Winter Storm Warning 1, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
906 PM PST SAT JAN 17 2015

.SYNOPSIS...A STRONG COLD FRONT WILL MOVE ACROSS WESTERN WASHINGTON
TONIGHT WITH RAIN CHANGING TO SHOWERS AND VERY WINDY CONDITIONS
DEVELOPING. WESTERLY FLOW ALOFT SUNDAY AND MONDAY WILL ALLOW
POST-FRONTAL SHOWERS TO CONTINUE...BUT GRADUALLY DIMINISH THROUGH
MONDAY. AN UPPER LEVEL RIDGE WILL BRING DRY WEATHER TUESDAY AND
WEDNESDAY AS IT MOVES SLOWLY EAST ACROSS THE REGION.

&&

.SHORT TERM...IR SATELLITE IMAGERY AT 340Z SHOWED THE BACK EDGE OF
THE FRONT ABOUT 150 NM SW OF GRAYS HARBOR...AND IT IS SHOWING UP ON
THE COASTAL RADAR AS WELL. LATEST MODELS SHOW FROPA ON THE CENTRAL
COAST AROUND 07Z/11 PM AND OVER PUGET SOUND AROUND 09Z/1 AM.

HEAVY RAIN HAS DEVELOPED OVER THE MOUNTAINS IN THE WARM SECTOR AHEAD
OF THE COLD FRONT. AIRCRAFT OBS OVER PUGET SOUND HAVE THE FREEZING
LEVEL BETWEEN 7000 AND 8000 FEET. CLOSE TO 2 INCHES OF RAIN HAVE
FALLEN OVER THE SW SLOPES OF THE OLYMPICS IN THE PAST 12 HOURS WHICH
MEANS THE FORECAST QPF IS PRETTY CLOSE. RAINFALL OVER THE CENTRAL
AND S CASCADES RANGED FROM 0.05 TO ABOUT 1.40 WHICH IS ALSO CLOSE
BUT STILL A LITTLE BELOW THE QPF FORECAST. WITH THE FRONT E OF THE
AREA BY 12Z THIS SHOT OF HEAVY RAIN MAY BE TOO SHORT TO PRODUCE MUCH
RIVER FLOODING. STRONG WESTERLY 850 MB FLOW 40-50KT CONTINUES
THROUGH SUNDAY MORNING BEHIND THE FRONT BUT RAIN OVER THE MOUNTAINS
FALL WILL BE MUCH LESS WITH THE MAIN MOISTURE SOURCE GONE. AT THIS
POINT THE SKOKOMISH RIVER HAS THE BEST CHANCE OF REACHING FLOOD
STAGE...BUT AT 04Z/8 PM IT WAS JUST STARTING TO RISE.

VERY WINDY CONDITIONS BEHIND THE FRONT ARE STILL A CONCERN TONIGHT.
S-SW SUSTAINED WINDS ARE STILL EXPECTED TO RISE TO 20-35 MPH BEHIND
THE FRONT. THE MAIN PROBLEM IS THAT THE LOWER AIR MASS BECOMES
ALMOST DRY ADIABATIC BEHIND THE FRONT WHICH WILL ALLOW STRONGER
WINDS ALOFT TO MIX DOWN TO THE SURFACE. THE NEW 00Z NAM HAS 925 MB
WINDS ALOFT SW 45-50 KT FROM THE SW INTERIOR UP THROUGH PUGET SOUND
AND 50-60 KT ALONG THE COAST. THIS WOULD PUT WIND GUSTS IN THE HIGH
END ADVISORY RANGE OVER THE INTERIOR AND BORDERLINE HIGH WIND FOR
THE COAST. AT THIS POINT THE HIGH WIND WARNING FOR THE COAST LOOKS
OK AS DOES THE WIND ADVISORY FOR THE INTERIOR. WINDS WILL DIMINISH
THROUGH SUNDAY MORNING.

