River Flood Warning 28, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
306 AM PST FRI FEB 6 2015

.SYNOPSIS...MOIST SOUTHWEST FLOW ALOFT WILL CONTINUE OVER THE
PACIFIC NORTHWEST THROUGH SUNDAY. UPPER LEVEL TROUGHS EMBEDDED THE
FLOW WILL BRING PERIODS OF MODERATE TO HEAVY RAIN AND LOCALLY WINDY
CONDITIONS TO THE AREA THROUGH SATURDAY NIGHT. AFTER A BRIEF LULL ON
SUNDAY AN UPPER LEVEL LOW WILL BRING MORE RAIN LATE SUNDAY THROUGH
MONDAY NIGHT. A LARGE UPPER LEVEL RIDGE WILL BRING DRY WEATHER
TUESDAY THROUGH THURSDAY.

&&

.SHORT TERM...MOIST SW FLOW ALOFT CONTINUES OVER W WA THIS
MORNING...BRINGING RAIN TO THE LOWLANDS AND HEAVY RAIN TO THE
MOUNTAINS. THE 100-120 KT 300 MB JET STREAK OVER THE AREA IS
SUPPORTING THE HEAVY RAIN. WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL
SHORTWAVE TROUGH EMBEDDED IN THE FLOW OVER SW WA AT 09Z PROVIDING
EXTRA LIFT...WITH AN ADDITIONAL SHORTWAVE OFF THE OREGON COAST THAT
COULD IMPACT THE AREA. THE OLYMPICS HAVE BEEN GETTING THE HEAVIEST
RAIN BY FAR...OVER 3 INCHES IN SPOTS IN THE PAST 12 HOURS.

THE MODELS REMAIN CONSISTENT IN MAINTAINING THE HEAVIEST RAIN OVER W
WA UP THROUGH ABOUT 18Z. SOUTHERLY 850 MB FLOW WILL BE PEAKING AT
50-65 KT AT 12Z WHILE THE 300 MB JET STREAK IS STILL OVERHEAD. BY
18Z 850 MB WINDS WILL BE WEAKENING AND THE 300 MB JET STREAK WILL BE
SHIFTING E. THIS EXPECTED DECREASE OR LULL IN THE RAIN WILL LAST
THROUGH THIS EVENING. ANOTHER UPPER LEVEL SHORTWAVE TROUGH
APPROACHING FROM THE S WILL BRING A PERIOD OF RAIN FROM EARLY
SATURDAY MORNING THROUGH SATURDAY AFTERNOON. AND YET ANOTHER
TRAILING SHORTWAVE WILL KEEP THE RAIN GOING THROUGH SATURDAY NIGHT.
WITH 850 MB WINDS IN THE 30-40 KT RANGE THESE NEXT TWO SHORTWAVES
WILL BE MUCH WEAKER AND PACK LESS RAIN.

PRESSURE GRADIENTS ACROSS THE AREA ARE STRONG ENOUGH THIS MORNING
FOR WINDY CONDITIONS ALONG THE COAST AND OVER THE N INTERIOR. SO FAR
THE WINDIEST SPOTS HAVE TOPPED OUT RIGHT AT THE BOTTOM END OF
ADVISORY LEVEL WINDS. THE SURFACE WINDS ARE EXPECTED TO PEAK THIS
MORNING.

AFTER THE SATURDAY NIGHT SHORTWAVE...THE NEXT LULL IN THE RAIN WILL
STILL BE ON SUNDAY AS EXPECTED. SW FLOW ALOFT OVER W WA WILL BE
WEAKENING AS A LARGER DEEPENING UPPER LEVEL LOW TRACKS NE TOWARD THE
AREA. THE GFS AND ECMWF SOLUTIONS ARE FAIRLY CLOSE...BUT THE GFS IS
A LITTLE FASTER WITH THE ASSOCIATED COLD FRONT...BRINGING RAIN UP
ACROSS THE S HALF OF W WA IN THE AFTERNOON.

