FXUS66 KSEW 280508
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
907 PM PST FRI NOV 27 2009

.SYNOPSIS...THE SOUTHERN END OF A WARM FRONT WILL EDGE INTO WESTERN 
WASHINGTON LATE TONIGHT INTO SATURDAY NIGHT THEN LIFT NORTH SUNDAY.  
A WEAK COLD FRONT WILL SLIDE THROUGH THE REGION MONDAY FOR A CHANCE 
OF SHOWERS.  THIS WILL BE FOLLOWED BY AN UPPER LEVEL RIDGE WHICH IS 
EXPECTED TO PROVIDE DRY WEATHER THROUGH MOST OF THE COMING WEEK. 

&&

.SHORT TERM...SKIES CLEARED OUT EARLY THIS EVENING AND AS A RESULT 
TEMPS DROPPED TO NEAR FORECAST LOWS ALREADY...MAINLY IN THE 
INTERIOR. DO NOT THINK WE WILL DROP ANY LOWER THOUGH AS THE SURFACE 
FLOW HAS SWITCHED TO SOUTHERLY. ALSO WILL SEE INCREASING CLOUDS AS A 
WARM FRONT OFFSHORE APPROACHES WA. THE FRONT WILL LIFT N/NE THROUGH 
THE REGION EARLY SAT MORNING BUT OVERALL PRECIP AMOUNTS LOOK LIGHT. 

WESTERN WA WILL LIE IN THE WARM SECTOR THROUGH SUNDAY LEADING TO 
CLOUDY AND MILD CONDITIONS...WITH OCCASIONAL LIGHT RAIN AND MORNING 
FOG. AN UPPER LEVEL RIDGE WILL AMPLIFY OVER THE PAC NW EARLY NEXT 
WEEK LEADING TO DRIER WEATHER ACROSS THE REGION. THIS OF COURSE WILL 
LEAD TO COOLER NIGHTTIME LOWS WITH TEMPS NEAR FREEZING...ESPECIALLY 
THE SW INTERIOR. LATE NIGHT/EARLY MORNING FOG WILL ALSO BE MORE 
EXTENSIVE. A WEAK SHORT WAVE TROUGH MAY RIDE TROUGH SOUTHERN B.C. 
MON NIGHT WHICH WILL FLATTEN THE RIDGE OVER WA. THE NAM DIGS THE 
TROUGH FARTHER SOUTH INTO WA BUT THE GFS AND ECMWF ARE BOTH DRIER. 33

.LONG TERM...PREVIOUS DISCUSSION...THE OVERALL PATTERN WILL CONTINUE 
TO MAKE A MAJOR SHIFT AND AN UPPER LEVEL RIDGE WILL BUILD OVER THE 
EASTERN PACIFIC AND BLEED OVER INTO THE WEST COAST.  THIS WILL BRING 
ABOUT A MUCH DRIER PATTERN FOR THE REGION NEXT WEEK.  

THERE IS A BUNDLE OF ENERGY THAT THE VARIOUS LONG RANGE MODELS TRY 
TO GRAB ONTO AND MOVE EAST EITHER THROUGH OR OVER THE RIDGE.  
HOWEVER...EACH RUN AND MODEL IS DIFFERENT WITH THE 
TRACK...DEPTH...AND WHAT DAY THIS WILL MOVE THROUGH THE WESTERLIES.  
IN EACH CASE THE RIDGE POSITION IS PRETTY MUCH LOCKED IN WITH THIS 
FEATURE PLOWING THROUGH OR OVER THE TOP OF IT.  IF THIS COMES TO 
PASS IN SOME FORM IT COULD BRING A CHANCE OF SHOWERS TO THE AREA FOR 
ONE DAY.  FOR NOW WILL CONTINUE TO GO WITH THE DRY FORECAST AS THIS 
IS WHAT IS THE MOST PROBABLE SOLUTION FOR NOW.  CERNIGLIA 

&&

.HYDROLOGY...THE WARM ADVECTION SYSTEMS THAT WILL SPREAD LIGHT 
PRECIPITATION OVER WESTERN WASHINGTON THIS WEEKEND WILL BE RATHER 
WEAK AND AS A RESULT WILL NOT PRODUCE ENOUGH RAIN TO CAUSE ANY RIVER 
PROBLEMS.  

