000
FXUS66 KSEW 200948
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
248 AM PDT MON MAY 20 2013

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL MOVE ACROSS THE AREA TODAY
GIVING A DRY AND WARM DAY TO THE INTERIOR. CONDITIONS ON THE COAST
WILL BE COOLER WITH CLOUDS AND ONSHORE FLOW. BIG CHANGES TO A COOL
AND WET PATTERN WILL BEGIN LATE TONIGHT AND PERSIST INTO NEXT
WEEKEND AS AN UPPER LEVEL LOW MOVES SOUTHEAST FROM THE GULF OF
ALASKA THEN SPINS AROUND OVER THE PACIFIC NORTHWEST.

&&

.SHORT TERM...ENJOY TODAY. WHILE THERE WILL BE AN INCREASE IN HIGH
CLOUDS THIS AFTERNOON...A PASSING UPPER LEVEL RIDGE WILL BRING DRY
AND WARM WEATHER TO THE INTERIOR. CONDITIONS WILL BE COOLER AND
CLOUDIER ON THE COAST AS LOW LEVEL ONSHORE FLOW INCREASES WITH PRE
FRONTAL RIDGING AHEAD OF A WEAK LOW NEAR 46N 136W. TEMPERATURES
ALONG THE COAST WILL REMAIN AROUND 60 TODAY WHILE TEMPERATURES IN
THE INTERIOR RISE TO 65 TO 75 DEGREES.

MODELS ALL ADVERTISE A MAJOR PATTERN CHANGE BEGINNING LATE TONIGHT
AS A STRONG UPPER LEVEL RIDGE OFF SOUTHERN CALIFORNIA RETROGRADES
AND AMPLIFIES ALONG 145W-150W. AS THE RIDGE BUILDS OFFSHORE...AN
UPPER LEVEL LOW OVER THE YUKON WILL DROP SOUTHWARD OFF WESTERN
VANCOUVER ISLAND AND TO JUST OFFSHORE. THIS UPPER LOW AND THE COLD
AIR ASSOCIATED WITH IT GAVE A LATE SEASON SNOWFALL TO PARTS OF
CENTRAL AND EASTERN ALASKA OVER THE PAST COUPLE OF DAYS. THE NAM12
IS SLIGHTLY FASTER THAN THE GFS AND ECMWF SOLUTIONS IN BRINGING
RAINFALL AND COOLING INLAND TONIGHT...BUT THE MODELS OVERALL ARE IN
GOOD AGREEMENT.

THE LOW IS FORECAST TO LINGER AROUND THE PACIFIC NORTHWEST THROUGH
THE END OF THE WEEK. 850 MB TEMPERATURES WILL FALL TO BELOW 0C
AROUND TUESDAY MORNING AND STAY -2C TO -4C THROUGH WED...THEN ONLY
SLOWLY MODERATE AFTER THAT. SNOW LEVELS IN THE MOUNTAINS ARE
EXPECTED TO DROP TO AROUND 3500 FEET LATER TUE INTO WED. MOISTURE
COMBINED WITH THE COOL AND UNSTABLE AIR MASS WILL GIVE ABUNDANT
SHOWER ACTIVITY THROUGH MIDWEEK. TEMPERATURES TUE-WED WILL STRUGGLE
TO GET INTO THE MID 50S AND WILL FALL INTO THE 40S AT NIGHT. THIS IS
5-10 DEGREES BELOW NORMAL FOR LATE MAY.

NAM12 BUFR SOUNDINGS DO NOT SHOW THUNDERSTORMS TUE/WED AS CAPE
REMAINS BELOW ABOUT 300 J/KG IN A SKINNY CAPE PROFILE. CONVECTIVE
TEMPERATURES WILL BE LOW HOWEVER...IN THE UPPER 40S TO AROUND
50...SO GRAUPEL IS LIKELY AROUND HEAVIER SHOWERS STARTING LATER
TUESDAY.  ALBRECHT

.LONG TERM...TEMPERATURES ARE LIKELY TO SLOWLY MODERATE LATE IN
THE WEEK THROUGH NEXT WEEKEND AS THE UPPER LOW SPINS AROUND THE
AREA. SHOWERS MAY DECREASE SOMEWHAT TOWARD THE END OF THE WEEK AS
WELL. FORECASTING THE DETAILS WILL BE QUITE DIFFICULT AS SMALL
CHANGES IN THE POSITION AND STRENGTH OF THE UPPER LOW CAN RESULT IN
BIG SENSIBLE WEATHER CHANGES. NONETHELESS IT APPEARS THAT
TEMPERATURES WILL REMAIN AT LEAST 5 DEG BELOW NORMAL THROUGH NEXT
WEEKEND AND THERE WILL BE QUITE A FEW SHOWERS AROUND THE
AREA...ESPECIALLY OVER THE MOUNTAINS. ALBRECHT

&&

.AVIATION...THE RIDGE IS FLATTENING ACROSS THE PAC NW THIS MORNING
AS A DEEP UPPER LEVEL LOW SPINS INTO NORTHERN B.C. THE FLOW ALOFT IS
WESTERLY. EXPECT SCT-BKN CIRRUS OVER WESTERN WA TODAY WITH FEW-SCT
CUMULUS FORMING THIS AFTERNOON. VFR CONDITIONS WILL PREVAIL. CLOUDS
WILL INCREASE THIS EVENING AS THE UPPER LOW SHIFTS FARTHER SOUTH.
MODELS SHOW DIFFLUENCE OVER THE REGION WITH RAIN DEVELOPING ALONG
THE COAST BY MIDNIGHT. THE INTERIOR WILL SEE PRECIP EARLY TUE
MORNING AS THE UPPER LOW SPINS OFFSHORE AND THE SURFACE LOW MOVES
INLAND. 33

KSEA...VFR CONDITIONS WILL PREVAIL TODAY WITH LIGHT NORTHERLY
SURFACE WINDS. CLOUDS WILL INCREASE TONIGHT WITH RAIN IN THE VC
EARLY TUE MORNING. 33

&&

.MARINE...WEST TO NORTHWEST FLOW WILL PREVAIL ACROSS WESTERN WA
TODAY. PRES GRADIENTS WILL INCREASE TONIGHT WITH SMALL CRAFT
ADVISORY WINDS LIKELY THROUGH THE STRAIT OF JUAN DE FUCA.

