Small Craft Advisory 48, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST WED MAR 5 2014

.SYNOPSIS...A SERIES OF FRONTAL SYSTEMS WILL BRING RAINY AND WINDY
WEATHER TO WESTERN WASHINGTON TODAY THROUGH THURSDAY NIGHT. THE SNOW
LEVEL WILL BE ABOVE THE MOUNTAIN PASSES...AND TEMPERATURES WILL BE
MILD IN THE LOWLANDS. AN UPPER RIDGE WILL PROVIDE DRIER WEATHER AND
SOME SUN BREAKS ON FRIDAY...BUT ANOTHER FRONT WILL BRING MORE RAIN
THIS WEEKEND AND EARLY NEXT WEEK.

&&

.SHORT TERM...HEAVY RAIN ACROSS THE PUGET SOUND METRO CORRIDOR
THROUGH THIS EVENING. IR SATELLITE IMAGERY SHOWS RAPIDLY COOLING
CLOUD TOPS ASSOCIATED WITH A STRONG WARM FRONT LIFTING INTO WRN WA.
COASTAL RADAR AND OBS CONFIRM THAT MODERATE RAIN HAS SPREAD AS FAR N
AS OLYMPIA AND WILL BE INTO PUGET SOUND NEAR OR PRIOR TO COMMUTE
TIME. WV IMAGERY SHOWS THIS SYSTEM HAS ENTRAINED SUB-TROPICAL
MOISTURE WAY OUT NEAR HAWAII. THE DEEP MOISTURE AND STRONG FLOW WILL
PROVIDE HEAVY OROGRAPHIC RAINFALL ALONG S/SW FACING SLOPES OF THE
OLYMPICS AND N/CENTRAL CASCADES. 2 TO 5 INCHES OF RAIN ARE POSSIBLE
OVER FAVORED SLOPES THE NEXT 24 HOURS. THE 4K WRFGFS PROBABLY HAS A
GOOD A HANDLE ON THIS SYSTEM AS ANY. IT GIVES 1 OR 2 INCHES OF RAIN
TO THE INTERIOR LOWLANDS AND 1 TO 3 INCHES TO THE SW INTERIOR AND
THE COAST THROUGH THURSDAY MORNING. THIS WILL BE ENOUGH TO CAUSE
RIVER FLOODING IN SOME BASINS AND EVEN URBAN AND SMALL STREAM
FLOODING. RAIN WILL BE HEAVIEST THIS EVENING AND COULD CAUSE
DIFFICULT DRIVING CONDITIONS DURING THE EVENING COMMUTE. RAIN RATES
NEAR A QUARTER INCH OF RAIN PER HOUR COULD OCCUR DURING A 2-3 HOUR
TIME FRAME EARLY TO MID EVENING. REFER TO THE HYDRO DISCUSSION BELOW
AND ALSO TO THE LATEST FLOOD STATEMENTS FOR UP TO DATE INFORMATION.

THE STRONG FLOW ALOFT WILL WILL ALSO PARTIALLY MIX DOWN TO THE
SURFACE AT TIMES. SO EXPECTED GUSTS WINDS TO REALLY PICK UP ONCE THE
WARM FRONT LIFTS THROUGH THIS EVENING. GRADIENTS DO NO SUPPORT
ADVISORY LEVEL WINDS ACROSS THE INTERIOR BUT GUSTS TO 35 OR 40 ARE
POSSIBLE. EVEN THESE GUSTS COULD BRING DOWN SOME TREES DUE TO THE
SATURATED SOILS. LAND SLIDES/MUD SLIDES WILL AGAIN BE A BIG CONCERN
AND WILL MAINTAIN THE SPECIAL WEATHER STATEMENT HIGHLIGHTING THE
DANGERS.