ALL THIS WARM MOIST SW FLOW ALOFT WILL KEEP THE AIR MASS OVER W WA
RATHER MILD THROUGH THIS WEEKEND...EVEN WITH THE RAIN. MAX TEMPS
WILL BE IN THE MID 50S WITH MIN TEMPS IN THE UPPER 40S TO NEAR 50.
SNOW LEVELS WILL REMAIN BETWEEN 5000-6000 FEET THROUGH MOST OF THE
WEEKEND. KAM

.LONG TERM...THE LARGER MATURE SYSTEM APPROACHING W WA SUNDAY WILL
ARRIVE AS A SLOWER MOVING VERTICALLY STACKED UPPER LEVEL AND SURFACE
LOW. MODELS AGREE ON BRINGING THE ASSOCIATED COLD FRONT NORTHWARD
ACROSS THE AREA SUNDAY NIGHT WITH MAINLY LIGHT RAIN. THE UPPER LEVEL
AND SURFACE LOW WILL FOLLOW RIGHT BEHIND...CROSSING W WA ON
MONDAY...THEN SLIDING E OF THE CASCADES MONDAY NIGHT. GFS LIFTED
INDICES AND MID-LEVEL LAPSE RATES SHOW THE AIR MASS BECOMING MORE
UNSTABLE FOR LOTS OF SHOWERS...BUT WITH LIFTED INDICES TOPPING OUT
AROUND 4...NOT UNSTABLE ENOUGH FOR THUNDER.

GFS/ECMWF REPLACE THE DEPARTING LOW WITH A MODERATE TO HIGH
AMPLITUDE UPPER LEVEL RIDGE ON TUESDAY. THERE COULD BE SOME
LINGERING LIGHT SHOWERS OVER THE CASCADES TUESDAY MORNING...BUT
OTHERWISE IT LOOKS DRY. THE GFS KEEPS THE RIDGE OVER THE AREA AND
THE DRY STRETCH GOING THROUGH FRIDAY WHILE THE ECMWF BRINGS A WEAK
FRONT TO THE COAST ON THURSDAY. WITH THE AIR MASS ALOFT DRYING
RAPIDLY THERE WILL PROBABLY BE A BUNCH OF FOG AROUND TUESDAY MORNING
AND ESPECIALLY WEDNESDAY MORNING. LOW LEVEL OFFSHORE FLOW SHOULD
INCREASE ENOUGH FOR MORE WIDESPREAD SUNSHINE WEDNESDAY AFTERNOON AND
THURSDAY. KAM

&&

.HYDROLOGY...THE HEAVIEST RAIN SO FAR HAS BEEN OVER THE OLYMPIC
MOUNTAINS AS EXPECTED...WITH 24-HOUR AMOUNTS MAINLY IN THE 3 TO 6
INCH RANGE. UP TO 4.5 INCHES OF RAIN HAS FALLEN DURING THE PAST 24
HOURS IN THE WILLAPA HILLS...WHICH MAKES UP THE HEADWATERS OF THE
CHEHALIS RIVER. 2 TO 4 INCHES OF RAIN HAS FALLEN IN THE CASCADES OF
WHATCOM AND SKAGIT COUNTIES...MAINLY AROUND MOUNT BAKER...WITH 1 TO
2.5 INCHES FURTHER SOUTH IN THE CASCADES.

THE SKOKOMISH RIVER ROSE QUICKLY ABOVE FLOOD STAGE THURSDAY
AFTERNOON AND IS JUST A FEW INCHES BELOW ITS MAJOR FLOOD STAGE EARLY
THIS MORNING.

MODELS INDICATE THAT THE PRECIPITATION RATES THAT HAVE BEEN
OCCURRING OVERNIGHT WILL CONTINUE THROUGH LATE THIS MORNING.
EXTRAPOLATING THE BACK EDGE OF THE FRONTAL WAVE OFFSHORE THROUGH
WESTERN WASHINGTON SUPPORTS THAT IDEA.

THE OLYMPICS SHOULD RECEIVE ANOTHER 1 TO 2 INCHES OF PRECIPITATION
THIS MORNING WITH THE SNOW LEVEL STILL AROUND 7000 FT. THE SKOKOMISH
COULD YET REACH ITS MAJOR FLOOD STAGE...AND WE WILL KEEP THAT AS THE
FORECAST THERE. THE OTHER RIVERS THAT FACE THE MOST IMMEDIATE THREAT
OF FLOODING ARE ALSO ON THE OLYMPIC PENINSULA -- NAMELY THE
BOGACHIEL...ELWHA...AND DUNGENESS. FLOOD WARNINGS COULD BE ISSUED
FOR THESE RIVERS ANYTIME THIS MORNING.

