FXUS66 KSEW 050554
AFDSEW

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

.SYNOPSIS... A COLD SPELL WILL IMPACT WESTERN WASHINGTON THROUGH THE 
MIDDLE OF 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...SATELLITE IMAGERY SHOWS SKIES CLEARING ACROSS WESTERN 
WASHINGTON THIS EVENING WITH NORTHEASTERLY FLOW ALOFT OVER THE AREA. 
SOME HIGH CLOUDS OVER SOUTHERN BRITISH COLUMBIA WILL DRIFT ACROSS 
THE REGION EARLY SATURDAY MORNING. FOG HAS STARTED TO FORM OVER THE 
CENTRAL AND SOUTHERN PUGET SOUND. KOLM-KBLI GRADIENTS AROUND MINUS 
1.5 MB AT 05Z. MODELS KEEP THE GRADIENT PRETTY CONSTANT OVERNIGHT. 
WINDS OVER THE MARINE AREAS HAVE PICKED UP WITH WEST POINT NEAR 20 
KNOTS AND BOTH POINT WILSON AND POINT NO POINT OVER 20 KNOTS OUT OF 
THE NORTH. SANDPOINT PROFILER HAS LIGHT WINDS UP TO AROUND 400 
METERS WITH THE WINDS ABOVE NORTHERLY 20-30 KNOTS. WITH THE 
INCREASING NORTHERLIES OVER THE WATER DON'T EXPECT THE FOG TO BECOME 
WIDESPREAD BUT WILL STILL ADD SOME TO THE FORECAST FOR TONIGHT INTO 
EARLY SATURDAY MORNING. BEYOND THAT NEXT SHORTWAVE TO COME DOWN OUT 
OF THE NORTHEASTERLY FLOW ALOFT MOVING THROUGH THE AREA SATURDAY 
NIGHT. EVEN COLDER AIR MASS THAN THE ONE OVER THE AREA RIGHT NOW 
WILL DROP DOWN INTO WESTERN WASHINGTON BEHIND THE SHORTWAVE FOR 
SUNDAY. STRONG OUTFLOW WINDS DEVELOPING OVER THE NORTHERN INTERIOR 
SATURDAY NIGHT WITH MODEL KBLI-CYWL GRADIENTS UP IN THE MINUS 14 TO 
MINUS 17 MB RANGE. STRONG ENOUGH FOR POSSIBLE GALE FORCE WINDS OVER 
THE MARINE WATERS. WITH THE STRONG OUTFLOW...UPSLOPE CONDITIONS INTO 
THE NORTHERN SLOPES OF THE OLYMPICS COULD RESULT IN SOME SNOW LATE 
SATURDAY NIGHT INTO SUNDAY MORNING FOR THAT AREA. FOR THE REMAINDER 
OF THE CWA JUST A FEW CLOUDS. THE MAIN STORY BEGINNING SUNDAY WILL 
BE THE COLD TEMPERATURES OVER THE CWA. DAYTIME HIGHS WILL BE IN THE 
30S SUNDAY AND MONDAY WITH THE COLDER LOCATIONS REMAINING BELOW 
FREEZING ALL DAY. LOWS IN THE TEENS AND 20S WITH BE COMMON. SOME OF 
THE COLDER LOCATIONS COULD GET DOWN INTO THE SINGLE DIGITS MONDAY 
NIGHT. FELTON

.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 TEENS TO LOWER 
20S...WITH A CHANCE OF SINGLE DIGITS IN THE COLDER LOCATIONS. 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...A DEEP UPPER LEVEL LOW IS DIVING SOUTH THROUGH MONTANA 
THIS EVENING...WHILE A HIGH AMPLITUDE RIDGE RESIDES OFFSHORE. LIGHT 
SHOWERS HAVE ENDED IN THE INTERIOR BUT THE LOW LEVEL AIR MASS 
REMAINS MOIST WITH FZFG IN THE SOUTH SOUND. NORTHERLY PRES GRADIENTS 
WILL INCREASE OVERNIGHT WHICH SHOULD LIMIT FOG DEVELOPMENT SEATTLE 
NORTHWARD. THE FLOW WILL REMAIN NORTHERLY ON SAT...WITH ANOTHER 
CLOSED LOW NUDGING INTO W WA SAT NIGHT. 33

KSEA...A SCT-BKN020 LAYER REMAINS IN THE VICINITY THIS EVENING...BUT 
SHOULD CLEAR OUT OVERNIGHT. MAY SEE A BRIEF REDUCTION IN VIS THIS 
EVENING WITH A TIGHT DEW POINT DEPRESSION. NORTHERLY WINDS WILL 
INCREASE OVERNIGHT WHICH SHOULD LIMIT FOG DEVELOPMENT. 33

&&

.MARINE...HIGH PRES OVER INTERIOR B.C. WILL MAINTAIN OFFSHORE N/NE 
FLOW ACROSS WESTERN WASHINGTON. PRESSURE GRADIENTS WILL INCREASE SAT 
NIGHT AS THE HIGH SHIFTS FARTHER S/SE. FRASER RIVER OUTFLOW IS 
EXPECTED...WITH GALE FORCE WINDS POSSIBLE IN THE NORTHERN INLAND 
WATERS AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA. A GALE WATCH 
IS ALREADY POSTED FOR THESE TWO ZONES. ELSEWHERE WILL LIKELY SEE 
SMALL CRAFT WINDS THOUGH THE WEEKEND. OFFSHORE FLOW WILL EASE EARLY 
NEXT WEEK. 33

&&

.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. 
     GALE WATCH NORTHERN INLAND WATERS AND WEST ENTRANCE JUAN DE 
     FUCA SAT/SAT NIGHT. 
     SMALL CRAFT ADVISORY ROUGH BAR CONDITIONS GRAYS HARBOR BAR. 

$$

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