Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 291608
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SUN MAR 29 2015

.SYNOPSIS...A STALLED FRONTAL BOUNDARY WILL BRING SOME LIGHT RAIN AT
TIMES TO THE COAST AND NORTH INTERIOR THROUGH MONDAY. THE FRONT WILL
PUSH INLAND MONDAY NIGHT BRINGING RAIN TO THE REST OF THE AREA. A
TROUGH OF LOW PRESSURE WILL MOVE INTO THE REGION TUESDAY THROUGH THE
END OF NEXT WEEK. THE UPPER TROUGH WILL GIVE COOL AND SHOWERY
WEATHER TO THE AREA AND SNOW LEVELS WILL FALL TO AROUND 3000 FEET IN
THE MOUNTAINS TUESDAY NIGHT OR WEDNESDAY.

&&

.SHORT TERM...RADAR SHOWS WARM ADVECTION RAIN EXTENDING FROM THE N
WA COAST ACROSS THE N INTERIOR OF WRN WA THIS MORNING. EVERETT
REPORTED SOME OFF AND ON SPRINKLES EARLIER AND IT HAS STAYED DRY TO
THE S. THE GFS/NAM-12 APPEAR TO BE PERFORMING WELL AND KEEP QPF
LIMITED TO THE FAR NRN PART OF WRN WA THROUGH MONDAY. ELSEWHERE...IT
WILL BE PARTLY TO MOSTLY CLOUDY WITH HIGHS ABOVE AVERAGE IN THE LOW
TO MID 60S.

AN UPPER TROUGH WILL DIG SWD TOWARD THE PAC NW MONDAY AFTERNOON AS A
1000 MB SURFACE LOW TRACKS INTO CENTRAL BRITISH COLUMBIA. THE
ASSOCIATED COLD FRONT WILL BRING RAIN TO THE COAST BY THE
EVENING...THEN QUICKLY SPREADING INLAND. MODELS DEPICT A RATHER
VIGOROUS SYSTEM WITH MUCH COOLER AIR BEHIND THE FRONT. SNOW LEVELS
AHEAD OF THE FRONT WILL BE AROUND 6000 TO 7000 FEET...THEN FALLING
TO NEAR 3000 FEET BY LATER MONDAY NIGHT AND TUESDAY. STRONG ONSHORE
FLOW AND AN UNSTABLE AIR MASS WILL KEEP SHOWERS AND BREEZY
CONDITIONS GOING THROUGH TUESDAY AFTERNOON. THERE COULD EVEN BE SOME
ISOLATED THUNDERSTORMS GIVEN THE GFS40 FORECAST  LI`S OF -1 TO -2C.
WILL HOLD OFF MENTIONING THUNDER FOR NOW BUT WILL CONSIDER ADDING A
MENTION IN THE NEXT FORECAST PACKAGE. HIGH TEMPERATURES WILL BE
NOTICEABLY COOLER...ONLY IN THE MID 50S TUESDAY. AS FOR THE
MOUNTAINS...THE WRN SLOPES OF THE CASCADES SHOULD PICK UP SEVERAL
INCHES OF SNOW GIVEN SOME ADDED OROGRAPHIC ENHANCEMENT. BECAUSE OF
THE SHOWERY PATTERN IT MAY BE TOUGH TO GET SOLID ADVISORY LEVEL
AMOUNTS OF SNOW. THE EXCEPTION MIGHT BE THE CASCADES NEAR STEVENS
PASS WHERE A CONVERGENCE ZONE MAY FORM. MESO MODELS ARE SHOWING A
HEAVIER QPF BULLSEYE AROUND THE S SNOHOMISH/N KING COUNTY CASCADES
NEAR STEVENS PASS. SOMETHING TO CONSIDER ONCE WE GET CLOSER TO THE
EVENT. MERCER

.LONG TERM...FROM PREVIOUS DISCUSSION...AN UPPER LEVEL TROUGH WILL
GIVE COOL AND SHOWERY WEATHER TO THE AREA ON WEDNESDAY. THURSDAY MAY
SEE SOME DECREASE IN SHOWER ACTIVITY AND A LITTLE MORE SUNSHINE AS A
SHORT WAVE RIDGE MOVES THROUGH THE REGION.