A 1010-1016MB LOW WILL TRACK OVER THE OFFSHORE WATERS TONIGHT...THEN
SLIDE INLAND EARLY TUE MORNING OVER SOUTHERN OREGON. ONSHORE FLOW
WILL INCREASE ACROSS WESTERN WA TUE NIGHT AS THIS SYSTEM MOVES
FARTHER INLAND. MODELS ARE SHOWING ANOTHER WEAK SURFACE LOW SPINNING
OVER THE COASTAL WATERS TOWARD THE END OF THE WEEK. HOWEVER EXACT
TIMING AND TRACKING OF THIS FEATURE IS STILL UNCLEAR. MODEL OUTPUT
IS RATHER SWIRLY WITH THE WINDS. FOR NOW WILL STICK WITH THE
PREDOMINANT WEST TO NORTHWEST FLOW ACROSS THE REGION. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 200442
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
940 PM PDT SUN MAY 19 2013

.SYNOPSIS...AN UPPER LEVEL RIDGE AXIS WILL CROSS WESTERN WASHINGTON
TONIGHT...BRINGING A RELATIVELY WARM AND DRY DAY ON MONDAY. AN UPPER
TROUGH WILL DEVELOP OFFSHORE ON MONDAY...THEN MOVE EAST ON MONDAY
NIGHT. THIS FEATURE WILL EVOLVE INTO A CUTOFF LOW BY TUESDAY...
BECOMING NEARLY STATIONARY AND PERSISTING OVER THE PACIFIC NORTHWEST
THROUGH THE END OF THIS WEEK. THIS WILL PUSH A STRONG COLD FRONT
ONTO THE COAST ON MONDAY NIGHT...PUSHING QUICKLY INLAND EARLY
TUESDAY MORNING. A COOL AND SHOWERY PATTERN WILL THEN PERSIST FOR
THE REST OF THE WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS SOME PERSISTENT SC OVER THE
CASCADES AND OLYMPICS ALONG WITH SOME HIGH CLOUDS MOVING IN FROM THE
NORTHWEST. SKIES ARE PARTLY CLOUDY OVER THE REMAINDER OF THE AREA.
WITH THE DIFFERENCES IN CLOUD COVER THERE WAS A BIT OF A TEMPERATURE
SPREAD ACROSS THE AREA FROM UPPER 40S TO LOWER 60S.

UPPER LEVEL RIDGE AXIS OVER THE AREA THIS EVENING WILL MOVE EAST OF
THE CASCADES ON MONDAY. 00Z MODEL RUNS ARE 6 TO 12 HOURS FASTER WITH
THE TRANSITION OF THE RIDGE MOVING EAST AND THE COLD UPPER TROUGH
OFF THE COAST DEVELOPING. THIS FASTER TRANSITION INCREASES THE
ONSHORE FLOW QUICKER ON MONDAY WHICH COULD RESULT IN SLIGHTLY COOLER
HIGH TEMPERATURES THAN IS CURRENTLY IN THE FORECAST. STILL A DRY DAY
IN STORE WITH TEMPERATURES A COUPLE OF DEGREES ABOVE NORMAL.

WITH THE FASTER PATTERN CHANGE THE TIMING OF THE ONSET OF THE
PRECIPITATION INTO THE INTERIOR OF WESTERN WASHINGTON IS ALSO
QUICKER. WILL UPDATE THE FORECAST AND INCREASE THE POPS INTO THE
LIKELY CATEGORY FOR MONDAY NIGHT FOR THE INTERIOR.

BOTH THE NAM AND THE GFS ARE IN GOOD AGREEMENT ON THE FASTER TIMING
MONDAY NIGHT INTO TUESDAY WITH THE UPPER LEVEL LOW RIGHT OFF THE
COAST BY 18Z TUESDAY WITH THE LOW DRIFTING TOWARD THE COAST BY 00Z
WEDNESDAY. MUCH COOLER AIR MASS MOVING INTO WESTERN WASHINGTON WITH
THE SNOW LEVEL DOWN TO 3500 FEET TUESDAY EVENING WHICH MEANS THE
PRECIPITATION WILL BE IN THE FORM OF SNOW ON ALL THE PASSES EXCEPT
SNOQUALMIE. FELTON

PREVIOUS DISCUSSION FOLLOWS...ON WED AND THU...THE CENTER OF THE
CUTOFF UPPER LOW WILL BE LOCATED TO OUR SOUTH. WRN WA WILL BE PRONE
TO EMBEDDED SHORTWAVES ROTATING INTO WRN WA FROM THE SOUTHEAST AND
EAST. BOTH THE GFS AND ECMWF SHOW WET PERIODS ON WED. WITH COLD AIR
IN PLACE AND SOME WET WX...THE FCST MAX TEMP OF 54F AT KSEA WOULD
TIE THE RECORD LOW MAX TEMP FOR THE DAY. OF COURSE...THE WET WEATHER
WITH SNOW LEVELS OF 3000-4000 FEET WILL PROVIDE SNOW TO THE HIGHER
MTN PASSES. SNOQUALMIE PASS IS UNLIKELY TO GET MORE THAN AN INCH OF
ACCUMULATION...BUT THE OFFICIAL FORECAST SHOWS 30-HOUR SNOWFALL
TOTALS FROM TUE EVNG THROUGH WED EVNG OF 2.5 INCHES AT STEVENS
PASS...4 INCHES AT CHINOOK PASS...5 INCHES AT RAINY PASS...6 INCHES
AT PARADISE AND 9 INCHES AT HARTS PASS ALONG THE FAR NORTH CASCADE
CREST. THOSE VENTURING INTO HIGHER ELEVATIONS AND THE BACKCOUNTRY
SHOULD BE PREPARED FOR A QUICK CHANGE TO COLD AND WET OR SNOWY
WEATHER EARLY TUE MRNG. WILL ISSUE A SPECIAL WEATHER STATEMENT TO
HIGHLIGHT THIS CONCERN. MAY EVENTUALLY NEED WINTER WEATHER
HIGHLIGHTS FOR THE CASCADES ABOVE 4000 FEET.    HANER