BEYOND THAT...THE FORECAST IS DRY WELL INTO NEXT WEEK.  AS A RESULT 
NO NEW FLOODING IS EXPECTED THROUGH NEXT WEEK AND AREA RIVERS WILL 
RETURN TO LOWER FLOW LEVELS.  

NO FLOODING IS EXPECTED ON THE GREEN RIVER THROUGH NEXT WEEK.  
CERNIGLIA

&&

.AVIATION...NORTHWEST FLOW WILL CONTINUE ALOFT OVER WESTERN 
WASHINGTON TONIGHT AND SATURDAY. A WEAK UPPER RIDGE CURRENTLY 
OFFSHORE WILL SHIFT INTO THE PACIFIC NORTHWEST SATURDAY...AND A WEAK 
WARM FRONT MOVING OVER THE NORTH SIDE OF THE RIDGE WILL BRUSH THE 
REGION. THE FRONT IS ALREADY BRINGING SOME LIGHT RAIN TO THE NORTH 
COAST. LATER TONIGHT AND SATURDAY IT WILL BRING SOME LIGHT RAIN TO 
THE FORECAST AREA...MAINLY ALONG THE COAST...OVER THE MOUNTAINS... 
AND IN THE INTERIOR LOWLANDS NORTH OF SEATTLE.

THE AIR MASS WILL REMAIN STABLE WITH SOME MOISTURE TRAPPED AT LOW 
LEVELS AND INCREASING MOISTURE AT MID AND HIGH LEVELS DUE TO THE 
WARM FRONT. MOST TERMINALS IN WESTERN WASHINGTON WILL HAVE LOWER 
CONDITIONS LATE TONIGHT AND INTO SATURDAY -- DUE EITHER TO LIGHT 
RAIN WHERE IT FALLS OR DUE TO PATCHY FOG IN THE SOUTH INTERIOR.

KSEA...SOUTHERLY WIND 3-8 KT THROUGH SATURDAY. HIGH CLOUDS WILL 
ARRIVE AROUND MIDNIGHT...GRADUALLY LOWER TO AROUND 5000 FT AT 15Z... 
AND DETERIORATE FURTHER TO MVFR CONDITIONS WITH SOME LIGHT RAIN 
AROUND 20Z.

MCDONNAL

&&

.MARINE...A WARM FRONT WILL MOVE ONTO THE BRITISH COLUMBIA COAST 
LATE TONIGHT AND SATURDAY...WITH ITS SOUTHERN END BRUSHING NORTHWEST 
WASHINGTON. THIS FEATURE WILL PRODUCE SMALL CRAFT ADVISORY WINDS 
OVER THE COASTAL WATERS...AT THE ENTRANCES TO THE STRAIT...IN 
ADMIRALTY INLET...AND OVER THE NORTHERN INLAND WATERS SATURDAY AND 
INTO SATURDAY NIGHT.

AFTER THE WARM FRONT HIGH PRESSURE WILL BUILD OVER THE REGION 
THROUGH SUNDAY NIGHT...THEN SHIFT NORTHWARD INTO BRITISH COLUMBIA ON 
MONDAY. THE HIGH PRESSURE TO OUR NORTH WILL RESULT IN OFFSHORE FLOW 
EARLY NEXT WEEK.

MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.    

PZ...SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR.
    .SMALL CRAFT ADVISORY COASTAL WATERS...STRAIT OF JUAN DE
     FUCA...ADMIRALTY INLET...NORTHERN INLAND WATERS.

$$

WWW.WEATHER.GOV/SEATTLE

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.