Small Craft Advisory 32, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1007 AM PST THU FEB 13 2014

.SYNOPSIS...A LULL IN THE WEATHER IS EXPECTED THIS AFTERNOON AND
EVENING. A STORM SYSTEM WILL ARRIVE LATE THIS EVENING AND OVERNIGHT.
A SECOND STORM WILL ARRIVE SATURDAY...FOLLOWED BY A THIRD STORM ON
SUNDAY AFTERNOON. EACH STORM WILL CONTAIN STRONG WIND...PERIODS OF
HEAVY RAIN AND LOTS OF MOUNTAIN SNOW.

&&

.SHORT TERM...AN ANCHORING UPPER LOW OVER SOUTH-CENTRAL ALASKA WILL
HELP TO KEEP THE POSITIVELY TILTED LONGWAVE TROUGH OVER THE ERN PAC
THROUGH THIS WEEKEND. THIS LONGWAVE TROUGH HAS DIRECTED AN ACTIVE
AND ENERGETIC FLOW OF W-SW JET STREAM WINDS INTO THE PAC NW...WITH A
SERIES OF FRONTS AND STORMS WAITING UPSTREAM. THROUGH SUNDAY
NIGHT...THREE SEPARATE FRONTS OR STORMS ARE EXPECTED TO AFFECT THE
WRN WA WEATHER...EACH PERHAPS MORE IMPACTFUL THAN THE LAST. WEATHER
SYSTEMS WILL ARRIVE LATE THIS EVENING...SATURDAY...AND SUNDAY. EACH
SYSTEM WILL BRING ITS SHARE OF RAIN...WIND AND MOUNTAIN SNOW. LULLS
OF 6-12 HOURS WILL OCCUR BETWEEN WEATHER SYSTEMS...ALLOWING FOR
BREAKS WITH LESS WIND...BREAKS IN THE CLOUDS AND A BREAK IN PRECIP.

FOR TONIGHT...LOOKS LIKE A PREDOMINANTLY DRY EVNG FOR WRN WA. BY
LATE TONIGHT...A 975 MB LOW WILL PASS NW OF HAIDA GWAII WITH A
TRAILING FRONT SPREADING INTO WRN WA. A 500 MB HEIGHT FALL CENTER
WILL PASS EAST ALONG THE U.S./CANADIAN BORDER...AND 140-160 KT UPPER
JET WILL CUT ACROSS WRN WA...ENERGIZING THE FRONT AS IT PASSES
THROUGH THE REGION. RAIN WILL QUICKLY SPREAD ACROSS WRN WA BTWN 06Z
AND 12Z TONIGHT. SNOW LEVELS OF 2500-3500 FEET WILL SUPPORT MODERATE
TO HEAVY SNOW IN THE MTNS. A COLD FRONT WILL PASS THROUGH WRN WA
FROM 12Z-15Z...TURNING PRECIP TO A MORE SHOWERY REGIME. FROM A WIND
PERSPECTIVE...GRADIENTS IN THE PRE-FRONTAL ENVIRONMENT ARE MORE
DECIDEDLY SE...FAVORING STRONGER ADVISORY-LEVEL WIND FOR THE COAST
AND THE NORTH INTERIOR ZONES. STRONGER WINDS POSSIBLE TOO IN
THURSTON AND PIERCE COUNTIES. WILL BE CONSIDERING WIND ADVISORIES
WITH THE AFTN FCST. BREEZY AND WINDY ONSHORE WINDS WILL FOLLOW
DURING THE DAY ON FRI. LOOKS LIKE A BREAK IN THE WEATHER FROM LATE
FRI AFTN INTO EARLY SAT MRNG.

