National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSEW 101701
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1001 AM PDT MON MAR 10 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM OVER THE AREA WILL MOVE EAST
TODAY. LOOK FOR HIGH PRESSURE ALOFT WILL PREVAIL OVER THE REGION
TONIGHT THROUGH TUESDAY. EXPECT A WEAK LOW PRESSURE SYSTEM TO
MOVE OVER THE AREA ON WEDNESDAY...HOWEVER THIS SYSTEM IS
ANTICIPATED TO HAVE LITTLE IMPACT ON OUR WEATHER.

&&

.SHORT TERM...
THERE WERE SCATTERED SHOWERS OVER THE CWA THIS MORNING. MUCH OF
THIS ACTIVITY WAS OVER THE CASCADES AND WITHIN THE PUGET SOUND
CONVERGENCE ZONE /PSCZ/ OVER THE SOUTH SOUND. EXPECT THE PSCZ TO
DISSIPATE LATE TODAY OR EARLY THIS EVENING.

MEANWHILE...AN UPPER TROF OVER THE AREA WILL MOVE INTO THE
NORTHERN GREAT BASIN THIS AFTERNOON. EXPECT AN UPPER RIDGE TO
BUILD INTO THE AREA FROM THE WEST THIS AFTERNOON. AN UPPER RIDGE
WILL PREVAIL OVER THE PACIFIC NORTHWEST THROUGH WED FOR DRY AND
SUNNIER WEATHER. THE LOW LEVEL FLOW WILL BECOME FLAT TONIGHT...
THUS EXPECT AREAS OF FOG TO DEVELOP OVERNIGHT...ESPECIALLY ON THE
SOUTHWEST INTERIOR.

THE UPPER RIDGE WILL WEAKEN AND MOVE EAST OF THE AREA ON WED. THIS
WILL ALLOW A WEAK UPPER TROF TO MOVE ACROSS THE CWA. THE MAIN
IMPACT THIS FEATURE WILL HAVE ON OUR WEATHER WILL BE TO STRENGTHEN
THE ONSHORE FLOW AND DECREASE THE SUNSHINE.

.LONG TERM FROM THE PREV DISCUSSION...
EXTENDED MODELS IN GOOD AGREEMENT WITH ONE MORE DRY DAY ON
THURSDAY WITH A FLAT UPPER LEVEL RIDGE OVER THE AREA. GFS SOLUTION
WAS MORE IN LINE WITH THE ECMWF SHOWING A SYSTEM MOVING INTO
WESTERN WASHINGTON FRIDAY. THE ECMWF WAS STILL STRONGER THAN THE
GFS WITH THE SYSTEM. GOOD AGREEMENT CONTINUED IN THE MODELS
SATURDAY WITH A TEMPORARY RIDGE BUILDING OVER THE AREA FOLLOWED BY
ANOTHER SHORTWAVE ON SUNDAY. EVEN WITH THE MODELS IN GOOD
AGREEMENT ON THE 00Z RUN...CONFIDENCE STILL NOT HIGH ENOUGH TO
CHANGE THE POPS OUT OF THE CHANCE CATEGORY FOR THE EXTENDED
PERIOD YET. FELTON

&&

.HYDROLOGY...
HYDROLOGICALLY SIGNIFICANT PRECIPITATION IS NOT EXPECTED THE NEXT
7 DAYS. HOWEVER...FLOODING WAS OCCURRING ON THE SNOHOMISH...
GREEN...AND PUYALLUP RIVERS. THE SKOKOMISH...COWLITZ...AND
SNOQUALMIE RIVERS HAVE FALLEN BELOW FLOOD STAGE.

THE PUYALLUP RIVER NEAR ORTING IS EXPECTED TO CREST LATE THIS
MORNING BEFORE FALLING BELOW FLOOD FLOW LATE THIS AFTERNOON.
EXPECT THE GREEN NEAR AUBURN TO FLUCTUATE ABOVE FLOOD FLOW BEFORE
RECEDING LATE TODAY. THE SNOHOMISH AT SNOHOMISH WILL CREST LATE
THIS MORNING. THE REMAINING RIVERS IN THE CWA WILL CONTINUE TO
RECEDE.

THE FLOOD WATCH REMAINS IN EFFECT FOR GRAYS HARBOR COUNTY...
ALTHOUGH IT WAS STARTING TO LOOK LIKE THE CHEHALIS AT PORTER WILL
REMAIN BELOW FLOOD STAGE TODAY.

