Storm Watch 3, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1030 AM PST SUN NOV 15 2009...CORRECTED TYPO

.SYNOPSIS...A WARM FRONT WILL BRING RAIN TO WESTERN WASHINGTON
TODAY. A VIGOROUS FRONTAL SYSTEM WILL REMAIN OVER WESTERN WASHINGTON
AND SOUTHWEST BRITISH COLUMBIA TONIGHT THROUGH TUESDAY. HEAVY RAIN
WILL FALL IN THE OLYMPICS AND AT TIMES IN THE NORTH CASCADES.
ANOTHER STRONG FRONTAL SYSTEM WILL ARRIVE WEDNESDAY NIGHT OR
THURSDAY. THE WEATHER PATTERN WILL REMAIN ACTIVE INTO NEXT WEEKEND.

&&

.SHORT TERM...LOTS TO TALK ABOUT THIS MORNING IN REGARDS TO THE
INCOMING SYSTEM THAT IS EXPECTED TO BRING A VARIETY OF SEVERE
WEATHER CONDITIONS TO WESTERN WASHINGTON LATER TONIGHT THROUGH
TUESDAY. FOR TODAY THROUGH THIS EVENING...THE INITIAL WARM FRONTAL
MOISTURE WILL BRING PERIODS OF MAINLY LIGHT RAIN TO THE AREA. HIGHER
AMOUNTS OF AN INCH OR TWO ARE POSSIBLE IN THE OLYMPICS AS THE FLOW
ALOFT BEGINS TO PICK UP BUT THIS SHOULD SIMPLY CAUSE RISES ON RIVER
WITH FLOODING TO HOLD OFF UNTIL THE HEAVIER RAINFALL ARRIVES LATER
TONIGHT.

MODELS HAVE ALL TRENDED FURTHER SOUTH WITH THE MAIN FRONTAL
BAND...NOW TARGETING THE OLYMPICS AND N CASCADES WITH THE HEAVIEST
RAINFALL BEGINNING LATE TONIGHT THROUGH MIDDAY TUESDAY. THE CENTRAL
CASCADES STILL LOOK TO BE SPARED FROM THE HEAVIER RAIN...MAYBE ONLY
2-3 INCHES OVER THE 24-36 HOUR PERIOD. THE LOWLANDS WILL SHADOW AT
TIMES HELPING TO LIMIT RAINFALL AMOUNTS THERE AS WELL. A MUCH
DIFFERENT STORY UP IN THE NORTH CASCADES AND OLYMPICS. MODELS ARE
SHOWING SOME VERY STRONG SW FLOW...COMING IN BURSTS THROUGH THE
MONDAY/TUESDAY PERIOD AS A SERIES OF STRONG WAVES RIPPLE ACROSS TO
THE NORTH. HEAVY RAINFALL RATES WILL RESULT FROM STRONG OROGRAPHIC
ENHANCEMENT. THE PW VALUES OF 1-1.5 INCHES WOULD NOT NORMALLY BE
ENOUGH FOR MAJOR FLOODING BUT THE FLOW IS SO STRONG IN THIS CASE
THAT A GREAT DEAL OF THE MOISTURE SHOULD RING OUT AND OVER A
PROLONGED PERIOD OF TIME. SEE THE HYDROLOGY DISCUSSION BELOW FOR ALL
THE DETAILS ON THE POTENTIAL FLOODING.