.LONG TERM...THE CUTOFF UPPER LOW WILL MEANDER AROUND THE INLAND
NORTHWEST ON THU AND FRI...THEN START TO FILL AND SLOWLY LIFT OUT
NEXT SAT AND SUN. THIS WILL LEAD TO A SLOW WARMING TREND LATE THIS
WEEK AND NEXT WEEKEND...BUT TEMPS WILL STILL STRUGGLE TO RISE BACK
AS HIGH AS NORMAL. SHOWER COVERAGE WILL ALSO TREND DOWNWARD FROM FRI
THROUGH SUN...BECOMING DRIVEN MORE BY DAYTIME HEATING AND DIURNALLY
DRIVEN CONVECTIVE ELEMENTS. HOWEVER...THERE WILL STILL BE ENOUGH
MOISTURE AND INSTABILITY TO WARRANT A CHANCE OF SHOWERS NEXT SAT AND
SUN. LOOKING OUT TOWARD MEMORIAL DAY...MODELS HINT AT EITHER ZONAL
FLOW OR HEIGHT FALLS SPREADING ONSHORE. AT BEST...THIS WOULD SUGGEST
DEEP MARINE AIR AND CLOUDS. AT WORST...MORE ORGANIZED RAIN.  HANER

&&

.AVIATION...WEAK RIDGING OVER THE PAC NW WILL LEAD TO DRY/STABLE
WEATHER ACROSS WESTERN WA TONIGHT. THE FLOW ALOFT IS NORTHWESTERLY.
LOW CLOUDS ARE CLEARING OUT WITH JUST SCT-BKN CIRRUS MOVING IN FROM
THE WEST. VFR CONDITIONS WILL PREVAIL ALTHOUGH MAY SEE PATCHY VALLEY
FOG EARLY MON MORNING. 33

KSEA...VFR CONDITIONS TONIGHT AND MON WITH LIGHT NLY SURFACE WINDS.
33

&&

.MARINE...HIGH PRES OVER THE NE PACIFIC WILL MAINTAIN NORTHWESTERLY
FLOW ACROSS WESTERN WA TONIGHT AND MON. THE COASTAL WATERS AND
CENTRAL/EAST STRAIT WILL CONTINUE TO SEE SMALL CRAFT ADVISORY WINDS
THIS EVENING...WINDS WILL GRADUALLY EASE OVERNIGHT.

A WEATHER SYSTEM WILL TRACK OVER THE OFFSHORE WATERS MON
NIGHT...THEN SLIDE INLAND TUE MORNING /OVER OREGON OR NORTHERN CA/.
WESTERN WA WILL CONTINUE TO SEE WESTERLY ONSHORE FLOW...WITH A SW
PUSH ON TUE AS THIS SYSTEM MOVES FARTHER INLAND. THE COASTAL WATERS
AND STRAIT OF JUAN DE FUCA MAY SEE SMALL CRAFT ADVISORY WINDS OVER
THIS PERIOD. WESTERLY ONSHORE FLOW WILL PERSIST THROUGH AT LEAST
MIDWEEK.

&&

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

&&

$$

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

000
FXUS66 KSEW 192246
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
345 PM PDT SUN MAY 19 2013

.SYNOPSIS...AN UPPER LEVEL RIDGE AXIS WILL CROSS WESTERN WASHINGTON
TONIGHT...BRINGING A RELATIVELY WARM AND DRY DAY ON MONDAY. AN UPPER
TROUGH WILL DEVELOP OFFSHORE ON MONDAY...THEN MOVE EAST ON MONDAY
NIGHT. THIS FEATURE WILL EVOLVE INTO A CUTOFF LOW BY TUESDAY...
BECOMING NEARLY STATIONARY AND PERSISTING OVER THE PACIFIC NORTHWEST
THROUGH THE END OF THIS WEEK. THIS WILL PUSH A STRONG COLD FRONT
ONTO THE COAST ON MONDAY NIGHT...PUSHING QUICKLY INLAND EARLY
TUESDAY MORNING. A COOL AND SHOWERY PATTERN WILL THEN PERSIST FOR
THE REST OF THE WEEK.

&&

.SHORT TERM...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 LATE 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 DAYS IN ADVANCE OF TUESDAY`S STRONG COLD FRONT. LOOKING FOR 70+
FROM KSEA ON SOUTH ALONG I-5 MON AFTN.

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 COAST...REACHING NW ORE ON TUE EVNG. AS A RESULT...A STRONG
COLD FRONT WILL PUSH ONSHORE AND INLAND ON TUE MRNG. THE FRONT WILL
BE ACCOMPANIED BY A BAND OF BRIEFLY HEAVY RAIN...FOLLOWED BY
CONVECTIVE SHOWERS ON TUE AFTN AND EVNG GIVEN THE COLD AIR ALOFT. 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 -3C TO 0C RANGE BY
TUE NGT. THIS WILL LOWER SNOW LEVELS AS LOW AS 3000 FEET AT SUNRISE
ON WED MORNING.

