FXUS66 KSEW 042349
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
350 PM PST FRI DEC 4 2009

.SYNOPSIS... A COLD SPELL WILL IMPACT WESTERN WASHINGTON THROUGH 
EARLY NEXT WEEK AS MODIFIED ARCTIC AIR SPILLS INTO THE REGION FROM 
WESTERN CANADA. TEMPERATURES WILL RUN WELL BELOW NORMAL DURING THIS 
TIME. A DUSTING OF SNOW IS POSSIBLE SATURDAY NIGHT WITH UPSLOPE 
SNOWS POSSIBLE ALONG THE NORTHERN SHORE OF THE OLYMPIC PENINSULA. 
COOL AND DRY NORTHERLY UPPER LEVEL FLOW WILL REMAIN IN PLACE OVER 
THE AREA THROUGH LATE NEXT WEEK.

&&

.SHORT TERM...COOL NORTHWESTERLY FLOW REMAINS OVER THE AREA WITH AN 
AMPLIFIED UPPER LEVEL RIDGE OUT NEAR 135W THAT EXTENDS NORTHWARD 
INTO ALASKA. THE UPPER LOW OVER ALBERTA/BC BORDER IS DROPPING SOUTH 
INTO THE INTERIOR PAC NW CURRENTLY. THE ASSOCIATED WEAK FRONT HAS 
BEEN DROPPING SOUTH THROUGH THE AREA TODAY...AND ALTHOUGH FORECAST 
GUIDANCE HAS SHOWED LITTLE AVAILABLE MOISTURE THE FRONT HAS BEEN 
ABLE TO SQUEEZE OUT A FEW SHOWERS. THE FRONT WILL DISSIPATE AS IT 
MOVES SOUTH THIS EVENING. SKIES WILL GENERALLY CLEAR TONIGHT AS 
NORTHERLY GRADIENTS STRENGTHEN.

THE RIDGE WILL CONTINUE TO AMPLIFY INTO ALASKA ON SATURDAY...AND 
ANOTHER SHORTWAVE WILL DIG SOUTH IN THE NORTHERLY FLOW. THE NEXT 
SHORTWAVE WILL DIG FURTHER WEST SATURDAY NIGHT...WITH AN UPPER LOW 
SETTING UP SHOP OFF THE SOUTH OREGON COAST BY SUNDAY. STRONG 
ARCTIC HIGH PRES WILL SLIDE SOUTH FROM THE YUKON DOWN JUST EAST OF 
THE SPINE OF THE CANADIAN ROCKIES PUSHING COLDER AIR OVER THE 
REGION.  AGAIN MOISTURE PROFILES LOOK MOSTLY DRY...BUT MAV MOS 
MAINTAINS 30/40 POPS OVER THE AREA SATURDAY NIGHT AS THE LOW PASSES 
SOUTH THROUGH OUR AREA...SO HAVE LEFT CHANCE OF SNOW SHOWERS FOR 
SATURDAY NIGHT. UPPED PRECIP AND QPF ALONG THE STRAIT OF JUAN DE 
FUCA WHERE AN UPSLOPE COMPONENT MAY CAUSE ACCUMULATING SNOWS. ALMOST 
ALL MODELS ARE BEGINNING TO SHOW SOME LIGHT QPF FOCUS ON THIS AREA 
AROUND 12Z SUNDAY...AND FORECAST WILL NEED TO BE MONITORED. OUTFLOW 
GRADIENTS WILL PICK UP SATURDAY EVENING INTO SUNDAY...AND WINDY 
CONDITIONS WILL DEVELOP ALONG THE STRAIT AND NORTHERN INTERIOR. 
WINDS COULD REACH ADVISORY LEVELS. WINDS WILL EASE SUNDAY AFTERNOON 
AS THE UPPER LOW SINKS OFF THE CA COAST AND GRADIENTS EASE SOMEWHAT 
INTO MONDAY. THE TREND OF WELL BELOW NORMAL TEMPERATURES WILL 
CONTINUE WITH HIGHS ONLY REACHING INTO THE 30S MONDAY.

