Small Craft Advisory 232, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
912 AM PDT THU OCT 29 2015

.SYNOPSIS...SHOWERS WILL DIMINISH TODAY AS AN UPPER TROUGH MOVES
EAST OF THE AREA. A STRONG PACIFIC FRONTAL SYSTEM WILL BRING RAINY
AND BREEZY WEATHER FRIDAY AND SATURDAY. A COOL UPPER TROUGH WILL
CROSS THE REGION ON SUNDAY FOR SHOWERS. A STRONG UPPER RIDGE OFFSHORE
WILL BRING DRIER WEATHER EARLY NEXT WEEK.

&&

.SHORT TERM...A WEAK UPPER RIDGE WILL MOVE OVER THE AREA TODAY.
SOME SHOWERS WILL LINGER HOWEVER IN MOIST ONSHORE FLOW. THE BEST
CHANCES WILL BE OVER THE MOUNTAINS.

MOIST ZONAL FLOW WILL DEVELOP FRIDAY AND CONTINUE INTO SATURDAY
WITH A FRONTAL SYSTEM DRAPED ACROSS THE REGION FOR WET AND
BLUSTERY WEATHER.

THE HEAVIER PRECIPITATION LOOKS LIKE IT WILL COME IN TWO WAVES.
THE FIRST WAVE WILL BE FRIDAY MORNING. THE SECOND HEAVIER SHOT OF
RAIN WILL DEVELOP LATER FRIDAY NIGHT AND CONTINUE INTO SATURDAY.

THE HEAVY RAINS WILL END FROM NORTH TO SOUTH SATURDAY AFTERNOON
AND EVENING AS THE FRONTAL FEATURE SAGS SOUTH OF THE AREA. MINOR
RIVER FLOODING IS POSSIBLE BY SATURDAY OR SATURDAY NIGHT. SEE THE
HYDROLOGY SECTION BELOW FOR MORE DETAILS.

AN UPPER TROUGH WILL MOVE OVER THE AREA ON SUNDAY FOR COOLER
SHOWERY WEATHER. SNOW LEVELS WILL FALL TO 4000 TO 5000 FEET WHICH
MEANS THE HIGHER MOUNTAIN PASSES COULD PICK UP A FEW INCHES OF
SNOW. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...A STRONG UPPER LEVEL RIDGE
WILL FORM OVER THE NE PAC EARLY NEXT WEEK WITH NORTHERLY FLOW
ALOFT OVER WESTERN WA. A WEAK UPPER LEVEL DISTURBANCE MAY TRACK
DOWN FROM THE NORTH FOR A CHANCE OF SHOWERS MONDAY AND MONDAY
NIGHT. THE RIDGE WILL THEN SHIFT EAST AND INLAND TUESDAY AND
WEDNESDAY FOR DRIER WEATHER. THE NORTHERLY FLOW WILL KEEP
TEMPERATURES ON THE COOLSIDE WITH TEMPS A FEW DEGREES BELOW
NORMAL. THE RIDGE MAY LINGER OVER THE PAC NW THROUGH THE END OF
NEXT WEEK FOR MORE DRY WEATHER. 33

&&

.AVIATION...AN UPPER LEVEL RIDGE WILL PREVAIL OVER THE REGION
TODAY FOR STRONG NLY FLOW ALOFT. CONTD LOW LEVEL ONSHORE FLOW.
WIDESPREAD MVFR CIGS THIS MORNING WILL BECOME AREAS OF MVFR CIGS
THIS AFTERNOON. THE MTNS WILL BE PARTIALLY OBSCD.

KSEA...ANTICIPATE CIGS IN THE 1500 TO 2500 FT RANGE TIL 2100
UTC...WITH VFR CONDITIONS PREVAILING AFTER 2100 UTC. HOWEVER...
CIGS WILL LOWER BACK INTO THE MVFR CATEGORY RANGE THIS EVENING.
WINDS WILL BE SLY 9-13 KT WITH OCNL GUSTS TO 20 KT TODAY.

&&

.MARINE...LOW LEVEL SOUTHERLY OR ONSHORE FLOW WILL CONTINUE
THROUGH TONIGHT. A FRONTAL SYSTEM WILL MOVE ACROSS THE AREA ON
FRI...RESULTING IN WIND SPEEDS REACHING SMALL CRAFT ADVISORY
CRITERION ACROSS ALL WATERS. ANOTHER...POSSIBLY STRONGER
SYSTEM...WILL IMPACT THE AREA ON SATURDAY. FELTON/05

&&

.HYDROLOGY...PREVIOUS DISCUSSION...A WET PATTERN WILL DEVELOP
FRIDAY AND CONTINUE INTO SATURDAY. SNOW LEVELS WILL BE HIGH AND
SEVERAL INCHES OF RAIN ARE LIKELY OVER THE OLYMPICS AND WEST
SLOPES OF THE CASCADES.

MODELS DIFFER A BIT WITH THE DETAILS BUT THE GENERAL IDEA IS THERE
WILL BE HYDROLOGICALLY SIGNIFICANT RAIN OVER THE MOUNTAINS DURING
THIS PERIOD. MODELS SHOW 5-10 INCHES OF RAIN POSSIBLE OVER A 48-HOUR
PERIOD ENDING SATURDAY AFTERNOON. THE FIRST SHOT OF HEAVY RAIN
APPEARS TO BE DURING THE FIRST HALF OF FRIDAY...THEN PERHAPS A
RELATIVE LULL...FOLLOWED BY ANOTHER ROUND OF HEAVY RAIN LATE FRIDAY
NIGHT OR SATURDAY.

A HYDROLOGIC OUTLOOK IS IN EFFECT FOR MOST OF THE FORECAST AREA
TO HIGHLIGHT THE GENERAL THREAT FOR MINOR FLOODING ON AREA RIVERS
BY SATURDAY.

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT CENTRAL STRAIT.

&&

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