&&

.AVIATION...AN UPPER LEVEL TROUGH OVER THE COASTAL WATERS WILL PUSH
ACROSS THE CASCADES MIDDAY. SW FLOW ALOFT WILL TURN NWLY BEHIND THE
TROUGH. LOW LEVEL FLOW IS ONSHORE. THE AIR MASS IS MOIST AND
STABLE...AND WILL BECOME MOIST AND SOMEWHAT UNSTABLE THIS AFTERNOON
AND EVENING. RIDGING ALOFT WILL BUILD OFFSHORE TONIGHT TURNING FLOW
ALOFT NORTHERLY AND STABILIZING THE AIR MASS.

SCATTERED SHOWERS CONTINUE ALONG THE COAST AND ALONG THE WEST SLOPES
OF THE CASCADES. IN THE MEAN TIME...A PUGET SOUND CONVERGENCE ZONE
EXTENDS FROM THE KITSAP PENINSULA SE TO JUST SOUTH OF SEATAC
AIRPORT...THEN SOUTHEASTWARD TO AROUND MT RAINIER. ANOTHER WEAK AREA
OF CONVERGENCE EXTENDS FROM EAST OF BELLINGHAM TO AROUND STEVENS
PASS. CONVERGENCE ZONE ACTIVITY WILL CONTINUE THROUGH THIS EVENING
AS LOW AND MID LEVEL FLOW CONTINUES TO SPLIT AROUND THE OLYMPIC
MOUNTAINS AND THE MOUNTAINS OF VANCOUVER ISLAND.

CONDITIONS ARE MVFR THIS MORNING WITH LOCAL IFR CEILINGS AROUND
HEAVIER SHOWERS AND CONVERGENCE ZONE ACTIVITY. CONDITIONS WILL
IMPROVE TO VFR WITH LOCAL MVFR AROUND CONVERGENCE ZONES AND HEAVIER
SHOWERS THIS AFTERNOON AND EVENING AS THE AIR MASS DESTABILIZES
SOMEWHAT.

THE LOWER LEVELS WILL REMAIN QUITE MOIST TONIGHT AS THE AIR MASS
STABILIZES. SOME FOG CAN BE EXPECTED IN FOG PRONE RIVER
VALLEYS...AND PLACES LIKE KOLM AND KAWO LATE TONIGHT INTO EARLY
TUESDAY...BUT IT IS GETTING LATE ENOUGH IN THE YEAR THAT GIVEN THE
FLOW AND INITIALLY SOMEWHAT UNSTABLE AIR MASS THIS EVENING MOST
TERMINALS SHOULD JUST SEE SCT-BKN CLOUDS AROUND 007-012 AROUND THE
DISSIPATING CONVERGENCE ZONES UNTIL 15Z TUE. ALBRECHT

KSEA...THE PUGET SOUND CONVERGENCE ZONE IS SITTING JUST SOUTH OF THE
TERMINAL THIS MORNING. WITH FLOW ALOFT AND IN THE BOUNDARY LAYER
TURNING A BIT MORE NWLY...EXPECT THE CONVERGENCE ZONE TO STAY AROUND
THE SAME LOCATION THROUGH THIS EVENING AND POSSIBLY INTO EARLY
TUESDAY MORNING. IFR CIGS THIS MORNING WILL GENERALLY IMPROVE TO
SCT-BKN015 BKN-OVC040 WITH VIS OCCASIONALLY DOWN TO 3-5SM -SHRA.
THERE IS ABOUT A 50 PERCENT CHANCE THAT CIGS WILL DETERIORATE TO
BKN-OVC007 06Z-15Z TUE AS THE CONVERGENCE ZONE DISSIPATES OVERNIGHT
AND THE AIR MASS STABILIZES. WIND WILL GENERALLY BE LIGHT NORTHERLY
TROUGH THIS EVENING. ALBRECHT

&&

.MARINE...MODERATE ONSHORE FLOW WILL CONTINUE THROUGH THIS EVENING
AS HIGH PRESSURE OFFSHORE GRADUALLY BUILDS INLAND LATE TONIGHT.
SMALL CRAFT ADVISORY CONDITIONS ARE OCCURRING AT THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA AND IN ADMIRALTY INLET AND WILL
CONTINUE UNTIL ABOUT 06Z TONIGHT.

HIGH PRES WILL SETTLE OVER THE AREA EARLY TUE MORNING GIVING LIGHT
WINDS. FLOW WILL TURN WEAKLY OFFSHORE LATER TUE INTO WED AS THE HIGH
SHIFTS EAST OF THE CASCADES.

ANOTHER RIDGE OF HIGH PRES WILL APPROACH THE COAST WED GIVING
ONSHORE FLOW WED AFTERNOON THROUGH THU. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES AND/OR WARNINGS ARE IN EFFECT FOR PARTS OF THE
     CWA.

PZ...SMALL CRAFT ADVISORY IN EFFECT UNTIL 11 PM TONIGHT FOR THE
     ADMIRALTY INLET AND CENTRAL/EASTERN STRAIT OF JUAN DE FUCA.


&&

$$

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML