Weather Service Report


580 
FXUS66 KSEW 231033
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT THU OCT 23 2014

.SYNOPSIS...AN UPPER TROUGH WILL MAINTAIN SHOWERY WEATHER OVER 
WESTERN WASHINGTON TODAY. THE AIR MASS WILL BE UNSTABLE ENOUGH FOR A 
CHANCE OF THUNDERSTORMS. SHOWERS WILL GRADUALLY DECREASE LATER 
THURSDAY NIGHT. FRIDAY WILL BE MOSTLY DRY BETWEEN WEATHER SYSTEMS. A 
WARM FRONT WILL BRING SOME RAIN BACK TO THE AREA FRIDAY NIGHT AND 
SATURDAY. LOW PRESSURE WILL BRING MORE RAIN SATURDAY NIGHT AND 
SUNDAY WITH SOME LOCALLY WINDY CONDITIONS POSSIBLE. 

&&

.SHORT TERM...A STRONG WESTERLY 140-150KT JET WILL STAY AIMED INTO 
OREGON TODAY KEEPING WRN UNDER A FAVORED REGION OF LIFT. A SHORT 
WAVE SEEN ON SATELLITE IMAGERY APPROACHING THE COAST WILL HELP TO 
ENHANCE SHOWER ACTIVITY ACROSS THE AREA. THE IR SATELLITE IMAGE 
INDICATES COOLING CLOUD TOPS SO THE IDEA OF INCREASED INSTABILITY 
TODAY LOOKS ON TRACK. MODEL LI'S ARE FORECAST -1 TO -2C WITH CAPE UP 
TO 500J/KG WHICH WILL SUPPORT A CHANCE FOR EMBEDDED THUNDERSTORMS. 
LIGHTING DETECTION IS ALREADY SHOWING STRIKES JUST OFFSHORE AND ALSO 
OVER WHATCOM COUNTY UNDER AN ENHANCED BAND OF SHOWERS. MODELS ARE 
HINTING THAT SURFACE RIDGING MAY DEVELOP LATER TODAY W OF PUGET 
SOUND. THIS COULD GENERATE A CONVERGENCE ZONE AROUND WRN SNOHOMISH 
COUNTY LATER IN THE DAY. IT IS UNLIKELY TO PERSIST VERY LONG AS THE 
JET LIFTS NWD DIRECTLY OVER WRN WA AND THE SURFACE PATTERN WEAKENS 
TONIGHT. 

THE FLOW BECOME MORE ZONAL TONIGHT BUT THE GFS STILL BRINGS ANOTHER 
WEAK DISTURBANCE INTO THE AREA. SHOWERS WILL BE POSSIBLE UNTIL THE 
FLOW LIFTS FAR ENOUGH TO THE N SO THAT THE JET BECOMES DIRECTED INTO 
B.C. RATHER THAN WA. THIS SHOULD HAPPEN FRIDAY MORNING...SO SHOWERS 
SHOULD BE ON THE DECREASE AND MOSTLY END BY AFTERNOON. ANY BREAK IN 
RAINFALL FRIDAY WILL BE BRIEF AS ANOTHER SYSTEM WILL BE ORGANIZING 
OFFSHORE. 

00Z MODELS ARE COMING INTO BETTER AGREEMENT WITH REGARDS TO THE 
SYSTEM EXPECTED TO AFFECT THE REGION OVER THE WEEKEND. A COLD NRN 
STREAM TROUGH ORIGINATING FROM THE BERING SEA CAN BEEN SEEN ON WATER 
VAPOR QUICKLY DRIVING SWD OVER THE PACIFIC. THE COLD AIR MASS WILL 
ENCOUNTER THE ATMOSPHERIC RIVER OF MOISTURE THAT HAS TAPPED THE 
TROPICS. WHEN THESE TWO MERGE LATER TODAY AND TONIGHT...CYCLOGENESIS 
WILL OCCUR ALONG THE BAROCLINIC BOUNDARY JUST S OF 40 N AND 
130-140W. AS SURFACE LOW PRESSURE DEEPENS THE FLOW OVER THE PAC NW 
WILL LIFT NWD. A WARM FRONT OUT AHEAD OF THIS SYSTEM WILL REACH WRN 
WA FRIDAY NIGHT WITH SOME WARM ADVECTION RAIN DEVELOPING ACROSS THE 
AREA. AREAS SUSCEPTIBLE TO ELY FLOW SUCH AS THE FOOTHILLS AND GAPS 
NEAR THE COASTAL WATERS MAY BECOME BREEZY UNTIL THE WARM FRONT LIFTS 
N.