MODELS AGREE FAIRLY WELL THAT A 995 MB OR SO SURFACE LOW WILL TRACK
NE OFF THE WA COAST AND REACH CENTRAL VANCOUVER ISLAND NEAR 18Z LATE
THURSDAY MORNING. AFTER A LULL IN WINDS EARLY THURSDAY MORNING...SW
GRADIENTS WILL INCREASE BECOMING LOCALLY WINDY ACROSS THE INTERIOR
AND PLACES FAVORED BY SW WINDS LIKE PUGET SOUND. PREVIOUS MODELS
WERE SHOWING ALMOST 12 MB PDX-BLI BUT MODELS HAVE BACKED OFF AND THE
SECOND BOUT OF WINDS MAY NOT REACH ADVISORY LEVEL. SOMETHING TO
WATCH REGARDLESS.

HIGH PRESSURE WILL MIGRATE OVER THE PAC NW FRIDAY AND FRIDAY NIGHT.
THE RIDGE IS DIRTY WITH MOISTURE MOVING OVER THE TOP POSSIBLY
PRODUCING SPOTTY LIGHT RAIN. THERE MAY ALSO BE SOME SUNSHINE SO
CLOUD COVER WAS DECREASED IN THE GRIDS. THE NEXT MOIST FRONTAL
SYSTEM ARRIVES SATURDAY. MODELS ARE SOMEWHAT FASTER WITH RAIN OVER
THE WEEKEND INSTEAD OF ANY BREAK.

.LONG TERM...WEAK HIGH PRESSURE OVER THE INTERIOR PAC NW SUNDAY
MOVES E ON MONDAY. THIS OPENS THE DOOR TO STRONG WESTERLY FLOW AND A
SERIES OF FRONTS MAINTAINING UNSETTLE WEATHER. THE ECMWF SHOWS THE
WEEKEND SYSTEM TO BE STRONG WITH SLOW MOVEMENT AND TONS OF MOISTURE
BEING ENTRAINED. THE GFS IS A SOMEWHAT WEAKER BUT STRONG REGARDLESS.
LOW PRESSURE MOVES E OF TUESDAY WITH MAYBE A CHANGE TO SHOWERS BUT
TIMING IS HIGHLY UNCERTAIN.  MERCER

&&

.HYDROLOGY...QPF FORECASTS FOR THE STORM LAST NIGHT WERE MOSTLY ON
TARGET EXCEPT OVER THE SOUTHERN OLYMPICS WHERE MORE RAIN THAN
FORECAST FELL. GAUGES RECORDED 2-3 INCHES IN 24 HOURS OVER THE
SOUTHERN OLYMPICS MOST OF WHICH FELL OVERNIGHT. THE SKOKOMISH RIVER
IS ABOVE FLOOD STAGE AND A WARNING IS ALREADY OUT. THE SATSOP RIVER
IS RISING RAPIDLY AND COULD MAKE A RUN AT FLOOD STAGE TODAY. HEAVY
RAINFALL HAS ENDED AND THERE WILL BE A LULL IN THE RAIN TODAY SO
RIVERS SHOULD LEVEL OFF OR EVEN FALL A BIT LATER TODAY AND TONIGHT.

ANOTHER WARM FRONT WILL ARRIVE TONIGHT AND THIS IS ALSO FORECAST TO
HAVE HEAVY RAIN. A COLD FRONT WILL THEN MOVE THROUGH ON THURSDAY
WHICH WILL KEEP THE RAIN GOING UNTIL IT PASSES. HEAVY RAIN SHOULD
END ROUGHLY BY 00Z FRIDAY IN THE OLYMPICS AND 06Z FRIDAY IN THE
CASCADES. THE SNOW LEVEL WILL FALL TO 4000-4500 FEET AS WELL.
HEAVIEST AMOUNTS ARE AGAIN IN THE OLYMPICS AND CENTRAL CASCADES. THE
LIKELY OUTCOME OF ALL THIS RAIN IS MINOR FLOODING ON A NUMBER OF
RIVERS...MOSTLY IN THE OLYMPICS AND SOUTH INTERIOR UP TO ABOUT THE
SNOQUALMIE BASIN.

