FXUS66 KSEW 062307
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
310 PM PST SUN DEC 6 2009

.SYNOPSIS...STRONG SURFACE HIGH PRESSURE OVER THE INTERIOR OF 
WESTERN CANADA IS PUSHING MODIFIED ARCTIC AIR INTO WESTERN 
WASHINGTON. THE HIGH IS EXPECTED TO SLIDE SOUTHEAST INTO THE MIDDLE 
OF THE U. S. THE NEXT FEW DAYS. YET THE COLD DRY CONDITIONS ARE 
EXPECTED TO CONTINUE THROUGH MUCH OF THIS WEEK WITH THE JETSTREAM 
WELL SOUTH OF THE PACIFIC NORTHWEST INTO CALIFORNIA.

&&

.SHORT TERM...THE STRONG REX BLOCK REMAINS PARKED ALONG 140W WITH AN 
UPPER LOW WRAPPING UP IT HEADS INTO THE GREAT BASIN AND ANOTHER NEAR 
48/170W. NORTHERLY FLOW ALOFT OVER WA. 

THE BIG STORY WITH THIS PATTERN IS THE PACIFIC NW WILL REMAIN IN THE 
COLD NORTHERLY FLOW ALOFT THIS WEEK. PROGS AGREE ON MOVING THE 
STRONG SURFACE IN WESTERN CANADA SOUTHEAST INTO THE MIDDLE OF THE 
U.S. OUTFLOW OF MODIFIED ARCTIC AIR CONTINUES ACROSS WESTERN WA AND 
SHOULD EASE AS THE HIGH MOVES INLAND. THE WIND ADVISORY IN THE NORTH 
INTERIOR CONTINUES TONIGHT. 

THE REMAINING CLOUDS OVER WESTERN WA WERE DISSIPATING THIS 
AFTERNOON. WITH THE DRY COLD AIR MASS NOW IN PLACE..SHOULD HAVE GOOD 
RADIATIONAL COOLING TONIGHT WITH THE COLDEST TEMPERATURES OF THE 
SEASON QUITE LIKELY. AND IN LOOKING AT THE COLDEST TEMPS OF THE 
YEAR..YEP CAN TOP (OR IS THAT DROP) THEM TOO. HIGHS WILL STRUGGLE TO 
EXCEED THE FREEZING MARK ON MON.

PROGS AGREE ON A WEAK SHORTWAVE EMBEDDED IN THE NORTHERLY FLOW TO 
SCOOT THROUGH LATER MON NIGHT AND EARLY TUE. HAVE ADDED SOME CLOUDS 
AND A THREAT OF SNOW FLURRIES. THEN CLEARING BEHIND THE SHORTWAVE ON 
TUE. HEIGHTS BEGIN TO RISE BY WED AND SHOULD START A SLOW MODERATING 
TREND THAT CONTINUES INTO THE WEEKEND. BUEHNER

.LONG TERM...THE ECMWF/CANADIAN/GFS ARE RELATIVELY SIMILAR IN 
BREAKING DOWN THE REX BLOCK AS THE WEEK WEARS ON AND THE SOUTHERN 
JET STREAM BRANCH BEGINS TO BREAK THROUGH. WITH A MORE NNW FLOW 
DEVELOPING WED NIGHT INTO FRI..WILL LOOK FOR AN INCREASE IN MIDDLE 
CLOUDS AND THE POSSIBILITY OF SNOW FLURRIES. THE AIR MASS SHOULD 
GRADUALLY MODIFY EVEN THOUGH LOW LEVEL OFFSHORE FLOW REMAINS. TEMPS 
SHOULD WARM A BIT EACH DAY AND NIGHTS WILL NOT BE AS COLD WITH THE 
ADDED CLOUD COVER. 

