Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 190548 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED DATE
NATIONAL WEATHER SERVICE SEATTLE WA
858 PM PDT SAT OCT 18 2014

.SYNOPSIS...AN UPPER RIDGE WILL GIVE DRY AND WARMER WEATHER SUNDAY
OVER THE INTERIOR WHILE THE NEXT FRONT APPROACHES THE COAST. THE
FRONT WILL BRING RAIN TO THE COAST LATE SUNDAY...AND TO THE INTERIOR
SUNDAY NIGHT AND MONDAY. THE ASSOCIATED UPPER LEVEL TROUGH WILL
FOLLOW MONDAY NIGHT...THEN ANOTHER FRONT WILL REACH THE AREA
TUESDAY. MOIST SOUTHWEST FLOW ALOFT WILL CONTINUE THE REST OF NEXT
WEEK.

&&

.SHORT TERM...RADAR IS STILL SHOWING SOME REALLY SPOTTY RAIN ALONG
THE COAST THIS EVENING BUT IT SHOULD DIE OUT BEFORE MIDNIGHT.

A LOW AMPLITUDE UPPER LEVEL RIDGE BUILT OVER THE PACNW TODAY WITH A
RIDGE AT THE SURFACE. MODELS REMAIN ON TRACK SHIFTING THE UPPER
LEVEL AND SURFACE RIDGE AXES OVER THE ID PANHANDLE LATE
TONIGHT...THEREBY INCREASING THE LOW LEVEL OFFSHORE FLOW OVER W WA.
THIS WILL DRY OUT THE W WA INTERIOR A BIT MORE ON SUNDAY AND BOOST
MAX TEMPS TO THE 65-70 RANGE. NAM AND GFS ARE NOW SHOWING A LAYER OF
MID LEVEL MOISTURE FROM 850MB-700MB MOVING N OVER PUGET SOUND FOR
MUCH OF SUNDAY...SO IT MAY CUT BACK A BIT MORE ON SUNSHINE.

THE NEXT FRONTAL SYSTEM OFFSHORE WAS APPROACHING 130W THIS EVENING.
A WAVE PROPAGATING UP THE FRONT IS CAUSING IT TO SLOW A BIT AND
STRENGTHEN BUT IT SHOULD REMAIN ON SCHEDULE FOR ITS ARRIVAL OVER W
WA. RAIN IS STILL EXPECTED REACH THE N COAST SUNDAY MORNING THEN
SPREAD ACROSS THE REMAINDER OF THE COAST IN THE AFTERNOON. THE FRONT
WILL DRAG ACROSS THE INTERIOR SUNDAY NIGHT AND MONDAY WITH RAIN
EXPECTED EVERYWHERE. TOTAL PRECIP ON THE COAST WILL BE 1.00-1.80
INCHES WITH 0.20-0.50 OVER THE INTERIOR. PRESSURE GRADIENTS WILL
TIGHTEN ENOUGH AS THE FRONT APPROACHES THE COAST TO PRODUCE BREEZY
S-SE WINDS ALONG THE COAST AND OVER THE PARTS OF THE N INTERIOR
PRONE TO STRONGER S-SE WINDS.

THE ASSOCIATED UPPER LEVEL TROUGH WILL REACH THE COAST MONDAY NIGHT.
IR SATELLITE IMAGERY SHOWS A CONVECTIVE AIR MASS OFFSHORE WITH THE
UPPER TROUGH SO SHOWERS LOOK GOOD MONDAY NIGHT.

ALL MODELS NOW SHOW A SKINNY WEAKENING FRONT REACHING THE COAST ON
TUESDAY. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 3 PM AFD...MODELS BRING
THE NEXT SYSTEM TO THE COAST TUESDAY AFTERNOON AND INLAND TUESDAY
NIGHT. AS BEFORE THE GFS IS MORE PROGRESSIVE...BRINGING ANOTHER
SYSTEM WEDNESDAY AND ANOTHER THURSDAY WITH...CRUCIALLY...LULLS IN
THE RAINFALL BETWEEN SYSTEMS. THE EURO PATTERN IS MORE OF AN
ATMOSPHERIC RIVER TUESDAY NIGHT THROUGH THURSDAY NIGHT. BOTH MODELS
TURN MORE SHOWERY FRIDAY WITH PERHAPS A DRY SATURDAY. THE CANADIAN
MODEL IS SIMILAR TO THE GFS. THE QPF GRIDS ARE BASICALLY THE
WRF-GFS-EXTENDED WHICH HAS SOME LULLS BUT ALSO HAS A PARTICULARLY
WET PERIOD OVER THE OLYMPICS FROM TUESDAY AFTERNOON THROUGH
WEDNESDAY. THERE IS A BROAD AREA OF 4-5 INCHES OF RAINFALL OVER THE
OLYMPICS DURING THIS PERIOD. TEMPERATURES ARE REMARKABLY STEADY OVER
THE NEXT WEEK OR SO WITH HIGHS NEAR 60 AND LOWS NEAR 50. BURKE

