Wind Advisory 16, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
401 PM PDT SUN MAY 2 2010

.SYNOPSIS...A POWERFUL...WINTER LIKE STORM WILL IMPACT THE REGION
TONIGHT THROUGH MONDAY FOR WINDY CONDITIONS ALONG WITH HEAVY SNOW IN
THE MOUNTAINS. THE STRONG...COLD FRONT ASSOCIATED WITH THIS SYSTEM
WILL SWEEP ACROSS THE AREA LATE TONIGHT THROUGH EARLY MONDAY MORNING
AND USHER IN A COLDER AIR MASS. EXPECT THE SNOW LEVEL TO PLUMMET TO
NEAR 2500 FEET MONDAY MORNING. EXPECT SOMEWHAT MORE SETTLED
CONDITIONS MONDAY NIGHT. AN UPPER LOW WILL THEN SAG SOUTH OVER THE
AREA ON TUESDAY FOR A RISK OF THUNDERSTORMS OVER PORTIONS OF THE
INTERIOR. HIGHER PRESSURE WILL MOVE OVER THE PACIFIC NORTHWEST ON
WEDNESDAY FOR MORE SETTLED CONDITIONS.

&&

.SHORT TERM...
A POWERFUL...WINTER-LIKE STORM WILL BRING HEAVY SNOW TO THE
MOUNTAINS AND HIGH WINDS TO PARTS OF THE INTERIOR LATER TONIGHT THRU
MON. THEREFORE A WINTER STORM WARNING WILL BE ISSUED FOR THE
OLYMPICS AND CASCADES...AND A HIGH WIND WARNING WILL BE ISSUED FOR
THE ADMIRALTY INLET AREA AND WRN SKAGIT/SNOHOMISH COUNTIES.

WINDS WERE RESPONDING TO THE TIGHTENING OF THE PRES AND THERMAL
GRADIENTS THIS AFTERNOON...WITH LOCALLY WINDY CONDITIONS ALREADY
OCCURRING. PREFER THE STRONGER NAM WIND FIELD OVER THE GFS. IN
FACT...THE SFC LOW WAS ALREADY DEEPER THAN WHAT THE MODELS
PREDICTED. THUS ANTICIPATE SLY WINDS TO INCREASE FURTHER TONIGHT
AHEAD OF THE FRONTAL SYSTEM OFFSHORE...WITH HIGH WINDS LIKELY OVER
THE ADMIRALTY INLET AREA IN ESPECIALLY. WINDS WILL ALSO KICK UP
ELSEWHERE...THUS A WIND ADVISORY WAS ISSUE FOR MUCH OF THE INTERIOR
LOWLANDS. THE NAM INDICATED HAT THE KOTH TO KSEA PRES GRADIENT WILL
PEAK NEAR +14.5 MB LATE TONIGHT OR EARLY MON.

THE VIGOROUS CDFNT WILL SWEEP ACROSS THE CWA LATE TONIGHT THROUGH
EARLY MON...RESULTING IN STRONG CAA AND INCREASED WLY FLOW IN ITS
WAKE. HIGH END GALE FORCE WINDS ARE LIKELY OVER THE WATERS OF THE
CENTRAL AND WRN STRAIT OF JUAN DE FUCA ON MON. THE MOMENTUM WILL BE
CARRIED ACROSS THE ADMIRALTY INLET AREA...AND FAR WRN SKAGIT/
SNOHOMISH COUNTIES BY LATE MON MORNING. THE NAM WAS INDICATING 33
KNOT...WLY WIND SPEEDS OVER WHIDBEY ISLAND MON MORNING...WHICH
WARRANTED A HIGH WIND WARNING. THE GFS SOLUTION INDICATED THAT THE
KUIL TO KBLI PRES GRADIENT WILL PEAK NEAR +6 MB ON MON.

IN ADDITION TO THE STRONG WINDS...ANTICIPATE HEAVY...UPSLOPE FLOW TO
DEVELOP OVER THE WEST FACING SLOPES OF THE OLYMPICS AND CASCADES
LATER TONIGHT THROUGH MON NIGHT. THE SNOW LEVELS WILL START OUT
ABOVE 5500 FEET BUT WILL PLUMMET TO NEAR 2500 FEET BEHIND THE CDFNT.
AMOUNTS OF 6 TO 12 INCHES...WITH LOCALLY HIGHER AMOUNTS...ARE LIKELY
ON THE CASCADES BY TUE MORNING...WITH SLIGHTLY LESSER AMOUNTS OVER
THE OLYMPICS.

