Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241041
AFDSEW

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

.SYNOPSIS...AN UPPER LEVEL LOW WILL KEEP THE WEATHER COOL AND
SHOWERY AS IT MOVES SLOWLY ACROSS THE REGION THROUGH SATURDAY. A
WEAK UPPER LEVEL RIDGE WILL BRING DRIER WEATHER SATURDAY NIGHT AND
SUNDAY MORNING. A WARM FRONT MAY BRING A LITTLE LIGHT RAIN TO THE
AREA SUNDAY AFTERNOON THROUGH MONDAY. A WEAK COLD FRONT MAY CROSS
THE AREA ON TUESDAY.

&&

.SHORT TERM...EXPECT OFF-AND-ON SHOWERS ACROSS WESTERN WASHINGTON
TODAY AS AN UPPER LEVEL LOW SPINS OVERHEAD. THE AIR MASS IS COOL AND
UNSTABLE AND A FEW THUNDERSTORMS MAY ALSO DEVELOP THIS AFTERNOON.
SNOW LEVELS REMAIN LOW NEAR 3000 FT WITH A FEW INCHES OF SNOW
EXPECTED IN THE MOUNTAINS. TEMPS ARE BELOW NORMAL TODAY WITH HIGHS
MAINLY IN THE 50S. SHOWERS AND A CHANCE OF THUNDERSTORMS WILL
CONTINUE THROUGH THIS EVENING...THEN DIMINISH BY MIDNIGHT 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 SUNBREAKS 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 SHOW LITTLE PRECIP
IN THE INTERIOR...A FEW HUNDREDTHS POSSIBLE. SKIES WILL REMAIN
CLOUDY BUT TEMPS WILL MODERATE WITH HIGHS NEAR 60 IN THE INTERIOR.

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. 33

.LONG TERM...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. WESTERLY FLOW ALOFT BECOMING MORE
SOUTHWESTERLY TONIGHT. ORGANIZED BAND OF SHOWERS SPINNING OUT OF THE
LOW MOVING THROUGH THE INTERIOR IN THE NEXT COUPLE OF HOURS. MORE
SHOWERS ROTATING AROUND THE LOW MOVING THROUGH THE AREA THROUGH
TONIGHT. AIR MASS WILL REMAIN MOIST AND UNSTABLE.

MULTIPLE CLOUD LAYERS OVER WESTERN WASHINGTON THIS MORNING. IN
GENERAL MULTIPLE CLOUD LAYERS BETWEEN 2000 AND 7000 FEET WITH THE
2000 FOOT LAYER MOSTLY SCATTERED EXCEPT DURING SHOWER ACTIVITY.
CEILINGS FOR THE MOST PART OUTSIDE OF THE SHOWERS WILL REMAIN IN THE
LOW END OF VFR. THERE IS ALSO A CHANCE OF THUNDERSTORMS OVER THE
NORTH PART OF THE FORECAST AREA THIS AFTERNOON.

KSEA...SOUTHERLY WINDS 6 TO 10 KNOTS WITH GUSTS TO 20 KNOTS WITH THE
SHOWERS. CEILINGS NEAR 3500 FEET LOWERING DOWN TO AROUND 2000 FEET
WITH SHOWERS. FELTON

&&

.MARINE...SURFACE LOW NEAR VANCOUVER ISLAND WITH SOUTHERLY SURFACE
GRADIENTS ACROSS THE WATERS THIS MORNING. THE LOW WILL WEAKEN THIS
AFTERNOON WITH THE GRADIENTS BECOMING MORE SOUTHWESTERLY. SMALL
CRAFT ADVISORY WINDS ALONG THE COAST AND OVER THE INLAND WATERS
TODAY. WINDS WILL EASE TONIGHT OVER MOST OF THE WATERS. THE
EXCEPTION WILL BE THE STRAIT WITH A PUSH OF WESTERLIES GIVING SMALL
CRAFT ADVISORY WINDS TO THE CENTRAL AND EASTERN STRAIT.

WEAK HIGH PRESSURE BUILDING OVER THE WATERS ON SATURDAY WITH THE
WINDS BELOW 20 KNOTS. NEXT FRONT CURRENTLY TIMED INTO THE AREA LATER
SUNDAY INTO SUNDAY NIGHT FOR ANOTHER ROUND OF SMALL CRAFT ADVISORY
WINDS. AFTER A BREAK ON MONDAY A WEAKER FRONT WILL ARRIVE ON
TUESDAY. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL MARINE ZONES.

&&

$$

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






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