FXUS66 KSEW 281653
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
850 AM PST SAT NOV 28 2009

.SYNOPSIS...A WEAK SYSTEM PASSING TO OUR NORTH WILL BRING LIGHT 
PRECIPITATION TO THE AREA THROUGH TONIGHT.  EXPECT DRY WEATHER TO 
RETURN SUNDAY UNDER STRENGTHENING HIGH PRESSURE ALOFT.  HIGH 
PRESSURE ALOFT WILL THEN PREVAIL OVER THE AREA SUNDAY NIGHT. A WEAK 
LOW PRESSURE SYSTEM CLIPPING THE AREA ON MONDAY WILL RESULT IN A 
CHANCE OF SHOWERS OVER MAINLY THE NORTH CASCADES IN THE AFTERNOON.

&&

.SHORT TERM...WARM ADVECTION RAINS HAVE SPREAD ACROSS THE NORTHERN 
PORTION OF THE FORECAST AREA AND THE COAST THIS MORNING WITH CLOUDS 
LOCKED IN EVERYWHERE ELSE.  AS THE DAY PROGRESSES THE RAIN SHOULD 
SPREAD FURTHER SOUTH WITH MOST AREAS RECEIVING AT LEAST A LITTLE 
TODAY AND/OR TONIGHT BEFORE IT ALL RETREATS NORTHWARD LATE TONIGHT 
INTO EARLY SUNDAY MORNING.  EXPECT THE SOUTHERLY BREEZE TO CONTINUE 
THROUGH THE DAY WITH TEMPERATURES REMAINING IN THE 40S FOR THE MOST 
PART.  

FOR SUNDAY THE MOISTURE WILL DIMINISH AS THE UPPER LEVEL RIDGE 
BUILDS AND THIS WILL RESULT IN THE RAIN TAPERING OFF AND THE CLOUDS 
THINNING THROUGH THE DAY.  IF WE MANAGE TO GET A BIT OF SUNSHINE IT 
WILL HELP TO BOOST TEMPS A COUPLE OF DEGREES.  

SUNDAY NIGHT INTO MONDAY THE SURFACE PRESSURE GRADIENTS FLATTEN OUT 
AND THE MID AND HIGH CLOUDS EVAPORATE...SO WITH ALL THE LOW LEVEL 
MOISTURE AROUND WE ARE EXPECTING FOG TO FORM ACROSS THE LOWLANDS OF 
WESTERN WASHINGTON.  A COLD FRONT WILL BRUSH BY THE REGION AND JUST 
CLIP THE REGION LATE MONDAY WHICH SHOULD HELP TO STIR UP THE LOW 
LEVELS AND CLEAR THINGS OUT LATER IN THE DAY.  CERNIGLIA

.LONG TERM...THE PREV 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.  WITH MORE 
RECENT RUNS...THE LOW IS MUCH FURTHER SOUTH AND WILL IMPACT 
CALIFORNIA.  IN EACH CASE THE RIDGE POSITION IS PRETTY MUCH LOCKED 
IN WITH THIS FEATURE PLOWING THROUGH OR OVER THE TOP OF IT.  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 SYSTEM THAT WILL BRING LIGHT 
PRECIPITATION TO WESTERN WASHINGTON THROUGH TONIGHT WILL BE 
WEAK...AND WILL NOT PRODUCE ENOUGH RAIN TO RESULT IN ANY RIVER 
PROBLEMS.  

BEYOND TONIGHT...THE FORECAST WAS ESSENTIALLY DRY WELL INTO NEXT 
WEEK.  THUS...RIVER FLOODING WILL NOT BE A CONCERN.  EXPECT AREA 
RIVERS TO RETURN TO LOWER FLOW LEVELS.  

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

&&

.AVIATION...NORTHWEST FLOW ALOFT TDY BACKING TO WESTERLY TONIGHT. 
WEAK UPPER RIDGE WILL SHIFT OVR THE PACIFIC NORTHWEST TODAY AS A 
WARM FRONT MOVING INTO B.C. BRUSHES WRN WA. THE FRONT WILL BRING 
SOME LIGHT RAIN TO THE FORECAST AREA THRU TONIGHT...MAINLY COAST 
MOUNTAINS AND NORTH OF SEATTLE. THE AIR MASS WILL REMAIN STABLE WITH 
LOW LEVEL MOISTURE THRU SUN MORNING...WITH CIGS LOWERING IN AREAS OF 
LIGHT RAIN OR DRIZZLE THRU TNGT. FEW CHANGES TO THE CURRENT TAFS 
EXPECTED.  

KSEA...SOUTHERLY WIND TO ARND 15KT THROUGH TNGT AND CURRENT TAF 
LOOKS GOOD WITH LOWER CIGS AS THE WARM FRONT GIVES OUT TNGT BUT LOW 
LEVEL MOISTURE REMAINS.

&&

.MARINE...A WARM FRONT WILL MOVE INTO BRITISH COLUMBIA THRU TNGT 
WITH THE SOUTHERN PTN BRUSHING WRN WA. SMALL CRAFT ADVISORY WINDS 
ALL WATERS XCP CENTRAL STRAIT AND SW WIND AT TATOOSH HAS BEEN ARND 
30KT THIS MORNING. GRADIENTS WILL RELAX LATER TNGT AND SUN AND 
WEAK HIGH PRESSURE WILL SIT OVER WESTERN WASHINGTON SUNDAY THROUGH 
MONDAY AS ANOTHER FRONT MOVES BY TO THE NORTH. THEN HIGH PRESSURE 
WILL STRENGTHEN AND SHIFT NORTHWARD INTO BRITISH COLUMBIA MONDAY 
NIGHT...PROVIDING OFFSHORE FLOW ACROSS WESTERN WASHINGTON THROUGH 
WEDNESDAY.

&&

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

PZ...SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR.
    .SMALL CRAFT ADVISORY COASTAL WATERS...ENTRANCES TO THE 
    STRAIT OF JUAN DE FUCA...ADMIRALTY INLET...NORTHERN INLAND
    WATERS...PUGET SOUND AND HOOD CANAL.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.    
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR ALL WATERS EXCEPT THE
     CENTRAL STRAIT OF JUAN DE FUCA TIL 10 PM TONIGHT.

     A SMALL CRAFT ADVISORY IS IN EFFECT FOR ROUGH GRAYS HARBOR
     BAR CONDITIONS TIL 4 PM SUNDAY.

$$

WWW.WEATHER.GOV/SEATTLE

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