THE AREA AROUND MOUNT BAKER...IE THE HEADWATERS OF THE NOOKSACK AND
SKAGIT RIVERS...SHOULD RECEIVE ANOTHER 1 TO 2 INCHES OF RAIN THIS
MORNING AS WELL. NORTHWEST RIVER FORECAST CENTER GUIDANCE SHOWS BOTH
OF THESE RIVERS REACHING FLOOD STAGE LATE TODAY OR THIS EVENING...
BUT CONFIDENCE IN THAT IS NOT ESPECIALLY HIGH.

THE SHORT-TERM FLOOD THREAT ON ALL THE OTHER RIVERS APPEARS TO BE
SOMEWHAT LOWER...BUT THE MOST FLOOD-PRONE OF THEM STILL WARRANT A
FLOOD WATCH AND BEAR WATCHING. IN PARTICULAR THE NISQUALLY...
PUYALLUP NEAR ORTING...AND STILLAGUAMISH RIVERS COULD FLOOD. THE
FLOOD WATCH WILL REMAIN IN EFFECT.

RAINFALL RATES WILL EASE SOMEWHAT LATE TODAY THROUGH TONIGHT...WITH
ANOTHER WAVE OF HEAVIER RAIN ARRIVING SATURDAY. THIS WAVE IS FAST
MOVING AND MAY SERVE ONLY TO PROLONG MINOR FLOODING ON ANY RIVER
THAT IS FLOODING BY THAT POINT. NEW RIVER FLOODING SEEMS UNLIKELY.
THEN MODELS SHOW A LONGER LULL IN PRECIPITATION ON SUNDAY THAT LASTS
INTO SUNDAY EVENING. THE WAVE THAT ARRIVES SUNDAY NIGHT IS ALSO FAST
MOVING AND SEEMS UNLIKELY TO CAUSE ANY MORE FLOODING. PRECIPITATION
WILL TURN MORE SHOWERY MONDAY AND THE FLOOD THREAT SHOULD END.
MCDONNAL

&&

.AVIATION...A FRONTAL SYSTEM WILL MOVE ONSHORE THIS MORNING. ANOTHER
FRONTAL WAVE WILL REACH THE AREA TONIGHT. THE AIR MASS WILL REMAIN
MOIST AND STABLE. THERE WILL BE A MIX OF MID AND LOW CLOUDS WITH
OCCASIONAL REDUCED VISIBILITIES IN HEAVIER RAIN...MOSTLY COAST AND
MOUNTAINS.

KSEA...CEILINGS ARE EXPECTED TO MOSTLY STAY IN THE 4000-7000 FOOT
RANGE BUT LOWER CEILINGS ARE CERTAINLY POSSIBLE AT TIMES. SOUTHERLY
WIND 8-12 KNOTS. SCHNEIDER

&&

.MARINE...A SERIES OF FRONTAL SYSTEMS WILL MOVE THROUGH THE WATERS
OVER THE NEXT FEW DAYS. GALES WILL BE ENDING THIS MORNING AS THE
FIRST FRONT MOVES ONSHORE. ANOTHER ROUND OF GALES IS POSSIBLE FOR
MOST WATERS TONIGHT AS A SECOND FRONTAL WAVE MOVES THROUGH.

THE WEATHER WILL BECOME MORE TRANQUIL EARLY NEXT WEEK AS WEAK HIGH
PRESSURE MOVES OVER THE AREA. THERE WILL BE 12-15 FOOT SOUTHWEST
SWELL OVER THE COASTAL WATERS THROUGH THE WEEKEND. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNINGS/WATCHES ARE IN EFFECT FOR PARTS OF THE CWA.

PZ...GALE WARNING COASTAL WATERS THROUGH 10 AM.
    .GALE WARNING ENTRANCES STRAIT OF JUAN DE FUCA AND NORTHERN
     INLAND WATERS THROUGH 4 AM.
    .GALE WATCH COASTAL WATERS...ENTRANCES STRAIT OF JUAN DE FUCA...
     AND NORTHERN INLAND WATERS TONIGHT.
    .SMALL CRAFT ADVISORY ALL OTHER WATERS.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR.

&&

WWW.WEATHER.GOV/SEATTLE

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

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