Areal Flood Warning 2, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST SUN JAN 16 2011

.SYNOPSIS...A WET FRONTAL SYSTEM ASSOCIATED WITH A STREAM OF
SUBTROPICAL MOISTURE WILL BRING RAIN TO WESTERN WASHINGTON THROUGH
TODAY. HEAVY RAIN IN THE MOUNTAINS WITH SNOW LEVELS AROUND 8000 FEET
WILL PRODUCE FLOODING ON SOME RIVERS. RAIN WILL GRADUALLY DECREASE
MONDAY AND THE SNOW LEVEL WILL FALL TO AROUND 3000 FEET MONDAY
NIGHT. A WEAK RIDGE WILL BUILD WEDNESDAY AND THURSDAY.

&&

.SHORT TERM...THE AXIS OF A BROAD FLAT UPPER LEVEL RIDGE IS ALONG
THE PACIFIC NORTHWEST COAST EARLY THIS MORNING. A FRONTAL SYSTEM
RIDING OVER THE NORTH SIDE OF THE RIDGE IS BEING FED BY A WARM MOIST
SOUTHWESTERLY JET THAT EXTENDS SOUTHWEST TO AROUND 30N/170W. THE
WARM FRONT ASSOCIATED WITH THIS SYSTEM MOVED INTO WESTERN WASHINGTON
SATURDAY...AND IT HAS BROUGHT SUBSTANTIAL RAINFALL TO THE FORECAST
AREA. THIS IS ESPECIALLY TRUE IN THE MOUNTAINS -- PARTICULARLY IN
THE CASCADES FROM THE SNOHOMISH BASIN SOUTHWARD -- WHERE ROUGHLY 1
TO 3 INCHES OF PRECIPITATION HAS FALLEN SO FAR WITH THE SNOW LEVEL
AROUND 8000 FT.

AT 3 AM RADAR STILL SHOWED RAIN WIDESPREAD ACROSS WESTERN WASHINGTON
WITH TEMPERATURES MOSTLY IN THE UPPER 40S AND LOWER 50S. IN ADDITION
ISOLATED THUNDERSTORMS HAVE DEVELOPED ALONG THE COAST...OVER THE
OLYMPIC PENINSULA...AND OVER THE ADJACENT WATERS.

LOTS OF MOISTURE WILL CONTINUE STREAMING INTO WESTERN WASHINGTON
TODAY WITH STRONG LOW LEVEL WESTERLY FLOW...AND SIGNIFICANT AMOUNTS
OF RAIN WILL FALL AGAIN TODAY...ESPECIALLY THIS MORNING ALONG THE
COAST AND IN THE MOUNTAINS. THE HEAVIEST AMOUNTS WILL BE IN THE
CASCADES...AND THE FOCUS OF THE HEAVIEST PRECIPITATION WILL LIKELY
SHIFT A BIT NORTHWARD. WE WILL PROBABLY BEGIN TO SEE FAIRLY
PRONOUNCED RAIN SHADOWING OVER MUCH OF THE PUGET SOUND AND NORTHWEST
INTERIOR.

THE CONVEYOR OF WARM MOISTURE INTO THE REGION WILL GRADUALLY
DECREASE STARTING ROUGHLY MIDDAY TODAY AND CONTINUING TONIGHT AND
MONDAY AS AN UPPER RIDGE STARTS BUILDING OFFSHORE ALONG 135W. THIS
WILL CAUSE THE FLOW OVER THE PACIFIC NORTHWEST TO BECOME MORE
NORTHWESTERLY...CUT OFF THE TAP TO WARM MOISTURE...AND GRADUALLY
COOL THE AIR MASS.

PRECIPITATION DURING THE 24 HOURS ENDING LATE TONIGHT WILL AMOUNT TO
ROUGHLY 2 TO 5 INCHES IN THE MOUNTAINS...WITH ONLY 0.5 TO 2.0 INCHES
DURING THE FOLLOWING 24 HOUR PERIOD. THE SNOW LEVEL WILL FALL
GRADUALLY TO AROUND 6000 FT TONIGHT...4500 FT MONDAY...AND FINALLY
3000 FT MONDAY NIGHT. SHADOWING WILL CONTINUE OVER MOST OF THE
INTERIOR LOWLANDS WITH SHOWERS BECOMING GENERALLY LIGHTER AND MORE
SCATTERED.

TODAY AND TONIGHT WILL BE WINDY IN PARTS OF WESTERN WASHINGTON AS
WELL. FOR THE LOWLANDS THE COAST AND PUGET SOUND REGION WILL HAVE
WINDS IN THE 20 TO 30 MPH RANGE WITH GUSTS TO 45 MPH...WITH SOMEWHAT
LESS WINDY CONDITIONS ELSEWHERE. EXPOSED RIDGES IN THE MOUNTAINS
WILL BE EVEN WINDIER...IN THE 30 TO 40 MPH RANGE WITH GUSTS TO 60
MPH. THOSE VALUES HOWEVER ARE BELOW HIGH WIND WARNING AND EVEN WIND
ADVISORY CRITERIA.

A WEAK SHORTWAVE WILL MOVE THROUGH THE PACIFIC NORTHWEST TUESDAY AND
TUESDAY NIGHT. THE GFS HAS SHOWN THIS FEATURE FAIRLY CONSISTENTLY
OVER THE PAST SEVERAL RUNS...BUT IT HAS NOT BEEN CONSISTENT WITH THE
DETAILS OF ITS LOCATION AND TIMING. THE NAM ALSO SHOWS THIS FEATURE
BUT MUCH WEAKER. AND WHILE SOME PREVIOUS RUNS OF THE EUROPEAN MODEL
DID NOT SHOW IT AT ALL...THE MOST RECENT ONE DOES. AT ANY RATE...IT
WILL NOT HAVE ANY SPECIAL IMPACT EXCEPT SOME RAIN OVER THE LOWLANDS
AND SNOW IN THE MOUNTAINS.   MCDONNAL

.LONG TERM...WEDNESDAY AND PERHAPS THURSDAY WILL BE DRIER DAYS...AS
THE UPPER RIDGE ESTABLISHES ITSELF ONCE AGAIN OFFSHORE AND GIVES
NORTHWEST FLOW ALOFT OVER THE PACIFIC NORTHWEST. AGREEMENT BETWEEN
MODELS AND RUN TO RUN CONSISTENCY CONTINUES TO BE POOR BEYOND
THURSDAY...THOUGH THERE IS DECENT INDICATION THAT ANOTHER ORGANIZED
FRONTAL SYSTEM WILL ARRIVE FRIDAY OR SATURDAY.   MCDONNAL

&&

.HYDROLOGY...FOCUS OF HEAVIEST RAIN SATURDAY NIGHT AND SUNDAY
MORNING HAS BEEN OVER THE SOUTH CENTRAL CASCADES. PARADISE AT 5500
FEET ON MOUNT RAINIER RECEIVED 2.5 INCHES BY MIDNIGHT AND COULD
EASILY GET 6 INCHES IN 24 HOURS ENDING SUNDAY AFTERNOON. THIS IS ALL
RAIN AS PARADISE IS 38 DEGREES AND THE FREEZING LEVEL IS LIKELY
ABOVE 8000 FEET. THE UPSHOT IS FLOOD WARNINGS ARE ALREADY OUT FOR
RIVERS THAT FLOW OFF MOUNT RAINIER...INCLUDING THE COWLITZ...
NISQUALLY...DESCHUTES...AND THE REACH OF THE PUYALLUP NEAR ORTING.

THE NEXT BATCH OF RIVERS THAT MAY REQUIRE A WARNING ARE IN THE
SNOHOMISH BASIN. SNOQUALMIE PASS APPEARS TO HAVE RECEIVED NEARLY 3
INCHES SINCE SATURDAY AFTERNOON. THE TOLT WILL PROBABLY BE THE FIRST
TO FLOOD. THE SNOQUALMIE...SKYKOMISH...AND SNOHOMISH WILL ALSO
LIKELY FLOOD. MAY LEAVE THE WARNING ON THE SNOHOMISH FOR A LATER
SHIFT BUT THE REST WILL PROBABLY BE WARNED SOON. THE STILLAGUAMISH
IS PRETTY FLASHY AND MAY ALSO NEED A WARNING SOON.

RAINFALL SO FAR HAS BEEN LIGHTER FARTHER NORTH. THE SKAGIT AND
NOOKSACK HAVE NOT YET RISEN SHARPLY AND MAY HAVE TO WAIT FOR THE
HEAVIEST RAIN TO MOVE NORTH...AS PREDICTED BY MODELS...SUNDAY
AFTERNOON OR NIGHT.