HIGH WINDS ARE A GROWING CONCERN AND NOT JUST FOR THE COAST AS THE
12Z MODELS HAVE TRENDED STRONGER WITH THE JET AND ASSOCIATED SURFACE
LOWS TRACKING INTO VANCOUVER ISLAND. THE FIRST SUB 980 MB LOW WILL
TRACK FURTHEST NORTH INTO N VANCOUVER ISLAND ON MONDAY WITH THE
STRONG FRONTAL BAND SAGGING SWD OVER THE COASTAL WATERS. NAM-12
BOUNDARY LAYER WINDS RAMP UP THROUGH THE MORNING TO NEARLY 50+ ALONG
THE COAST BY MIDDAY...AND TO 40 KT OVER INTERIOR FROM AROUND WHIDBEY
ISLAND NWD. THIS WARRANTS A CONTINUATION OF THE WATCH FOR THE COAST
AND WILL ADD THE NRN INTERIOR AREAS AS WELL. WINDS BRIEFLY COME DOWN
MONDAY EVENING BUT RAMP UP AGAIN OVERNIGHT INTO TUESDAY AS ANOTHER
MUCH STRONGER SURFACE LOW...PERHAPS DOWN TO 975 MB...TRACKS INTO
SRN/CENTRAL VANCOUVER ISLAND. THIS RESULTS IN VERY STRONG SLY
GRADIENTS ALONG THE COAST...KAST-KUIL +12 MB...WITH THE BENT BACK
OCCLUSION MOVING ON THE COAST AND THEN INTO THE INTERIOR BY TUESDAY
MORNING. THESE NEWER SOLUTIONS FAVOR HIGH WIND FOR ALL OF WRN WA
WITH 925 MB WINDS 60-75 KT ACROSS ALL OF THE AREA...HIGHEST NORTH.
SOME OF THIS WILL LIKELY SURFACE IN GUSTS AS THE BENT BACK LIFTS
ACROSS THE AREA TUESDAY MORNING. THE NAM-12 IS SHOWING +16 MB
KPDX-BLI AT 15Z TUESDAY MORNING WHICH WOULD LIKELY RESULT IN A BRIEF
PERIOD OF HIGH WIND EVEN FOR THE PUGET SOUND AND SW INTERIOR AREAS.
THE WATCH FOR THE COAST WILL LIKELY BE CONVERTED TO A WARNING THIS
AFTERNOON AND WILL ADD IN THE WATCH FOR THE REST OF WESTERN
WASHINGTON LATER TODAY. I MAY BE ABLE TO GO RIGHT TO A WARNING FOR
THE NORTH INTERIOR AS WELL BUT NEED TO SEE THE 12Z 4KM MM5GFS FIRST.
MERCER

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS...THE NEXT VIGOROUS FNTL
SYS IS TIMED FOR PM WED OR THURSDAY...FOR NOW THE GFS TAKES A DEEP
SFC LOW IN THE 970S TO THE CHARLOTTES WED EVENING AND THEN A
SECONDARY LOW IN THE 990S TO NEAR TOFINO MIDDAY THU...AND ANOTHER
SFC LOW PRES TROF TO FOLLOW THU NITE. IT LOOKS WET AT TIMES THRU
NEXT WEEKEND...BUT THE DETAILS HAVE NOT BEEN CONSISTENT IN THE
MODELS AND THE ECMWF IS A NOTCH COOLER AND FASTER WITH THAT SYSTEM.
BOTH MODELS HAVE A COOL UPPER TROF ALONG THE WEST COAST BY FRI WITH
A FLAT DIRTY RIDGE OFFSHORE AND ADDITIONAL SYSTEMS UPSTREAM. 19

&&

.HYDROLOGY...MODELS HAVE ALL TRENDED TOWARD AIMING THE MOISTURE
PLUME DIRECTLY INTO WESTERN WASHINGTON LATER TONIGHT THROUGH AT
LEAST MIDDAY TUESDAY. A SERIES OF STRONG WAVES MOVING ACROSS THE
NORTH WILL CREATE VERY STRONG SW FLOW ALOFT AND AT THE SURFACE. THE
00Z MM5GFS RUN CONTINUES TO PAINT A 24 HOUR 12 INCH RAINFALL TOTAL
OVER THE OLYMPICS DURING THAT PERIOD WHICH WILL LIKELY CAUSE
WIDESPREAD FLOODING ON THE OLYMPIC PENINSULA. THE SKOKOMISH RIVER IS
ALMOST CERTAIN TO FLOOD WITH MOST THE OTHER RIVERS COMING CLOSE TO
OR POSSIBLY REACHING FLOOD AS WELL...INCLUDING THE
SATSOP...BOGACHIEL...ELWAH...AND DUNGENESS RIVERS. THE WATCH WAS
EXPANDED OVERNIGHT AS WELL TO INCLUDE CLALLAM COUNTY.

THERE ARE GROWING CONCERNS FOR THE NORTH CASCADES AS WELL GIVEN THAT
THE FRONTAL BAND IS NOW FORECAST TO BE FURTHER SOUTH THAN PREVIOUSLY
EXPECTED. THIS MAKES THE 5+ INCH SCENARIO MUCH MORE LIKELY PUTTING
THE NOOKSACK RIVER BASIN AT HIGHER RISK OF FLOODING. THE 00Z 4KM
MM5GFS FROM LAST NIGHT IS ALSO SHOWING SOME 4+ INCH AMOUNTS ALONG SW
FACING SLOPES IN SKAGIT AND SNOHOMISH COUNTY AS WELL. FLOODING HERE
IS NOT A GIVEN BUT THE ODDS APPEAR TO HAVE GONE UP GIVEN THE HIGHER
QPF TREND. WILL PLAY IT SAFE AND EXPAND THE WATCH TO COVER SKAGIT
AND SNOHOMISH COUNTIES AS WELL...AREAS NORTH OF STEVENS PASS.

THE CENTRAL CASCADES WILL EXPERIENCE MUCH LESS RAINFALL SINCE THE
FRONT PUSHES THROUGH THIS AREA RATHER QUICKLY ON TUESDAY. 1-3 INCHES
ARE POSSIBLE OVER A 36 HOUR PERIOD BUT THIS SHOULD NOT PRODUCE
FLOODING. HOWEVER...FORECASTS SHOULD BE MONITORED CLOSELY.

FLOODING ON THE GREEN RIVER OVER THE NEXT WEEK IS NOT EXPECTED AT
THIS TIME.

THE WEATHER PATTERN WILL REMAIN ACTIVE AND WET THRU NEXT WEEKEND.
THE NE PACIFIC WILL HAVE A STRONG JET STREAM AND PROGRESSIVE FRONTAL
SYSTEMS. THE SYSTEM TIMED FOR WED NITE OR THURSDAY LOOKS LIKE A
TYPICAL STRONG FNTL SYS AND NO REAL CHARACTERISTICS OF A FLOODING
EVENT...BUT WOULD CERTAINLY DELAY THE RIVERS RECEDING AND MIGHT VERY
WELL CAUSE THE SKOKOMISH RIVER IN MASON COUNTY TO JUMP BACK UP TO
FLOOD STAGE...IF IT HAS EVEN RECEDED BY THEN. NEXT WEEKEND IS A
NOTCH WARMER AND RATHER WET IN BOTH THE GLOBAL MODELS AND WILL NEED
TO BE WATCHED...IF YOU COMBINED THE WETTER AND WARMER GFS WITH THE
COOLER AND MORE PROGRESSIVE ECMWF AND IMAGINE AN AVERAGE SOLUTION IT
IS POSSIBLE THAT A MORE WLY SO CALLED ATMOSPHERIC RIVER OF MOISTURE
COULD PERSIST OVER WRN WA FOR 48-72HRS. MERCER/19

&&

.AVIATION...A WARM FRONT OVER WESTERN WASHINGTON WILL LIFT NORTH OF
THE AREA TODAY. A STRONG WAVE OF LOW PRES WILL DEVELOP OFFSHORE
TODAY AND MOVE INTO CENTRAL VANCOUVER ISLAND MON. THIS WILL BRING
STRONG WIND AT THE SURFACE TO THE NORTH INLAND AREA MONDAY.

WITH STRONG FLOW ALOFT IN A MOIST AIR MASS WITH INCREASING FLOW
ALOFT AND STABLE TO NEUTRAL STATIC STABILITIES...EXPECT CEILINGS TO
RANGE FROM 010-020 ON THE COAST AND 020-030 INLAND THRU MON MORNING.
LOCAL IFR CIGS AND VISIBILITIES ARE LIKELY LATE TONIGHT AND MON ON
THE COAST...BUT THEY SHOULD REMAIN IN THE MVFR CATEGORY INLAND.

WINDS ALOFT WILL BECOME STRONG TONIGHT AND REMAIN SO THRU MON.
EXPECT 50-60 KT S/SW FLOW AT 5000 FT TO DEVELOP THIS EVENING. BY MON
MORNING 50 KT SLY FLOW SHOULD LOWER TO BLO 020.

KSEA...SOUTHERLY WIND 5-10 KT RISING TO 7-14 KT THIS AFTERNOON AND
TONIGHT. S WIND WILL RISE TO 25G35KT MON MORNING. CIGS 020-030.
PERIODS OF LIGHT RAIN THRU TONIGHT WITH POSSIBLY MODERATE RAINFALL
MON. ALBRECHT

&&

.AVALANCHE...RECENT RELATIVELY LARGE AMOUNTS OF COLDER..WEAKER SNOW
SHOULD BE LOADED AND STRESSED BY INCREASINGLY HEAVY...DENSER SNOW OR
RAIN OVER THE NEXT 24 HOURS...ESPECIALLY IN THE OLYMPICS AND
NORTHERN WA CASCADES. AS A RESULT A SIGNIFICANT INCREASE IN THE
AVALANCHE DANGER IS LIKELY. WATCHES ARE ALREADY OUT AND WILL ISSUE
APPROPRIATE WARNINGS SHORTLY. HEAVIEST PRECIPITATION AMOUNTS HEADED
FOR THE OLYMPICS AND NORTH...WHERE PERIODS OF HEAVY PRECIPITATION
WILL LIKELY PERSIST INTO LATER MONDAY BEFORE FREEZING LEVELS LOWER
MONDAY NIGHT AND EARLY TUESDAY. THOUGH THE PRECIPITATION BULLSEYE
APPEARS CENTERED MOSTLY NORTH AND OLYMPICS...THE RESULTS OF THE
HIGHER FREEZING LEVELS AND MORE MODEST RAINFALL AMOUNTS FURTHER
SOUTH SHOULD STILL PRODUCE SIGNIFICANT INCREASES IN THE AVALANCHE
DANGER IN ALL AREAS. EARLY SEASON BACK COUNTRY TRAVELERS SHOULD
RATCHET BACK THEIR TIME IN AND EXPOSURE TO STEEPER AVALANCHE TERRAIN
UNTIL THE RECENT SNOWPACK BEGINS TO STABILIZE ...EITHER THROUGH
SETTLEMENT OR AVALANCHES. MOORE

&&

.MARINE...SOUTHEASTERLY GALES ON THE COAST AND IN THE NORTH INTERIOR
WILL BRIEFLY RELAX THIS AFTERNOON BEHIND THE WARM FRONT. EXPECT
STORM FORCE WINDS TO DEVELOP ON THE COASTAL WATERS LATE TONIGHT WITH
GALES REDEVELOPING OVER ALL OTHER WATERS EXCEPT PUGET SOUND AND HOOD
CANAL BY EARLY MON MORNING. THIS NEXT BURST OF WIND WILL BE
ASSOCIATED WITH A WAVE OF LOW PRES MOVING N ALONG A STRONG COLD
FRONT JUST OUTSIDE OF THE COASTAL WATERS. THERE WILL BE A 12 HOUR
WEAKENING OF THE WINDS LATER MON AFTN INTO MON NIGHT.

