Small Craft Advisory 853, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
845 PM PST SAT NOV 19 2011

.SYNOPSIS...A WEAK UPPER LEVEL RIDGE OFFSHORE COMBINED WITH LOW
LEVEL OFFSHORE FLOW OVER WESTERN WASHINGTON WILL RESULT IN COOL AND
DRY WEATHER THROUGH SUNDAY. A WEAK DISTURBANCE WILL MOVE INTO
WESTERN WASHINGTON ON MONDAY. A SLOW-MOVING FRONTAL BOUNDARY WILL
STALL OVER WESTERN WASHINGTON LATER MONDAY THROUGH WEDNESDAY
BRINGING A RETURN TO WINDY AND WET WEATHER...ESPECIALLY ON TUESDAY.

&&

.SHORT TERM...DRIER NORTHWESTERLY FLOW ALOFT HAS MOVED OVER THE AREA
THIS EVENING. WITH PARTIAL CLEARING AND LIGHT OFFSHORE FLOW...LOWS
TONIGHT WILL FALL INTO THE 20S MOST AREAS. SUNDAY WILL BE ANOTHER
COOL BUT DRY DAY WITH INCREASING WESTERLY FLOW ALOFT BUT LIGHT
OFFSHORE FLOW AT THE SURFACE.

A PACIFIC FRONTAL SYSTEM WILL SPREAD CLOUDS OVER THE AREA SUNDAY
NIGHT WITH RAIN REACHING THE COAST BY MORNING. THE TIMING IS SUCH
THAT SOME COLD AIR COULD REMAIN TRAPPED AT THE SURFACE IN THE HOOD
CANAL AREA MONDAY MORNING AS PRECIPITATION OVERSPREADS THE
INTERIOR...LEADING TO SOME SNOW IN THE MORNING BEFORE CHANGING OVER
TO RAIN. OTHERWISE...RAIN WILL SPREAD OVER THE INTERIOR BY LATE
MORNING THEN CHANGE TO SHOWERS IN THE AFTERNOON BEHIND THE FRONT
WITH A BIT OF A LULL IN THE PRECIPITATION LATE IN THE DAY IN ADVANCE
OF THE NEXT FRONT. THERE WILL BE SOME BREEZY TO WINDY SOUTHERLY
WINDS SUNDAY NIGHT AND MONDAY WITH THIS FIRST FRONT AT THE COAST AND
IN THE USUAL SOUTHEAST SUCKER LOCATIONS...BUT PROBABLY BELOW
ADVISORY LEVELS. THERE MIGHT ALSO BE ADVISORY AMOUNTS OF SNOW IN THE
MOUNTAINS MONDAY...ESPECIALLY FOR THE VOLCANOES.

A STRONGER FRONTAL SYSTEM WILL QUICKLY MOVE TO THE COAST MONDAY
NIGHT AND ONSHORE TUESDAY...STALLING OVER THE AREA DURING THE DAY.
COMBINED WITH THE RAINS FROM THE MONDAY SYSTEM...THIS WILL INTRODUCE
SOME FLOODING CONCERNS. SEE THE HYDROLOGY SECTION BELOW FOR MORE
DETAILS. THIS FRONT WILL BRING ANOTHER ROUND OF RAIN AND
WIND...POSSIBLY APPROACHING HIGH WIND FOR THE COAST WHILE AT LEAST
ADVISORY LEVELS ARE PRETTY LIKELY FOR THE NORTHERN INTERIOR. SNOW
LEVELS WILL RISE TO 5000 TO 6000 FEET TUESDAY SO SNOW WILL NOT BE AS
MUCH OF A CONCERN IN THE MOUNTAINS ALTHOUGH EASTERLY FLOW THROUGH
THE PASSES WILL HANG ON FOR AWHILE PERHAPS CAUSING ISSUES THERE. NO
UPDATES PLANNED THIS EVENING. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...THE THREAT OF FLOODING WILL
CONTINUE THROUGH WEDNESDAY AS A NEARLY STATIONARY FRONT CONTINUES
PUMPING MOISTURE INTO WESTERN WA. RIVER FLOODING IS A
CONCERN...ESPECIALLY THOSE FLOWING OFF THE OLYMPICS AND NORTH
CASCADES. THE FLOW MAY CUT OFF WED NIGHT AS A TROUGH FORMS
OFFSHORE...WITH THE BULK OF THE PRECIP SHIFTING SOUTH INTO ORE AND
CA. MODELS ARE TRENDING LIGHTER WITH PRECIP AMOUNTS BUT THERE IS
STILL A LOT OF UNCERTAINLY. AS PREVIOUSLY MENTIONED...THE OLYMPICS
MAY SEE 6-10 INCHES OF RAIN...WITH 4-8 IN THE NORTH CASCADES.

