FXUS66 KSEW 080511
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
907 PM PST SAT NOV 7 2009

.SYNOPSIS...MOIST ONSHORE FLOW AND A COOL AND UNSTABLE AIRMASS OVER 
THE REGION WILL KEEP SHOWERS OVER WESTERN WASHINGTON INTO SUNDAY. A 
WEAK WARM FRONT WILL BRUSH THE AREA SUNDAY NIGHT FOLLOWED BY A 
TRAILING COLD FRONT MONDAY. A WEAKER FRONT AND A COOL UPPER LEVEL 
TROUGH WILL BRING RAIN THEN SHOWERS TUESDAY AND WEDNESDAY FOLLOWED 
BY DRIER WEATHER THURSDAY AND THURSDAY NIGHT. ANOTHER PACIFIC 
FRONTAL SYSTEM WILL MOVE INTO THE AREA FRIDAY AND SATURDAY. 

&&

.SHORT TERM...CLOUD COVER TODAY MAY HAVE PREVENTED JUST ENOUGH 
DIURNAL HEATING TO KEEP MORE WIDESPREAD THUNDERSTORM ACTIVITY AT BAY 
DESPITE THE OVERALL UNSTABLE CONDITIONS. HOWEVER...COOL AND UNSTABLE 
PATTERN REMAINS IN PLACE AND WILL CONTINUE TO SUPPORT BANDS OF 
SHOWERS AND POSSIBLY ISOLATED THUNDERSTORMS TONIGHT. LIGHTNING 
ACTIVITY TAPERED OFF QUICKLY AFTER SUNDOWN...WITH A FEW LINGERING 
LIGHTNING STRIKES OVER PACIFIC COUNTY AND ALONG THE OREGON COAST. 
SHOWERS WILL LIKELY PICK UP AGAIN AFTER MIDNIGHT AS A WEAK UPPER 
LEVEL WAVE JUST INSIDE OF 130W MOVES OVER HEAD. SNOW LEVELS WILL 
REMAIN AROUND 3000 TO 3500 FEET OVERNIGHT...WITH ADVISORY LEVEL 
SNOWFALL CONTINUING OVER THE CASCADES INTO SUNDAY MORNING. 

THE EASTERN PACIFIC UPPER TROUGH WILL BEGIN TO DEEPEN SUNDAY ALONG 
140W AS THE FIRST OF A SERIES OF EMBEDDED SHORTWAVE TROUGHS SLIDE 
INTO THE REGION SOUTH OF 50 N. HEIGHTS WILL RISE SOMEWHAT SUNDAY 
EVENING OVER WESTERN WASHINGTON AS A WEAK WARM FRONT BRUSHES THE 
AREA FROM THE SOUTHWEST. THE WARM FRONT WILL BRING A CHANCE OF RAIN 
MOSTLY TO THE COAST...OLYMPICS AND NORTH CASCADES...WITH THE 
INTERIOR AND CENTRAL CASCADES REMAINING RELATIVELY DRY. A TRAILING 
COLD FRONT WILL MOVE INTO WESTERN WASHINGTON MONDAY...BRINGING 
VIGOROUS S-SE WINDS MONDAY MORNING IN ADVANCE OF THE FRONT AND A FEW 
HOURS OF HEAVY RAIN AS THE FRONT PASSES. MODELS CONTINUE TO SUPPORT 
THE IDEA OF THE FRONT MOVING THROUGH QUICKLY...KEEPING THE HEAVIEST 
RAINFALL OVER A SHORT PERIOD AND NOT FOCUSED OVER A PARTICULAR 
LOCATION. COLD AIR ALOFT WILL MOVE INTO THE REGION TUESDAY WITH THE 
UPPER LEVEL TROUGH FOR A TYPICAL POSTFRONTAL PATTERN. COOK 

.LONG TERM...MEDIUM RANGE MODELS REMAIN IN GOOD AGREEMENT FOR THE 
EXTENDED...BRINGING A WEAK COLD FRONT TO THE AREA TUESDAY NIGHT AND 
A COOL AND UNSTABLE AIR MASS WEDNESDAY AS THE UPPER LEVEL TROUGH 
MOVES IN FROM THE NORTHWEST.  THE PATTERN REMAINS VERY PROGRESSIVE 
WITH ANOTHER DEEP UPPER LEVEL TROUGH SETTING UP OVER THE NORTHEAST 
PACIFIC THURSDAY...WHICH IN TURN BRINGS A BIT OF RIDGING AND DRIER 
WEATHER TO THE PACIFIC NORTHWEST THURSDAY AFTERNOON AND EVENING.
TRUE TO FORM THE NEXT IN THE SERIES OF FRONTS SHOULD BEGIN TO MOVE 
THROUGH THE REGION AGAIN FRIDAY...BRINGING ANOTHER ROUND OF 
RELATIVELY SHORT LIVED HEAVY RAIN WITH THE FRONT FOLLOWED BY  
POST-FRONTAL SHOWERS FOR SATURDAY. COOK

&&

.HYDROLOGY...NO SIGNIFICANT FLOODING IS EXPECTED IN WESTERN 
WASHINGTON DURING THE NEXT WEEK. THIS INCLUDES THE GREEN RIVER. 

