Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 251156
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST TUE NOV 25 2014

.SYNOPSIS...A WARM FRONT WILL BRING RAINY BREEZY WEATHER TO WESTERN
WASHINGTON TODAY AND TONIGHT...WITH HEAVY RAIN IN THE MOUNTAINS.
AFTER A RELATIVE LULL WEDNESDAY...ANOTHER FRONTAL SYSTEM WILL BRING
MORE RAINY WINDY WEATHER WEDNESDAY NIGHT AND THANKSGIVING. RAIN WILL
DECREASE FRIDAY AS THE COLD FRONT MOVES SOUTHEAST...AND COLDER DRIER
WEATHER IS EXPECTED FOR THE WEEKEND.

&&

.SHORT TERM...MOIST WEST-NORTHWEST FLOW CONTINUES ALOFT OVER WESTERN
WASHINGTON...JUST DOWNSTREAM OF THE FLAT UPPER RIDGE CENTERED
OFFSHORE ALONG 130W. THE WARM FRONT MOVING INTO THE AREA OVERNIGHT
RENEWED WIDESPREAD RAINFALL...AND TEMPERATURES ROSE SLIGHTLY INTO
THE UPPER 40S TO LOWER 50S.

A BAROCLINIC BAND CARRYING SUB-TROPICAL MOISTURE OVER THE NORTH SIDE
OF THE OFFSHORE RIDGE WILL CONTINUE TO BRING RAIN TO WESTERN
WASHINGTON TODAY. THE MODELS HAVE COME INTO FAIRLY STRONG AGREEMENT
THAT THE BAND WILL BEGIN LIFTING NORTHWARD TONIGHT AND WEDNESDAY...
AS THE RIDGE OFFSHORE AMPLIFIES AHEAD OF ANOTHER APPROACHING FRONTAL
SYSTEM.

THE WESTERN WASHINGTON LOWLANDS WILL RECEIVE FAIRLY SIGNIFICANT
RAINFALL THIS MORNING -- UP TO 0.75 INCH IN PLACES. FROM THE PUGET
SOUND AREA SOUTHWARD...THE RAIN SHOULD GENERALLY LET UP DURING THE
DAY. RAINFALL AMOUNTS OVER THE LOWLANDS WILL BE LESS TONIGHT AND
LESS YET ON WEDNESDAY...WITH THE PUGET SOUND REGION LARGELY IN THE
RAIN SHADOW OF THE OLYMPICS MUCH OF THE TIME. IT WILL ALSO BE BREEZY
AT TIMES OVER THE LOWLANDS TONIGHT AND WEDNESDAY.

THIS PATTERN FAVORS HEAVY RAIN IN THE CASCADES...AS WE HAVE BEEN
ADVERTISING FOR SEVERAL DAYS. IT WILL BE FOCUSED ON THE WASHINGTON
CASCADES FROM ABOUT SNOQUALMIE PASS SOUTHWARD THIS MORNING...THEN
GRADUALLY SHIFT NORTHWARD THIS AFTERNOON AND TONIGHT. PRECIPITATION
IN THE MOUNTAINS WILL DECREASE ON WEDNESDAY. THE SNOW LEVEL WILL BE
6500 TO 7500 FT. STORM TOTAL RAINFALL OF 2.5 TO 5 INCHES SEEMS
REASONABLE FOR THE NEXT 36 HOURS...HOWEVER THE 00Z TUE MODEL RUNS
DID BACK OFF ON PRECIPITATION AMOUNTS.