MODELS MOSTLY AGREE THAT THE SURFACE LOW WILL DEEPEN TO ROUGHLY 
980-985 MB AS IT WOBBLES NWD ALONG 130 W OFF THE NRN CA/S OREGON 
COASTS FRIDAY NIGHT. THE LOW SHOULD REACH THE NRN OREGON OR S WA 
COASTAL WATERS ON SATURDAY BUT SHOULD ALSO BE IN THE PROCESS OF 
FILLING. IT REMAINS UNCLEAR HOW DEEP AND CONSOLIDATED THE LOW WILL 
REMAIN AS IT APPROACHES ON SATURDAY. THE 00Z MODEL TRACKS ARE 
CLUSTERED AROUND THE LOW REACHING THE S WA COAST BY SATURDAY EVENING 
BUT FILLING AS IT MOVES ONSHORE. THIS SYSTEM BARES WATCHING AS THE 
REGION OF DEVELOPMENT AND TRACK ARE FAVORABLE FOR STRONG WINDS IN 
OUR AREA. IT IS IMPORTANT TO NOTE HOWEVER THAT MOST MODELS ARE 
SHOWING MATURE DEVELOPMENT BY LATE FRIDAY...THEN SLOWLY FILL THE LOW 
AS IT REACHES THE PAC NW WHICH WOULD LIMIT WIND POTENTIAL. SOME 
MODELS ALSO DO NOT FULLY CONSOLIDATE THE LOW OR THEY BRING IT INLAND 
S OF PUGET SOUND WHICH COULD KEEP STRONGER WINDS S OF THE AREA. A 
LOT COULD CHANGE OVER THE NEXT COUPLE DAYS SO IT WILL BE A GOOD IDEA 
TO MONITOR FORECASTS. 
 
.LONG TERM...MOST MODELS TRACK LOW PRESSURE NE ACROSS WA ON SUNDAY. 
IT COULD BE BREEZY TO LOCALLY WINDY DEPENDING ON THE TRACK. RAIN IS 
LIKELY EARLY ON BUT WILL BECOME SHOWERY AS ONSHORE FLOW INCREASES 
BEHIND THE LOW. SHOWERS WILL PERSIST INTO SUNDAY NIGHT WILL A LULL 
ON MONDAY BETWEEN SYSTEMS.

THE GFS BRINGS THE NEXT SYSTEM CONTAINING THE REMNANTS OF ANNA INTO 
THE AREA MONDAY NIGHT AND TUESDAY. MOST MODELS RAPIDLY FILL THE LOW 
RAPIDLY AS IT APPROACHES SO WIND MAY NOT BE AN ISSUE BUT IT ALSO 
BARES WATCHING. IT SHOULD BRING RAIN BACK INTO THE AREA BUT AT THIS 
POINT IT LOOKS TO BE A PROGRESSIVE SYSTEM WHICH WILL LIMIT THE FLOOD 
POTENTIAL. ADDITIONAL LOW PRESSURE SYSTEM MAY BRING RAIN INTO THE 
AREA THROUGH MID WEEK.  MERCER

&&

.HYDROLOGY...SHOWERS WILL PERSIST TODAY BUT ADDITIONAL RAIN AMOUNTS 
WILL NOT BE HYDROLOGICALLY SIGNIFICANT. THE SKOKOMISH RIVER WILL 
REMAIN ABOVE FLOOD STAGE BUT GRADUALLY RECEDE TODAY...FALLING BELOW 
FLOOD STAGE LATER TODAY OR THIS EVENING. REFER TO THE LATEST FLOOD 
STATEMENT BULLETIN FOR THE MOST UP TO DATE INFORMATION.

