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000
FXUS66 KSEW 191638
AFDSEW

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

.SYNOPSIS...AN UPPER RIDGE WILL BUILD INTO THE REGION TODAY...THEN
CROSS THE AREA ON MONDAY MORNING...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...HAVE ALREADY UPDATE THE FIRST PERIOD FORECAST TO ADD
20-40 POPS TO THE PUGET SOUND LOWLANDS DUE TO ONGOING LIGHT SHOWERS
AND SPRINKLES MOVING SOUTH FROM ADMIRALTY INLET. WITH A NORTHERLY
SFC BREEZE AND A SUBSIDENCE INVERSION ARND 8000 FEET TODAY...EXPECT
THE LOWLAND SHOWERS TO DISSIPATE THIS AFTN. LOOKING FOR CLEARING TO
DEVELOP OVER THE INLAND WATERS THIS AFTN...WITH SUNNIER SKIES
SPREADING OUT OVER LAND AREAS THIS AFTN. WITH ONSHORE FLOW AND
SHALLOW INSTABILITY BENEATH THE SUBSIDENCE INVERSION...WOULD EXPECT
SHOWERS OR SPRINKLES TO CONTINUE THROUGH THIS AFTN OVER THE
CASCADES...FOOTHILLS...AND AROUND THE PERIMETER OF THE OLYMPICS.

AN UPPER RIDGE AXIS WILL CONTINUE TO BUILD INTO WRN WA TONIGHT. THE
RIDGE AXIS SHOULD MOVE ACROSS WRN WA DURING THE OVERNIGHT HOURS.
WITH CLEAR SKIES TONIGHT...EXPECT COOL TEMPS. SHOULD BE A FEW COLD
POCKET LOCATIONS...SUCH AS KOLM...DOWN INTO THE UPPER 30S TONIGHT.

ON MONDAY...THE RIDGE AXIS WILL BE EAST OF THE CASCADES...AND AN
UPPER TROUGH WILL DIG AND AMPLIFY OUT AROUND 135W-140W. WITH
OFFSHORE LOW PRESSURE EASING THE ONSHORE PRESSURE GRADIENT...AND
LIGHT SOUTHERLY FLOW AT 850 MB...MON SHOULD BE ONE OF THOSE WARM AND
DRY DAY IN ADVANCE OF TUESDAY`S STRONG COLD FRONT.

SPEAKING OF TUE...THE OFFSHORE UPPER TROUGH WILL ADVANCE EAST BTWN
130W AND THE COAST AND THEN BECOME A CUTOFF LOW THAT SINKS SE OFF
THE WA AND ORE COASTS. A STRONG COLD FRONT WILL PUSH ONSHORE AND
INLAND ON TUE MRNG. THE FRONT WILL BE ACCOMPANIED BY A BAND OF
RAIN...THEN FOLLOWED BY CONVECTIVE SHOWERS ON TUE AFTN AND EVNG. IN
TYPICAL FASHION...SHOWERS WILL FOCUS ON WINDWARD SIDE OF MTNS AND IN
THE PUGET SOUND CONVERGENCE ZONE. AN UNSEASONABLY COOL AIR MASS WILL
FOLLOW THE FRONT...WITH 850 MB TEMPS DOWN IN THE -1C TO +1C RANGE BY
TUE EVNG. THIS WILL LOWER SNOW LEVELS AS LOW AS 3000 FEET AT SUNRISE
ON WED MORNING. A FEW INCHES OF SNOW ARE EXPECTED AT THE HIGHER
HIGHWAY PASSES WHICH HAVE ALREADY OPENED FOR THE SUMMER...INCLUDING
CHINOOK PASS.       HANER

.LONG TERM...FROM PREVIOUS DISCUSSION...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
PRESSURE OFFSHORE. THERE WERE SCATTERED SHOWERS POPPING UP IN THE
EASTERN STRAIT OF JUAN DE FUCA AREA DRIFTING SSE ACROSS PORT
TOWNSEND AND DOWN ADMIRALTY INLET...BUT THE SHOWERS SHOULD END LATER
THIS MORNING WITH MORE CLEARING INTO THE AFTERNOON. AREAS OF MORNING
CLOUDS SHOULD LIFT TO MAINLY SCATTERED CU THIS AFTERNOON...ALTHOUGH
A FEW AREAS OF BROKEN CLOUDS MAY PERSIST NEAR THE MOUNTAINS. SKIES
SHOULD BE MOSTLY CLEAR TONIGHT.


KSEA...MORNING CLOUDS THEN INCREASING SUN IN THE AFTERNOON. A FEW OF
THE SHOWERS COMING DOWN ADMIRALTY INLET MAY WORK INTO THE METRO AREA
THIS MORNING. NLY BREEZE.

&&

.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 AND I HAVE ADDED ONE FOR THE TWO NORTHERNMOST OUTER COASTAL
ZONES SINCE THERE IS A SHIP REPORT OUT THERE WITH NW 25KT WIND. THE
NW WIND MAY INCREASE AND WORK TOWARD THE COASTLINE LATER TODAY AND I
WOULD NOT BE SURPRISED TO HAVE TO PUT UP AN ADVISORY FOR ALL OF THE
COASTAL WATERS WITH THE AFTERNOON FORECAST PACKAGE.

A FRONTAL SYSTEM WILL TRACK OVER THE OFFSHORE WATERS MON
NIGHT...THEN SHIFT SOUTH AND MOVE INLAND OVER OREGON OR NORTHERN CA
TUE MORNING. MODELS SHOW A SOUTHWEST PUSH TUE NIGHT AS THIS SYSTEM
MOVES FARTHER INLAND AND WEAKENS. THE FLOW WILL REMAIN ONSHORE
THROUGH AT LEAST MIDWEEK.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY OUTER COASTAL WATERS FROM CAPE FLATTERY TO
POINT GRENVILLE...AND THE CENTRAL AND EAST STRAIT OF JUAN DE FUCA.

&&

$$