River Flood Warning 34, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
940 AM PDT SAT OCT 31 2015

.SYNOPSIS...A FRONTAL SYSTEM WILL MOVE SOUTHEAST ACROSS THE AREA
THIS AFTERNOON THROUGH THIS EVENING BRINGING LOCALLY HEAVY RAIN AND
WINDY CONDITIONS. SHOWERS AND A CHANCE OF THUNDERSTORMS CAN BE
EXPECTED TONIGHT AS A STRONG TROUGH OF LOW PRESSURE MOVES ACROSS THE
AREA. WINDY CONDITIONS WITH SHOWERS AND A CHANCE OF THUNDERSTORMS
WILL ACCOMPANY AN UPPER LEVEL TROUGH AS IT MOVES ACROSS THE AREA ON
SUNDAY. LOCALLY HEAVY SNOW IS POSSIBLE ABOVE ABOUT 4500 FEET IN THE
MOUNTAINS. SHOWERS WILL DECREASE MONDAY AND TUESDAY...AND DRY
WEATHER IS LIKELY WEDNESDAY AND THURSDAY.

&&

.SHORT TERM...THE FRONTAL SYSTEM THAT IS RESPONSIBLE FOR BRINGING
WINDY CONDITIONS AND LOCALLY HEAVY RAINFALL TO THE AREA THIS MORNING
SITS FROM ABOUT WESTERN WHATCOM COUNTY SOUTHWEST TO THE NORTH
WASHINGTON COAST AND INTO THE PACIFIC. THE CAPE ELIZABETH BUOY HAS
REPORTED A WIND SHIFT TO THE NORTHWEST OVER THE PAST HOUR...SO THE
FRONT IS STARTING TO SHOW SIGNS OF DRIFTING SLOWLY SOUTHEAST. SHORT
TERM MODELS ARE ON TRACK IN TAKING THE FRONT SOUTH OF THE FORECAST
AREA EARLY THIS EVENING. HEAVY RAINFALL WILL CONTINUE AHEAD OF AND
WITH THE FRONT. SEE THE HYDROLOGY SECTION BELOW FOR A DISCUSSION ON
THE IMPACT ON AREA RIVERS. WINDS WILL WAIT UNTIL THE FRONT PASSES TO
THE SOUTH OF AN INDIVIDUAL POINT TO SUBSIDE...SO THE WIND ADVISORY
FOR THE CENTRAL COAST AND FOR THE INTERIOR LOWLANDS FROM EVERETT
SOUTHWARD THROUGH THE SOUTHWEST INTERIOR WAS EXTENDED UNTIL 3 PM PDT
THIS AFTERNOON.

FOR TONIGHT...A POCKET OF COLD AIR ALOFT AND WHAT APPEARS TO BE A
DEVELOPING INSTANT OCCLUSION IS SEEN EXTENDING SOUTH FROM A 980 LOW
W OF HAIDA GWAII TO 45N 135W THEN SOUTHWESTWARD. THIS WILL MOVE INTO
THE COASTAL WATERS THIS EVENING AND INTO THE INTERIOR LATE TONIGHT.
THE AIR MASS WILL BECOME UNSTABLE ENOUGH TO SUPPORT A CHANCE OF
TSTMS OVER THE COASTAL WATERS THIS EVENING AND LATE TONIGHT IN THE
INTERIOR. IT WILL LIKELY BE WINDY OVERNIGHT ALONG THE COAST AND IN
PORTIONS OF THE INTERIOR AS THIS TROUGH OR OCCLUSION MOVES THROUGH
THE AREA. SEE THE MARINE SECTION BELOW THAT ADDRESSES LARGE WAVES
THAT HAVE DEVELOPED WITH THIS SYSTEM OFFSHORE THAT WILL PUSH ONTO
THE WASHINGTON COAST LATE TONIGHT INTO SUNDAY EVENING.

FOR SUNDAY...THE LOW OFF HAIDA GWAII IS FORECAST BY THE LATEST GFS20
TO SHIFT SE ALONG THE COAST OF VANCOUVER ISLAND THEN MOVE EAST AS A
1000 MB LOW CENTER ALONG THE CANADIAN BORDER LATE IN THE AFTERNOON.
THE AIR MASS WILL BE COOL ALOFT...SO A CHANCE OF TSTMS WILL CONTINUE
THROUGH THE DAY. IT WILL BE QUITE WINDY ON THE COAST AND IN THE N/S
ORIENTED VALLEYS OF THE INTERIOR THROUGH THE DAY. WILL ADDRESS THE
POTENTIAL OF EXTENDING/EXPANDING WIND ADVISORIES FOR THE COAST AND
INTERIOR VALLEYS TONIGHT INTO SUNDAY WITH THE AFTERNOON PACKAGE
AFTER GETTING A GOOD LOOK AT INCOMING GUIDANCE.

