FXUS66 KSEW 142245
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
245 PM PST MON DEC 14 2009

.SYNOPSIS...RAIN THIS EVENING WILL TAPER AFTER MIDNIGHT AS A WARM 
FRONT MOVES THROUGH. PRECIPITATION WILL START AS SNOW IN THE NORTH 
INTERIOR AND HOOD CANAL AREA AND MAY NOT CHANGE TO RAIN BEFORE THE 
PRECIPITATION ENDS LATE TONIGHT. HEAVY SNOW WILL FALL IN THE 
MOUNTAINS THROUGH TUESDAY. A SERIES OF FRONTAL SYSTEMS WILL AFFECT 
THE REGION THROUGH LATER THIS WEEK.

&&

.SHORT TERM...THE WARM FRONT OFF THE COAST WILL SPREAD PRECIPITATION 
OVER THE AREA TONIGHT. THIS MAY BEGIN AS RAIN AND SNOW IN SOME SPOTS 
BUT SHOULD CHANGE TO RAIN MOST PLACES. THE EXCEPTIONS WILL BE THE 
HOOD CANAL AREA...WHERE COLD AIR IS LIKELY TO REMAIN TRAPPED...AND 
THE FAR NORTH...WHERE COLD AIR OUTFLOW FROM THE FRASER RIVER CANYON 
WILL CONTINUE ALL NIGHT. WINTER WEATHER ADVISORY FOR BOTH ZONES 
CONTINUES TONIGHT. BOTH AREAS COULD SEE 1-3 INCHES OF SNOW. 
PRECIPITATION WILL END LATE TONIGHT.

ANOTHER SYSTEM IS DUE TUESDAY NIGHT. THIS ONE SHOULD SCOUR OUT ANY 
REMAINING COLD AIR THOUGH THERE IS A SMALL CHANCE THE PRECIPITATION 
IN THE FAR NORTH COULD START AS SNOW AGAIN. BY WEDNESDAY MORNING THE 
PATTERN SHOWS A RETURN TO NORMAL...SYSTEMS EVERY FEW DAYS BRINGING 
RAIN...WITH THE SNOW LEVEL SOMEWHERE AROUND 4000 FEET.

UNTIL THEN THE CASCADES AND OLYMPICS WILL GET SNOW...HEAVY AT 
TIMES...AND A WINTER STORM WARNING IS IN EFFECT.

ANOTHER SYSTEM ARRIVES ABOUT WEDNESDAY AFTERNOON OR EVENING. THIS 
SHOULD BE ALL RAIN IN THE LOWLANDS AND WILL BRING MORE SNOW TO THE 
MOUNTAINS. THEN AFTER A BREAK ON THURSDAY...ANOTHER SYSTEM ARRIVES 
ABOUT THURSDAY NIGHT. TEMPERATURES SHOULD BE RIGHT AROUND NORMAL ALL 
THREE DAYS...WITH HIGHS IN THE MID TO UPPER 40S AND LOWS IN THE MID 
30S TO AROUND 40. BURKE
    
.LONG TERM...HAVE LIKELY POPS FOR THE THURSDAY NIGHT SYSTEM. THEN ON 
FRIDAY HAVE A MORE SHOWERY SITUATION AND HAVE PUT IN CHANCE 
POPS...WITH LIKELIES FOR THE MOUNTAINS. ONE MORE SYSTEM ON SATURDAY 
BRINGS ANOTHER BATCH OF LIKELY POPS. THEN BOTH THE GFS AND THE EURO 
SHOW A SMALL DRYING TREND...THE GFS IS KIND OF DRY OVER THE PACIFIC 
NORTHWEST AND THE EURO SHUNTS THE MOISTURE INTO BRITISH COLUMBIA. 
ANYWAY HAVE GIVEN CHANCE POPS TO THE SUNDAY-MONDAY PERIOD. BURKE