ON WED AND THU...THE CENTER OF THE CUTOFF UPPER LOW WILL BE LOCATED
TO OUR SOUTH. WRN WA WILL BE PRONE TO EMBEDDED SHORTWAVES ROTATING
INTO WRN WA FROM THE SOUTHEAST AND EAST. BOTH THE GFS AND ECMWF SHOW
WET PERIODS ON WED. WITH COLD AIR IN PLACE AND SOME WET WX...THE
FCST MAX TEMP OF 54F AT KSEA WOULD TIE THE RECORD LOW MAX TEMP FOR
THE DAY. OF COURSE...THE WET WEATHER WITH SNOW LEVELS OF 3000-4000
FEET WILL PROVIDE SNOW TO THE HIGHER MTN PASSES. SNOQUALMIE PASS IS
UNLIKELY TO GET MORE THAN AN INCH OF ACCUMULATION...BUT THE OFFICIAL
FORECAST SHOWS 30-HOUR SNOWFALL TOTALS FROM TUE EVNG THROUGH WED
EVNG OF 2.5 INCHES AT STEVENS PASS...4 INCHES AT CHINOOK PASS...5
INCHES AT RAINY PASS...6 INCHES AT PARADISE AND 9 INCHES AT HARTS
PASS ALONG THE FAR NORTH CASCADE CREST. THOSE VENTURING INTO HIGHER
ELEVATIONS AND THE BACKCOUNTRY SHOULD BE PREPARED FOR A QUICK CHANGE
TO COLD AND WET OR SNOWY WEATHER EARLY TUE MRNG. WILL ISSUE A
SPECIAL WEATHER STATEMENT TO HIGHLIGHT THIS CONCERN. MAY EVENTUALLY
NEED WINTER WEATHER HIGHLIGHTS FOR THE CASCADES ABOVE 4000 FEET.
HANER

.LONG TERM...THE CUTOFF UPPER LOW WILL MEANDER AROUND THE INLAND
NORTHWEST ON THU AND FRI...THEN START TO FILL AND SLOWLY LIFT OUT
NEXT SAT AND SUN. THIS WILL LEAD TO A SLOW WARMING TREND LATE THIS
WEEK AND NEXT WEEKEND...BUT TEMPS WILL STILL STRUGGLE TO RISE BACK
AS HIGH AS NORMAL. SHOWER COVERAGE WILL ALSO TREND DOWNWARD FROM FRI
THROUGH SUN...BECOMING DRIVEN MORE BY DAYTIME HEATING AND DIURNALLY
DRIVEN CONVECTIVE ELEMENTS. HOWEVER...THERE WILL STILL BE ENOUGH
MOISTURE AND INSTABILITY TO WARRANT A CHANCE OF SHOWERS NEXT SAT AND
SUN. LOOKING OUT TOWARD MEMORIAL DAY...MODELS HINT AT EITHER ZONAL
FLOW OR HEIGHT FALLS SPREADING ONSHORE. AT BEST...THIS WOULD SUGGEST
DEEP MARINE AIR AND CLOUDS. AT WORST...MORE ORGANIZED RAIN.  HANER

&&

.AVIATION...LIGHT NW FLOW ALOFT. AIR IS STABLE AND DRYING AS HIGH
PRESSURE BUILDS INTO THE REGION. THE LAYER OF STRATOCU THAT
PERSISTED FOR MUCH OF WESTERN WA THIS AFTERNOON SHOULD CLEAR UP BY
EVENING. MONDAY SHOULD BE SUNNY WITH JUST A LITTLE PATCHY RIVER
VALLEY FOG OR LOW CLOUDS AROUND DAYBREAK.

KSEA...SKIES OUGHT TO BE SCATTERING OUT LATE THIS AFTERNOON. LIGHT
AND VARIABLE WIND EXCEPT NLY TO 10KT AFTERNOON AND EVENING HOURS.

&&

.MARINE...HIGH PRES OVER THE NE PACIFIC WILL MAINTAIN NORTHWESTERLY
FLOW ACROSS WESTERN WA TODAY AND MON. WE PROBABLY WILL SEE SEVERAL
HOURS OF 15-25KT NW WIND COAST AND STRAIT THIS EVENING...ALTHOUGH
THE SEA LEVEL PRESSURE ANALYSIS DOESN`T SHOW A GREAT DEAL OF
GRADIENT THIS AFTERNOON OVER WRN WA. A WEATHER SYSTEM WILL MOVE OVER
THE REGION TUE AND WED...IN FACT AN UPPER LEVEL LOW MAY PERSIST OVER
THE PACNW THROUGH THE END OF THE WEEK. WHAT IS LIKELY TO HAPPEN IS
THAT WESTERN WA WILL HAVE A REGIME OF ONSHORE FLOW AND A LOT OF
SHOWER ACTIVITY...PROBABLY A FEW PERIODS OF RAIN...BUT THE STRONGER
PRESSURE GRADIENT IS LIKELY TO STAY WELL OFFSHORE OR DOWN OVER
OREGON TUE-THU.

&&

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

&&

$$

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

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.

&&

$$

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.

&&

$$

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

000
FXUS66 KSEW 190441
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
940 PM PDT SAT MAY 18 2013

.SYNOPSIS...AN UPPER TROUGH OVER THE CASCADES THIS EVENING WILL
CONTINUE TO MOVE EAST. AN UPPER RIDGE WILL START TO BUILD IN ON
SUNDAY...THEN CROSS THE AREA ON MONDAY...LEADING TO WARMER AND DRIER
WEATHER. A LARGE UPPER LOW WILL DROP INTO THE AREA ON
TUESDAY...CAUSING A STRONG COLD FRONT TO PUSH INLAND DURING THE DAY.
THE UPPER LOW WILL SIT IN PLACE THROUGH THE END OF THE
WEEK...MAINTAINING SHOWERY WEATHER AND BELOW NORMAL TEMPERATURES.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS UPPER LEVEL TROUGH AXIS OVER
THE CASCADES THIS EVENING. A FEW PRECIPITATION ECHOES LEFT ON THE
DOPPLER RADARS WITH THE SHOWERS MOVING NORTHWEST TO SOUTHEAST
INDICATING THAT NORTHWESTERLY FLOW ALOFT HAS DEVELOPED OVER THE
STATE. WITH THE CLOUD COVER AT 9 PM PRETTY NARROW TEMPERATURE RANGE
ACROSS THE AREA WITH MOST PLACES IN THE MID 50S.

