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000
FXUS66 KSEW 170434
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
934 PM PDT SUN MAR 16 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM WILL MOVE OVER THE AREA TONIGHT
AND WILL BE FOLLOWED BY HIGH PRESSURE ON MONDAY. EXPECT AN
APPROACHING WARM FRONT TO BRING SOME LIGHT PRECIPITATION TO
MAINLY THE COAST MONDAY NIGHT. THE TAIL END OF THIS FRONT WILL
MOVE ACROSS THE AREA ON TUESDAY. A STRONG AND COLD SYSTEM WILL
MOVE ACROSS THE REGION ON WEDNESDAY.

&&

.SHORT TERM...
THE MAIN COLD FRONT WAS MOVING SOUTHEAST ACROSS THE CWA AT THIS
TIME. BEHIND THE FRONT...THE PRECIP HAS TAPERED OFF TO SCATTERED
SHOWERS. STEADY...LOCALLY HEAVY PRECIP...CONTINUED AHEAD OF THE
FRONT OR OVER ROUGHLY THE SOUTHEAST PART OF THE CWA. LOOK FOR
SCATTERED SHOWERS /MORE NUMEROUS OVER THE CASCADES/ ACROSS THE
CWA AFTER MIDNIGHT.

MEANWHILE...A PUGET SOUND CONVERGENCE ZONE /PSCZ/ DEVELOPED THIS
EVENING. AT THE SURFACE...IT WAS LOCATED OVER THE SOUTH SOUND
/BETWEEN KSEA AND KTCM/ BUT ALOFT IT APPEARED TO BE FARTHER NORTH
OR BETWEEN KPAE AND KAWO. THE ONSHORE PRESSURE GRADIENT CONTINUED
TO TIGHTEN... WITH THE GRADIENT BETWEEN KUIL AND KBLI NOW UP TO
PLUS 2.5 MB AT THIS HOUR. BOTH THE NAM AND 4 KM WRF-GFS INDICATED
THAT THE PSCZ WILL END UP BECOMING CONFINED TO THE SOUTH-CENTRAL
OR SOUTH SOUND BEFORE DISSIPATING MON MORNING. HOWEVER...SUSPECT
THAT THESE MODELS WERE GETTING RID OF THE PSCZ TOO SOON. MOST
LIKELY...IT WILL DRIFT NORTHWARD DURING THE DAY MON /AS THE LOW
LEVEL FLOW DEVELOPS A SOUTHERLY COMPONENT/ BEFORE EVENTUALLY
DISSIPATING.

THE SNOW IN THE CASCADES WILL GRADUALLY TAPER OFF OR BECOME LIGHT
OVERNIGHT BUT EVEN MORE MON MORNING. THE PRECIP HAS ALREADY
SCATTERED OVER THE OLYMPICS...SO THE WARNING WAS ENDED.

AN UPPER RIDGE WILL MOVE OVER THE REGION ON MON FOR MORE SETTLED
CONDITIONS BUT THERE WILL STILL BE SOME SHOWERS AROUND. AN
APPROACHING WARM FRONT WILL BRING SOME LIGHT PRECIP TO THE MAINLY
THE COAST MON NIGH. EXPECT THE PRECIP TO OVERSPREAD THE REMAINDER
OF THE CWA ON TUE.

A VIGOROUS UPPER TROF AND ASSOCIATED COLD FRONT EMANATING OUT OF
THE GULF OF AK WILL APPROACH THE PACIFIC NORTHWEST TUE NIGHT.
ANTICIPATE THIS SYSTEM TO SWEEP ACROSS THE REGION ON WED. THERE IS
A POSSIBILITY OF SIGNIFICANT SNOWFALL IN THE MOUNTAINS WITH THIS
SYSTEM.

.LONG TERM FROM THE PREV DISCUSSION...
ONSHORE FLOW WILL PREVAIL ON THURSDAY FOR COOLER WEATHER AND A
FEW MORE SHOWERS ACROSS WESTERN WA. SNOW LEVELS WERE STILL LOW AT
THIS POINT - AROUND 2000 FT. THE LOW LEVEL FLOW WILL START TO TURN
OFFSHORE ON FRIDAY AS A SURFACE TROUGH FORMS ALONG THE COAST. THIS
SHOULD HELP CLEAR OUT SOME LOW LEVEL CLOUDS. A WEAK SYSTEM MAY
CLIP THROUGH B.C. ON SAT BUT IT WAS STARTING TO LOOK DRY FOR
WESTERN WA. POPS WERE SCALED BACK FOR NOW. THE MODELS WERE HAVING
A DIFFICULT TIME WITH THE STRENGTH OF A RIDGE OVER THE PAC NW
EARLY NEXT WEEK. THE ECMWF WAS SHOWING A RIDGE OVER THE REGION
SUN-WED WHILE THE GFS BROUGHT A FRONT INTO WESTERN WA ON MON.
CONFIDENCE REMAINED LOW AND LITTLE CHANGES WERE MADE FROM THE
PREVIOUS FORECAST. 33