SNOW LEVELS WILL LOWER DOWN TO AROUND 4000 FEET SUNDAY MORNING
BEHIND THE COLD FRONT. WITH WESTERLY FLOW ALOFT CONTINUING TO
PRODUCE SOME OROGRAPHIC SNOW FALL THE WINTER WEATHER ADVISORY FOR
THE MT BAKER AND MT RAINIER AREA WILL CONTINUE FOR 3-8 INCHES OF
SNOW ON SUNDAY. MORE PROBLEMATIC IS STEVENS PASS. WHILE ALL OTHER
MOUNTAIN LOCATIONS HAVE WARMED ABOVE FREEZING...EASTERLY FLOW IS
KEEPING STEVENS PASS IN THE UPPER 20S. SNOW HAS RAMPED UP WITH THE
COLD FRONT APPROACHING SO IT LOOKS LIKE THE SNOW ADVISORY WILL NEED
TO BE EXTENDED TO STEVENS PASS.

ONCE THE COLD FRONT IS THROUGH THE AREA EARLY SUNDAY
MORNING...WESTERLY FLOW ALOFT ACROSS THE NE PACIFIC WILL KEEP
POST-FRONTAL SHOWERS GOING OVER THE AREA THROUGH MONDAY. NAM HI-RES
SOUNDINGS SHOW THE AIR MASS BECOMING UNSTABLE ALONG THE COAST AND
OVER THE SW INTERIOR SUNDAY AFTERNOON FROM ABOUT 20Z-23Z...RIGHT
WHEN THE UPPER LEVEL SHORTWAVE TROUGH...CURRENTLY NEAR 44N/144W...IS
MOVING INLAND. I WILL LET THE MID SHIFT LOOK A LITTLE CLOSER BEFORE
ADDING THUNDERSTORMS TO THE FORECAST.

AN UPPER LEVEL RIDGE WILL BEGIN BUILDING OVER THE AREA TUESDAY FOR
THE START OF A DRY PERIOD. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 340 PM AFD...SHOWERS WILL
EASE BY EARLY MONDAY EVENING AS A WEAK UPPER LEVEL RIDGE BEGINS TO
BUILD OVER THE REGION AND WEAK LOW LEVEL OFFSHORE FLOW DEVELOPS. TUE
AND WED LOOK TO BE DRY WITH OFFSHORE FLOW AND STRENGTHENING LOW
LEVEL INVERSIONS. A WEAKENING FRONT WILL BRUSH THE AREA THURSDAY
BRINGING A CHANCE OF A LITTLE RAIN FOLLOWED BY A SECOND STRONGER
FRONT FRIDAY MORNING.

&&

.HYDROLOGY...HEAVY RAIN HAS DEVELOPED OVER W WA THIS EVENING...BUT
THE COLD FRONT WILL MOVE THROUGH A LITTLE MORE QUICKLY THAN
EXPECTED. FROPA OVER PUGET SOUND WILL BE AROUND 09Z...AND OVER THE
CASCADES BEFORE 12Z. EVEN THOUGH STRONG W FLOW ALOFT IMMEDIATELY
BEHIND THE FRONT WILL CONTINUE...RAINFALL AMOUNTS WILL BE LOWER IN
DRIER AIR MASS. 12 HR QPF OVER THE SW OLYMPICS WAS AROUND 2 INCHES
AT 04Z AND BETWEEN 0.50 AND 1.40 OVER THE CENTRAL AND S CASCADES.
THIS WAS ABOUT WHAT WAS EXPECTED OVER THE OLYMPICS AND A LITTLE
LOWER THAN EXPECTED OVER THE CASCADES. WITH THE FRONT E OF THE AREA
BY 12Z THIS SHOT OF HEAVY RAIN MAY BE TOO SHORT TO PRODUCE MUCH
RIVER FLOODING. AT THIS POINT THE RIVER WITH THE BEST CHANCE OF
FLOODING IS THE SKOKOMISH...AND EVEN THAT RIVER IS ONLY JUST
BEGINNING TO RISE. THE FLOOD WATCH WILL CONTINUE FOR NOW. THERE IS
STILL A CHANCE THAT SOME OTHER RIVERS MAY REACH FLOOD STAGE...BUT
THE CHANCES ARE APPEARING LOWER.