AFTER THE BRIEF LULL ON WEDNESDAY...A RATHER VIGOROUS COLD FRONT
WILL MOVE THROUGH THE PACIFIC NORTHWEST WEDNESDAY NIGHT AND
THANKSGIVING...FOLLOWED QUICKLY BY ANOTHER FRONT DIGGING ACROSS THE
AREA FROM THE NORTHWEST THURSDAY NIGHT. THIS WILL BE ANOTHER RAINY
AND WINDY PERIOD. PRECIPITATION AMOUNTS IN THE OLYMPICS AND NORTH
CASCADES COULD BE IN THE 3 TO 5 INCH RANGE...WITH THE SNOW LEVEL
MAINLY IN THE 5500 TO 7000 FT RANGE.   MCDONNAL

.LONG TERM...PRECIPITATION OVER WESTERN WASHINGTON SHOULD DECREASE
ON FRIDAY...IN THE WAKE OF THE FRONT THAT DIGS THROUGH THE AREA
THURSDAY NIGHT. MODELS HAVE COME INTO FAIRLY STRONG AGREEMENT THAT
AN UPPER TROUGH WILL DIG INTO THE AREA FROM THE NORTHWEST FRIDAY
NIGHT AND SATURDAY...WHILE SURFACE HIGH PRESSURE OVER SOUTHERN
BRITISH COLUMBIA PRODUCES NORTHEAST PRESSURE GRADIENTS. THE WEEKEND
WILL BE QUITE COOL WITH LOWS IN THE MID 20S TO LOWER 30S AND HIGHS
IN THE MID 30S TO MID 40S. THE DAYS SHOULD BE AT LEAST PARTLY SUNNY.
WE WILL KEEP A LOW-END CHANCE OF A SHOWER IN THE FORECAST FOR
NOW...BUT ANY PRECIPITATION WOULD BE VERY LIGHT. IT LOOKS LIKE THE
COOL DRY SPELL WILL BE SHORT LIVED...WITH ANOTHER FRONTAL SYSTEM
LIFTING INTO WESTERN WASHINGTON FROM THE SOUTHWEST SUNDAY NIGHT OR
MONDAY.   MCDONNAL

&&

.HYDROLOGY...AS MENTIONED ABOVE 2.5 TO 5 INCHES OF PRECIPITATION IS
LIKELY ALONG THE WEST SLOPES OF THE CASCADES TODAY THROUGH
WEDNESDAY...WITH THE MAJORITY OF THAT FALLING TODAY AND TONIGHT.
MODELS AGREE WELL THAT THE FOCUS OF HEAVY RAIN WILL BE OVER THE
WASHINGTON CASCADES FROM AROUND SNOQUALMIE PASS SOUTHWARD THIS
MORNING...THEN GRADUALLY SHIFT NORTHWARD THIS AFTERNOON AND
TONIGHT...AND THEN DECREASE ON WEDNESDAY. THE SNOW LEVEL WILL BE IN
THE 6500 TO 7500 FT RANGE.

THE PRECIPITATION AMOUNTS EXPECTED ARE HEAVY BUT NOT EXTREME...AND
IT IS ALSO WORTH NOTING THAT THE 00Z TUE MODEL RUNS BACKED OFF
SLIGHTLY ON PRECIPITATION AMOUNTS. SO WE ARE STILL LOOKING AT A
THREAT OF GENERALLY MINOR FLOODING ON THE MOST FLOOD-PRONE OF THE
RIVERS THAT FLOW OFF THE WEST SLOPES OF THE CASCADES. A FLOOD WATCH
IS IN EFFECT FOR THIS...WHICH WILL BE UPDATED EARLY THIS MORNING.
THAT INCLUDES THE COWLITZ...PUYALLUP NEAR ORTING...SNOQUALMIE...
TOLT...SKYKOMISH...SNOHOMISH...STILLAGUAMISH...AND NOOKSACK RIVERS.