&&

.HYDROLOGY...
SOME RIVERS WERE ALREADY RECEDING BUT THERE WERE STILL QUITE A FEW
THAT HAVE NOT CRESTED YET. EXPECT THESE RIVERS TO CREST BELOW
FLOOD STAGE LATER TONIGHT OR MON MORNING. ADDITIONAL RAINFALL
OVERNIGHT IS NOT EXPECTED TO BE HYDROLOGICALLY SIGNIFICANT. ALSO...
SNOW LEVELS HAVE PLUMMETED AND WERE RUNNING NEAR 2K FT ACROSS THE
NORTHWEST PART OF THE CWA TO NEAR 3500 FEET ACROSS THE FAR
SOUTHEAST THIS EVENING. BY SUNRISE MON...THE SNOW LEVEL IS
EXPECTED TO BE IN THE 1500-2K FOOT RANGE.

HYDROLOGICALLY SIGNIFICANT RAINFALL IS NOT EXPECTED MON THROUGH
THIS WEEKEND...THUS FLOODING ON AREA RIVERS IS NOT ANTICIPATED
DURING THIS PERIOD.

&&

.AVIATION...AN UPPER TROUGH AND AN ASSOCIATED COLD FRONT WILL MOVE
THROUGH THE AREA TONIGHT...FOLLOWED BY MODERATE LOW LEVEL ONSHORE
FLOW AND NORTHWEST FLOW ALOFT ON MONDAY. AIR MASS MOIST AND
STABLE...BECOMING SLIGHTLY UNSTABLE BEHIND THE FRONT WITH GRADUAL
DRYING.

MOSTLY MVFR CEILINGS TONIGHT BUT SOME IFR IN HEAVIER RAIN UNTIL
EARLY MORNING. CEILINGS SHOULD LIFT AND BECOME MOSTLY VFR MONDAY. A
PUGET SOUND CONVERGE ZONE IS LIKELY OVER CENTRAL PUGET SOUND MONDAY.
SCHNEIDER

KSEA...IFR CEILINGS THIS EVENING SHOULD BECOME MVFR AFTER MIDNIGHT
TONIGHT AS A FRONT PUSHES EAST OF THE TERMINAL. CEILINGS SHOULD
IMPROVE TO VFR ON MONDAY AS THE LOWEST LEVELS DRY A BIT. NORTH WINDS
HAVE MADE IT DOWN TO THE TERMINAL THIS EVENING. THESE WILL PROBABLY
CONTINUE FOR A FEW HOURS...THEN BECOME SOUTHERLY AGAIN OR AT LEAST
VARIABLE LATER TONIGHT. A PUGET SOUND CONVERGENCE ZONE COULD COME AS
FAR SOUTH AS THE TERMINAL MONDAY WHICH WOULD POTENTIALLY BRING SOME
MORE NORTH WINDS AGAIN. SCHNEIDER

&&

.MARINE...A COLD FRONT WILL MOVE INLAND TONIGHT. MODERATE TO STRONG
ONSHORE FLOW BEHIND THE FRONT WILL BRING GALE WEST WINDS TO THE
STRAIT AND SMALL CRAFT ADVISORY WINDS MOST OTHER WATERS. WEST SWELL
AROUND 15 FEET OVER THE COASTAL WATERS WILL SUBSIDE TO 10 FEET OR
LOWER BY MONDAY EVENING.

ONSHORE FLOW WILL EASE RAPIDLY MONDAY NIGHT AS A WEAK SURFACE RIDGE
BUILDS OVER THE AREA. A SECOND FRONTAL SYSTEM WILL MOVE THROUGH THE
WATERS TUESDAY NIGHT AND WEDNESDAY. THIS WILL BE FOLLOWED BY MORE
MODERATE TO STRONG ONSHORE LATER WEDNESDAY AND WEDNESDAY
NIGHT...EASING ON THURSDAY...THEN BECOMING WEAKLY OFFSHORE ON
FRIDAY. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING IN EFFECT UNTIL MIDNIGHT TONIGHT FOR
     THE NORTH CASCADES ABOVE 2000 FEET.

     HIGH SURF ADVISORY IN EFFECT UNTIL 3 AM MONDAY FOR THE
     COAST.

     WINTER WEATHER ADVISORY IN EFFECT UNTIL 6 AM MONDAY FOR THE
     CENTRAL CASCADES ABOVE 2000 FEET.

PZ...GALE WARNING IN EFFECT UNTIL 7 PM MONDAY FOR THE CENTRAL AND
     EASTERN STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING
     WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH BAR UNTIL 9 PM
     MONDAY FOR THE GRAYS HARBOR BAR.

&&

$$

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