OTHERWISE...FLOODING IS UNLIKELY THE NEXT 7 DAYS.
&&

.AVIATION...NEGATIVE TILT UPPER TROUGH SWINGING THROUGH WESTERN WA
OVERNIGHT TONIGHT. STRONG SW FLOW ALOFT BECOMING MORE WESTERLY AFTER
12Z SUNDAY. ASSOCIATED WARM FRONT HAS PASSED AND COLD FRONT JUST OFF
THE COAST AT 04Z SUNDAY TO MOVE THROUGH WESTERN WA AND INTO THE
CASCADES BY 12Z SUNDAY. AIR MASS TO BECOME MORE UNSTABLE POST-
FRONTAL SUNDAY. BLUSTERY CONDITIONS POST-FRONTAL AS WELL EASING BY
SUNDAY AFTERNOON.

IFR OR MVFR CEILINGS AND VSBY WITH THE FRONTAL SYSTEM. PRIMARILY VFR
CONDITIONS POST-FRONTAL THOUGH LOCAL MVFR CEILINGS IN SHOWERS.

KSEA...CEILINGS AND VSBY TO SAG INTO MVFR CONDITIONS WITH THE
FRONTAL SYSTEM THROUGH 10Z SUNDAY. COULD TEMPORARILY SLIDE INTO IFR
CONDITIONS. BLUSTERY S TO SW WINDS POST-FRONTAL 10Z OR SO SUNDAY -
WIND GUSTS TO 30-35 KT WITH CEILINGS AND VSBY IMPROVING TO VFR.
WINDS EASING BY AFTERNOON.

&&

.MARINE...GALE WARNINGS ALL AREAS WITH THE INCOMING VIGOROUS FRONTAL
SYSTEM. ASSOCIATED AND DEVELOPING 988 MB LOW 250 NM OFF CAPE
FLATTERY TO SWING NE INTO NORTHERN VANCOUVER ISLAND BY DAY BREAK
SUNDAY AND WEAKEN. INCREASING SOUTHERLY GRADIENTS THROUGH WESTERN WA
AS THE LOW MOVES ONSHORE THEN EASE SUNDAY AFTERNOON. HIGHER SURFACE
PRES TO BUILD OVER THE REGION MONDAY AND SHIFT EAST OF THE CASCADES
BY MID WEEK WITH WEAK LOW LEVEL OFFSHORE FLOW.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...FLOOD WATCH FOR KING...PIERCE...THURSTON...LEWIS...MASON...AND
     GRAYS HARBOR COUNTIES.

     HIGH WIND WARNING FOR THE NORTH AND CENTRAL WASHINGTON COAST
     FROM 4 PM PST THIS AFTERNOON UNTIL 10 AM PST SUNDAY.

     WIND ADVISORY FOR THE INTERIOR LOWLANDS FROM 10 PM PST THIS
     EVENING THROUGH NOON PST SUNDAY.

     WINTER WEATHER ADVISORY FOR THE CASCADES OF
     WHATCOM...SKAGIT...PIERCE...AND LEWIS COUNTIES FROM 6 AM TO 6
     PM SUNDAY.

PZ...GALE WARNING ALL WATERS.
     SMALL CRAFT ADVISORY GRAYS HARBOR BAR.

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
813 PM PST SAT JAN 17 2015

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

0812 PM     HEAVY RAIN       5 NNW GRAND MOUND       46.88N 123.04W
01/17/2015  M1.28 INCH       THURSTON           WA   TRAINED SPOTTER

            1.28 INCHES OF RAIN IN 12 HOURS FROM 8 AM TO 8 PM.

&&