FXUS66 KSEW 291636
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PST SUN NOV 29 2009

.SYNOPSIS...LOW CLOUDS AND AREAS OF LIGHT RAIN OR DRIZZLE WILL 
COME TO AN END BY LATER THIS MORNING AS HIGH PRESSURE BUILDS OVER 
WASHINGTON. EXPECT THE TAIL END OF A LOW PRESSURE SYSTEM 
TO BRING A THREAT OF SHOWERS TO THE AREA MONDAY AFTERNOON AND EVENING. 
DRY WEATHER WILL RETURN ON TUESDAY IN RESPONSE TO HIGH PRESSURE ALOFT 
BUILDING OVER THE PACIFIC NORTHWEST.

&&

.SHORT TERM...THE WARM FRONT WHICH LIFTED N ACROSS WRN WA LAST NIGHT IS 
NOW LOCATED ACROSS B.C. THIS MORNING. RESIDUAL LOW LEVEL MOISTURE IS 
STILL ABUNDANT ACROSS THE AREA THIS MORNING WITH SOME VERY WEAK LIFT IN 
THE LOW LEVELS RESULTING IN AREAS OF DRIZZLE. DID A QUICK ZONE UPDATE 
TO INDICATE AREAS OF FOG AND DRIZZLE THROUGH THE MORNING HOURS. THE 
LATEST NAM-12 TIME HEIGHT SECTION SHOWS A PERIOD OF POSSIBLE SCATTERING 
FOR A BRIEF PERIOD FROM LATE THIS AFTERNOON THROUGH THE EVENING. NOT 
ALL AREAS WILL SEE THE SUN BREAKS THOUGH AS VERY LITTLE MIXING IS 
EXPECTED UNDER BUILDING HIGH PRESSURE TODAY. LOW CLOUDS AND AREAS OF 
FOG WILL LIKELY REFORM TONIGHT AS WA WILL REMAIN IN THE WARM SECTOR 
AHEAD OF THE NEXT FRONT.

MODELS TRENDED BACK TO A SLIGHTLY WETTER SOLUTION WITH THE FRONT TO 
CLIP WA ON MONDAY. IT STILL APPEARS ONLY THE TAIL END OF THE SYSTEM 
WILL CLIP THE AREA BUT THE GFS IS SHOWING AS MUCH AS A HALF INCH QPF 
ACROSS THE N COAST...AND N INTERIOR. MUCH LESS PRECIP IS EXPECTED SOUTH 
OF ROUGHLY EVERETT BUT THE CURRENT FORECAST IS COMPLETELY DRY. IF THE 
NAM-12 IS CORRECT THIS COULD BE THE CASE BUT EVEN THIS MODEL HAS SOME 
LOW CHANCE POPS. WILL WAIT FOR THE NEW 12Z GFS AND MM5 RUNS AND WILL 
PROBABLY HAVE TO REINTRODUCE SOME LOW CHANCE POPS FOR THE INTERIOR 
MONDAY AFTERNOON.

THERE MAY BE SOME RESIDUAL SHOWERS MONDAY EVENING WITH ONSHORE FLOW AND 
LOTS OF LOW LEVEL MOISTURE AROUND. HIGH PRESSURE BUILDS LATER MONDAY 
NIGHT AND TUESDAY WITH SURFACE HIGH PRESSURE OVER SRN B.C. RESULTING IN 
LIGHT OFFSHORE FLOW. THIS MAY NOT BE STRONG ENOUGH TO SCOUR OUT LOW 
CLOUDS AND FOG TUESDAY MORNING BUT SOME CLEARING SHOULD DEVELOP DURING 
THE AFTERNOON. MERCER

.LONG TERM FROM THE PREV DISCUSSION...
PREVIOUS DISCUSSION FOLLOWS...AT LEAST THROUGH WEDNESDAY WE WILL BE 
UNDER THE INFLUENCE OF THE UPPER RIDGE AND SO WILL REMAIN DRY AND 
PARTLY CLOUDY.  BEYOND THAT...THINGS GET REAL FUZZY IN THE MODEL WORLD 
AND CONFIDENCE IS RATHER LOW IN THE DETAILS OF THE FORECAST.  NONE OF 
THE SOLUTIONS ARE VERY WET...BUT NOT DRY EVERY DAY EITHER.  THE 
VARIANCE IN THE MODELS IS RATHER STRIKING OUT OVER THE PACIFIC WHICH OF 
COURSE AFFECT OUR WEATHER.  AT THIS POINT WE...ALL THE OFFICES IN THE 
NORTHWEST...DECIDED TO INTRODUCE A SLIGHT CHANCE OF PRECIPITATION... 
STILL WELL BELOW CLIMATOLOGY...INTO THE FORECAST WITH A BIT OF 
ADDITIONAL CLOUDS FOR THE THURSDAY ONWARD TIME FRAME.  WE WILL HAVE TO 
SEE HOW THIS PLAYS OUT.  CERNIGLIA

&&

.HYDROLOGY...SIGNIFICANT PRECIP IS NOT EXPECTED THROUGH TUE.

