FXUS66 KSEW 010506
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST MON NOV 30 2009

.SYNOPSIS...LOW CLOUDS AND FOG WILL BECOME WIDESPREAD ACROSS WESTERN 
WASHINGTON TONIGHT BEHIND A COLD FRONT. AN UPPER LEVEL RIDGE AND 
SURFACE HIGH BUILDING OVER THE REGION LATER TONIGHT WILL KEEP THE 
AREA DRY THROUGH THURSDAY. AN UPPER LEVEL LOW WILL BRING COOLER 
TEMPERATURES AND A CHANCE OF RAIN TO THE AREA FRIDAY THOUGH MONDAY.

&&

.SHORT TERM...A WEAK COLD FRONT HAS CLEARED THE AREA BUT LEFT PLENTY 
OF RESIDUAL LOW LEVEL MOISTURE AROUND WRN WA IN IT'S WAKE. TEMP AND 
DEW POINTS HAVE CLOSED IN AT MOST SPOTS SO EXPECT FOG AND LOW CLOUDS 
TO BECOME RATHER WIDESPREAD OVERNIGHT THROUGH TUESDAY MORNING. THE 
PUGET SOUND CONVERGENCE ZONE WAS A BIT ACTIVE EARLIER THIS EVENING 
ACROSS WRN KING COUNTY BUT IT APPEARS TO BE FIZZLING OUT AS LIGHT 
NORTHERLIES TAKE HOLD THROUGH THE SOUND. 

MODELS BUILD A 1035 MB SURFACE HIGH OVER SRN B.C. ON TUESDAY WHICH 
WILL INCREASE OFFSHORE NE GRADIENTS. THE LATEST NAM-12 SHOWS OUTFLOW 
PICKING UP ACROSS THE N INTERIOR BY LATE TUESDAY MORNING...A LITTLE 
LATER THAN THE MM5. EXPECT ANY FOG AND CLOUDS TO CLEAR OUT UP NORTH 
FIRST DURING THE MID MORNING HOURS. THE NAM-12 IS MUCH WEAKER WITH 
NE FLOW FURTHER SOUTH WITH THE TIME-HEIGHT SECTION KEEPING LOW 
CLOUDS AROUND THROUGH THE AFTERNOON...WITH SOME CLEARING BY THE 
EARLY EVENING HOURS. THE CURRENT FORECAST IS ON TRACK WITH THIS IDEA.

HIGH PRESSURE ALOFT BUILDS ALONG THE W COAST WEDNESDAY AND THURSDAY 
WITH LOW LEVEL ELY FLOW. MODELS SHOW THIS TO BE STRONG ENOUGH TO DRY 
OUT THE LOWER LEVELS WITH ONLY POCKETS OF LATE NIGHT/EARLY MORNING 
FOG IN THE MOST PRONE LOCATIONS LIKE AROUND OLYMPIA. WITH THE DRIER 
AIR COMES THE COOLER NIGHTTIME TEMPS...POSSIBLY DOWN INTO THE 20S IN 
MANY OF THE VALLEYS. MERCER

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS...GFS AND ECMWF ARE STILL 
BUTTING HEADS WITH OPPOSITE SOLUTIONS WITH AN APPROACHING UPPER 
LEVEL SHORTWAVE TROUGH ON FRIDAY. OPERATIONAL GFS HAS TRENDED DRIER 
AND FASTER AND TAKES THE SHORTWAVE ACROSS SE B.C. FRIDAY WITH NO 
PRECIP OVER W WA. ECMWF IS SLOWER AND FURTHER SOUTH WITH THE 
SHORTWAVE...FORMING A CLOSED LOW JUST OFFSHORE NEAR 48N/130W 12Z 
FRIDAY...THEN KEEPING IT AROUND THE AREA THROUGH THE WEEKEND. GFS 
EVENTUALLY HAS A CLOSED LOW OVER ID ON SATURDAY BUT STAYS DRY FOR W 
WA. ECMWF IS A LITTLE WETTER. THE 12Z CANADIAN SHIFTED AROUND TOWARD 
THE ECMWF SOLUTION AND 7 OF THE 12 ENSEMBLE MEMBERS FROM THE 12Z GFS 
FAVOR SOME FORM OF CLOSED LOW OVER THE REGION SATURDAY. NONE OF THE 
SOLUTIONS SEEMS COMPLETELY REASONABLE BUT THE VARIOUS SOLUTIONS TILT 
TOWARD SOMETHING CLOSER TO THE ECMWF SCENARIO. THE BEST COURSE FOR 
NOW IS TO CONTINUE WITH LOW CHANCE POPS FOR RAIN FRIDAY THROUGH 
SUNDAY. THE ECMWF IS NOT PARTICULARLY WET SO POPS BELOW CLIMO WORK 
OK. KAM

&&

.HYDROLOGY...HIGH PRESSURE WILL KEEP GENERALLY DRY CONDITIONS OVER 
WRN WA THROUGH THURSDAY. A FRONT ON FRIDAY WILL BRING SOME LIGHT 
RAIN TO THE AREA BUT NOTHING SIGNIFICANT. LONG RANGE MODELS DISAGREE 
ON WEATHER WE TRANSITION TO A DRY AND COLDER OFFSHORE PATTERN OR 
KEEP AN UPPER LOW NEAR THE AREA WITH A CHANCE OF SHOWERS. EITHER 
WAY...ALL LONG RANGE MODELS SUGGEST NO HYDROLOGICALLY SIGNIFICANT 
RAINFALL OR FLOODING IS EXPECTED FOR THE NEXT 10 DAYS. 