BY THE TIME THE WEEKEND ARRIVES..A SOUTHERN STREAM SYSTEM PUSHES 
INTO CAL AND OREGON. SOME MOISTURE SHOULD MOVE FAR ENOUGH NORTH AND 
THE OFFSHORE FLOW WEAKENS FOR A THREAT OF RAIN. QUITE POSSIBLE SOME 
AREAS WILL STILL HAVE SOME LINGERING COLDER AIR SUCH AS THE CASCADE 
PASSES AND NEAR THE FRASER UP NORTH. SO WILL NEED TO KEEP AN EYE ON 
WHETHER THE TRANSITION TO WARMER AIR WILL INVOLVE ANY TRANSITION 
PRECIPITATION. BUT FOR MUCH OF WESTERN WA..IT LOOKS LIKE WE MIGHT 
GET AWAY WITH A MINIMAL MESSY TRANSITION TO WARMER WEATHER. IN 
ADDITION..IT DOES LOOK LIKE THE OVERALL FLOW PATTERN IS BECOMING A 
MORE TYPICAL EL NINO AS SPLIT FLOW DEVELOPS WITH THE JET AIMED AT 
CALIFORNIA. BUEHNER

&&

.HYDROLOGY...COLD AND DRY WEATHER WILL PERSIST THIS WEEK. WHILE 
TEMPERATURES WILL MODERATE STARTING LATE IN THE WEEK..PRECIPITATION 
THAT FALLS IS EXPECTED TO BE LIGHT. THE RISK OF RIVER FLOODING IN 
THE FORECAST AREA FOR THE NEXT WEEK OR MORE IS QUITE LOW AND 
INCLUDES THE GREEN RIVER. BUEHNER

&&

.AVIATION...STRONG NE FLOW ALF WITH SOME AREAS OF MID LEVEL CLOUDS 
AND A FEW FLURRIES SOUTH HALF OF THE CASCADES AND OLYMPICS THIS 
AFTERNOON. CLEARING FROM THE NORTH BY EVENING. NE PRESSURE GRADIENTS 
ARE STRONG WITH FRASER OUTFLOW LIKELY TO CONTINUE THRU THE NIGHT 
THEN EASE MON. CLEAR AND COLD WITH A DRY AIR MASS MON...BUT SOME MID 
AND HIGH CLOUDS AND PERHAPS EVEN A FLURRY ARE NOW EXPECTED MON NITE 
AS THE SYSTEM CURRENTLY TOPPING THE RIDGE AND MOVG THRU THE 
YUKON...PART OF THIS SYS DROPS SOUTH IN THE NLY FLOW ALF AND MID AND 
HIGH CLOUDS COULD ARRIVE AS EARLY AS MON AFTERNOON FROM THAT. 19

KSEA...DRY AIR MASS WITH THE MID AND HIGH CLOUD SCATTERING OUT THIS 
EVENING. THE ESE WIND IS HARD TO EXPLAIN...MOVING AGAINST THE NLY 
GRADIENT AND THE CROSS CASCADE GRADIENT IS NOT ENUF TO DO THAT SO 
WILL JUST PLAY PERSISTENCE AND WAIT TO SEE IF IT COMES BACK TO NE 
TNGT.  

&&

.MARINE...STRONG NE FLOW WITH FRASER OUTFLOW CONTINUES AND NO BIG 
CHANGES TO THE FCST. IT IS HARD TO EXPLAIN THE LACK OF WIND OVER THE 
NORTH PART OF PUGET SOUND...BUT IT HAS BEEN BREEZY IN THE SOUTH 
SOUND AND TACOMA AREA HAS BEEN NE 20-30 THIS AFTERNOON. I EXPECT NE 
NE15-25 FOR THE SOUTH PUGET SOUND SO WILL KEEP THE SMALL CRAFT 
ADVISORY UP. THE GALE WARNINGS FOR THE FRASER OUTFLOW THRU THE SAN 
JUANS AND STRAIT CONTINUE...AND THE NE WIND SHUD FINALLY COME UP AT 
TATOOSH THIS EVENING WHERE THE GALE HAS NOT YET VERIFIED. WINDS 
SHOULD EASE MONDAY...BUT IT WOULD NOT SURPRISE ME TO FIND THE NIGHT 
SHIFT HAS TO KEEP THE GALE WARNING UP FOR THE SAN JUANS TIL MIDDAY 
MON. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY NORTHWEST INTERIOR...AND EAST STRAIT THROUGH 4 AM 
     MONDAY.
PZ...GALE WARNING STRAIT OF JUAN DE FUCA...NORTHERN INLAND WATERS
             
     SMALL CRAFT ADVISORY COASTAL WATERS...PUGET SOUND AND HOOD CANAL

$$

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