CONDITIONS WILL IMPROVE SOMEWHAT MON NIGHT...WITH WINDS DIMINISHING
AND SNOWFALL INTENSITY LETTING UP. RELAXING OF THE PRES GRADIENT
WILL ALLOW A PUGET SOUND CONVERGENCE ZONE /PSCZ/ TO DEVELOP MON
NIGHT. EXPECT A RISK OF TSTMS WITHIN THE PSCZ. THE PSCZ WILL LIKELY
SLIDE SWD DURING THE DAY TUE BEFORE DISSIPATING OVER THE S SOUND.

AN UPPER LOW WILL MOVE OVER THE CWA TUE...SERVING TO DESTABILIZE THE
AIR MASS FURTHER. THUS HAVE INTRODUCED A CHANCE OF TSTMS OVER
PORTIONS OF THE INTERIOR ON TUE OR FOR THOSE ZONES WHERE THE COLD
POOL ALOFT WILL TRACK.

A WEAK...RIDGE WILL MOVE OVER THE REGION ON WED FOR MORE SETTLED
CONDITIONS.

.LONG TERM...
CONFIDENCE IN THIS PERIOD WAS SOMEWHAT LOW. THE MEDIUM RANGE
SOLUTIONS WERE BACKING OFF ON A COMPLETELY DRY FORECAST THE REST OF
THIS WEEK AND SHOWED A WEAKER RIDGE OVER THE PAC NW. THEREFORE HAVE
MENTIONED A CHANCE OF SHOWERS OVER THE MOUNTAINS DURING MUCH OF HIS
PERIOD. A N UPPER TROF MAY AFFECT THE PAC NW ON DAY 7.

&&

.AVIATION...FLOW ALOFT OVER WESTERN WASHINGTON WILL BECOMING WEST
AND STRENGTHEN OVERNIGHT INTO MONDAY. BELOW 6000 FT...THE SW WIND
WILL INCREASE TO NEAR 50 KT LATE THIS EVENING BEFORE EASING TO 20-30
KT MONDAY.  AT THE SURFACE THE SOUTHERLY FLOW WILL RAMP UP THROUGH
07Z.  A STRONG COLD FRONT WILL MOVE ACROSS THE AREA JUST BEFORE DAWN
MONDAY WITH STRONG ONSHORE DEVELOPING BEHIND THE FRONT.

CIGS ACROSS THE AREA DID LIFT THROUGH THE DAY AND ARE GENERALLY VFR.
THE EXCEPTIONS ARE ALONG THE COAST AND PARTS OF THE NORTHERN AREAS
WHERE THE RAIN HAS SPREAD IN AND HELPED TO LOWER THE CIGS.  THIS
TREND WILL SPREAD THROUGHOUT WESTERN WASHINGTON THIS EVENING WITH
CIG SETTLING IN AROUND BKN-OVC015-025.  VSBYS WILL OCNLLY DROP TO
3-5SM IN RAIN AND FOG.  CIGS AND VSBYS EXPECTED TO IMPROVE
SIGNIFICANTLY A COUPLE OF HOURS AFTER THE FRONT PASSES MONDAY
MORNING.

KSEA...THE RAIN WILL BEGIN ANYTIME NOW WITH THE CIGS QUICKLY
DROPPING TO AROUND BKN020 OVC035 SHORTLY AFTER THE RAIN BEGINS. CIGS
REMAINING BKN-OVC015-025 TONIGHT WITH VSBYS DROPPING TO 4-6SM IN
RAIN AND MIST AT TIMES.  SOUTH WINDS WILL CONTINUE TO RAMP UP
TONIGHT AND WITH STRONG ONSHORE FLOW WILL REMAIN STRONG SW THROUGH A
LARGE PART OF MONDAY.  CERNIGLIA

&&

.MARINE...A STRONG LATE SEASON STORM WILL AFFECT THE REGION THROUGH
MON NIGHT WITH GALE FORCE WINDS AFFECTING AT LEAST PARTS OF ALL
MARINE ZONES FOR SHORT PERIODS OF TIMES.  A SYNOPSIS...A 1012 MB LOW
NEAR 47N 130W WILL DEEPEN TO AROUND 1002 MB AS IT CROSSES SOUTHERN
VANCOUVER ISLAND DURING THE EARLY MORNING HOURS MON.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES INTO BRITISH COLUMBIA.  THE
ASSOCIATED WARM FRONT WILL MOVE ACROSS THE AREA LATER THIS EVENING
WITH THE TRAILING COLD FRONT PASSING THROUGH AROUND DAWN MON.
STRONG ONSHORE FLOW WILL DEVELOP IN THE WAKE OF THIS SYSTEM AND
CONTINUE INTO MON EVENING.

