000
FXUS66 KSEW 161627
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PDT MON MAR 16 2009

.SYNOPSIS...A LARGE UPPER LEVEL TROUGH OVER THE NORTHEAST PACIFIC 
WILL STEER MORE COOL AND SHOWERY WEATHER ACROSS WESTERN WASHINGTON 
TODAY AND TUESDAY. ANOTHER MOIST PACIFIC WEATHER SYSTEM WILL MOVE 
OVER THE AREA TUESDAY NIGHT...WITH RAIN OVER THE LOWLAND AND 
MOUNTAIN SNOW CONTINUING THROUGH WEDNESDAY NIGHT...FOLLOWED BY 
SHOWERS THURSDAY. COOL SHOWERY WEATHER WILL CONTINUE THROUGH THE 
WEEKEND AS THE OFFSHORE TROUGH APPROACHES THE AREA FRIDAY...THEN 
MOVES INLAND SATURDAY.

&&

.SHORT TERM...AIR MASS OVER WA WILL REMAIN COOL AND UNSTABLE WITH 
SHOWERY WEATHER EXPECTED TODAY. 140KT JET LIES ALONG THE WA/ORE 
BORDER WITH WESTERLY FLOW ALOFT. INFRARED SATELLITE SHOWS A MASSIVE 
CU FIELD OVER THE NE PAC STREAMING INLAND. WILL ALSO SEE SOME ADDED 
LIFT AS A WEAK SFC TROUGH MOVES INLAND THIS MORNING. WITH THE 
UNSTABLE CONDITIONS...500 MB TEMPS ARE IN THE -30S C WITH LIFTED 
INDEX VALUES NEAR -1...COULD SEE ISOLD THUNDERSTORMS DEVELOP TODAY. 
THERE WERE A FEW LIGHTNING STRIKES THIS MORNING ACROSS PACIFIC  
COUNTY. SMALL HAIL ALSO POSSIBLE WITH STRONGER CELLS. IT IS STILL 
SNOWING IN THE MOUNTAINS WITH SNOW LEVELS BELOW THE HIGHWAY PASSES. 
WITH STRONG ONSHORE FLOW...WESTERLY UPSLOPE FLOW AROUND 30KT WILL 
CONTINUE THE WINTER WEATHER ADVISORY THROUGH THIS AFTERNOON. 

BACK AROUND 125W...IR SHOWS SOME ENHANCEMENT WITH COLDER CU TOPS 
ALONG THE UPPER LEVEL TROUGH AXIS. THE TROUGH AXIS WILL SHIFT 
FARTHER EAST TODAY AND WILL REACH W WA TONIGHT. LOW TEMPS WILL BE IN 
THE 30S AND COULD SEE BRIEF RAIN/SNOW SHOWERS ACROSS THE HIGHER 
ELEVATIONS. THE JET WILL SHIFT NORTH IN S B.C. ON TUE BUT THE FLOW 
OVER WA WILL REMAIN NEARLY ZONAL. DEVELOPING SYSTEM TUE NIGHT INTO 
WED WILL CLIP W WA AS A WARM FRONT LIFTS NORTH OVER THE REGION. 
TRAILING COLD FRONT WILL THEN PASS THROUGH WED MORNING. 33

.LONG TERM...PREVIOUS DISCUSSION...BOTH GFS/ECMWF BEGIN SHIFTING THE 
BIG OFFSHORE UPPER LEVEL TROUGH EASTWARD BY ABOUT 
FRIDAY...EVENTUALLY MOVING IT ACROSS W WA EITHER SATURDAY OR SUNDAY. 
BOTTOM LINE...THE WET PATTERN WILL CONTINUE. KAM

&&

.AVIATION...BROAD UPPER LEVEL TROUGH IS OVER THE NORTHEAST PACIFIC 
WITH SOUTHWEST FLOW ALOFT OVER OUR REGION. THE AIRMASS IS COLD AND 
UNSTABLE...AND WIDESPREAD SHOWER ACTIVITY WILL BE PREVALENT 
THROUGHOUT TODAY.  A WEAK SURFACE TROUGH OFFSHORE AND MOVING THROUGH 
THIS MORNING WILL HELP MAINTAIN SURFACE SHOWER ACTIVITY THROUGH THE 
EARLY AFTERNOON. DAYTIME HEATING WILL HELP PRIME THIS UNSTABLE 
ATMOSPHERE FOR MORE SHOWERS IN THE AFTERNOON. WITH 500 MB TEMPS 
BELOW -30C AND STEEP LAPSE RATES...CANNOT RULE OUT A RUMBLE OF 
THUNDER TODAY FOR ANYONE.  

CEILINGS WILL BE FLOP AROUND QUITE A BIT WITH SHOWER ACTIVITY. 
SHOWERS IN THE 1500 TO 3000 FOOT RANGE WHILE OUTSIDE OF THE SHOWER 
ACTIVITY CONDITIONS 5000 SCATTERED TO BROKEN. VISIBILITY COULD DROP 
DOWN TO NEAR 3SM IN THE HEAVIER SHOWERS. 

SHOWER ACTIVITY WILL CONTINUE OVERNIGHT WITH THE TROUGH AXIS 
SWINGING THROUGH AROUND 12Z TUESDAY...BACKING THE FLOW ALOFT TO 
WESTERLY. 

KSEA...TEMPO GROUPS IN THE TAF TODAY WITH SHOWERS MOVING OVER THE 
AIRPORT THROUGHOUT THE DAY. A THUNDERSTORM IS POSSIBLE AT ANYTIME 
TODAY DUE TO THE UNSTABLE AIRMASS OVERHEAD. CEILINGS NEAR 2000 FEET 
WITH THE SHOWER ACTIVITY AND NEAR 5000 FEET DURING THE LONGER BREAKS 
IN THE ACTION. SOUTHWESTERLY WINDS 5 TO 15 KTS WITH GUSTS NEAR 20 
KNOTS BEGIN LATER THIS MORNING WITH SHOWER ACTIVITY AS THE STRONGER 
WINDS BEGIN TO MIX DOWN. DAMICO

&&

.MARINE...WINDS HAVE EASED THIS MORNING AFTER THE STRONG FRONTAL 
SYSTEM THAT PASSED THROUGH THE REGION YESTERDAY. SMALL CRAFT WINDS 
WILL DIE OFF EARLY THIS AFTERNOON FOR MOST WATERS EXCEPT FOR THE 
COAST AND PUGET SOUND. THERE WILL PROBABLY BE A LULL IN SCA WINDS 
FOR THE PUGET SOUND LATE THIS MORNING/EARLY AFTERNOON...BUT STRONGER 
WINDS SHOULD MIX DOWN IN THE AFTERNOON SO KEPT THE SCA GOING. 

WESTERLY SWELLS OF 15 TO 16 FEET ON THE COAST THIS MORNING WILL 
CONTINUE TO SLOWLY TREND DOWN...FALLING TO AROUND 12 FEET BY 
12Z TUESDAY. 

A WARM FRONTAL SYSTEM WILL PASS TO OUR NORTH LATE TUESDAY 
AFTERNOON...INCREASING SOUTHERLY WINDS ALONG THE COAST TO HIGH END 
SCA BY TUESDAY NIGHT. DAMICO

&&

.SEW WATCHES/WARNINGS/ADVISORIES... 
WA...WINTER WEATHER ADVISORY OLYMPICS AND CASCADES.

PZ...SMALL CRAFT ADVISORY COAST...WEST ENTRANCE...ADMIRALTY          
     INLET...AND PUGET SOUND AND HOOD CANAL.
     SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.
          
$$

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