Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 241615
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 AM PDT FRI APR 24 2015

.SYNOPSIS...AN UPPER LOW OVER THE PACIFIC NORTHWEST WILL KEEP THE
WEATHER COOL AND UNSETTLED THROUGH SATURDAY. HIGH PRESSURE ALOFT
WILL PREVAIL OVER THE AREA SATURDAY NIGHT AND SUNDAY...HOWEVER
ANTICIPATE A WARM FRONT TO BRING SOME RAIN TO THE AREA ON SUNDAY.

&&

.SHORT TERM...
AN UPPER LOW CENTERED OVER SOUTHERN BRITISH COLUMBIA WILL SLOWLY
DRIFT SOUTH. BY EARLY SATURDAY...IT SHOULD BE CENTERED OVER
NORTHWEST WA. THE MAIN IMPACTS WILL BE BELOW NORMAL TEMPS AND A
RISK OF TSTMS. IT LOOKS LIKE THE BEST CHANCE OF TSTMS WILL BE OVER
THE NORTHERN PART OF THE CWA TODAY. EXPECT A FEW OF THE STRONGER
TSTMS TO PRODUCE A LARGE QUANTITY OF HAIL AND...POSSIBLY...A
FUNNEL CLOUD. THE TSTMS WILL BE DIURNALLY DRIVEN...THUS LOOK FOR
THE RISK OF TSTMS TO WANE AFTER SUNSET. OTHERWISE...EXPECT
SCATTERED SHOWERS...MORE NUMEROUS THIS AFTERNOON...OVER THE CWA
THROUGH TONIGHT.

THE UPPER LEVEL LOW WILL REMAIN OVER THE PAC NW ON SATURDAY WITH A
FEW MORE SHOWERS EXPECTED ACROSS WESTERN WA. THERE IS A CHANCE OF
THUNDERSTORMS IN THE CASCADES AS THE UPPER LOW MOVES INTO EASTERN
WA. BUT WE SHOULD SEE A FEW SUN BREAKS AS WELL. THE AIR MASS WILL
STABILIZE AND DRY OUT SATURDAY NIGHT AS THIS UPPER LOW EXITS.

A WARM FRONT WILL CLIP WESTERN WA ON SUNDAY FOR A CHANCE OF
RAIN...MAINLY OVER THE OLYMPIC PENINSULA. MODELS SHOWED LITTLE
PRECIP IN THE INTERIOR...A FEW HUNDREDTHS POSSIBLE. SKIES WILL
REMAIN CLOUDY BUT TEMPS WILL MODERATE WITH HIGHS NEAR 60 IN THE
INTERIOR. 33/05

.LONG TERM FROM THE PREV DISCUSSION...
THE UPPER LEVEL RIDGE WILL BUILD OVER THE PAC NW ON MONDAY...PUSHING
THE WARM FRONT NORTH INTO B.C. WHILE WE STILL HAVE A CHANCE OF RAIN
IN THE FORECAST IT IS LOOKING DRIER OVERALL. IT ALL DEPENDS HOW FAST
THIS FRONT MIGRATES NORTH. THE WARMER AIR MASS WILL PUSH SNOW LEVELS
TO AROUND 7000-8000 FT. EXCEPT WARMER TEMPS WITH HIGHS IN THE 60S TO
LOWER 70S.

THE MODELS STILL HAVE NOT LOCKED ONTO A SOLID SOLUTION REGARDING
THE FORECAST FOR TUESDAY. BOTH THE GFS AND ECMWF SHOW THE UPPER
LEVEL RIDGE SHIFTING FARTHER INLAND TOWARD IDAHO WHILE A TROUGH
DIGS OFFSHORE. THE ECMWF BRINGS THE NEXT FRONT INTO WESTERN WA
TUESDAY MORNING WHILE THE GFS STALLS THIS SYSTEM OFFSHORE...THEN
BRINGS IT INLAND WEDNESDAY MORNING. SO LOW CONFIDENCE CONTINUES IN
THE FORECAST DETAILS OVER THIS PERIOD. THERE IS A CHANCE OF
SHOWERS THOUGH THE REST OF THE FORECAST PERIOD WITH LONG WAVE
TROUGHING OVER THE PAC NW. OVERALL THE FORECAST IS NUDGED TOWARD
CLIMO. 33

&&

.AVIATION...AN UPPER LOW WILL MOVE SLOWLY SOUTHEAST OVER SOUTHERN
VANCOUVER ISLAND TODAY AND THEN OVER NORTHWEST WASHINGTON TONIGHT.
WESTERLY FLOW ALOFT. AIR MASS MOIST AND UNSTABLE...BECOMING A BIT
MORE STABLE TONIGHT.

MULTIPLE CLOUD LAYERS TODAY WITH CEILINGS MOSTLY VFR. 2000-3000 FOOT
CEILINGS POSSIBLE IN SHOWERS AT TIMES. THERE IS ALSO A CHANCE OF
THUNDERSTORMS OVER THE NORTH PART OF THE FORECAST AREA THIS
AFTERNOON AND EARLY EVENING.

KSEA...SOUTHERLY WINDS 6 TO 10 KNOTS WITH GUSTS TO 20 KNOTS
POSSIBLE. WINDS EASING TONIGHT. CEILINGS VARYING BETWEEN 3500 FEET
AND 10000 FEET TODAY...POSSIBLY LOWERING DOWN TO AROUND 2000 FEET
WITH SHOWERS AT TIMES. AN ISOLATED THUNDERSTORM CANNOT BE COMPLETELY
RULED OUT THIS AFTERNOON BUT THE CHANCES ARE TOO LOW TO MENTION IN
THE TAF. SCHNEIDER

&&

.MARINE...A TROUGH WILL MOVE THROUGH THE FORECAST AREA FROM THE
OFFSHORE WATERS TODAY AND TONIGHT. MOST WATERS WILL HAVE SMALL CRAFT
ADVISORY WINDS THROUGH THIS EVENING. 10 TO 12 FOOT WEST SWELLS OVER
THE COASTAL WATERS WILL SUBSIDE BELOW 10 FEET TONIGHT.

SURFACE HIGH PRESSURE WILL BUILD OVER THE WATERS ON SATURDAY FOR
LIGHTER WINDS. A WEAKENING FRONTAL SYSTEM WILL MOVE THROUGH THE AREA
SUNDAY AND SUNDAY NIGHT...BRINGING SMALL CRAFT ADVISORY WINDS TO THE
COASTAL WATERS. ANOTHER FRONT WILL REACH THE AREA AROUND TUESDAY.
SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR ALL WATERS.

     SMALL CRAFT ADVISORY FOR ROUGH BAR IN EFFECT TIL MIDNIGHT
     TONIGHT FOR THE GRAYS HARBOR BAR.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.