Winter Storm Warning 1, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
345 PM PST SUN JAN 6 2013

.SYNOPSIS...CLOUDY AND DRY CONDITIONS WILL GIVE WAY TO ACTIVE
WEATHER AS A WARM FRONT BEGINS TO MOVE INTO THE AREA TONIGHT.
LOWLAND RAIN AND MOUNTAIN SNOW WILL AFFECT THE AREA MONDAY WITH A
BRIEF BRIEF LULL IN THE WEATHER MONDAY NIGHT BEFORE A WETTER AND
STRONGER SYSTEM WILL IMPACT THE REGION ON TUESDAY BRINGING MORE
LOCALLY HEAVY RAIN...MOUNTAIN SNOW...AND WINDY CONDITIONS.

&&

.SHORT TERM...DRY CONDITIONS TONIGHT WILL GIVE WAY TO INCREASING
RAIN AS A STRONG WARM FRONT MOVES INTO THE AREA. THIS SYSTEM WILL
BRING PLENTY OF MOISTURE TO THE AREA WITH PERIODS OF HEAVY RAIN AND
MOUNTAIN SNOW EXPECTED THROUGH MONDAY. SNOW LEVELS WILL RISE TO
4000-5000 FT MONDAY KEEPING THE HEAVIEST SNOW ACCUMULATIONS TO THE
VOLCANOES AND HIGHER TERRAIN ABOVE 4000 FT. SNOW ACCUMULATIONS
AROUND 18 INCHES POSSIBLE...ESPECIALLY AT MT BAKER AND MT RAINIER
THROUGH EARLY TUESDAY MORNING. IN ADDITION...EAST WINDS IN THE
PASSES WILL KEEP THE PASS TEMPS AT FREEZING SUPPORTING A WINTRY MIX
OF FREEZING RAIN AND SNOW THROUGH THE MORNING HOURS.  LOW LEVEL FLOW
WILL BECOME WESTERLY MONDAY AFTERNOON ALLOWING CONDITIONS AT THE
PASSES TO CHANGE OVER TO RAIN AND OVERALL TAPERING SHOWERS MON
NIGHT. MODEL RUNS IN MUCH BETTER AGREEMENT ON NEXT SYSTEM BEGINNING
TO AFFECT THE AREA TUESDAY MORNING WITH MOST NOW SHOWING A 995 TO
990 MB SURFACE LOW MOVING INTO THE NORTH END OF VANCOUVER ISLAND
JUST NORTH. IN ADDITION TO ANOTHER ROUND OF HEAVY MOUNTAIN SNOW
TUESDAY...AND ADDITIONAL 1-3 INCHES OF RAIN IS EXPECTED IN THE
LOWLANDS WITH HEAVIEST AMOUNTS ALONG THE COAST THROUGH THE FIRST
PART OF THE WEEK. IN ADDITION...BREEZY TO WINDY CONDITIONS ARE ALSO
ANTICIPATED WITH SOUTHWESTERLY WINDS FOR THE COAST AND SOUTH
INTERIOR...AND SOUTHEASTERLIES FOR ADMIRALTY INLET. THE COAST AND
NORTH INTERIOR MAY SEE WIND ADVISORY CRITERIA ESPECIALLY IF THE
SURFACE LOW MOVES INTO SOUTHERN B.C.

.LONG TERM...MEDIUM MODELS CONTINUE TO HIGHLIGHT A SHIFT TO A COOLER
PATTERN AS A DEEP UPPER LEVEL TROUGH DIGS ACROSS THE REGION FROM THE
NORTH. SNOW LEVELS LOWER TO BELOW 500 FEET WITH ISOLATED RAIN/SNOW
SHOWERS POSSIBLE ACROSS THE LOWLANDS. FLOW ALOFT TURNS NORTHERLY FRI
THROUGH THE WEEKEND AS A STRONG RIDGE AMPLIFIES OFFSHORE SUPPORTING
THE IDEA THAT THE AIR MASS WILL REMAIN COOL ENOUGH TO SUPPORT
LOWLAND SHOW SHOWERS. MODELS DO HINT AT A PROGRESSIVE SYSTEM SLIDING
DOWN ALONG THE WEST COAST OF BRITISH COLUMBIA ON SATURDAY BRINGING
THE THREAT OF MORE ORGANIZED PRECIPITATION AS WELL AS BREEZY TO
WINDY CONDITIONS FOR SOME LOCATIONS.