EVEN THOUGH THERE IS SIGNIFICANT VARIANCE IN THE LONG RANGE MODELS 
BEYOND TUE...NONE OF THE SOLUTIONS WERE GOOD FOR HEAVY PRECIP. 
THEREFORE NO FLOODING PROBLEMS ANTICIPATED THROUGH NEXT WEEKEND. 

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

&&

.AVIATION...A WEAK WARM FRONT OVER NORTHERN WASHINGTON WILL LIFT NORTH 
INTO BRITISH COLUMBIA THIS MORNING. A WEAK RIDGE OF HIGH PRESSURE AT 
THE SURFACE WILL BUILD OVER WASHINGTON TONIGHT WITH ZONAL FLOW ALOFT. A 
COLD FRONT WILL MOVE SOUTHEAST INTO WASHINGTON MONDAY. CEILINGS ACROSS 
WESTERN WASHINGTON ARE MAINLY MVFR...BUT LOCAL IFR CIGS AND 
VISIBILITIES AT TIMES ARE OCCURRING WITH LIGHT RAIN AND DRIZZLE. 
CONDITIONS WILL GRADUALLY IMPROVE DURING THE DAY WITH MAINLY VFR 
EXPECTED AFTER 21Z OR SO.

GENERALLY LIGHT GRADIENTS AND ABUNDANT LOW LEVEL MOISTURE WILL BRING 
AREAS OF FOG OVERNIGHT. WITH LUCK THE APPROACHING COLD FRONT WILL 
IMPROVE THINGS BY MONDAY MORNING...BUT IT COULD BE MONDAY AFTERNOON 
BEFORE THE FOG LIFTS AND MVFR PREVAILS.

KSEA...SOUTHERLY WINDS CONTINUE TO SLOWLY RELAX AS PRESSURE 
GRADIENTS DECREASE OVER THE AREA. SOUTH WINDS 4-8 KT LIKELY THROUGH 
MIDDAY MONDAY. EXPECT CEILINGS TO GENERALLY PERSIST AROUND 010-015 
THROUGH MIDDAY...THEN TO INCREASE TO 4-5K FT THIS AFTERNOON. PARTIAL 
CLEARING IS POSSIBLE LIKELY LATE THIS AFTERNOON OR THIS EVENING... 
WHICH ONLY MEANS FOG AND LOW STRATUS WILL DEVELOP THIS EVENING AND 
CONTINUING THROUGH MONDAY MORNING. CHB

&&

.MARINE...A WEAK WARM FRONT IS BRINGING SCATTERED SHOWERS TO THE 
NORTHERN ZONES...ALONG WITH SMALL CRAFT ADVISORY STRENGTH WINDS TO 
THE WEST ENTRANCE AND NORTHERN INLAND WATERS. HAVE PUT UP A SMALL 
CRAFT ADVISORY FOR THOSE ZONES FOR TODAY. WINDS WILL DIMINISH THIS 
EVENING. SWELLS OF UP TO 15 FT WILL CONTINUE TO PRODUCE HAZARDOUS 
SEAS COAST AND WEST ENTRANCE THROUGH MONDAY...AND ROUGH BARS WILL 
DOMINATE AT THE ENTRANCE TO GRAYS HARBOR.
 
A WEAK TO MODERATE COLD FRONT WILL SWEEP SOUTHEAST MONDAY...LIKELY 
GIVING A BRIEF PERIOD OF SMALL CRAFT ADVISORY WINDS TO PORTIONS OF 
THE COASTAL WATERS AND THE STRAIT MONDAY AFTERNOON AND EVENING.

HIGH PRESSURE WILL BUILD OVER BRITISH COLUMBIA MONDAY NIGHT THEN 
SLIDE SOUTHEAST INTO EASTERN WASHINGTON DURING THE DAY WEDNESDAY. 
THIS WILL GIVE LIGHT TO MODERATE OFFSHORE FLOW TO THE WATERS OVER 
THE FIRST HALF OF THE WEEK. CHB

&&

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

PZ...SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR.
    .SMALL CRAFT ADVISORY COASTAL WATERS FOR HAZARDOUS SEAS.
    .SMALL CRAFT ADVISORY WEST ENTRANCE AND 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.