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000
FXUS66 KSEW 190945
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
245 AM PDT SUN MAY 19 2013

.SYNOPSIS...AN UPPER RIDGE WILL BUILD INTO THE REGION TODAY...THEN
CROSS THE AREA ON MONDAY...FOR WARMER AND DRIER WEATHER. A LARGE
UPPER LOW WILL DROP INTO THE AREA ON TUESDAY AND REMAIN OVER THE
REGION THROUGH THE REMAINDER OF THE WEEK FOR SHOWERY WEATHER AND
BELOW NORMAL TEMPERATURES.

&&

.SHORT TERM...AN UPPER LEVEL TROUGH AXIS HAS SHIFTED EAST OF THE
CASCADES OVERNIGHT. THE FLOW ALOFT HAS TURNED NORTHWESTERLY AS UPPER
LEVEL RIDGING BEGINS TO BUILD INTO THE REGION TODAY. SURFACE OBS AND
RADAR SHOW THAT SHOWER ACTIVITY OVER THE LOWLANDS HAS PRETTY MUCH
ENDED. I HAVE REMOVED THE SHOWER CHANCE WORDING FOR EVERYWHERE BUT
THE MOUNTAINS THIS MORNING. WITH RISING HEIGHTS AND SOME MODEST
WARMING IN THE LOWER LEVELS...HIGH TEMPERATURES TODAY SHOULD BE
GENERALLY RIGHT AROUND NORMAL. A FEW DECKS OF STRATOCUMULUS AROUND
THE REGION THIS MORNING SHOULD BREAK UP AS SUBSIDENCE TAKES OVER FOR
A PARTLY SUNNY DAY AHEAD. THE UPPER LEVEL RIDGE AXIS WILL BE
OVERHEAD THIS EVENING...THEN SHIFT EAST OF CASCADES MONDAY MORNING.
SURFACE GRADIENTS BECOME WEAK NORTH OR NORTHEASTERLY TONIGHT AND
EARLY MONDAY. THIS ALONG WITH SOME ADDITIONAL WARMING IN LOWER
LEVELS...AROUND 3C OR SO AT 850 MILLIBARS...TRANSLATES TO WARMER
TEMPERATURES FOR MONDAY. SOME HIGH CLOUDINESS AHEAD OF THE NEXT
SYSTEM MAY BE ON THE INCREASE LATE IN THE DAY...BUT HIGH
TEMPERATURES SHOULD BE A LITTLE ABOVE NORMAL FOR A SINGLE DAY THIS
WEEK. SPOTS FROM SEATTLE SOUTHWARD IN THE INTERIOR SHOULD BE IN THE
LOWER 70S.

THE MODELS CONTINUE THE SLOWER TREND WITH THE ARRIVAL OF THE NEXT
SYSTEM. THE COAST WILL SEE A CHANCE OF RAIN MONDAY EVENING...BUT
INTERIOR AREAS SHOULD REMAIN DRY. CLOUDS WILL INCREASE MONDAY NIGHT
WITH RAIN SPREADING INLAND ACROSS WESTERN WASHINGTON EARLY TUESDAY
MORNING. THE COLD FRONT SHOULD BE MOVING THROUGH THE PUGET SOUND
AREA BY MIDDAY. THIS WILL USHER IN A MUCH COOLER AIR MASS...WITH
SNOW LEVELS FALLING THROUGH THE DAY FROM ABOVE 6000 FEET EARLY TO
NEAR 3000 FEET BY LATE TUESDAY NIGHT OR WEDNESDAY MORNING. THIS WILL
BEGIN AN EXTENDED PERIOD OF UNSETTLED CONDITIONS AS A BROAD UPPER
LEVEL TROUGH TAKES UP RESIDENCE OVER THE WEST COAST THROUGH THE
EXTENDED FORECAST PERIOD.

.LONG TERM...AS THE CASE HAS BEEN FOR SOME TIME NOW...THE MODELS
CONTINUE TO BE AT ODDS WITH THE EVOLUTION OF THE TROUGH FROM
THURSDAY ON THROUGH THE HOLIDAY WEEKEND. THERE ARE LIKELY TO BE SOME
DRY PERIODS AT TIMES...BUT A SERIES OF DISTURBANCES ROTATING THROUGH
THE TROUGH WILL BRINGS SHOWERS OR PERHAPS A STEADY LIGHT RAIN.
HEIGHTS DO RECOVER SOME...SO TEMPERATURES SHOULD MODERATE WITH TIME.
THE 00Z RUN OF THE GFS TAKES MUCH OF THE TROUGHS ENERGY AND PRECIP
INTO THE CANADIAN ROCKIES BY NEXT WEEKEND...WHILE THE 00Z EURO KEEPS
THE TROUGH CENTERED RIGHT OVER WASHINGTON STATE WITH AREAS OF PRECIP
SPREADING INTO THE REGION FROM THE EAST AT TIMES. DETAILS ARE NEARLY
IMPOSSIBLE TO PUT ANY REAL CONFIDENCE IN FOR THE HOLIDAY
WEEKEND...BUT THE TREND OF COOLER THAN NORMAL TEMPERATURES AND A
CHANCE OF SHOWERS AT TIMES LOOKS LIKE A GOOD FORECAST. 27

&&

.AVIATION...THE FLOW ALOFT WILL REMAIN NORTHWESTERLY TODAY WITH HIGH
PRES OFFSHORE. ACROSS WESTERN WA...A FEW LIGHT SHOWERS REMAIN OVER
THE CASCADES THIS MORNING. THE LOW LEVEL AIR MASS IS MOIST WITH A
MIXED BAG OF CEILINGS - FROM MVFR TO BASES AROUND 7000 FT. LOW
CLOUDS WILL LIFT AND SCATTER THIS AFTERNOON WITH VFR CONDITIONS
EXPECTED. 33

KSEA...VFR CONDITIONS WILL PREVAIL TODAY. LIGHT/VARIABLE WIND WILL
BECOME NORTHERLY THIS AFTERNOON. 33

&&

.MARINE...HIGH PRES OVER THE NE PACIFIC WILL MAINTAIN NORTHWESTERLY
FLOW ACROSS WESTERN WA TODAY AND MON. A SMALL CRAFT ADVISORY IS IN
EFFECT FOR THE CENTRAL AND EAST STRAIT OF JUAN DE FUCA THROUGH
TONIGHT. A FRONTAL SYSTEM WILL TRACK OVER THE OFFSHORE WATERS MON
NIGHT...THEN SHIFT SOUTH AND MOVE INLAND OVER OREGON OR NORTHERN CA
TUE MORNING. THE ECMWF...NAM AND CANADIAN SHOW SIMILAR TRACKS.
MODELS SHOW A SOUTHWEST PUSH TUE NIGHT AS THIS SYSTEM MOVES FARTHER
INLAND AND WEAKENS. THE FLOW WILL REMAIN ONSHORE THROUGH AT LEAST
MIDWEEK. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA.

&&

$$

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