MOUNTAIN SNOW LEVELS WILL FALL TO AROUND 4500 FEET LATE TONIGHT INTO
SUNDAY THEN TO AROUND 4000 FEET SUNDAY NIGHT INTO MONDAY. STRONG
ONSHORE FLOW WILL CONTINUE THROUGH SUNDAY OR SUNDAY NIGHT AS SNOW
LEVELS FALL...SO WILL CONTINUE THE WINTER STORM WATCH FOR THE
MOUNTAINS LATE TONIGHT THROUGH EARLY MONDAY. A WARNING MAY BE ISSUED
FOR THIS TIME FRAME IN THE MOUNTAINS WITH THE AFTERNOON PACKAGE.

SHOWERS WILL DECREASE ON MONDAY. ALBRECHT

.LONG TERM...FROM THE PREVIOUS LONG TERM DISCUSSION...NORTHERLY FLOW
ALOFT WILL CONTINUE TUESDAY AHEAD OF AN UPPER RIDGE MOVING INTO
BRITISH COLUMBIA. THERE COULD BE SPOTTY LIGHT SHOWERS. THE RIDGE
WILL MOVE ACROSS WESTERN WASHINGTON WEDNESDAY...AND IT SHOULD BRING
SUNNY WEATHER. THE NEXT FRONTAL SYSTEM WILL PROBABLY ARRIVE AROUND
FRIDAY. MCDONNAL

&&

.AVIATION...HIGH PRESSURE WILL WEAKEN TODAY...THEN AN UPPER LEVEL
TROUGH WILL MOVE OVER THE REGION TONIGHT AND SUNDAY. STRONG WEST-
SOUTHWEST FLOW ALOFT. MOIST AT ALL LEVELS AND STABLE...BECOMING
UNSTABLE TONIGHT AND SUNDAY WITH A CHANCE OF THUNDERSTORMS OVER ALL
OF WRN WA. WILL NOT INCLUDE IN TAFS GIVEN THE LOW PROBABILITY AROUND
20 PERCENT AT ANY PARTICULAR TERMINAL. RAIN...HEAVY AT TIMES...WILL
TRANSITION TO SHOWERS AS THE FRONT MOVE SOUTH OF PUGET SOUND THIS
AFTERNOON.

SEA...MODERATE RAIN WILL CONTINUE AT TIMES UNTIL 19Z...THEN A
TRANSITION TO SHOWERS WILL OCCUR. VSBY OF 3-5SM WILL BE COMMON IN
MODERATE RAIN...AND BRIEFLY TO 2SM IN HEAVY RAIN UNTIL MID-DAY.
UNSTABLE CONDITIONS LATER TONIGHT AND SUNDAY WITH A 20 PERCENT
CHANCE OF A THUNDERSTORM IN THE VICINITY DURING THE PERIOD. WILL NOT
INCLUDE IN TAF GIVEN THE LOW CHANCE.

SURFACE WIND WILL ALSO PEAK THIS MORNING...WITH GUSTS AROUND 35 KT
EXPECTED...THEN EASE. WINDS WILL INCREASE AGAIN AFTER 9 PM WITH
SIMILAR SOUTHWESTERLY WINDS THROUGH SUNDAY. DTM/HANER

&&

.MARINE...A WARM FRONT IS BRINGING GALE FORCE SOUTHERLY WINDS TO
THE COASTAL WATERS/W ENTRANCE TO THE STRAIT/AND PUGET SOUND.
. A SMALL LULL IN THE WIND IS EXPECTED THIS AFTERNOON...THEN WIND
WILL PICK UP AGAIN THIS EVENING...IN RESPONSE TO A COLD FRONT MOVING
ACROSS THE REGION.

WESTERLY SWELL AROUND 10 TO 14 FEET WILL BUILD TO 15 FEET TONIGHT
AND 19 TO 22 FEET ON SUNDAY. A HIGH SURFACE ADVISORY IS IN EFFECT
FROM 4 AM SUNDAY THROUGH 11 PM SUNDAY NIGHT. DTM

&&

.HYDROLOGY...SATELLITE IMAGERY SHOWS LITTLE MOVEMENT OF A FRONT OVER
THE CENTRAL PART OF WESTERN WASHINGTON THIS MORNING. SIX HOUR
RAINFALL TOTALS SHOW A MAXIMUM OF 1-2 INCHES AROUND SNOQUALMIE PASS
AND THE SNOQUALMIE AND SKYKOMISH DRAINAGES. RIVER FORECASTS SHOW
MODERATE FLOODING AT GOLD BAR ON THE SKYKOMISH AND CARNATION ON THE
SNOQUALMIE. FLOOD WARNINGS ARE IN EFFECT FOR THE
TOLT...SNOQUALMIE... AND SKYKOMISH RIVERS.