BOTH THE ECMWF AND GFS MODELS SHOW COOL AND SHOWERY CONDITIONS
FRIDAY THROUGH NEXT WEEKEND WITH SNOW LEVELS 2500 TO 3000 FEET IN
THE MOUNTAINS. ENSEMBLES ARE RATHER CONSISTENT IN SHOWING THE CHANGE
TO THE COOLER WEATHER PATTERN WITH AN UPPER TROUGH OVER WESTERN
WASHINGTON. ALBRECHT

&&

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

&&

.AVIATION...A BROAD FLAT UPPER LEVEL RIDGE OVER THE PACIFIC
NORTHWEST WILL MAINTAIN FAIRLY MOIST WESTERLY FLOW ALOFT OVER W WA
THROUGH MONDAY MORNING. A NEARLY STATIONARY FRONT IS DRAPED ACROSS
SOUTHERN B.C. AND EXTENDS SW FROM VANCOUVER ISLAND ACROSS THE
OFFSHORE WATERS. THE FRONT WILL CONTINUE TO BRING A LITTLE LIGHT
RAIN AT TIMES ACROSS THE FAR N PART OF W WA...FROM KUIL TO KCLM TO
KBLI.

VFR CONDITIONS ARE EXPECTED TO CONTINUE OVER THE INTERIOR WITH CIGS
GENERALLY BKN050-060 WITH HIGHER OVC LAYERS. CIGS WILL PROBABLY BE A
LITTLE LOWER OVER THE N INTERIOR. MVFR CIGS ARE EXPECTED ON THE
COAST WITH POSSIBLE IFR CONDITIONS OVER THE N COAST CLOSER TO THE
STATIONARY FRONT.

A COLD FRONT WILL APPROACH THE AREA MONDAY...CROSSING THE COAST LATE
MONDAY AFTERNOON AND THE INTERIOR MONDAY EVENING.

KSEA...VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH TONIGHT WITH
CLOUD LAYERS GENERALLY SCT-BKN050-060 BKN-OVC080-100. SURFACE WINDS
WILL REMAIN SOUTHERLY 5-10 KT. KAM

&&

.MARINE...A SMALL WEAK SURFACE RIDGE WILL REMAIN OVER WESTERN
WASHINGTON THROUGH MONDAY MORNING. LOWER PRESSURE WILL CONTINUE OVER
BRITISH COLUMBIA AND THE WATERS OFFSHORE WHERE A BAROCLINIC ZONE
EXTENDS SOUTHWESTWARD FROM VANCOUVER ISLAND. THIS PATTERN WILL
RESULT IN MODERATE S FLOW ACROSS THE COASTAL WATERS THROUGH TONIGHT.
S FLOW OVER THE INLAND WATERS IS EXPECTED TO WEAKEN BELOW ADVISORY
CRITERIA THIS AFTERNOON.

AN APPROACHING COLD FRONT WILL INCREASE WINDS OVER THE COASTAL
WATERS ON MONDAY...AND BACK TO ADVISORY LEVELS OVER THE INLAND
WATERS. THE COLD FRONT IS EXPECTED TO CROSS THE COAST LATE MONDAY
AFTERNOON AND THE INLAND WATERS MONDAY EVENING. MODERATE TO STRONG
WESTERLY ONSHORE FLOW WILL DEVELOP OVER W WA MONDAY NIGHT BEHIND THE
COLD FRONT. GALE FORCE WINDS ARE LIKELY IN THE CENTRAL AND E STRAIT
OF JUAN DE FUCA MONDAY NIGHT AND TUESDAY...AND SCA WINDS ARE
EXPECTED OVER THE COASTAL WATERS AND THE WATERS ADJACENT TO THE
STRAIT.

THERE WILL BE A WESTERLY SWELL OF 10 TO 12 FT OVER THE COASTAL
WATERS THROUGH TUESDAY...WITH ROUGH BAR CONDITIONS AS WELL.

ONSHORE FLOW WILL WEAKEN TUESDAY NIGHT AS A WEAK RIDGE TRIES TO
BUILD OVER THE AREA. HOWEVER THE GFS NOW SHOWS AN UPPER LEVEL
SHORTWAVE TROUGH CROSSING THE REGION WEDNESDAY. THIS FEATURE MAY
CAUSE ANOTHER BRIEF PERIOD OF MODERATE ONSHORE FLOW WEDNESDAY NIGHT.
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.
     GALE WATCH FOR MONDAY NIGHT AND TUESDAY CENTRAL STRAIT AND
     EAST ENTRANCE STRAIT.

&&

$$

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.