WET WEATHER IS EXPECTED TO CONTINUE THROUGH THE UPCOMING WEEK. BUT 
RAINFALL AMOUNTS ARE NOT EXPECTED TO DRIVE ANY RIVERS ABOVE FLOOD 
STAGE. MERCER

&&

.AVIATION...AIR MASS UNSTABLE OVER WESTERN WASHINGTON TODAY AND 
TONIGHT WITH SOUTHWESTERLY FLOW ALOFT.   

NOTHING REALLY ORGANIZED MOVING THROUGH THE AREA TODAY BUT SATELLITE 
IMAGERY SHOWS PLENTY OF SHOWERS EMBEDDED IN THE SOUTHWESTERLY FLOW 
ALOFT OFFSHORE EXTENDING BACK TO NEAR 160W. IN GENERAL CEILINGS IN 
THE 4000 TO 6000 FOOT RANGE LOWERING DOWN TO NEAR 2000 FEET WITH 
VISIBILITIES 3-5SM BRIEFLY IN THE HEAVIER SHOWERS. THE AIR MASS IS 
UNSTABLE ENOUGH FOR THE POSSIBILITY OF ISOLATED THUNDERSTORMS. THE 
CHANCE FOR THUNDERSTORMS IS NOT HIGH ENOUGH TO INCLUDE IN THE TAFS.  

KSEA...CEILINGS IN THE 4000-6000 FOOT RANGE DROPPING DOWN TO NEAR 
2000 FEET IN THE HEAVIER SHOWERS LATE THIS MORNING INTO THE 
AFTERNOON HOURS. SOUTHERLY WINDS 6 TO 10 KNOTS WITH BRIEF HIGHER 
GUSTS IN THE VICINITY OF SHOWER ACTIVITY. FELTON

&&

.MARINE...SURFACE RIDGE BUILDING INTO WESTERN WASHINGTON TODAY BUT 
WITH THE UNSTABLE AIR MASS OVER THE AREA STRONGER WINDS ALOFT 
GETTING MIXED DOWN TO THE SURFACE THROUGH THE AFTERNOON HOURS. THIS 
WILL KEEP SMALL CRAFT ADVISORIES UP THROUGHOUT THE DAY TODAY FOR THE 
INLAND WATERS. SWELL OVER THE COASTAL WATERS STILL IN DOUBLE DIGITS 
BUT WILL SUBSIDE BELOW 10 FEET TONIGHT. THE SMALL CRAFT FOR 
HAZARDOUS SEAS REMAINS IN EFFECT TODAY. 

SURFACE HIGH SHIFTING EAST LATER TONIGHT INTO FRIDAY WITH LIGHT 
EASTERLY FLOW OVER THE WATERS. A 988 MB LOW WILL DEVELOP OFF THE 
NORTHERN CALIFORNIA COAST AND MOVE INTO THE OREGON COASTAL WATERS ON 
SATURDAY. THE LOW WILL CONTINUE TO MOVE NORTHEAST THROUGH THE INLAND 
WATERS SATURDAY NIGHT. THE TRACK OF THE LOW WILL BE CRUCIAL IN HOW 
MUCH WIND DEVELOPS OVER THE MARINE AREAS. AT THIS POINT GALE FORCE 
WINDS ARE POSSIBLE SATURDAY NIGHT INTO SUNDAY MORNING OVER ALL OF 
THE WATERS. THE WINDS WILL EASE ON SUNDAY AS ANOTHER WEAK RIDGE OF 
HIGH PRESSURE BUILDS INTO THE AREA.  

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...FLOOD WARNING IN EFFECT FOR THE SKOKOMISH RIVER IN MASON        
      COUNTY. 
 
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR HAZARDOUS SEAS  
     FOR THE COASTAL WATERS.
     SMALL CRAFT ADVISORY FOR ROUGH BAR IN EFFECT UNTIL 8 PM         
     TODAY.
     SMALL CRAFT ADVISORY TONIGHT INLAND WATERS AND                  
     ADMIRALTY INLET TODAY.
     SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT THIS            
     AFTERNOON.   

$$

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