&&

.HYDROLOGY...A TRANSITION TO A WETTER PATTERN WILL BEGIN TONIGHT 
THROUGH AT LEAST THE MIDDLE OF THE WEEK AS A SERIES OF PACIFIC 
FRONTAL SYSTEMS SWEEP THROUGH WESTERN WASHINGTON. INITIALLY SNOW 
LEVELS REMAIN LOW WITH HEAVY SNOW EXPECTED TONIGHT THROUGH TUESDAY 
AFTERNOON IN THE MOUNTAINS. SNOW LEVELS WILL RISE TO AROUND 4000 FT 
ON WEDNESDAY AS ANOTHER SYSTEMS REACHES THE REGION. THE FLOOD 
POTENTIAL LOOKS LOW AT THE MOMENT AS RIVERS HAVE BEEN RUNNING LOW 
WITH LITTLE TO NO PRECIPITATION ACROSS THE REGION SINCE LATE 
NOVEMBER. NO FLOOD CONCERNS FOR THE GREEN RIVER.

MODELS TRY TO BUILD AN UPPER LEVEL RIDGE ACROSS THE PACIFIC 
NORTHWEST BEGINNING ABOUT SUNDAY...WITH A BREAK IN THE WEATHER 
POSSIBLE. THE RIDGE WILL BREAK DOWN EARLY NEXT WEEK BUT EXACT TIMING 
REMAINS UNCLEAR AS BOTH THE GFS AND ECMWF DIFFER. BURKE

&&

.AVIATION...LOW LEVEL COLD AND DRY AIR CONTINUES TO FLOW OUT THROUGH 
THE FRASER RIVER VALLEY INTO KBLI AND THE NORTHERN INLAND WATERS. IT 
WHILE SOME COOL AIR CONTINUES BANKED UP AGAINST HOOD CANAL...THE 
REMAINDER OF THE AREA IS SEEING RELATIVELY MILD MARINE AIR WITH 
OCCASIONAL LIGHT RAIN IN WEAK LOW LEVEL WARM ADVECTION. THE LOWER 
LEVELS ARE GENERALLY QUITE MOIST...SO THERE ARE ABUNDANT CIGS BELOW 
010 AND VIS 1-2SM -RA BR. ONCE THE MAIN PRECIPITATION 
SHIELD...MOVING ONTO THE COAST THIS AFTERNOON...MOVES INLAND THIS 
EVENING EXPECT IT TO REMAIN QUITE MURKY WITH VIS EVERYWHERE 3/4-2SM 
-RA BR AND CIGS 005-010. WARM ADVECTION PRECIPITATION WILL BE IN THE 
FORM OF SNOW AROUND KBLI WHERE FRASER OUTFLOW WILL CONTINUE 
OVERNIGHT. 

THE WARM FRONT WILL REACH THE COAST AROUND 09Z AND LIFT NE THROUGH 
THE AREA AROUND 13Z. BEHIND THE FRONT EXPECT PRECIPITATION TO 
GENERALLY COME TO AN END...BUT EXPECT CIGS TO REMAIN 015-020 THRU 
THE DAY TUE. CONDITIONS WILL DETERIORATE AGAIN LATE TUE AFTERNOON IN 
ADVANCE OF ANOTHER WARM OCCLUSION THAT WILL PASS ACROSS THE AREA TUE 
NIGHT.

KSEA...GENERALLY IFR TO LOW IFR CONDITIONS ARE EXPECTED THROUGH 
ABOUT 12Z TUE. BEHIND THE WARM FRONT EXPECT PRECIPITATION TO COME TO 
AN END BUT CIGS TO ONLY RISE TO AROUND 020 TUE. CIGS DROP BACK 
TOWARD 010 WITH 3-5SM -RA BR AGAIN LATER TUE AFTERNOON. IT IS 
LOOKING INCREASINGLY UNLIKELY THIS EVENING THAT EVEN WET SNOW WILL 
BE SEEN AT KSEA AS DEWPOINT TEMPERATURES HAVE RISEN INTO THE MID AND 
UPPER 30S AND TEMPERATURES INTO THE LOWER 40S. AT THE SURFACE EXPECT 
E TO SE WIND 4-7 KT TO BECOME S/SE 8 KT TUE. A PERIOD OF S WIND 50 
KT IS EXPECTED THIS EVENING THRU TONIGHT AT 050 AS THE WARM FRONT 
PASSES...WITH WINDS ALOFT DECREASING AFTER FROPA AND INCREASING 
AGAIN TUE EVENING WITH THE NEXT FRONT. ALBRECHT

