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 232203
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT THU APR 23 2015

.SYNOPSIS...SHOWERS AND COOL CONDITIONS REMAIN IN THE FORECAST
THROUGH SATURDAY AS AN UPPER LEVEL LOW PASSES. THERE IS A CHANCE OF
THUNDERSTORMS OVER THE NORTH FRIDAY AFTERNOON AND EVENING. A WEAK
UPPER LEVEL RIDGE WILL BRING DRIER WEATHER SATURDAY NIGHT AND SUNDAY
MORNING. A WARM FRONT MAY CLIP THE AREA ON SUNDAY. THE WEATHER WILL
REMAIN UNSETTLED INTO NEXT WEEK.

&&

.SHORT TERM...FRONT IS NOW MOVING THROUGH WESTERN WASHINGTON. THE
OLYMPIC PENINSULA HAS RECEIVED A FEW TO SEVERAL TENTHS OF AN INCH OF
RAIN BUT AROUND PUGET SOUND AMOUNTS HAVE GENERALLY BEEN LESS THAN A
TENTH OF AN INCH. SHOWERS WILL CONTINUE THIS EVENING THEN TAPER LATE
TONIGHT OVER INLAND AREAS. ANOTHER IMPULSE WILL ARRIVE ON THE COAST
LATE TONIGHT THEN SPREAD INLAND. SHOWERS WILL BE ENHANCED SOMEWHAT
FRIDAY AFTERNOON AS THE UPPER LEVEL LOW TO THE NORTH CREEPS CLOSER.
THERE IS INSTABILITY ASSOCIATED WITH THE UPPER LOW SO HAVE PUT A
CHANCE OF THUNDERSTORMS OVER NORTHERN AREAS INTO THE FRIDAY
AFTERNOON AND EVENING FORECAST.

THE UPPER LOW WILL MOVE SLOWLY SOUTHEAST FRIDAY NIGHT AND SATURDAY
AND WILL FINALLY EXIT THE REGION SATURDAY NIGHT. SHOWERS WILL BE
MORE SCATTERED DURING THIS PERIOD WITH CHANCE POPS OVER THE LOWLANDS
AND LIKELY POPS OVER THE MOUNTAINS. HIGHS ON BOTH FRIDAY AND
SATURDAY WILL BE IN THE 50S. THE SNOW LEVEL IN THE MOUNTAINS WILL
FALL AS LOW AS 3000 FEET AS THE UPPER LOW PASSES...AND A FEW INCHES
OF SNOW WILL FALL FROM TIME TO TIME...EVEN IN THE HIGHWAY PASSES.

AN UPPER RIDGE BUILDS OVER THE AREA SATURDAY NIGHT...BUT DISARRAY IN
THE MODELS IS EVIDENT BY SUNDAY AS ANOTHER FRONT APPROACHES THE
AREA. THE GFS BRINGS A LITTLE RAIN ALL THE WAY TO THE CASCADES
SUNDAY AFTERNOON. THE EURO IS A LITTLE SLOWER AND THE NAM HOLDS ANY
PRECIPITATION OFF THE COAST. AS A COMPROMISE HAVE PUT LIKELY POPS ON
THE COAST AND CHANCE POPS OVER THE INTERIOR FOR SUNDAY. IT DOES SEEM
LIKE THERE SHOULD BE AT LEAST SOME CLEARING UNDER THE UPPER RIDGE SO
PERHAPS THERE WILL BE SOME SUN INLAND SUNDAY MORNING. HIGHS WILL BE
IN THE LOW 60S INLAND AND IN THE 50S ON THE COAST. BURKE

.LONG TERM...BOTH THE EURO AND GFS HOLD ON TO SOME PRECIPITATION
MONDAY MORNING BEFORE LIFTING IT NORTH AS AN UPPER RIDGE BUILDS.
BOTH MODELS BRING A WEAK FRONT INLAND TUESDAY...KEEP WEDNESDAY
DRY...AND HAVE ANOTHER FRONT THURSDAY. IT WOULD ALL SEEM VERY
ORDERLY EXCEPT FOR THE FACT THAT DAY TO DAY CONSISTENCY IN THE
MODELS HAS BEEN ABYSMAL. FOR NOW HAVE KEPT CHANCE POPS EACH DAY.
HIGH TEMPERATURES SHOULD BE AT LEAST NORMAL OR SLIGHTLY ABOVE...
MAINLY IN THE 60S. BURKE

&&

.AVIATION...A COLD FRONT OVER WESTERN WASHINGTON WILL MOVE EAST OF
THE CASCADES THIS EVENING...AND AN UPPER LOW WILL MOVE SLOWLY
SOUTHEAST ALONG THE COAST OF BRITISH COLUMBIA TONIGHT AND OVER
SOUTHERN VANCOUVER ISLAND FRIDAY. SOUTHWEST FLOW ALOFT WILL CONTINUE
TONIGHT AND BECOME WESTERLY FRIDAY. THE AIR MASS WILL REMAIN
MOIST...AND IT WILL BECOME UNSTABLE FRIDAY.

FRONTAL PRECIPITATION WAS FALLING OVER MOST OF WESTERN WASHINGTON AT
2 PM WITH A MIX OF VFR AND MVFR CONDITIONS. CONDITIONS WILL
DETERIORATE SOMEWHAT OVER THE NEXT FEW HOURS AS THE FRONT MOVES
FURTHER INLAND AND LOW LEVEL ONSHORE FLOW FOLLOWS IT. WIDESPREAD
MVFR TO LOW-END VFR CONDITIONS ARE LIKELY TONIGHT AND FRIDAY. THERE
IS ALSO A CHANCE OF THUNDERSTORMS OVER THE NORTH PART OF THE
FORECAST AREA FRIDAY AFTERNOON.

KSEA...SOUTHERLY WINDS 6-10 KT WILL STRENGTHEN TO 8-14 KT GUSTING 24
KT LATE THIS AFTERNOON AND EVENING. CEILINGS SHOULD LOWER TO MVFR
THIS EVENING -- PROBABLY 2000 TO 3000 FT -- AND REMAIN THAT WAY MOST
OF THE TIME THROUGH FRIDAY.   MCDONNAL

&&

.MARINE...ONSHORE FLOW WILL DEVELOP THIS EVENING AS THE COLD FRONT
OVER WESTERN WASHINGTON MOVES EAST OF THE CASCADES...THEN EASE LATER
TONIGHT AS HIGH PRESSURE MOVES INLAND. SMALL CRAFT ADVISORY
POST-FRONTAL WINDS ARE LIKELY THIS EVENING FOR MOST MARINE ZONES...
WITH WESTERLY 20 TO 30 KT WINDS IN THE CENTRAL AND EASTERN STRAIT OF
JUAN DE FUCA.

A TROUGH WILL MOVE THROUGH THE FORECAST AREA FROM THE OFFSHORE
WATERS FRIDAY AND FRIDAY NIGHT. MARGINAL SMALL CRAFT ADVISORY WINDS
AND HAZARDOUS SEAS WILL AFFECT THE COASTAL WATERS.

FRONTAL SYSTEMS WILL MOVE THROUGH THE AREA SUNDAY AND SUNDAY NIGHT
AND AGAIN MONDAY NIGHT AND TUESDAY. MODELS SHOW THE SUNDAY SYSTEM
COULD PRODUCE SOUTHERLY GALES OVER THE COASTAL WATERS AT LEAST...BUT
CONFIDENCE IS LOW DUE TO INCONSISTENCY FROM ONE MODEL RUN TO THE
NEXT.   MCDONNAL

&&

.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




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