&&

.HYDROLOGY...PREVIOUS DISCUSSION FROM 3 PM...THE SYSTEM SUNDAY NIGHT
AND MONDAY IS WET BUT DOES NOT HAVE ENOUGH RAIN TO CAUSE FLOODING.
THE SYSTEM LAST NIGHT BROUGHT AN INCH PLUS TO THE OLYMPICS...AND THE
NEXT ONE WILL BRING PERHAPS ANOTHER 2 INCHES. THESE WILL SERVE TO
PRIME THE PUMP...SO TO SPEAK. PREVIOUSLY DRY AREAS WILL BECOME WET
AND NEARLY EMPTY RIVERS ON THE OLYMPIC PENINSULA WILL RISE TO WET
SEASON LEVELS.

THE GFS AND WRF VERSION OF THE HEAVY RAIN BEGINNING TUESDAY NIGHT IS
PROBABLY ENOUGH TO BRING THE SKOKOMISH RIVER TO FLOOD STAGE. IF THE
OUTLIER EURO SOLUTION IS CORRECT THEN SOME MORE RIVERS ON THE
OLYMPIC PENINSULA SHOULD RISE SIGNIFICANTLY...PERHAPS TO FLOOD
STAGE. MODELS DO CONFINE FLOOD-PRODUCING RAINFALL TO THE OLYMPIC
PENINSULA. ANY FLOODING ON THE SKOKOMISH RIVER WOULD PROBABLY OCCUR
WEDNESDAY NIGHT OR THURSDAY. BURKE

&&

.AVIATION...UPPER LEVEL HIGH PRESSURE OVER THE INTERIOR PAC NW
TONIGHT WILL SHIFT EWD OVER THE ROCKIES/GREAT BASIN ON SUNDAY. A
TROUGH WILL BRING A FRONT ONTO THE COAST SUNDAY AFTERNOON AND
THROUGH THE INTERIOR EARLY IN THE EVENING. STRONG S-SW FLOW ALOFT.
AIR MASS STABLE WITH MID AND HIGH LEVEL MOISTURE OVER THE AREA.
THE COAST...SW INTERIOR...AND STRAIT OF JUAN DE FUCA CAN EXPECT LOW
LEVEL MOISTURE AND MVFR OR IFR STRATUS AFTER MIDNIGHT AND INTO EARLY
SUNDAY MORNING.

KSEA...CIGS MAINLY ABOVE 7K FT TONIGHT. THERE IS ONLY A SLIGHT
CHANCE THAT PATCHY MVFR STRATUS COULD DEVELOP AROUND THE TERMINAL.
WILL NOT INCLUDE IN TAF GIVE THE AMOUNT OF UNCERTAINTY. ELY WIND 4-8
KT BECOMING SLY TO 10 KT AFTER MIDDAY SUNDAY. DTM

&&

.MARINE...A FRONT WILL ENTER THE COASTAL WATERS SUNDAY AFTERNOON
AND PUSH THROUGH THE INTERIOR WATERS EARLY IN THE EVENING. GALES ARE
EXPECTED AHEAD OF THE FRONT IN THE COASTAL WATERS AND THE W ENTRANCE
TO THE STRAIT OF JUAN DE FUCA SUNDAY MORNING...THEN EASING LATE IN
THE DAY. SMALL CRAFT WINDS ARE LIKELY ALONG THE FRONT OVER THE
CENTRAL AND ERN STRAIT AND NRN INLAND WATERS. WINDS WILL EASE BELOW
20 KT THROUGHOUT AFTER MIDNIGHT SUNDAY NIGHT.

A SECOND VIGOROUS FRONT WILL MOVE THROUGH THE WATERS TUESDAY
FOLLOWED BY A THIRD SYSTEM ON WEDNESDAY. EACH OF THESE SYSTEMS WILL
BRING AT LEAST SMALL CRAFT ADVISORY WINDS TO MOST OF THE WATERS.
GALES ARE LIKELY FOR THE COASTAL WATERS AS EACH FRONT MOVES THROUGH.
SCHNEIDER/DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING COASTAL WATERS AND WEST ENTRANCE STRAIT OF
     JUAN DE FUCA.
    .SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT AND NORTHERN
     INLAND WATERS.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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