THE NEXT WEATHER SYSTEM SHOULD ARRIVE AROUND MID-DAY ON SATURDAY. AN
ENERGETIC NEGATIVELY TILTED TROUGH...PRECEDED BY STRONG UPPER LEVEL
DIVERGENCE...WILL HELP A 975 MB LOW TO SPIN UP BTWN VANCOUVER ISLAND
AND HAIDA GWAII...WITH A NEGATIVELY TILTED COLD FRONT QUICKLY
CROSSING WRN WA ARND 00Z-03Z ON SAT AFTN/EVNG. HEAVY RAIN WILL
QUICKLY OVERSPREAD WRN WA ON SAT AFTN...AND SE GRADIENTS WILL AGAIN
SUPPORT ADVISORY-LEVEL WINDS FOR AT LEAST THE COAST AND NORTH
INTERIOR...PERHAPS A FEW OTHER ZONES AS WELL IN THE AFTN AND EARLY
EVNG. ONCE AGAIN...THE MTNS SLATED FOR MORE HEAVY SNOW...THOUGH THE
SNOW LEVEL MAY BRIEFLY SPIKE TO NEAR 4000 FEET JUST AHEAD OF THE
COLD FRONT. A SHORT BREAK IN THE WEATHER IS EXPECTED ON SUNDAY
MORNING.

PERHAPS MOST CONCERNING IS THE THIRD SYSTEM...SLATED TO ARRIVE ON
SUNDAY AFTN. A STRONG FRONTAL WAVE WILL DEVELOP IN THE FAVORED LEFT
EXIT REGION OF AN UPPER JET AS IT APPROACHES THE WA COAST. DESPITE A
980 MB LOW CENTER WEST OF NORTHERN VANCOUVER ISLAND ON SUN
AFTN...THE OPEN FRONTAL WAVE WILL BRING A STRONG PRESSURE FALL
CENTER ACROSS SOUTHERN VANCOUVER ISLAND...AND S-SW 850 MB WINDS UP
TO AN IMPRESSIVE 70-80 KNOTS OVER SW WA ON SUN AFTN. WITH THE 12Z
GFS FORECASTING THE AST-UIL GRADIENT ARND +7 MB AT THAT TIME...THIS
COULD SPELL A DAMAGING HIGH WIND EVENT FOR THE COAST. OTHER ZONES
COULD ALSO EXPERIENCE HIGH WIND...WHICH BY DEFINITION MEANS
SUSTAINED WINDS OF 40+ MPH OR GUSTS OF 58+ MPH. WINDS THIS STRONG
AND OUR TERRAIN COULD FOCUS 1-3 FEET OF SNOW IN THE MTNS FROM
MID-DAY SUNDAY THROUGH MID-DAY MONDAY.      HANER

.LONG TERM...FROM PREVIOUS DISCUSSION...
BEYOND MON...IT APPEARED THAT THE WEATHER PATTERN WILL TREND TOWARD
A COLDER ONE...WITH HIGHS ANTICIPATED TO RUN BELOW NORMAL.

&&

.HYDROLOGY...
THE SNOW LEVEL WILL REMAIN FAIRLY LOW THROUGH FRI OR MAINLY IN THE
2500 TO 3K FOOT RANGE. THE FRI SYSTEM WILL ALSO BE FAST-MOVING.
RIVER FLOODING IS NOT ANTICIPATED THRU FRI...ALTHOUGH THERE WILL
LIKELY BE SOME SHARP RISES FRI ON THE LOWER ELEVATION BASIN RIVERS
SUCH AS THE SKOKOMISH. ANOTHER STRONG AND WET SYSTEM WILL IMPACT THE
REGION ON SATURDAY. THE SNOW LEVELS ARE EXPECTED TO BRIEFLY CLIMB TO
4500 TO NEAR 5K FEET WITH THIS SYSTEM. THIS COMBINED WITH HEAVY
RAINFALL COULD LEAD TO SOME MINOR FLOODING ON SATURDAY ON THE
FLASHIER RIVERS SUCH AS THE SKOKOMISH AND THE LOWER ELEVATION BASIN
RIVERS SUCH AS THE CHEHALIS.