&&

.MARINE...A WARM FRONT WILL MOVE INTO THE AREA FROM THE SOUTHWEST 
AND PASS THROUGH THE INLAND WATERS LATE TONIGHT. EXPECT GALE FORCE E 
TO SE WIND TONIGHT IN THE COASTAL WATERS AND AHEAD OF THE FRONT 
LATER THIS EVENING AT THE EAST ENTRANCE TO THE STRAIT. THE OTHER 
WATERS...WITH EXCEPTION TO PUGET SOUND AND HOOD CANAL...WILL SEE 
SMALL CRAFT ADVISORY E/NE WINDS AHEAD OF THE WARM FRONT. EXPECT 
WINDS TO DIMINISH BEHIND THE WARM FRONT EARLY TUE...THEN PICK UP 
AGAIN LATE IN THE DAY THROUGH TUE NIGHT AS YET ANOTHER WARM FRONT 
MOVES NE THROUGH THE WATERS. 

A SERIES OF WARM FRONTS ASSOCIATED WITH LOWS MOVING THROUGH THE EAST 
PACIFIC TOWARD THE QUEEN CHARLOTTE ISLANDS WILL MOVE THROUGH THE 
WATERS WED THROUGH THU NIGHT. 

A LESS ACTIVE TIME IS SEEN FRI THROUGH NEXT WEEKEND. EXTENDED MARINE 
FORECASTS GENERALLY FOLLOW THE ECMWF...THAT KEEPS LOWER PRES MOVING 
N AND WEST OF THE AREA IN LIEU OF THE 12Z GFS THAT MOVES LOW PRES 
SYSTEMS INTO OREGON. ALBRECHT

&&

.AVALANCHE...COLD WEATHER THE PAST WEEK GENERALLY CREATED WEAK 
SURFACE SNOW LAYERS. A FRONT SHOULD CAUSE INCREASING STRONG 
WINDS...INCREASING MODERATE TO HEAVY SNOW AND WARMING TEMPERATURES 
MONDAY AFTERNOON AND NIGHT. THIS SHOULD BUILD INCREASING DEEP 
UNSTABLE LAYERS ON SOME SLOPES. NATURAL OR TRIGGERED AVALANCHES 
SHOULD BECOME LIKELY MONDAY NIGHT AND TO PERSIST TUESDAY MORNING. AN 
AVALANCHE WARNING IS NOW IN EFFECT FOR MONDAY NIGHT FOR BACK COUNTRY 
AREAS OF THE OLYMPICS AND CASCADES.

ANOTHER FRONT IS CURRENTLY EXPECTED TO CAUSE RENEWED HIGH AVALANCHE 
DANGER TUESDAY AFTERNOON AND TUESDAY NIGHT. PLEASE VISIT WWW.NWAC.US 
FOR DETAILS. FERBER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE HOOD             
     CANAL AREA AND WESTERN WHATCOM COUNTY TONIGHT.

     A WINTER STORM WARNING IS IN EFFECT FOR THE OLYMPICS AND        
     CASCADES THROUGH TUESDAY. 

     AN AVALANCHE WATCH IS IN EFFECT FOR THE OLYMPICS AND
     CASCADES TONIGHT.

PZ...GALE WARNING COAST AND EAST ENTRANCE TO THE STRAIT.    
    .SMALL CRAFT ADVISORY WEST ENTRANCE TO THE
     STRAIT...CAMANO ISLAND TO POINT ROBERTS AND ADMIRALTY INLET.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR CONDITIONS.

$$