FXUS66 KSEW 061100
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST SUN DEC 6 2009

.SYNOPSIS...MODIFIED ARCTIC AIR WILL POUR INTO WESTERN WASHINGTON 
FROM THE NORTHEAST THROUGH TONIGHT. ALTHOUGH HIGH PRESSURE TO THE 
NORTHEAST OF THE AREA WILL WEAKEN STARTING MONDAY...COLD AND DRY 
CONDITIONS WILL CONTINUE THROUGH MUCH OF THE UPCOMING WEEK.

&&

.SHORT TERM...A STRONG REX BLOCK SITS ALONG 140W. AN UPPER LOW OVER 
WEST CENTRAL OREGON COMBINED WITH A STRONG 1060 MB HIGH OVER 
NORTHERN B.C. IS COMBINING TO GIVE MODIFIED ARCTIC OUTFLOW TO THE 
AREA TODAY. WILLIAMS LAKE TO BELLINGHAM PRES GRADIENTS ARE OVER 14 
MB THIS MORNING AND WILL STAY STRONG THROUGH THIS EVENING. 

WHILE ARCTIC OUTFLOW HAS BEGUN...THE COLD AIR REMAINS BOTTLED UP 
JUST TO THE NORTH OF THE AREA...NORTH OF THE CANADIAN COASTAL 
MOUNTAINS. IN RESPONSE TO BUILDING PRESSURES AND STRONG NNE FLOW 
ALOFT THAT COLD AIR IS DEEPENING AND IS EXPECTED TO START SPILLING 
SOUTHWARD THIS MORNING. 850 MB TEMPERATURES ACROSS THE AREA EARLY 
THIS MORNING ARE AROUND -7C AND WILL FALL TO -12C DURING THE 
AFTERNOON HOURS. WITH THE STRONG N/NE WINDS AND COOLING 
ALOFT...EXPECT SURFACE TEMPERATURES TO MAX OUT DURING THE MORNING 
HOURS AND SLOWLY FALL DURING THE AFTERNOON.

VERY WINDY CONDITIONS WILL CONTINUE IN AREAS EXPOSED TO FRASER 
VALLEY OUTFLOW. WILL MAINTAIN THE WIND ADVISORY FOR THE NORTH 
INTERIOR ZONES TO ACCOMMODATE THIS. N/NE WINDS AT RACE ROCKS HAVE 
BEEN RUNNING 30-40 KT. WHILE WINDS HAVE DIED DOWN OVERNIGHT ALONG 
THE EASTERN STRAIT OF JUAN DE FUCA...EARLIER THE LIGHTHOUSE AT PORT 
ANGELES WAS NORTH 25 KNOTS SUSTAINED. THESE STRONGER NORTH WINDS 
WILL LIKELY MIX DOWN INTO THE AREA LATER THIS MORNING. 

OTHER AREAS IN WESTERN WASHINGTON WILL BE WINDY TODAY...ESPECIALLY 
AROUND THE HOOD CANAL...AND NEAR TACOMA NARROWS. 

WINDS ALL AREAS WILL DIE DOWN LATER TONIGHT. WITH LOW DEWPOINTS AND 
MODIFIED ARCTIC AIR IN PLACE...IT WILL GET QUITE COLD TONIGHT 
THROUGH TUESDAY WITH LOWS FALLING INTO THE TEENS TO LOWER 20S AT 
NIGHT...AND STRUGGLING TO GET MORE THAN A COUPLE DEGREES ABOVE 
FREEZING DURING THE DAY. ALBRECHT