IN ADDITION THERE COULD BE SOME SMALL STREAM AND URBAN FLOODING AS
WELL AS LANDSLIDES. WILL KEEP THE FLOOD WATCH GOING FOR MOST OF THE
CWA FOR NOW. MIGHT FEEL CONFIDENT ENOUGH TO LOWER IT OVER NORTHERN
BASINS THIS AFTERNOON. BURKE

&&

.AVIATION...SOUTHWESTERLY FLOW ALOFT WILL CONTINUE OVER WESTERN
WASHINGTON INTO THURSDAY MORNING. A WARM FRONT MOVED THROUGH THE
AREA FROM SOUTHWEST TO NORTHEAST OVERNIGHT. THE AIR MASS IS MOIST
AND STABLE IN THE WARM SECTOR THAT COVERS THE WHOLE AREA. ANOTHER
WARM FRONT WILL PASS EARLY THURSDAY MORNING FOLLOWED BY A COLD FRONT
THURSDAY AFTERNOON. SOUTHEASTERLY SURFACE FLOW WILL INCREASE TONIGHT
THEN BECOME ONSHORE THURSDAY AFTERNOON.

LOTS OF IFR CEILINGS WITH VISIBILITIES 2-4SM IN MIST OR LIGHT RAIN.
CONDITIONS SHOULD IMPROVE TO MVFR THIS MORNING WITH POSSIBLY A FEW
HOURS OF VFR IN THE AFTERNOON AND EVENING. AS THE NEXT WARM FRONT
APPROACHES TONIGHT CEILINGS AND VISIBILITIES WILL FALL TO MVFR.

KSEA...IFR CEILINGS LIKELY TO LAST A FEW MORE HOURS. VISIBILITIES
WILL IMPROVE BUT CEILINGS WILL REMAIN LOW INTO THE EARLY AFTERNOON
HOURS. SOME IMPROVEMENT IN THE CEILINGS MID AFTERNOON AS THE NEXT
WARM FRONT APPROACHES. CEILINGS COULD REACH 4000 FEET THIS EVENING
BUT WILL SINK WITH VISIBILITIES AS LOW AS 2 SM IN MODERATE RAIN AS
WARM FRONTAL RAIN BEGINS. SOUTHERLY WIND 8-12 KT THIS MORNING EASING
THIS AFTERNOON. CHB

&&

.MARINE...IN THE POST WARM FRONTAL AIR MASS WINDS ARE TOUCHING SMALL
CRAFT ADVISORY LEVELS ON THE COAST AND ARE BELOW THAT INLAND. WINDS
WILL DIMINISH TODAY BUT INCREASE AGAIN TONIGHT AS THE NEXT WARM
FRONT APPROACHES. THIS WARM FRONT WILL PRODUCE ANOTHER ROUND OF
SMALL CRAFT ADVISORY WINDS FOR ALL OF THE WATERS EXCEPT THE CENTRAL
STRAIT. THERE IS A CHANCE THIS SYSTEM COULD PRODUCE LOW END GALES
OVER THE COASTAL WATERS AND AT THE WEST ENTRANCE.

ONSHORE FLOW WILL COMMENCE AFTER A COLD FRONT PASSES THURSDAY
AFTERNOON. WINDS WILL SWITCH BACK TO SOUTHEASTERLY FRIDAY AS A FRONT
MOVES TOWARD THE COAST. THIS FRONT IS FORECAST TO MOVE THROUGH THE
AREA ON SATURDAY WITH AT LEAST SMALL CRAFT ADVISORY WINDS AND
POSSIBLY SOME GALES ASSOCIATED WITH IT. ANOTHER SYSTEM ARRIVES
SUNDAY WITH RIDGING POSSIBLE NEXT WEEK. CHB

&&

WA...WIND ADVISORY IN EFFECT FOR THE NORTH AND CENTRAL WASHINGTON
     COAST THROUGH 4 AM THURSDAY.
     VARIOUS FLOOD WATCHES AND/OR WARNINGS FOR PARTS OF THE FORECAST
     AREA.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT CENTRAL STRAIT.

&&

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