Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 201024
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PM PDT MON OCT 20 2014

.SYNOPSIS...A SLOW MOVING FRONT WILL SPREAD RAIN ACROSS WESTERN
WASHINGTON THIS MORNING. THE TRAILING UPPER LEVEL TROUGH WILL BRING
SHOWERS TO THE AREA THIS AFTERNOON THROUGH TONIGHT. A STRONGER AND
MUCH WETTER FRONTAL SYSTEM WILL REACH THE AREA TUESDAY
AFTERNOON...WITH PERIODS OF RAIN CONTINUING INTO THURSDAY. UNSETTLED
WEATHER WILL CONTINUE INTO THE WEEKEND AS AN UPPER LEVEL LOW PASSES
OVERHEAD.

&&

.SHORT TERM...A COLD FRONT HAS BEEN SLOWLY SHIFTING EAST THROUGH
WESTERN WA OVERNIGHT AND IS NOW OVER THE INTERIOR. RAIN WILL BE
HEAVY AT TIMES ALONG THE I-5 CORRIDOR DURING THE MORNING COMMUTE.
THIS FRONT WILL MOVE INTO THE CASCADES LATE THIS MORNING WITH STEADY
RAIN COMING TO AN END. HOWEVER THE AIR MASS WILL REMAIN MOIST AND
UNSTABLE THIS AFTERNOON AS AN UPPER LEVEL TROUGH MOVES INLAND. SO
EXPECT MORE SHOWERS ACROSS THE AREA. THERE IS ALSO A CHANCE OF
THUNDERSTORMS ALONG THE COAST AND OVER THE COASTAL WATERS. SHOWERS
WILL TAPER DOWN THIS EVENING AS THE UPPER TROUGH MOVES FARTHER
INLAND AND WEAKENS.

WE WILL SEE A BRIEF BREAK IN THE WEATHER ON TUE ALTHOUGH THERE IS
STILL A CHANCE OF LIGHT SHOWERS...MAINLY COAST AND MOUNTAINS.

EXPECT A WET PERIOD OF WEATHER TUE NIGHT THROUGH WED AS AN UPPER LOW
OVER THE GULF OF AK STEERS A PLUME OF MOISTURE THROUGH WESTERN WA.
THE COAST MAY SEE 1-3 INCHES OF RAIN WITH UP TO 5 INCHES POSSIBLE IN
THE OLYMPIC MOUNTAINS. RAINFALL TOTALS ARE GENERALLY 1-2 INCHES IN
THE INTERIOR AND 1-3 INCHES IN THE CASCADES. THE SNOW LEVEL IS
AROUND 6000-7000 FT. MODELS SHOW THE HEAVY PRECIP COMING IN BATCHES
SO WE MAY SEE A FEW BREAKS IN BETWEEN...ALTHOUGH THAT IS RATHER
TOUGH TO PIN DOWN EXACTLY. THE COAST AND NORTH INTERIOR WILL ALSO
SEE GUSTY SOUTH WINDS AT TIMES...ESPECIALLY TUE NIGHT. THE UPPER
LEVEL LOW WILL SAG SOUTH WED NIGHT WHICH WILL SHIFT THE FOCUS FOR
HEAVY PRECIP SOUTH INTO OREGON.

MOIST SOUTHWEST FLOW WILL CONTINUE ON THUR BUT WE ARE MAINLY LOOKING
AT SHOWERS ACROSS THE REGION...STEADY HEAVY PRECIP NOT EXPECTED. 33

.LONG TERM...MODELS ARE NOW SHOWING MORE SHOWERS FRIDAY THROUGH THE
WEEKEND AS AN UPPER LEVEL LOW CROSSES WESTERN WA. TEMPS WILL LIKELY
REMAIN AT OR BELOW NORMAL THROUGHOUT. BOTH THE GFS AND ECMWF TRY TO
BUILD A RIDGE OVER THE PAC NW EARLY NEXT WEEK FOR A BRIEF PERIOD OF
DRY WEATHER...MAYBE SUN NIGHT OR MON. THEN ANOTHER WET PAC SYSTEM
WILL DRAG THROUGH THE REGION MON NIGHT OR TUE. 33

&&

.HYDROLOGY...FORECAST MODELS SHOW THAT HEAVY RAIN TUESDAY NIGHT
THROUGH WEDNESDAY IS PROBABLY ENOUGH TO BRING THE SKOKOMISH RIVER TO
FLOOD STAGE. MODELS ARE SHOWING UP TO 5 INCHES OF RAIN IN THE
OLYMPICS OVER THIS PERIOD. THE MODELS CONFINE FLOOD-PRODUCING
RAINFALL TO THE OLYMPIC PENINSULA AND PROBABLY JUST TO THE SKOKOMISH
RIVER BASIN. ANY FLOODING ON THE SKOKOMISH RIVER WOULD PROBABLY
OCCUR WEDNESDAY NIGHT OR THURSDAY.

&&

.AVIATION...A TROUGH WILL SHIFT ACROSS THE PAC NW THROUGH TONIGHT.
LIGHT TO MODERATE SW FLOW ALOFT. MOIST AND WEAKLY UNSTABLE. RAIN
CHANGING TO SHOWERS TODAY WITH ISOLATED THUNDERSTORMS POSSIBLE NEAR
THE COAST AND SW INTERIOR.

KSEA...RAIN AT TIMES...BECOMING SHOWERS DURING THE MORNING. SE WIND
4-6 KT...BECOMING S-SW 5-10 KT AFTER 18Z.

&&

.MARINE...A FRONT WILL DISSIPATE OVER THE INLAND WATERS EARLY THIS
MORNING. ANOTHER WEAK SURFACE TROUGH OFFSHORE WILL PRODUCE LOW-END
SMALL CRAFT WINDS OVER THE COASTAL WATERS TODAY BEFORE EASING. W-SW
SWELL OF 10 TO 14 FEET WILL CONTINUE THROUGH TONIGHT. THE SMALL
CRAFT FOR HAZARDOUS SEAS CONTINUES FOR THE WEST ENTRANCE TO THE
STRAIT AND WILL LIKELY BE NEEDED FOR THE COASTAL WATERS TONIGHT.
WINDS OVER THE INTERIOR HAVE EASED AND SHOULD REMAIN BELOW 20 KT
THROUGH TONIGHT.

A SURFACE LOW IS EXPECTED TO APPROACH OFFSHORE TUESDAY...AND MOVE NE
INTO VANCOUVER ISLAND TUESDAY NIGHT. THIS SYSTEM WILL LIKELY PRODUCE
GALES OVER THE COASTAL WATERS AND INLAND WATERS N OF ADMIRALTY
INLET. A GALE WATCH IS IN EFFECT LATE TUESDAY AND TUESDAY NIGHT. YET
ANOTHER SURFACE LOW WILL TRACK NEAR OR THROUGH THE WATERS AROUND
FRIDAY. THE STRENGTH AND TRACK OF THIS SYSTEM REMAINS HIGHLY
UNCERTAIN.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COAST TODAY.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR THROUGH
     TONIGHT.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS WEST ENTRANCE TO THE
     STRAIT OF JUAN DE FUCA THROUGH TONIGHT.
     GALE WATCH FOR THE COAST...EAST ENTRANCE TO THE STRAIT OF JUAN
     DE FUCA...AND THE NORTHERN INLET WATERS TUESDAY NIGHT.


&&

$$

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