FLAT UPPER LEVEL RIDGE ALREADY EVIDENT IN THE SATELLITE IMAGERY OUT
AROUND 130W WILL BUILD INTO WESTERN WASHINGTON ON SUNDAY. IN THE
MEANTIME WITH PLENTY OF LOW LEVEL MOISTURE AND A SLIGHTLY UNSTABLE
AIR MASS WILL KEEP THE CHANCE OF SHOWERS GOING INTO THE MORNING
HOURS ON SUNDAY. HAVE UPDATED THE ZONES AND TAKEN THE CHANCE OF
SHOWERS OUT OF THE LOWLANDS FOR THE AFTERNOON HOURS ON SUNDAY. IF
THE RIDGE BUILDS IN A LITTLE QUICKER LOOK FOR THE CHANCE OF SHOWERS
IN THE MORNING TO BE DROPPED IN THE MORNING FORECAST PACKAGE. WITH
THE LIGHT ONSHORE FLOW BECOMING MORE NORTHERLY IN THE AFTERNOON IT
WILL NOT BE A VERY WARM DAY WITH HIGH TEMPERATURES HOVERING NEAR
NORMAL FOR THIS TIME OF THE YEAR...MOSTLY IN THE 60S.

UPPER LEVEL RIDGE REMAINING OVER WESTERN WASHINGTON SUNDAY NIGHT
INTO MONDAY. TEMPERATURES ALOFT DO NOT WARM MUCH WITH THE 850 TEMPS
ONLY A COUPLE OF DEGREES C WARMER THAN SUNDAY BUT MODEL CROSS
SECTIONS SHOW THE WINDS IN THE 1000-850 LAYER BECOMING LIGHT
NORTHEASTERLY MONDAY MORNING. THIS PUFF OF OFFSHORE FLOW COMBINED
THE WARMER TEMPERATURES ALOFT SHOULD RESULT IN HIGHS ABOUT 5 DEGREES
WARMER ON MONDAY VERSUS SUNDAY WITH MANY PLACES FROM SEATTLE SOUTH
GETTING INTO THE LOWER 70S.

CONDITIONS DETERIORATE RAPIDLY ON TUESDAY AS A COLD UPPER LEVEL LOW
DROPS DOWN FROM THE NORTH BRINGING WITH IT WET AND UNSEASONABLY COOL
WEATHER FOR THE MIDDLE OF THE WEEK. THE RECORD LOW MAX FOR SEATTLE
ON TUESDAY IS 52 DEGREES WHICH DOES NOT LOOK TO BE THREATENED AT
THIS POINT BUT THE RECORD LOW MAX ON WEDNESDAY IS 54 DEGREES AND
THAT HAS THE POTENTIAL TO BE BROKEN. BY TUESDAY NIGHT 850 MB
TEMPERATURES WILL DROP BELOW 0C AND SNOW LEVELS COULD FALL AS LOW AS
3000 FEET FOR SNOW AT ALL OF THE PASSES. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. ON WED...THE UPPER TROUGH
WILL MORPH INTO A CUTOFF LOW...DUE TO THE DEVELOPMENT OF AN UPPER
RIDGE OVER THE YUKON AND NRN B.C.. THIS WILL EFFECTIVELY BRING A
BLOCKING PATTERN AND CUT THE UPPER LOW OFF FROM ANY STEERING FLOW
WHICH COULD PUSH IT OUT. SO...WE WILL BE STUCK WITH THE UPPER LOW
FROM WED THROUGH THE REST OF THE NEW WEEK. SAFE TO SAY THAT A
SHOWERY WEATHER REGIME WILL BE IN PLACE WITH BELOW NORMAL
TEMPERATURES. THIS PATTERN COULD ALSO BRING A FEW INCHES OF SNOW TO
THE HIGHER PASSES...SUCH AS RAINY PASS AND CHINOOK PASS...WHICH HAVE
ALREADY RE-OPENED FOR THE SEASON. MODELS SHOW THE UPPER LOW BECOMING
MORE RAG-TAG NEXT FRI AND SAT AS IT SLOWLY FILLS AND THE LOW-LEVEL
AIR MASS EVER SO SLOWLY MODIFIES. TEMPS WILL SLOWLY RISE BACK TO
WITHIN A FEW DEGREES OF NORMAL BY DAY 7...AND SHOWER COVERAGE MAY
DECREASE. ONE CAVEAT FOR THU THROUGH SAT IS THAT IF THE UPPER LOW
CENTER MEANDERS FURTHER SOUTH INTO NW ORE...IT WILL OPEN UP THE DOOR
TO MORE WIDESPREAD DEFORMATION-STYLE RAINFALL SPREADING IN FROM THE
EAST. HAVE SEEN THIS IN PAST MAYS...AND IT IS ONE WAY OF BRINGING A
LIGHT ALL-DAY RAIN TO WRN WA THIS TIME OF YEAR. HOWEVER...DETAILS OF
INDIVIDUAL WAVES OR ROUNDS OF SHOWERS WITHIN THE UPPER LOW ARE
IMPOSSIBLE TO PIN DOWN 5-7 DAYS IN THE FUTURE.   HANER

&&

.AVIATION...THE UPPER LEVEL TROUGH PUSHED EAST OF THE CASCADES THIS
EVENING WHILE HIGH PRES MOVES IN FROM THE WEST. THE AIR MASS ACROSS
WESTERN WA IS STABILIZING BUT REMAINS MOIST WITH LOW LEVEL ONSHORE
FLOW. ISOLATED LIGHT SHOWERS ACROSS THE REGION WILL DIMINISH AFTER
MIDNIGHT TONIGHT...MAINLY AFFECTING THE CASCADES. CIGS WILL HOVER
AROUND 3000-5000 FT TONIGHT. HIGH PRES WILL REMAIN OVER THE REGION
ON SUN FOR DRY/STABLE WEATHER. LOW CLOUDS WILL SCATTER BY THE
AFTERNOON FOR VFR CONDITIONS. 33