RAINFALL OVER THE SOUTHWEST HAS NOT BEEN AS HEAVY AS PREDICTED SO
FAR AND RIVERS HAVE BARELY BEGUN TO RESPOND. THE SKOKOMISH RIVER
WILL ALMOST CERTAINLY FLOOD...BUT OTHER RIVERS INCLUDING THE
CHEHALIS NEWAUKUM SKOOKUMCHUCK AND SATSOP MAY NOT.

THE GREEN RIVER IS FORECAST TO RISE SLIGHTLY ABOVE FLOOD STAGE AT
THE AUBURN GAUGE. THIS WOULD CAUSE MINOR FLOODING OVER LOW LYING
FARM LANDS UPSTREAM OF AUBURN.

A FLOOD WATCH REMAINS IN EFFECT FOR MOST OF WESTERN WASHINGTON.

THE FORECAST IS FOR RAIN TO SLOWLY TAPER BY MONDAY AFTERNOON. THERE
IS NO SIGNIFICANT RAIN IN THE FORECAST FOR THE WEEK AFTER MONDAY
AFTERNOON. THE GREEN RIVER WILL NOT FLOOD DURING THAT PERIOD. BURKE

&&

.AVIATION...STRONG AND MOIST WLY FLOW ALOFT AND LOW LEVEL ONSHORE
FLOW WILL CONTINUE. EXPECT A WEAKENING CDFNT TO SWEEP ACROSS THE
AREA THIS MORNING. THE AIR MASS HAS BECOME SLIGHTLY UNSTABLE AS
EVIDENCED BY THE LIGHTNING STRIKES OVER THE WRN PART OF THE FORECAST
AREA. THERE WILL PROBABLY BE A SLIGHT RISK OF ISOLATED TSTMS THE
REST OF TODAY.

LLWS WILL PERSIST OVER THE CENTRAL AND SRN PARTS OF THE FORECAST
AREA THIS MORNING AND WILL LIKELY REDEVELOP THIS EVENING.

KSEA...THE SANDPOINT PROFILER SHOWED SW WINDS OF 35 TO 40 KNOTS NEAR
2K FT EARLY THIS MORNING...THUS WILL KEEP THE MENTION OF LLWS IN THE
TAF TIL ABOUT MIDMORNING. THE THREAT OF LLWS SHOULD END BY 1800 UTC
OR ONCE THE STRONGER WINDS MIX DOWN TO THE SFC. HOWEVER LLWS WILL
LIKELY REDEVELOP LATE THIS AFTERNOON OR EARLY EVENING.

&&

.MARINE...
A WEAKENING COLD FRONT WILL SWEEP ACROSS THE AREA THIS MORNING IN
THE WAKE OF THE WARM FRONT THAT MOVED THROUGH EARLIER.

AS EXPECTED A MESOLOW HAS DEVELOP OVER THE N END OF THE ADMIRALTY
INLET...EXTENDING OVER PART OF THE E ENTRANCE TO THE STRAIT OF JUAN
DE FUCA. THIS LOW WILL REMAIN QUASISTATIONARY OVER THIS AREA TODAY
BEFORE DISSIPATING TONIGHT. THEREFORE...WITH THE EXCEPTION OF THE
COASTAL WATERS...ANTICIPATE THE STRONGEST WINDS TO OCCUR OVER THE
PUGET SOUND AND CENTRAL STRAIT OF JUAN DE FUCA.

ANOTHER...BUT STRONGER...COLD FRONT WILL MOVE SE ACROSS THE AREA ON
MON. MEANWHILE...MODERATE TO STRONG ONSHORE FLOW WILL CONTINUE
THROUGH MON BUT WILL RELAX ON TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES...WARNINGS...AND/OR ADVISORIES ARE IN EFFECT
     FOR MUCH OF THE CWA.

PZ...GALE WARNINGS ARE IN EFFECT FOR THE NEAR SHORE WATERS...
     PUGET SOUND/HOOD CANAL...AND CENTRAL STRAIT OF JUAN DE FUCA.

     A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE REMAINING
     WATERS EXCEPT THE EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS THRU LATE MON NIGHT.

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.