THE COMING WEEK WILL BE CHARACTERIZED BY SEVERAL FRONTAL SYSTEMS 
MOVING INTO WESTERN WASHINGTON. THE FIRST WILL ARRIVE 
MONDAY...FOLLOWED BY A SECOND WEAKER FRONT TUESDAY NIGHT...AND THEN 
FRIDAY OR FRIDAY NIGHT. EACH WILL BE ACCOMPANIED BY A PERIOD OF 
HEAVY RAINFALL WITH THE FRONT ITSELF FOLLOWED BY COOL AND SHOWERY 
WEATHER IN THE POST FRONTAL ENVIRONMENT. RAINFALL ACCUMULATIONS WILL 
ULTIMATELY BE LIMITED BY THE PROGRESSIVE MOVEMENT OF FRONTS. SNOW 
LEVELS ARE EXPECTED TO REMAIN AROUND 3500 FEET THROUGH WEDNESDAY... 
LOWERING TO NEAR 2000 BY THURSDAY. CONDITIONS ARE NOT FAVORABLE FOR 
RIVER FLOODING. AGAIN...THE RISK OF MAINSTEM RIVER FLOODING DURING 
THE NEXT WEEK IS VERY LOW.  

&&

.AVIATION...SCATTERED SHOWERS CONTINUE. THERE IS COLD AIR ALOFT OFF 
VANCOUVER ISLAND AND THE SHOWERS THERE AREA ESPECIALLY NUMEROUS AND 
CONVECTIVE LOOKING...WHILE THE AREA FURTHER SOUTH STRAIGHT WEST OF 
ASTORIA FOR INSTANCE LOOKS LIKE IT HAS BECOME A NOTCH MORE STABLE AS 
SOME WARM ADVECTION BEGINS. THE NAM 850MB WINDS AND TEMPS SHOW 
THIS...TEMPS ALOFT WARM A COUPLE DEGREES C OVERNIGHT...BUT THAT DOES 
NOT SEEM TO SUPPRESS THE SHOWERS AT ALL AND THE NAM12 ACTUALLY HAS 
THE SHOWERS INCREASING AROUND DAYBREAK SUN...PROBABLY FROM THE 
IMPULSE JUST NOW ARRIVING 130W. THE WARM ADVECTION DOES BEGIN IN 
EARNEST LATER SUNDAY HOWEVER...AND THAT WILL MARK THE END OF THE 
SCT-BKN LOWER CIGS AND SKIES WILL TRANSITION TO A MID LEVEL 
OVERRUNNING OVERCAST LATE IN THE AFTERNOON. RAIN WITH THE NEXT 
FRONTAL SYSTEM ARRIVES MON MORNING...BEFORE DAYBREAK ON THE COAST 
AND PERHAPS HOLDING OFF TIL 18Z FOR THE INTERIOR. 19


KSEA...HARD TO CHASE SHOWER ACTIVITY IN THE TAF SO PROBABLY WONT DO 
A LOT OF THAT UNLESS THE RADAR SHOWS ESPECIALLY WET SHOWERS MOVING 
TOWARD SEATTLE...I PROBABLY WILL FOLLOW THE NAM IDEA OF BRINGING 
ANOTHER BATCH OF SHOWERS THRU WRN WA AROUND DAYBREAK...DRYING UP IN 
THE AFTERNOON...AND THEN A MID LEVEL OVERCAST LOWERING LATER IN THE 
DAY AHEAD OF THE NEXT FNTL SYS...SO THE 06Z TAF WILL CHANGE A BIT 
FROM THE CURRENT FCST. 19

&& 

.MARINE...STILL GUSTY NEAR SHOWER BANDS...SHERINGHAM HAD A WIND OF 
30024G32KT AT 7PM AS SHOWERS WENT BY...AND SOUTHERLIES 20-25KT 
PERSIST IN PUGET SOUND...BUT WINDS FOR NOW HAVE DIED DOWN MANY OTHER 
AREAS. WESTERLY SWELL IS STILL FAIRLY IMPRESSIVE...ARND 18FT 
TONIGHT...BUT THE NEXT 24HRS WILL MARK A RELATIVE LULL IN THE 
WEATHER. THE LATEST UW MM5NAM BRINGS SSE GALES BACK TO THE COASTAL 
WATERS SUNDAY EVENING...AND TO THE NORTHERN INLAND WATERS AND EAST 
PART OF THE STRAIT BY 5AM MON. THAT MIGHT BE A TAD SLOWER THAN THE 
FCST BUT A LOT DEPENDS ON WHETHER THERE IS ONE FRONTAL WAVE AND LOW 
PRES SYS OR TWO...THE MODELS HAVE BEEN LEANING TOWARD TWO WITH THE 
FIRST INTO THE CHARLOTTES LATE SUN AFTERNOON AS A SECOND LOW FORMS 
ON THE FRONT JUST OUTSIDE OF 130W SUNDAY EVENING. THIS SECOND LOW IS 
THE ONE THAT REALLY TIGHTENS UP THE GRADIENT AND WILL DEVELOP THE 
GALES SUNDAY NIGHT/MON MORNING. THE NAM DEEPENS IT TO 992MB AT TAKES 
IT INTO NRN VRISL JUST BEFORE DAYBREAK MON...THE GFS IS NOT AS DEEP 
BUT STILL GIVES A SOLID SSE GALE TO THE COASTAL WATERS DVLPG SUN 
EVENING...AND TO THE NORTHERN WATERS FROM MIDNIGHT THRU DAYBREAK 
MON. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY FOR THE OLYMPIC AND CASCADE MOUNTAINS. 
PZ...SMALL CRAFT ADVISORY ALL WATERS. 
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR. 

$$

WWW.WEATHER.GOV/SEATTLE

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.

ZSE ARTCC PIREP REQUIREMENTS

Issued: 11/7/2009 7:45:18 PM

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