KSEA...LIGHT SHOWERS IN THE VICINITY WILL DIMINISH AFTER MIDNIGHT
TONIGHT. SURFACE FLOW IS LIGHT SOUTHERLY. CIGS 3000-5000 FT
TONIGHT. 33

&&

.MARINE...HIGH PRES OVER THE NE PACIFIC WILL MAINTAIN NORTHWESTERLY
FLOW ACROSS WESTERN WA TONIGHT THROUGH SUN. THE CENTRAL AND EAST
STRAIT OF JUAN DE FUCA MAY SEE SMALL CRAFT ADVISORY WINDS LATE SUN
AFTERNOON AND EVENING.

THE NEXT FRONTAL SYSTEM WILL FORM OFFSHORE ON MON...THEN MOVE INLAND
ON TUE. BUT MODELS DISAGREE ON THE EXACT TRACKING OF THE SURFACE LOW
AS IT MOVES ASHORE. THE GFS BRINGS A 1009 MB LOW INTO THE WA COAST
TUE MORNING...WHILE THE ECMWF AND NAM SOLUTIONS ARE BOTH WEAKER AND
FARTHER SOUTH /1017 MB LOW OVER NORTHERN CA/. THE CANADIAN IS CLOSER
TO THE ECMWF AND NAM...SO WILL LIKELY NUDGE THE FORECAST TOWARD
THESE SOLUTIONS. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 182249
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
348 PM PDT SAT MAY 18 2013

.SYNOPSIS...AN UPPER TROUGH WILL PASS ACROSS WESTERN WASHINGTON THIS
EVENING...ACCOMPANIED BY A FEW SHOWERS. AN UPPER RIDGE WILL START TO
BUILD IN ON SUNDAY...THEN CROSS THE AREA ON MONDAY...LEADING TO
WARMER AND DRIER WEATHER. A LARGE UPPER LOW WILL DROP INTO THE AREA
ON TUESDAY...CAUSING A STRONG COLD FRONT TO PUSH INLAND DURING THE
DAY. THE UPPER LOW WILL SIT IN PLACE THROUGH THE END OF THE
WEEK...MAINTAINING SHOWERY WEATHER AND BELOW NORMAL TEMPERATURES.

&&

.SHORT TERM...A WEAK UPPER TROUGH AXIS IS MOVING ONSHORE...WITH
SCATTERED SHOWERS AND CLOUDS PRECEDING THE TROUGH AXIS. ONCE THE
TROUGH AXIS MOVES EAST OF THE CASCADES LATE TONIGHT...UPPER HEIGHTS
WILL RISE QUICKLY AND SHOWER ACTIVITY WILL DIMINISH GREATLY. IN
FACT...VISIBLE SATELLITE SHOWS RAPIDLY CLEARING SKIES OFFSHORE
BEHIND THE TROUGH AXIS. ON SUNDAY OVER THE INTERIOR
LOWLANDS...LOOKING FOR A LARGELY DRY SUNDAY. A SUBSIDENCE INVERSION
WILL DEVELOP AROUND 8000 FT MSL...SO ANY SHOWER ACTIVITY WILL BE
LIGHT AND SPOTTY AT MOST. IN FACT...WOULD EXPECT SHOWERS ON SUNDAY
AFTN TO BECOME CONFINED TO THE CASCADES...FOOTHILLS AND THE
PERIMETER OF THE OLYMPICS. A NORTH WIND WILL KICK IN THROUGH THE
PUGET SOUND LOWLANDS IN THE AFTN...A FAIR WEATHER DIRECTION FOR THE
LOWLANDS.

THE UPPER HEIGHT RISES WILL SET THE STAGE FOR AN UPPER RIDGE AXIS TO
PASS ACROSS WRN WA ON MON...MAKING MONDAY THE WARMEST AND DRIEST OF
THE NEXT 7 DAYS FOR WRN WA. AFTER A COOL START OWING TO MOSTLY CLEAR
SKIES AT SUNRISE...INTERIOR LOWLANDS WILL RISE INTO 70S ON MON AFTN.

ON TUE...A BIG CHANGE TOWARD COOL AND SHOWERY WEATHER WILL TAKE
PLACE. A HIGH AMPLITUDE UPPER TROUGH WILL SETUP NEAR 130W...BRINGING
A STRONG MARINE PUSH AND COLD FRONT THROUGH WRN WA DURING THE DAY.
AFTER A MILD START TO THE DAY...AFTN TEMPS WILL FALL IN MOST
PLACES...AND SHOWERS WILL QUICKLY BECOME WIDESPREAD. AN UNSEASONABLY
COOL AIR MASS WILL OVERSPREAD WRN WA. BY TUE NIGHT...850 MB TEMPS OF
-1C TO +1C WILL BE COMMON...AND SNOW LEVELS COULD FALL AS LOW AS
3000 FT.        HANER