.LONG TERM...THE REX BLOCK IS ESTABLISHED AND WILL TAKE ITS TIME TO 
BREAK DOWN. NEW LONG TERM MODELS ARE GENERALLY HOLDING WESTERN 
WASHINGTON IN THE NORTHERN STREAM THROUGH ABOUT FRI AND KEEP HIGHER 
PRES TO THE NE OF THE AREA PREVENTING THE INFLUX OF MARINE AIR. 
SOUTHERN STREAM SYSTEMS COMING UNDER THE BLOCK APPEAR TARGETED TO 
HIT INTO CENTRAL AND SOUTHERN THROUGH THE WEEK. AS A RESULT WE 
LOWERED POPS THROUGH THU NIGHT OR FRI AND BROUGHT TEMPERATURES DOWN 
A FEW DEGREES WITH LESS CLOUD COVER. EVENTUALLY A VERY DEEP 500 MB 
LOW OVER THE NORTHERN CANADIAN ARCTIC MOVES W INTO THE YUKON AND THE 
BLOCK PINCHES OFF AND RETROGRADES INTO SIBERIA. WHILE FLOW IN THE 
FAR EXTENDED REMAINS SPLIT IN WHAT LOOKS LIKE AN INCREASINGLY 
TYPICAL EL NINO FASHION...ONSHORE FLOW SHOULD INCREASE SUFFICIENTLY 
TO ALLOW MILD MARINE AIR TO PUSH INLAND AND GIVE A CHANCE OF LIGHT 
RAIN NEXT WEEKEND. AT THIS TIME A WARM ADVECTION SNOW PATTERN TO END 
THE ARCTIC INTRUSION DOES NOT APPEAR TO BE LIKELY. ALBRECHT

&&

.HYDROLOGY...COLD AND DRY WEATHER WILL PERSIST THROUGH THE UPCOMING 
WEEK. WHILE TEMPERATURES WILL RISE STARTING NEXT 
WEEKEND...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. THIS INCLUDES THE GREEN RIVER. ALBRECHT

&&

.AVIATION...THE COLD UPPER LEVEL OVER CENTRAL ORE WILL SHIFT FARTHER 
S/SE TODAY. IR SATELLITE SHOWS SOME WRAP-AROUND MOISTURE MOVING INTO 
WESTERN WA BUT SHOWERS LOOK RATHER MEAGER ON KATX RADAR. THE LOW 
LEVEL AIR MASS IS QUITE DRY DUE TO FRASER RIVER OUTFLOW SO ANY 
PRECIP THAT DOES FALL WILL LIKELY EVAPORATE BEFORE IT REACHES THE 
SURFACE. THE EXCEPTION WILL BE THE NE OLYMPICS WHERE UPSLOPE FLOW 
MAY PRODUCE A FEW LIGHT SNOW SHOWS THIS MORNING...BUT SIGNIFICANT 
ACCUMULATIONS ARE NOT EXPECTED. WILL SEE CLEARING ACROSS THE REGION 
THIS AFTERNOON AS THE LOW PULLS FARTHER OUT. WINDS WILL BE GUSTY OUT 
OF THE N/NE AS HIGH PRES OVER INTERIOR B.C. SAGS SOUTH. HIGHEST 
WINDS WILL BE AT KBLI 25 GUST 35 KT. 33

KSEA...DRIER AIR WILL FILTER SOUTH INTO THE CENTRAL SOUND THIS 
MORNING WITH MODERATE NLY FLOW. SKIES WILL CLEAR OUT THIS AFTERNOON 
WITH CONTINUING VFR CONDITIONS. WRAP-AROUND SNOW SHOWERS POSSIBLE 
EARLY THIS MORNING BUT WITH A DRY LOW LEVEL AIR MASS WILL NOT SEE 
ACCUMULATIONS...JUST A FEW FLURRIES IF ANYTHING. 33

&&

.MARINE...FORECAST SO FAR REMAINS ON TRACK WITH STRONG NE FLOW  
CONTINUING ACROSS WESTERN WASHINGTON TODAY. HIGH PRES 1054 MB OVER 
INTERIOR B.C. WILL SAGS SOUTH TODAY WITH STRONG FRASER OUTFLOW. PRES 
GRADIENTS ARE RUNNING CLOSE TO SCHEDULE WITH KBLI-CYWL AROUND -14 
MB. GALES VERIFIED IN THE NORTHERN INLAND WATERS AND STRAIT OF JUAN 
DE FUCA...AND WILL STRETCH THE HAZARD HEADLINES THROUGH TONIGHT.  
ELSEWHERE EXPECT N/NE WINDS IN THE SCA RANGE. WINDS ARE EXPECTED TO 
EASE MON/MON NIGHT. 33

&&

.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...ADMIRALTY INLET...        
      PUGET SOUND AND HOOD CANAL.  

$$

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