BEYOND SATURDAY...IT APPEARED THAT THE TREND WAS TOWARD A COLDER
PATTERN AND THIS SHOULD DECREASE THE RISK OF ANY RIVER FLOODING...
ALTHOUGH THE SKOKOMISH RIVER MIGHT COME CLOSE TO FLOODING ON SUNDAY.

&&

.AVIATION...STRONG WESTERLY FLOW ALOFT WILL CONTINUE INTO THE
WEEKEND RESULTING IN A VERY ACTIVE WEATHER PATTERN OVER THE REGION.
STRONG ONSHORE SURFACE FLOW THIS MORNING WILL EASE THIS AFTERNOON AS
A SURFACE RIDGE MOVES OVER W WA. THE AIR MASS HAS DRIED OUT QUITE A
BIT UNDER THE STRONG W FLOW AND VFR CONDITIONS PREDOMINATE. THERE
WILL STILL BE SCATTERED SHOWERS OVER THE MOUNTAINS AND ISOLATED
SHOWERS OVER THE LOWLANDS. SHOWERS BLOWING E OFF THE OLYMPICS COULD
BRING SOME SPOTTY MVFR CIGS AROUND PUGET SOUND. UPSLOPE FLOW OVER
THE CASCADES WILL KEEP THEM OBSCURED TODAY.

THE STRONG WESTERLY ONSHORE FLOW WILL KEEP GUSTY W-SW WINDS
8-15G25KT GOING FROM ABOUT WHIDBEY ISLAND SOUTHWARD THROUGH
22Z...WITH WINDS WEAKENING AFTER THAT.

KSEA...VFR CONDITIONS THROUGH 08Z. JUST SCT CLOUDS TODAY...ALTHOUGH
THERE COULD BE SOME BRIEF CIGS BKN040-050 FROM CLOUDS BLOWING E OFF
THE OLYMPICS. SURFACE WINDS WILL REMAIN SW 15-24 KT THROUGH 22Z THEN
DIMINISHING TO 8-14KT. NO WIND SHIFTS EXPECTED. KAM

&&

.MARINE...WESTERLY ONSHORE FLOW IS WEAKENING RAPIDLY THIS MORNING AS
A SURFACE RIDGE MOVES INLAND. THE RIDGE WILL BE OVER W WA THIS
AFTERNOON BEFORE MOVING QUICKLY EAST. ALL GALES HAVE BEEN
DROPPED...WITH RESIDUAL SCA IN PLACE FOR THE INTERIOR INTO THIS
AFTERNOON TO HANDLE THE DIMINISHING WINDS.

THE NEXT STRONG FRONTAL SYSTEM IS ON TRACK FOR LATE TONIGHT. GALE
WARNINGS HAVE ALREADY BEEN RAISED FOR LATE THIS EVENING THROUGH
FRIDAY MORNING. MODELS HAVE BEEN PRETTY CONSISTENT WITH THIS SYSTEM
SHOWING THE STRONGEST SE GALES 12Z-15Z...THEN W GALES IN THE STRAIT
15Z-00Z FRIDAY.

PARADE OF GALE SYSTEMS CONTINUES WITH ANOTHER STRONG FRONTAL SYSTEM
ARRIVING ON SATURDAY AND THEN A SURFACE LOW ON SUNDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WATCH FOR THE NORTH AND CENTRAL CASCADES FROM
      LATE TONIGHT THROUGH FRIDAY.
     WINTER WEATHER ADVISORY FOR THE OLYMPIC MOUNTAINS FROM
      TONIGHT THROUGH FRIDAY.

PZ...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE.
     SMALL CRAFT ADVISORY THROUGH EARLY AFTERNOON ALL INLAND WATERS
      EXCEPT ADMIRALTY INLET.
     GALE WARNING MOST WATERS AGAIN TONIGHT AND FRIDAY.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

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