.LONG TERM...ON WED...THE UPPER TROUGH WILL MORPH INTO A CUTOFF
LOW...DUE TO THE DEVELOPMENT OF AN UPPER RIDGE OVER THE YUKON AND
NRN B.C.. THIS WILL EFFECTIVELY BRING A BLOCKING PATTERN AND CUT THE
UPPER LOW OFF FROM ANY STEERING FLOW WHICH COULD PUSH IT OUT.
SO...WE WILL BE STUCK WITH THE UPPER LOW FROM WED THROUGH THE REST
OF THE NEW WEEK. SAFE TO SAY THAT A SHOWERY WEATHER REGIME WILL BE
IN PLACE WITH BELOW NORMAL TEMPERATURES. THIS PATTERN COULD ALSO
BRING A FEW INCHES OF SNOW TO THE HIGHER PASSES...SUCH AS RAINY PASS
AND CHINOOK PASS...WHICH HAVE ALREADY RE-OPENED FOR THE SEASON.
MODELS SHOW THE UPPER LOW BECOMING MORE RAG-TAG NEXT FRI AND SAT AS
IT SLOWLY FILLS AND THE LOW-LEVEL AIR MASS EVER SO SLOWLY MODIFIES.
TEMPS WILL SLOWLY RISE BACK TO WITHIN A FEW DEGREES OF NORMAL BY DAY
7...AND SHOWER COVERAGE MAY DECREASE. ONE CAVEAT FOR THU THROUGH SAT
IS THAT IF THE UPPER LOW CENTER MEANDERS FURTHER SOUTH INTO NW
ORE...IT WILL OPEN UP THE DOOR TO MORE WIDESPREAD DEFORMATION-STYLE
RAINFALL SPREADING IN FROM THE EAST. HAVE SEEN THIS IN PAST
MAYS...AND IT IS ONE WAY OF BRINGING A LIGHT ALL-DAY RAIN TO WRN WA
THIS TIME OF YEAR. HOWEVER...DETAILS OF INDIVIDUAL WAVES OR ROUNDS
OF SHOWERS WITHIN THE UPPER LOW ARE IMPOSSIBLE TO PIN DOWN 5-7 DAYS
IN THE FUTURE.   HANER

&&

.AVIATION...SCATTERED SHOWERS ARE OVER THE AREA AS A WEAK FRONT
BREAKS UP OVER THE REGION. THE AIR MASS IS MOIST AND SOMEWHAT
UNSTABLE WITH FAIRLY LIGHT SW FLOW ALOFT BECOMING NW TONIGHT. THE
MOUNTAINS AND FOOTHILLS ARE MOSTLY OBSCURED. MORNING CLOUDS WILL
GIVE WA TO AFTERNOON SUNSHINE SUNDAY.

KSEA...SCATTERED SHOWERS WILL CONTINUE THROUGH THE EVENING AS A
FRONT BREAKS UP OVER THE AREA. THE SHOWER ACTIVITY WILL END
OVERNIGHT AS THE WEAK UPPER TROUGH IS REPLACED BY A RIDGE THROUGH
SUNDAY. LIGHT PRESSURE GRADIENTS...A LIGHT AND VARIABLE WIND.

&&

.MARINE...A COLD FRONT IS BREAKING UP OVER THE COASTAL WATERS THIS
AFTERNOON. NW FLOW WILL EVENTUALLY INCREASE BEHIND THE FRONT...BUT
IT DOES NOT LOOK LIKELY THAT THE CENTRAL AND EASTERN STRAIT OF JUAN
DE FUCA WILL SEE MORE THAN ABOUT 20KT WLY WINDS LATER THIS EVENING.
HIGH PRES OVER THE NE PAC WILL MAINTAIN NW FLOW SUN AND MON. ANOTHER
FRONT WILL ARRIVE FOR TUE AND WED.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 181635
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
935 AM PDT SAT MAY 18 2013

.SYNOPSIS...A WEAK COLD FRONT AND AN UPPER TROUGH WILL MOVE INLAND
TODAY GIVING A COOL SHOWERY DAY. AN UPPER RIDGE WILL BUILD
OFFSHORE SUNDAY AND MOVE INLAND MONDAY FOR WARMER AND MOSTLY DRY
WEATHER. A DEEP UPPER LOW WILL REACH THE AREA TUESDAY AND LINGER
THROUGH THE REST OF NEXT WEEK FOR SHOWERY AND UNSEASONABLY COOL
WEATHER.

&&

.SHORT TERM...A WEAK UPPER TROUGH AXIS WILL MOVE ONSHORE AND ACROSS
WRN WA FOR THE REST OF TODAY. HEIGHT RISES BEHIND THE TROUGH ARE
STRONGER THAN THE HEIGHT FALLS PRECEDING THE TROUGH...INDICATING
THAT THE TROUGH WILL BE WEAKENING AND FILLING AS IT MOVES OVERHEAD.
FOR NOW...KLGX RADAR SHOWS A LARGE AREA OF SHOWERS AND RAIN OFF THE
COAST...JUST IN ADVANCE OF THE TROUGH AXIS. THIS WILL MOVE ONTO THE
COAST LATER THIS MORNING...THEN INTO THE PUGET SOUND LOWLANDS LATE
THIS AFTN. WITH THE WEAKENING TREND OF THE TROUGH...RAINFALL FURTHER
INLAND SHOULD BE FAIRLY LIGHT THIS AFTN...WITH JUST A FEW HUNDREDTHS
OF AN INCH OF RAIN EXPECTED ALONG THE I-5 CORRIDOR NORTH OF OLYMPIA.
A LITTLE MORE RAIN SOUTH OF OLYMPIA...BUT REMAINING BELOW 1/4 INCH.

ONCE THE DISSIPATING TROUGH AXIS MOVES EAST OF THE CASCADES THIS
EVNG...UPPER HEIGHTS WILL RISE QUICKLY. THE AIR MASS WILL DRY
QUICKLY ON SUNDAY...ESPECIALLY ABOVE ABOUT 8000 FT MSL. A NORTH WIND
WILL KICK IN THROUGH THE PUGET SOUND LOWLANDS...A FAIR WEATHER
DIRECTION FOR THE LOWLANDS. WITH FAIRLY SHALLOW MOISTURE AND
NORTHERLY ONSHORE FLOW...WOULD EXPECT SHOWERS ON SUNDAY TO BE LIGHT
AND CONFINED TO THE CASCADES...FOOTHILLS AND THE PERIMETER OF THE
OLYMPICS.