FLOODING ON THE GREEN RIVER IS NOT EXPECTED OVER THE NEXT 10 DAYS.

&&

.AVIATION...THE WEAK COLD FRONT THAT MOVED THROUGH THE AREA THIS 
AFTERNOON HAS NOW DROPPED SE OF THE AREA. HIGH PRES IS NOW BUILDING 
OVER CENTRAL AND SE BRITISH COLUMBIA. SOME DRIER AIR IS FILTERING 
INTO THE NORTH INTERIOR WITH HIGHER PRES TO THE NE OF THE AREA 
BUILDING...BUT THIS WILL TAKE ITS TIME MOVING INTO THE CENTRAL PUGET 
SOUND AREA SOMETIME TUE. IN THE MEANTIME WEAK PUGET SOUND 
CONVERGENCE SITS FROM SHELTON TO TACOMA. THIS IS EXPECTED TO 
DISSIPATE BY ABOUT MIDNIGHT TONIGHT.

OVER THE N INTERIOR EXPECT CIGS TO REMAIN VFR TONIGHT THEN CLEAR 
FROM THE NE DURING THE MORNING HOURS. FROM KPAE SOUTHWARD EXPECT 
CIGS TO LOWER TO LOW IFR BY 09Z AND REMAIN THERE THROUGH EARLY TUE 
MORNING. THE LOW CLOUDS...AND FOG WHERE VERY LOW STRATUS INTERSECTS 
THE TERRAIN...WILL DRY FROM THE NORTH STARTING AROUND 16Z AND REACH 
THE MORE SHELTERED SW INTERIOR VALLEYS EARLY IN THE AFTERNOON. 
STATISTICAL GUIDANCE IS IN LINE WITH MODEL TRENDS. HIGHER TERMINALS 
MAY EXPERIENCE RATHER DENSE FOG WITHIN THIS STRATUS LAYER.

DRY CONDITIONS DEVELOP LATER TUE AND CONTINUE THRU THU. FOG OR 
STRATUS WILL BE CONFINED TO SHELTERED VALLEYS AND THE TYPICALLY MORE 
SHELTERED LOCATIONS IN THE SOUTH INTERIOR SUCH AS AT KOLM. AT KOLM 
FOG MAY BECOME QUITE PERSISTENT AND DENSE THRU THU MORNING.

KSEA...LIGHT N WIND WILL PERSIST THRU THIS EVENING THEN TURN MORE 
NELY OVERNIGHT 3-5 KT. EXPECT CIGS TO LOWER FROM 014 AT 06Z TO 005 
AT 07Z THEN 3SM BR OVC001 AT 10Z WITH TOWER VISIBILITIES QUITE LOW. 
CONDITIONS WILL RAPIDLY IMPROVE FROM THE NORTH 18Z-20Z TUE AND WILL 
BE FOLLOWED BY MAINLY CLEAR CONDITIONS LATE TUE INTO WED. ALBRECHT

&&

.MARINE...THE WEAK COLD FRONT THAT MOVED THROUGH THE AREA THIS 
AFTERNOON HAS NOW DROPPED S OF THE AREA. HIGH PRES IS NOW BUILDING 
OVER CENTRAL AND SE BRITISH COLUMBIA AND FLOW IS INCREASINGLY 
OFFSHORE WITH TIME. OFFSHORE FLOW WILL GENERALLY BE LIGHT TO 
MODERATE LATE TONIGHT THROUGH THU...BUT COULD TOUCH SMALL CRAFT 
ADVISORY CRITERIA AT THE WEST ENTRANCE TO THE STRAIT AND NEAR THE 
GAPS IN THE COASTAL WATERS...BUT GENERALLY WINDS ARE EXPECTED TO 
REMAIN 20 KT OR LOWER. 

SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE THROUGH TUE MORNING AT 
LEAST FOR HAZARDOUS SEAS IN THE COASTAL WATERS. BUT SEAS ARE 
GRADUALLY SUBSIDING AND SHOULD FALL BELOW 10 FT BY LATE IN THE 
AFTERNOON. ROUGH BAR CONDITIONS AT GRAYS HARBOR BAR WILL LIKELY 
CONTINUE TO JUST BEYOND THE VERY STRONG AFTERNOON EBB CURRENT TUE 
AFTN.

A MUCH STRONGER 1053 MB HIGH FORMING OVER THE YUKON FRI NIGHT 
APPEARS POISED TO MOVE RAPIDLY SOUTHWARD AND STRENGTHEN TO NEARLY 
1060 MB AS IT MOVES INTO CENTRAL B.C. SAT OR SAT NIGHT. THE CHANCES 
OF ARCTIC OUTFLOW FROM THE FRASER...AFFECTING THE NORTH INLAND 
WATERS...THE STRAIT...AND THE COASTAL WATERS...ARE INCREASING WITH 
TIME AND GALES MAY DEVELOP IF TRENDS CONTINUE. ALBRECHT.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE
PZ...SMALL CRAFT ADVISORY OUTER COASTAL WATERS.
    .SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS NEAR SHORE COASTAL      
     WATERS AND WEST ENTRANCE TO THE STRAIT.
    .SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

$$

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