AFTER A BRIEF BREAK IN THE WEATHER WED NIGHT...ANOTHER FRONT ARRIVES
ON THANKSGIVING. THIS SYSTEM IS NOT AS STRONG BUT MAY SEE LOCALLY
BREEZY WINDS...WITH SNOW LEVELS DROPPING DOWN TO 2500 FEET AGL.
CONFIDENCE IN THE FORECAST OVER THE HOLIDAY WEEKEND REMAINS LOW AS
THE MODELS ARE OUT OF PHASE. WILL TREND TOWARD CLIMO FOR NOW. 33

&&

.HYDROLOGY...PREVIOUS DISCUSSION...A WARM AND WET FRONTAL SYSTEM
WILL STALL OVER WESTERN WASHINGTON TUESDAY THROUGH WEDNESDAY WITH
HEAVY RAINFALL POSSIBLE IN THE MOUNTAINS. SNOW LEVELS WILL START OFF
LOW BUT QUICKLY RISE TO 5000 TO 6000 FEET. THE OLYMPICS MAY SEE 6-10
INCHES OF RAIN...WITH 4-8 INCHES IN THE NORTH CASCADES. THESE
AMOUNTS WILL FORCE SHARP RISES ON THE RIVERS WITH SOME RIVERS
POSSIBLY FLOODING. HOWEVER...THERE IS SOME UNCERTAINTY IN THE
MODELS. THE LATEST MODELS SOLUTIONS ARE TRENDING TOWARD LIGHTER
RAINFALL AMOUNTS AS THIS FRONT DROPS SOUTH OF THE REGION ON WED.

IT STANDS RIGHT NOW FLOODING IS STILL POSSIBLE ON ALL OF THE RIVERS
FLOWING OUT OF THE OLYMPICS AND ALSO THE RIVERS COMING OFF OF THE
NORTH CASCADES BEGINNING TUESDAY.

THIS PATTERN IS NOT AS CONDUCIVE FOR FLOODING IN THE CENTRAL
CASCADES. 33

&&

.AVIATION...COLD DRY NW FLOW ALOFT HAS MOVED OVER W WA AS THE UPPER
LEVEL TROUGH PREVIOUSLY OVER THE AREA HAS MOVED E AND WEAKENED.
EXPECT CLEAR SKIES OR SCATTERED CLOUDS FROM ABOUT SEATTLE
NORTHWARD...WITH ONLY LOCAL FOG FORMING AFTER 12Z. DENSE FOG...WITH
CLEAR SKIES ABOVE...HAS ALREADY FORMED AT METAR-ED AIRPORTS FROM
TACOMA SOUTHWARD AND THIS WILL LIKELY PERSIST THROUGH ABOUT 18Z
SUNDAY BEFORE CLEARING.

KSEA...WILL STICK WITH THE MOSTLY CLEAR SKIES AND LIGHT WINDS AT
KSEA THROUGH SUNDAY. THE AIR MASS SEEMS COLD AND DRY ENOUGH SO THAT
EVEN IF BRIEF FOG FORMS IT WILL QUICKLY SUBLIMATE INTO FROST.
SURFACE WINDS WILL REMAIN 5 KT OR LESS AND FAVORING AN E TO NE
DIRECTION THROUGH SUNDAY. KAM

&&

.MARINE...WEAK NE OFFSHORE FLOW WILL CONTINUE TONIGHT WITH WINDS
REMAINING GENERALLY LIGHT. MODELS REMAIN CONSISTENT IN BRINGING THE
NEXT SIGNIFICANT FRONTAL SYSTEM TO THE REGION SUNDAY
NIGHT...FOLLOWED RAPIDLY BY ANOTHER FRONT MONDAY EVENING...WHICH
THEN HAS A SURFACE LOW OR WAVE MOVE UP THE FRONT EARLY TUESDAY
MORNING. WILL PLAN ON PUTTING UP A GALE WARNING FOR THE COAST IN THE
3 AM PACKAGE...AND GALE PRECEDED BY A SCA FOR THE N INTERIOR WATERS.
THERE WILL BE BRIEF LULLS IN WIND IN-BETWEEN THE THREE SYSTEMS...BUT
THE LULLS WILL BE SHORT ENOUGH SO THAT FOR SIMPLICITY ONE LONG GALE
WILL PROBABLY BE BETTER THAN TRYING TO CATCH EACH LITTLE LULL WITH A
SCA. OVERALL MODEL TREND HAS BEEN TOWARD A SLIGHTLY SHORTER PERIOD
FOR THE THREE SYSTEMS AND TOPPING OUT AT A HIGH END GALE FOR
STRENGTH. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.