WARNING IN EFFECT TODAY.

PZ...GALE WARNING COAST.    
    .SMALL CRAFT ADVISORY ENTRANCES TO THE STRAIT...CAMANO ISLAND TO 
     POINT ROBERTS AND ADMIRALTY INLET.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR CONDITIONS.

$$