EXPECTING THE FOLLOWING AS A RESULT...FOR THE COAST...GENERALLY 20
TO 30 KT SW WINDS IN ADVANCE OF THE COLD FRONT BUT A SHORT PERIOD OF
35 TO 40 KT IS A GOOD BET TONIGHT...ESPECIALLY NEAR SHORE FROM CAPE
FLATTERY SOUTH TO THE QUINAULT RIVER.

INLAND WATERS INCLUDING THE PUGET SOUND AND ADMIRALTY INLET...EXPECT
THE S WIND TO CONTINUE TO GOOD RAMP UP THROUGH THE EVENING TO 25 TO
35 KT BY MIDNIGHT. THE STRONGEST WINDS SHOULD BE NORTH OF
EDMONDS...INCLUDING THE N HOOD CANAL...UP TO THE SOUTHERN EDGE OF
THE SAN JUANS.

THEN A STRONG WEST SURGE IS EXPECTED DOWN THE STRAIT EARLY MON
MORNING IN THE WAKE OF THE COLD FRONT WITH 30 TO 40 KT LIKELY AND
SUSTAINED 45 KT A FAIR BET WHICH WILL AFFECT THE CENTRAL AND EAST
ENTRANCE AS WELL AS THE ADMIRALTY INLET AREA AND WILL CONTINUE
THROUGH A LARGE PART OF MON.

AFTER THAT THE ONSHORE FLOW IS EXPECTED TO CONTINUE THROUGH THE
WEEK...GRADUALLY EASING MON NIGHT THROUGH TUE...BECOMING LIGHT TUE
NIGHT INTO FRI.  CERNIGLIA

&&

.AVALANCHE...
LATE SEASON SNOWFALL LAST WEEK WAS FAIRLY HEAVY AT HIGHER ELEVATIONS
NEAR AND WEST OF THE CREST ALONG WITH COOL TEMPERATURES AND MODERATE
RIDGETOP WINDS. CAREFUL SNOW PACK EVALUATION AND CAUTIOUS ROUTE
FINDING CONTINUE TO BE ESSENTIAL TODAY NEAR AND WEST OF THE CREST AT
HIGHER ELEVATIONS WITH SOME WIND SLABS OVERLYING WEAKER LAYERS OF
MOIST OR WET SNOW.

A STRONG ALMOST MID-WINTER LOOKING STORM EXPECTED TO ARRIVE LATER
TODAY THROUGH MONDAY SHOULD ADD FURTHER MODERATE TO HEAVY SNOWFALL
AMOUNTS AT PROGRESSIVELY LOWER ELEVATIONS. ADDITIONAL SNOWFALL
AMOUNTS SHOULD RANGE UP TO 1 TO 2 FEET ABOVE 5 TO 6000 FEET IN THE
OLYMPICS AND CASCADES NEAR AND WEST OF THE CREST WITH 6-12 INCHES
POSSIBLE DOWN TO AROUND 3000 FEET AND IN SOME EAST SLOPE LOCATIONS
NEAR THE CREST. ALONG WITH INCREASINGLY STRONG RIDGETOP AND PASS
WINDS THIS SHOULD CREATE A SIGNIFICANT INCREASE IN THE AVALANCHE
DANGER ESPECIALLY ON WIND LOADED TERRAIN AT HIGHER ELEVATIONS.
PLEASE CONSULT THE SPECIAL STATEMENT ON WWW.NWAC.US FOR DETAILS.
MOORE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WARNING IN EFFECT FOR THE ADMIRALTY INLET AREA AND
     FAR WESTERN SKAGIT/SNOHOMISH COUNTIES FROM 11 PM TONIGHT TIL
     9 PM PDT MON.

     WIND ADVISORY IN EFFECT FOR MUCH OF THE INTERIOR LOWLANDS FROM
     11 PM TONIGHT TIL 7 PM PDT MONDAY.

     A WINTER STORM WARNING IS IN EFFECT FOR THE OLYMPICS AND
     CASCADES ABOVE 2500 FEET FROM MIDNIGHT TONIGHT IL 6 AM PDT
     TUE.

PZ...A GALE WARNING IS IN EFFECT FOR ALL WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS TIL 11 PM MON.

WWW.WEATHER.GOV/SEATTLE

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