Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 031524
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE MAY 3 2016

.SYNOPSIS...STRONG ONSHORE FLOW WILL DEVELOP TODAY FOR MUCH COOLER
WEATHER COMPARED TO YESTERDAY. MEANWHILE...A LOW PRESSURE SYSTEM
ALONG OR OFF THE COAST WILL BRING SOMEWHAT UNSETTLED CONDITIONS TO
THE AREA THROUGH THURSDAY. MAX TEMPERATURES WILL BE NEAR NORMAL
WEDNESDAY AND THURSDAY. HIGH PRESSURE ALOFT WILL RETURN ON FRIDAY.

&&

.SHORT TERM...GRADIENTS ARE SOLIDLY ONSHORE THIS MORNING BRINGING
COOLER MARINE AIR INLAND. THE AIR MASS IS UNSTABLE ENOUGH TO PREVENT
LOWER STRATUS FROM FORMING AND ALLOWING FOR HIGH BASED SHOWER
ACTIVITY TO CONTINUE. THERE WERE SOME SHOWERS OVER THE INTERIOR
OVERNIGHT BUT LATEST RADAR LOOP INDICATES SHOWS REMAIN MOSTLY
CONFINED TOWARD THE COAST THIS MORNING. THE 06Z/12Z MODELS AVAILABLE
INDICATE SHOWERS WILL GENERALLY STAY NEAR THE COAST AND ALONG THE
CASCADES TODAY BUT A FEW SHOWERS OVER OTHER PORTIONS OF WRN WA
CANNOT BE RULED OUT. WILL MAINTAIN THE CHANCE OF SHOWERS IN THE
FORECAST TODAY. HIGHS WILL BE COOLER...IN THE LOW 70S AROUND PUGET
SOUND AND ONLY IN THE LOW 60S ALONG THE COAST.

MODELS INDICATE AN EMBEDDED SHORT WAVE WILL REACH THE OREGON COAST
LATE THIS AFTERNOON AND LIFT NWD TONIGHT. THE BULK OF MODEL QPF IS
CONCENTRATED ALONG THE CASCADES AND FOOTHILLS. SUB ZERO LI`S OVER
THE CASCADES AND SLY FLOW ALOFT WILLS TILL BE FAVORABLE FOR
THUNDERSTORMS DURING THE EVENING. THE AIR MASS WILL NOT BE AS
UNSTABLE OVER THE LOWLANDS WITH ONSHORE FLOW BUT THERE WILL BE
ENOUGH MOISTURE FOR SOME SHOWERS. QPF MAY NEED SOME UPWARD
ADJUSTMENT IN THE FOOTHILLS AND CASCADE ZONES FOR THE TONIGHT
PERIOD.

THE FLOW TURNS MORE SWLY WEDNESDAY WHICH WILL KEEP ANY THREAT OF
THUNDERSTORMS TO THE EAST OF THE CASCADES. THE NRN BRANCH OF THE
SPLIT TROUGH WILL STILL BE OFF THE COAST WITH A STALLED FRONTAL
BOUNDARY OVER WRN WA ENTRAINING MOISTURE FROM THE SRN STREAM LOW.
EXPECT CLOUDS...A CONTINUED THREAT OF SHOWERS...AND STRONGER
ONSHORE FLOW COOLING HIGH TEMPERATURES DOWN CLOSER TO AVERAGE.

THE NRN SPLIT TROUGH WILL MOVE INLAND ACROSS WA ON THURSDAY. MODELS
DIFFER A BIT ON TIMING BUT AGREE ON A GENERAL DRYING TREND THURSDAY
INTO THURSDAY NIGHT. SHOWERS WILL END FIRST ACROSS THE COASTAL AREAS
AND NORTH WITH THE REST OF INTERIOR WRN WA DRYING OUT THURSDAY
NIGHT. SUNBREAKS ARE POSSIBLE IN THE AFTERNOON DEPENDING ON HOW
QUICKLY THIS SYSTEM EXITS THE AREA AND HIGHS WILL BE LITTLE
CHANGED.

.LONG TERM...FROM PREVIOUS DISCUSSION...AN UPPER LEVEL RIDGE WILL
BUILD OVER THE AREA ON FRIDAY FOR SUNNIER AND WARMER CONDITIONS.
BEYOND FRIDAY...THE LATEST GFS SOLUTION WAS COMING MORE IN LINE WITH
THE ECMWF SOLUTION OF DIGGING AN UPPER TROF OVER WESTERN CANADA LATE
THIS WEEKEND. CONSEQUENTLY...THE GFS WAS FLATTER WITH THE RIDGE ON
SATURDAY. THE DEEPENING TROF WILL SERVE TO INITIATE AN ONSHORE PUSH
ON SATURDAY.

TEMPS ARE ANTICIPATED TO START OFF ABOVE NORMAL AT THE BEGINNING
OF THIS PERIOD BUT LOWER TO CLOSER TO NORMAL THE END OF THE
PERIOD. THE FORECAST TEMPS REFLECTED A COMPROMISE BETWEEN THE
WARMER GFS AND THE COOLER ECMWF SOLUTIONS. IN OTHER WORDS...THERE
IS A CHANCE THAT THE FORECAST TEMPS ARE TOO WARM FOR SUNDAY AND
MONDAY.

AT THIS TIME...KEPT THE FORECAST DRY DURING THIS PERIOD BUT
CANNOT RULE OUT THE POSSIBILITY OF A FEW SHOWERS OVER THE NORTH
CASCADES EARLY NEXT WEEK.

&&

.AVIATION...SOUTHERLY FLOW ALOFT WITH MID LEVEL MOISTURE AND
ISOLATED SHOWERS. A WEAK COLD FRONT WILL MOVE ASHORE TODAY AND
ONSHORE FLOW WILL INCREASE THIS AFTERNOON AND EVENING...FOR
INCREASING MOISTURE AND LOWERING CIGS THROUGH TONIGHT. THE LOW
CLOUDS ON THE COAST THIS MORNING SEEM TO HAVE BROKEN UP... BUT THEY
SHOULD REDEVELOP TODAY AND THEN PUSH INLAND TONIGHT WITH MORNING LOW
STRATUS A GOOD BET OVER ALL OF WRN WA WED.


KSEA...SW BREEZE SHOULD SHIFT TO NLY THIS EVENING...CLOUDS WILL
GRADUALLY INCREASE AND CIGS LOWER...CHANCE OF SHOWERS WITH A WEAK
COLD FRONT MOVING ASHORE...MORNING LOW STRATUS A GOOD BET WED.

&&

.MARINE...ONSHORE FLOW WILL INCREASE TODAY AND THIS EVENING AS LOW
PRESSURE MOVES INLAND AND HIGH PRESSURE BUILDS OFFSHORE. THERE IS A
GOOD CHANCE OF GALE WESTERLIES IN THE CENTRAL AND EASTERN STRAIT OF
JUAN DE FUCA THIS AFTERNOON AND TONIGHT...WITH SMALL CRAFT ADVISORY
WINDS LIKELY OVER ALL OTHER MARINE ZONES EXCEPT PUGET SOUND AND HOOD
CANAL WHERE THE WINDS WILL BE CONVERGING LATER TODAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING IN EFFECT FROM NOON TODAY TIL 3 AM WEDNESDAY FOR
     THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

  SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING
     WATERS...EXCEPT THE PUGET SOUND/HOOD CANAL...BEGINNING THIS
     AFTERNOON.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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



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