INCOMING MODELS SHOW A SIGNIFICANT AND DEEPENING 970-975 MB LOW JUST
OUTSIDE OF THE COASTAL WATERS MOVING INTO CENTRAL VANCOUVER ISLAND
MIDDAY TUE. THIS LOW WILL BE ASSOCIATED WITH VERY STRONG WINDS ALOFT
AND INTERACTING JET STREAMS. STORM FORCE WINDS ARE EXPECTED TO
REDEVELOP LATE MON NIGHT AND CONTINUE THRU MIDDAY TUE ON THE COAST.
GALES ARE LIKELY OTHER WATERS WITH POSSIBLE STORM CONDITIONS LATE
MON NIGHT OR TUE. EXPECT UPDATES TO THE MARINE FORECAST THIS
AFTERNOON AS NEW FORECAST GUIDANCE NARROWS IN ON A SOLUTION.

COASTAL FLOODING COULD BECOME A CONCERN ON THE CENTRAL WASHINGTON
COAST MIDDAY TUE AS THE DEEP LOW MOVES N INTO VANCOUVER ISLAND.
TIDES ARE MARGINAL...BUT THERE IS A POSSIBILITY FOR A 2-3 FT STORM
SURGE AND NEAR 20 FT SEAS. WILL LOOK AT MORE GUIDANCE BEFORE
POSSIBLY ISSUING A COASTAL FLOOD WATCH FOR THE CENTRAL COAST THIS
AFTERNOON. ALBRECHT

&&

.AVALANCHE...RECENT RELATIVELY LARGE AMOUNTS OF COLDER..WEAKER SNOW
SHOULD BE LOADED AND STRESSED BY INCREASINGLY HEAVY...DENSER SNOW OR
RAIN OVER THE NEXT 24 HOURS...ESPECIALLY IN THE OLYMPICS AND
NORTHERN WA CASCADES. AS A RESULT A SIGNIFICANT INCREASE IN THE
AVALANCHE DANGER IS LIKELY. WATCHES ARE ALREADY OUT AND WILL ISSUE
APPROPRIATE WARNINGS SHORTLY. HEAVIEST PRECIPITATION AMOUNTS HEADED
FOR THE OLYMPICS AND NORTH...WHERE PERIODS OF HEAVY PRECIPITATION
WILL LIKELY PERSIST INTO LATER MONDAY BEFORE FREEZING LEVELS LOWER
MONDAY NIGHT AND EARLY TUESDAY. THOUGH THE PRECIPITATION BULLSEYE
APPEARS CENTERED MOSTLY NORTH AND OLYMPICS...THE RESULTS OF THE
HIGHER FREEZING LEVELS AND MORE MODEST RAINFALL AMOUNTS FURTHER
SOUTH SHOULD STILL PRODUCE SIGNIFICANT INCREASES IN THE AVALANCHE
DANGER IN ALL AREAS. EARLY SEASON BACK COUNTRY TRAVELERS SHOULD
RATCHET BACK THEIR TIME IN AND EXPOSURE TO STEEPER AVALANCHE TERRAIN
UNTIL THE RECENT SNOWPACK BEGINS TO STABILIZE ...EITHER THROUGH
SETTLEMENT OR AVALANCHES. MOORE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WATCH CENTRAL AND NORTH WASHINGTON COAST LATE TONIGHT
     THROUGH NOON TUESDAY.
    .HIGH WIND WATCH NORTH INTERIOR FROM WHIDBEY ISLAND NORTHWARD
     MONDAY THROUGH NOON TUESDAY.
    .FLOOD WATCH FOR VARIOUS COUNTIES IN WESTERN WASHINGTON.
PZ...STORM WARNING COAST AND WEST ENTRANCE.
    .GALE WARNING EAST ENTRANCE...ADMIRALTY INLET...NORTH INLAND
     WATERS.
    .SMALL CRAFT ADVISORY CENTRAL STRAIT AND PUGET SOUND/HOOD
     CANAL.
    .SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH TO SEVERE BAR
     CONDITIONS.

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FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
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