RAINFALL ON DRAINAGES NORTH OF THE SKYKOMISH HAS BEEN LESS HEAVY AND
RISES ON THOSE RIVERS...INCLUDING THE STILLAGUAMISH...SKAGIT...AND
NOOKSACK...HAVE BEEN MINOR SO FAR. FLOODING ON THESE RIVERS IS
LOOKING LESS LIKELY. ANY FLOODING IS LIKELY TO BE MINOR.

THE AREA OF HEAVY RAIN IS FORECAST TO MOVE SOUTH THIS AFTERNOON AND
BRING RENEWED HEAVY RAIN TO THE RIVER BASINS AROUND MOUNT RAINIER.
RAINFALL HAS BEEN LESS THAN FORECAST OVER THESE SOUTHERN BASINS THIS
MORNING...GENERALLY LESS THAN AN INCH. FORECAST CRESTS ARE NOW A BIT
LOWER THAN BEFORE...EVEN ACCOUNTING FOR THE HEAVY RAIN EXPECTED THIS
AFTERNOON. THE FORECAST STILL CALLS FOR ANOTHER 2-3 INCHES AROUND
MOUNT RAINIER WHICH MAY BE ENOUGH TO CAUSE FLOODING ON THE CARBON...
NISQUALLY...PUYALLUP NEAR ORTING...AND COWLITZ RIVERS.

ON THE OLYMPIC PENINSULA THE SKOKOMISH RIVER IS EXPECTED TO FLOOD
THIS MORNING AND A WARNING IS ALREADY IN EFFECT. THE ELWHA AND
BOGACHIEL RIVERS ARE BOTH RISING RAPIDLY BUT ARE EXPECTED TO CREST
BELOW FLOOD STAGE. THE WYNOOCHEE AND SATSOP RIVERS ARE ALSO RISING
BUT ARE NOT FORECAST TO FLOOD EITHER. BURKE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY INTERIOR SOUTHWEST INTERIOR AND PUGET SOUND
      LOWLANDS SOUTH OF EVERETT...AND FOR THE CENTRAL WASHINGTON
      COAST UNTIL 3 PM PDT THIS AFTERNOON.
     HIGH SURF ADVISORY FOR THE NORTH AND CENTRAL COAST FROM
      4 AM PST TO 10 PM PST SUNDAY.
     WINTER STORM WATCH FOR THE CASCADES AND OLYMPICS ABOVE
      4000 FEET LATE TONIGHT THROUGH MONDAY MORNING.
     FLOOD WATCHES AND/OR WARNINGS FOR PORTIONS OF THE FORECAST
      AREA.

PZ...GALE WARNING FOR THE COASTAL WATERS...WEST ENTRANCE TO
      THE STRAIT AND PUGET SOUND.
     SMALL CRAFT ADVISORY ALL OTHER WATERS.
     SMALL CRAFT ADVISORY FOR ROUGH TO SEVERE GRAYS HARBOR BAR CONDITIONS.

&&

WWW.WEATHER.GOV/SEATTLE

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
920 AM PDT SAT OCT 31 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 AM     HEAVY RAIN       5 NNW GRAND MOUND       46.88N 123.04W
10/31/2015  M1.31 INCH       THURSTON           WA   TRAINED SPOTTER

            24 HOUR TOTAL. STILL RAINING HARD.

0900 AM     HEAVY RAIN       3 SSW ISSAQUAH          47.49N 122.06W
10/31/2015  M2.10 INCH       KING               WA   TRAINED SPOTTER

            24 HOUR TOTAL. STILL RAINING.

&&

JSMITH

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
1129 AM PDT SAT OCT 31 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1115 AM     HEAVY RAIN       1 ENE ELWHA             48.06N 123.57W
10/31/2015  M2.03 INCH       CLALLAM            WA   TRAINED SPOTTER

            14 HOUR TOTAL. NO LONGER RAINING.

&&

JSMITH

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
1222 PM PDT SAT OCT 31 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1218 PM     HEAVY RAIN       NE NAPAVINE             46.58N 122.90W
10/31/2015  M0.95 INCH       LEWIS              WA   TRAINED SPOTTER

            ONE HOUR TOTAL. STILL RAINING BUT HAS LIGHTENED UP.

&&

JSMITH