&&

.HYDROLOGY...HEAVY PRECIP IS FORECAST FOR THE MOUNTAINS THROUGH WED
WITH SEVERAL INCHES EXPECTED. HOWEVER MOST OF THE PRECIP WILL FALL
IN THE FORM OF SNOW WITH SNOW LEVELS LINGERING TO NEAR 3500 FT BY
TUESDAY. NONETHELESS THERE WILL LIKELY BE SOME SHARP RISES ON SOME
RIVERS...ESPECIALLY ON THE LOWER BASINS LIKE THE SKOKOMISH AND
CHEHALIS THAT WILL BEAR WATCHING OVER THE NEXT FEW PERIODS.

BEYOND WED...THE RISK OF FLOODING WILL BECOME EVEN LESS DUE TO A
COLDER AIR MASS SETTLING IN OVER THE REGION.

&&

.AVIATION...WEST TO NORTHWEST FLOW ALOFT WITH A BROAD UPPER RIDGE
OVER THE EASTERN PACIFIC. A FRONTAL SYSTEM WILL MOVE THROUGH THE
AREA TONIGHT THROUGH MONDAY MORNING. AIR MASS MOIST AND STABLE.

THERE IS CURRENTLY A MIX OF LOW CLOUDS AND HIGHER CLOUDS ACROSS THE
AREA. LOW CLOUDS WILL INCREASE THIS EVENING AS RAIN DEVELOPS AND
CONTINUE INTO MONDAY MORNING.

KSEA...SOUTH WIND 4-8 KNOTS. RAIN AND LOWERING CEILINGS EXPECTED TO
DEVELOP THIS EVENING. SOUTH/SOUTHWEST WINDS INCREASING AND BECOMING
GUSTY BEHIND THE COLD FRONT LATE MONDAY MORNING. SCHNEIDER

&&

.MARINE...SOUTHERLY WINDS WILL INCREASE TONIGHT AS A FRONTAL SYSTEM
BEGINS TO MOVE ONSHORE. THIS SYSTEM WILL BRING ANOTHER ROUND OF
SMALL CRAFT ADVISORY WINDS TO ALL WATERS TONIGHT AND MONDAY. THERE
COULD ALSO BE A FEW HOURS OF GALE FORCE WEST WINDS IN THE STRAIT OF
JUAN DE FUCA BEHIND THE FRONT MONDAY AFTERNOON. IN ADDITION TO THE
WINDS...WEST SWELL AROUND 10 FEET WILL CONTINUE OVER THE COASTAL
WATERS.

A SECOND SOMEWHAT STRONGER FRONTAL SYSTEM IS EXPECTED TO MOVE
THROUGH THE AREA TUESDAY AND TUESDAY NIGHT. MODELS ARE NOW IN BETTER
AGREEMENT WITH A 995 MB SURFACE LOW MOVING ONSHORE BETWEEN NORTHERN
VANCOUVER ISLAND AND QUEEN CHARLOTTE SOUND TUESDAY AFTERNOON. THIS
SYSTEM WILL BRING ANOTHER ROUND OF HIGH END SMALL SMALL CRAFT
ADVISORY WINDS TO ALL WATERS TUESDAY THROUGH WEDNESDAY MORNING.

A MUCH LESS STORMY PATTERN WILL PREVAIL LATER WEDNESDAY THROUGH
FRIDAY AS WEAK HIGH PRESSURE SETTLES OVER THE AREA. SCHNEIDER

&&

.AVALANCHE...WELL ADVERTISED FRONTAL SYSTEMS SHOULD MOVE ACROSS THE
NORTHWEST MONDAY AND TUESDAY. BOTH SYSTEMS SHOULD CAUSE A HIGH
AVALANCHE DANGER AT HIGHER ELEVATIONS. THE SYSTEM TUESDAY LOOKS
ESPECIALLY LIKELY TO STRONGLY IMPACT THE OLYMPICS AND NORTH CASCADES
WITH HEAVY SNOW AND WARMING. AN AVALANCHE WATCH IS ISSUED FOR THAT
AREA FOR TUESDAY. PLEASE SEE NWAC.US FOR DETAILS. FERBER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING CASCADES 4 AM MONDAY THROUGH 4AM PST
     TUESDAY.
PZ...GALE WATCH CENTRAL AND EASE STRAIT OF JUAN DE FUCA.
    .SMALL CRAFT ADVISORY ALL WATERS.
    .SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.

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