Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 282140
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT SAT MAR 28 2015

.SYNOPSIS...A STALLED FRONTAL BOUNDARY WILL BRING LIGHT RAIN TO THE
NORTH INTERIOR AND COAST AT TIMES THROUGH MONDAY. THE COLD FRONT
WILL REACH WESTERN WASHINGTON MONDAY NIGHT...BRINGING RAIN BACK INTO
THE REST OF THE INTERIOR. UPPER LEVEL LOW PRESSURE OVER THE REGION
NEXT WEEK WILL MAINTAIN A COOL AND SHOWERY WEATHER PATTERN.

&&

.SHORT TERM...SKIES ARE PARTLY CLOUDY ACROSS INTERIOR WRN WA WITH
JUST A FEW WEAK DIURNALLY DRIVEN SHOWERS ON RADAR THIS AFTERNOON.
SATELLITE IMAGERY SHOWS A THICK MASS CLOUDS MOVING IN FROM THE
PACIFIC...SO AN INCREASE IN MID/HIGH CLOUDS ARE EXPECTED TONIGHT.
THE KLGX COASTAL RADAR SHOWS A BAND OF STEADIER RAINFALL MOVING ONTO
THE N COAST. MODELS INDICATE A WARM FRONTAL FEATURE WILL LIFT ACROSS
WRN WA TONIGHT AND STALL MAINLY OVER BRITISH COLUMBIA SUNDAY INTO
MONDAY. MOST OF THIS RAINFALL WILL SKIRT THE N
COAST...OLYMPICS...STRAIT...AND FAR N INTERIOR. PUGET SOUND TO THE
SW INTERIOR WILL PROBABLY STAY MOSTLY DRY ALTHOUGH SOME SPRINKLES
ARE NOT OUT OF THE QUESTION...ESPECIALLY TONIGHT. THE GFS40 LOOKS TO
AGGRESSIVE WITH QPF WITH THE DRIER NAM-12 FAVORED WHICH KEEPS THE
PUGET SOUND REGION SWD GENERALLY DRY.

HIGH PRESSURE AMPLIFIES OVER THE ROCKIES AND A TROUGH DEEPENS
OFFSHORE. THE COLD FRONT LURKING OFFSHORE WILL FINALLY PUSH THROUGH
WRN WA MONDAY NIGHT...A LITTLE QUICKER THAN SOME PREVIOUS MODEL RUNS
SHOWED. LIKELY POPS ARE IN THE FORECAST MONDAY NIGHT AND TUESDAY FOR
THE FRONT AND TRAILING UPPER TROUGH. TEMPERATURES THE NEXT COUPLE
DAYS SHOULD MAKE THE LOW OR MID 60S AROUND PUGET SOUND BUT HIGHS
WILL COME DOWN A GOOD 10 DEGREES ON TUESDAY.

.LONG TERM...MODELS HAVE NOT BEEN AT ALL CONSISTENT IN THE EXTENDED
RANGE. THE OVERALL PATTERN LOOKS PROGRESSIVE AND SPLIT WITH A SERIES
OF WEAK SHORT WAVES PASSING NEAR WRN WA. TIMING THESE SYSTEMS IS
DIFFICULT AND IT DOESN`T SEEM PRUDENT TO TRY PICK OUT SHORT BLOCKS
OF DRY WEATHER. WILL KEEP THE CLIMO BROAD BRUSH CHANCE OF SHOWERS IN
THE FORECAST.  MERCER

&&

.HYDROLOGY...FLOODING IS UNLIKELY OVER THE NEXT 7 DAYS.

&&

.AVIATION...THE FLAT UPPER LEVEL RIDGE OVER W WA AT 21Z WILL SLIDE
OVER E WA BY 12Z AS A WARM FRONT MOVES OVER VANCOUVER ISLAND.
MODERATE W FLOW ALOFT WILL CONTINUE OVER THE AREA...AND WILL BECOME
INCREASINGLY MOIST FROM THE APPROACHING WARM FRONT.

THE LOWER AIR MASS OVER W WA WAS SOMEWHAT MOIST AND WEAKLY UNSTABLE
AT 21Z THIS AFTERNOON WITH AREAS OF VFR STRATOCUMULUS. MID AND HIGH
LEVEL MOISTURE JUST OFFSHORE ASSOCIATED WITH THE APPROACHING WARM
FRONT WAS BEGINNING TO REACH NW WA AND WILL COVER MAINLY THE N TWO
THIRDS OF WA WITH CIGS BKN-OVC050 AND HIGHER FROM AROUND 00Z TO
BEYOND 12Z. PRESSURE FALLS OVER SOUTHERN B.C. WILL ALLOW GUSTY S
WINDS TO DEVELOP OVER THE INTERIOR LATE TONIGHT.

KSEA...VFR CIGS WILL PREVAIL OVER THE TERMINAL THROUGH 12Z. MOISTURE
FROM A WARM FRONT HEADED TOWARD B.C. WILL SPREAD OVER THE TERMINAL
AS CIGS BKN-OVC050 AND HIGHER. SURFACE WINDS BE S 12G20KT THROUGH
ABOUT 00Z THEN WEAKEN TO S 5-10KT OVERNIGHT. KAM

&&

.MARINE...THE SMALL WEAK SURFACE RIDGE BUILDING OVER W WA THIS
AFTERNOON WILL REMAIN IN PLACE THROUGH MONDAY MORNING. THE DOMINANT
FEATURE WILL BE THE WARM FRONT THAT WILL MOVE OVER VANCOUVER ISLAND
TONIGHT. PRESSURE FALLS ALONG THE B.C. COAST AHEAD OF THE WARM FRONT
WILL ALLOW MODERATE S FLOW TO DEVELOP OVER WA WATERS TONIGHT AND
SUNDAY. SCA ARE UP FOR THE COAST AND FOR ALL INLAND WATERS EXCEPT
FOR THE CENTRAL STRAIT.

THE TRAILING COLD FRONT WILL CROSS W WA MONDAY EVENING...THEN STRONG
ONSHORE FLOW WILL DEVELOP BEHIND THE FRONT MONDAY NIGHT. PRESSURE
GRADIENT DEPICTED ON THE GFS AND ECMWF SEEM STRONG ENOUGH FOR
GALES...SIMILAR TO THE COLD FRONT LAST NIGHT...BUT THE WRF-GFS HOLDS
WINDS IN THE SCA RANGE. THE GFS AND ECMWF ALSO SEEM TO DELAY THE
STRENGTHENING ONSHORE FLOW JUST A BIT WHILE THE CANADIAN IS FASTER.
I WILL STICK WITH THE WRF-GFS TIMING FOR NOW BUT STRONG W FLOW
THROUGH THE STRAIT COULD BEGIN EARLIER MONDAY EVENING...AND
COULD REACH GALE FORCE. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT THE CENTRAL STRAIT.
     SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH BAR.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML













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