.LONG TERM...MONDAY NIGHT MAY BE THE COLDEST NIGHT IN THIS 
STRETCH...AS WINDS BEGIN TO EASE A BIT AND COLD AIR IS WELL 
ENTRENCHED OVER THE AREA. LOWS WILL RANGE FROM THE MID TEENS TO 
LOWER 20S...AND DEWPOINTS WILL BE EVEN LOWER. UPPER LEVEL NORTHERLY 
FLOW WILL PERSIST THROUGH AT LEAST MIDWEEK...WITH ONLY MINOR 
TEMPERATURE MODERATION. THE 12Z GFS KEEPS US DRY IN NORTHERLY FLOW 
THROUGH FRIDAY AS THE SOUTHERN STREAM ENERGY IS DIRECTED INTO 
CALIFORNIA. 12Z ECMWF SHOWS A NEW SHORTWAVE DIGGING OFFSHORE LATE 
THURSDAY INTO FRIDAY IN THE NORTHERLY FLOW SPREADING PRECIP OVER THE 
AREA. DUE TO MODEL DISAGREEMENT LEFT THE CLIMO CHANCE POPS IN 
TACK...BUT INCLUDED THE MENTION OF RAIN/SNOW DOWN TO SEA LEVEL DUE 
TO THE COLD AIR IN PLACE. DAMICO  

&&

.HYDROLOGY...THERE IS NO THREAT OF RIVER FLOODING IN THE FORECAST 
AREA FOR THE NEXT WEEK. THIS INCLUDES THE GREEN RIVER.

RIVERS WILL GRADUALLY RECEDE THROUGH MIDWEEK AS A RESULT OF BELOW 
NORMAL TEMPERATURES AND BELOW NORMAL PRECIPITATION THROUGH 
WEDNESDAY. A COLD WEATHER SYSTEM MAY IMPACT THE AREA THURSDAY AND 
FRIDAY...WITH LITTLE HYDRO IMPACT. DAMICO

&&

.AVIATION...UPPER TROF MOVG SOUTH THRU PACNW W/ NW FLOW ALF BECMG N 
SAT. NLY SFC GRADIENTS INCRG AND FRASER OUTFLOW WILL BEGIN SAT. A 
FEW AREAS OF MOISTURE OVER WRN WA WILL DRY OUT TNGT...SHOWERS OVER 
THE METRO AREA AT 230PM WILL SHIFT SOUTH THRU LATE AFTERNOON AND 
SHUD DRY UP BY 6PM. SKIES WILL BECOME MOSTLY CLEAR OVERNIGHT AND 
REMAIN CLEAR THRU THE WEEKEND...ONLY EXCEPTION WILL BE IF SOME 
CUMULUS DEVELOPS OVER THE NORTHERN WATERS OR STRAIT OF JUAN DE FUCA 
WHERE A FEW FLURRIES COULD DEVELOP AS THE FRASER OUTFLOW SWEEPS OVER 
THE SALISH SEA THIS WEEKEND. 19

KSEA...NOTHING LIKE A LITTLE PSCZ TO SPOIL A MOSTLY SUNNY FCST. BUT 
THERE WILL BE CLEARING FROM THE NORTH THIS EVENING...AND I EXPECT 
THE NLY PRES GRADIENT OLM-BLI BY RISE TO -3MB BY DAYBREAK SO THERE 
IS NO CHANCE OF FOG TONIGHT IF THAT PANS OUT...JUST SCATTERED CLOUDS 
LATER AND CLEAR THIS WEEKEND AS STRONG OFFSHORE NE FLOW DEVELOPS. 19

&&

.MARINE...GRADIENTS HAVE BEEN SLOW TO INCREASE BUT THEY WILL 
INCREASE RAPIDLY TONIGHT AND I HAVE MADE NO SGFNT CHANGE TO THE 
FCSTS. NE FRASER OUTFLOW GALES ARE LIKELY OVER THE NORTHERN WATERS 
THIS WEEKEND...AS WELL AS AROUND THE WEST ENTRANCE TO THE 
STRAIT...FOR THE CENTRAL AND EAST STRAIT PROBABLY NE20-30KT WILL DO 
IT AND NE 20-30KT IS A PRETTY GOOD FCST FOR THE COASTAL WATERS AS 
WELL...BUT GALES ARE POSSIBLE AT TIMES NEAR GAPS IN COASTAL 
TERRAIN...MAINLY WEST OF THE STRAIT. GRADIENTS SHOULD RELAX EARLY 
NEXT WEEK AND TURN ONSHORE AFTER THE MIDDLE OF THE WEEK BUT I WOULD 
NOT BE SURPRISED IF WE HAD TO KEEP THE OFFSHORE FLOW GOING AN EXTRA 
DAY OR TWO AND NOT SEE A SWITCH TIL LATE NEXT WEEK. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS...NORTHERN INLAND WATERS...
     EAST ENTRANCE JUAN DE FUCA...ADMIRALTY INLET AND PUGET SOUND
     HOOD CANAL. 
     SMALL CRAFT ADVISORY ROUGH BAR CONDITIONS GRAYS HARBOR BAR. 
  
$$

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