THERE WILL BE A LULL IN RAINFALL ON WEDNESDAY...BUT WE MIGHT NOT BE
OUT OF THE WOODS YET. AS DISCUSSED ABOVE...ANOTHER VIGOROUS FRONTAL
SYSTEM WILL MOVE THROUGH THE AREA WEDNESDAY NIGHT THROUGH THURSDAY
NIGHT...BRINGING PRECIPITATION AMOUNTS OF 3 TO 5 INCHES TO THE
OLYMPICS AND NORTH CASCADES. THE SNOW LEVEL FOR THAT EVENT WILL BE
IN THE 5500 TO 7000 FT RANGE.   MCDONNAL

&&

.AVIATION...MODERATE WEST TO NORTHWEST FLOW ALOFT. A STATIONARY
FRONT OVER THE AREA WILL GIVE LOW MVFR TO IFR CEILINGS AND
VISIBILITIES IN RAIN TO MOST TERMINALS. THE FRONT WILL START TO LIFT
NORTHWARD AS A WARM FRONT LATE THIS AFTERNOON AND WILL REACH THE
CANADIAN BORDER AROUND MIDNIGHT TONIGHT.

MODERATE LOW LEVEL SOUTHWEST FLOW JUST TO THE SOUTH OF THE AREA
EARLY THIS MORNING WILL SPREAD NORTHWARD BEHIND THE WARM FRONT THIS
AFTERNOON INTO TONIGHT. A SLIGHT IMPROVEMENT TO VISIBILITIES AND
CEILINGS CAN BE EXPECTED BEHIND THE WARM FRONT. ALBRECHT

KSEA...CIGS AROUND 005 WITH VIS 3-5SM IN -RA BR. THE WARM FRONT WILL
LIFT NORTH ACROSS THE TERMINAL ABOUT 00Z THIS AFTERNOON WITH VIS
RISING TO P6SM AND CIGS RISING TO 008-012. S WIND 8-12 KT WILL
BECOME LIGHT AFTER 14Z...THEN WILL BECOME 20010-14KT BEHIND THE WARM
FRONT ABOUT 00Z. W WIND 35-40 KT AT FL030 THROUGH THIS EVENING.
ALBRECHT

&&

.MARINE...A NEARLY STATIONARY FRONT EXTENDS FROM THE CENTRAL PUGET
SOUND WESTWARD TO 140W. THE FRONT WILL REMAIN STATIONARY THROUGH
MIDDAY TODAY THEN WILL LIFT NORTH TO THE CANADIAN BORDER ABOUT
MIDNIGHT TONIGHT. EXPECT LIGHT WINDS TO THE N OF THE FRONT TODAY
WITH SMALL CRAFT ADVISORY S TO SW WINDS SPREADING NORTHWARD BEHIND
THE WARM FRONT THIS AFTERNOON AND EVENING. SMALL CRAFT ADVISORY
CONDITIONS WILL COME TO AN END OVER THE NORTHERN WATERS ABOUT 4 AM
EARLY THIS MORNING...THEN WILL PICK UP AGAIN LATE THIS AFTERNOON AND
TONIGHT AS THE WARM FRONT LIFTS NORTHWARD.

WINDY CONDITIONS ARE GENERALLY EXPECTED TO CONTINUE FOR THE NEXT
SEVERAL DAYS. A COLD FRONT WILL SWEEP EASTWARD THROUGH THE WATERS
WEDNESDAY NIGHT. MOST WATERS WILL SEE 20-30 KT SWLY WINDS AHEAD OF
THE FRONT...BUT THE COASTAL WATERS AND PORTIONS OF THE NORTHERN
INLAND WATERS MAY SEE GALE FORCE WINDS.

ANOTHER COLD FRONT WILL DROP SOUTHWARD THROUGH THE WATERS ON FRIDAY.
THIS FRONT WILL BE FOLLOWED BY STRONG FRASER OUTFLOW IN THE NORTHERN
INLAND WATERS AND STRONG N TO NELY WINDS OVER THE OTHER WATERS.
LATER FRI INTO SAT. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH IN EFFECT FOR PORTIONS OF THE AREA.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND WEST ENTRANCE TO THE
       STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA
      AND PUGET SOUND AND HOOD CANAL UNTIL 4 AM EARLY THIS MORNING.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML





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