THE UPPER HEIGHT RISES WILL SET THE STAGE FOR AN UPPER RIDGE AXIS TO
PASS ACROSS WRN WA ON MON...MAKING MONDAY THE WARMEST AND DRIEST OF
THE NEXT 7 DAYS FOR WRN WA. INTERIOR LOWLANDS WILL RISE INTO 70S ON
MON AFTN.       HANER

.LONG TERM...FROM PREVIOUS DISCUSSION...THE EXTENDED MODELS ARE IN
GENERALLY GOOD AGREEMENT WITH THE ARRIVAL OF A RATHER DEEP UPPER
LEVEL TROUGH ON TUESDAY THAT SETTLES OVER THE PACIFIC NORTHWEST ON
WEDNESDAY. AS PREVIOUSLY DISCUSSED...THIS WILL LEAD TO SHOWERY AND
COOL WEATHER WITH RATHER LOW SNOW LEVELS FOR LATE MAY. THE MODELS
QUICKLY DIVERGE WITH THE EVOLUTION OF THE TROUGH AS WE GET INTO THE
LATER HALF OF NEXT WEEK. THE CANADIAN TAKES A CLOSED LOW CENTER INTO
NORTHERN CALIFORNIA BY LATE THURSDAY. THE EURO TAKES THE BASE OF THE
TROUGH INTO THE NORTHERN GREAT BASIN DURING THE SAME PERIOD WHILE
GFS KEEPS THE LOW CENTER RIGHT OVER WESTERN WASHINGTON. ALL OF THE
MODELS KEEP A BROAD TROUGH OVER THE WEST COAST INTO LATE NEXT
WEEK...BUT HAVE SIGNIFICANTLY DIFFERENT IDEAS WITH THE TRACKS OF
DISTURBANCES ROTATING THROUGH IT. CONFIDENCE IN ANY LEVEL OF DETAIL
FOR THE BEGINNING OF THE HOLIDAY WEEKEND FORECAST IS VERY LOW AT
THIS TIME. NO SIGNIFICANT CHANGES WERE MADE TO THE EXTENDED FORECAST
OVERNIGHT.      27

&&

.AVIATION...ANOTHER ROUND OF SHOWERS FOR WESTERN WA TODAY AS A COLD
FRONT MOVES OVER THE REGION. THE AIR MASS IS MOIST AND SOMEWHAT
UNSTABLE WITH FAIRLY LIGHT SW FLOW ALOFT BECOMING NW TONIGHT. THE
MOUNTAINS AND FOOTHILLS WILL BE OBSCURED. MORNING CLOUDS WILL GIVE
WA TO AFTERNOON SUN SUNDAY.

KSEA...SHOWERS WILL INCREASE THIS MORNING AS A COLD FRONT APPROACHES
AND MOVES INLAND. SHOWER ACTIVITY WILL DECREASE TONIGHT AS THE UPPER
LEVEL TROUGH EXITS. THE SURFACE FLOW WILL REMAIN SOUTHERLY.

&&

.MARINE...A COLD FRONT WILL CROSS THE REGION TODAY...WITH ONSHORE
FLOW INCREASING TONIGHT. THE CENTRAL AND EASTERN STRAIT OF JUAN DE
FUCA MAY SEE SMALL CRAFT ADVISORY WINDS THIS EVENING. HIGH PRES OVER
THE NE PAC WILL MAINTAIN NNW FLOW SUN AND MON. ANOTHER FRONT WILL
ARRIVE ON TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 181518
AFDSEW

.AVIATION...ANOTHER ROUND OF SHOWERS FOR WESTERN WA TODAY AS A COLD
FRONT MOVES OVER THE REGION. THE AIR MASS IS MOIST AND SOMEWHAT
UNSTABLE WITH FAIRLY LIGHT SW FLOW ALOFT BECOMING NW TONIGHT. THE
MOUNTAINS AND FOOTHILLS WILL BE OBSCURED. MORNING CLOUDS WILL GIVE
WA TO AFTERNOON SUN SUNDAY.

KSEA...SHOWERS WILL INCREASE THIS MORNING AS A COLD FRONT APPROACHES
AND MOVES INLAND. SHOWER ACTIVITY WILL DECREASE TONIGHT AS THE UPPER
LEVEL TROUGH EXITS. THE SURFACE FLOW WILL REMAIN SOUTHERLY.

&&

.MARINE...A COLD FRONT WILL CROSS THE REGION TODAY...WITH ONSHORE
FLOW INCREASING TONIGHT. THE CENTRAL AND EASTERN STRAIT OF JUAN DE
FUCA MAY SEE SMALL CRAFT ADVISORY WINDS THIS EVENING. HIGH PRES OVER
THE NE PAC WILL MAINTAIN NNW FLOW SUN AND MON. ANOTHER FRONT WILL
ARRIVE ON TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 180931
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 AM PDT SAT MAY 18 2013

.SYNOPSIS...A WEAK COLD FRONT AND AN UPPER TROUGH WILL MOVE INLAND
TODAY GIVING A COOL SHOWERY DAY. AN UPPER RIDGE WILL BUILD
OFFSHORE SUNDAY AND MOVE INLAND MONDAY FOR WARMER AND MOSTLY DRY
WEATHER. A DEEP UPPER LOW WILL REACH THE AREA TUESDAY AND LINGER
THROUGH MIDWEEK FOR SHOWERY AND UNSEASONABLY COOL WEATHER.

&&

.SHORT TERM...A WEAK COLD FRONT CONTINUES TO HOLD TOGETHER AS IT
APPROACHES THE COAST EARLY THIS MORNING. MODEL QPF IS QUITE LIGHT
WITH THIS SYSTEM AND IT IS EXPECTED TO WEAKEN AS IT MOVES ACROSS
WESTERN WASHINGTON TODAY. DESPITE THE LIKELY WORDING IN THE
FORECAST...INTERIOR AREAS WILL PROBABLY ONLY SEE A FEW HUNDREDTHS OF
PRECIP AT BEST. THE FRONT WILL BE EAST OF THE CASCADES BY THIS
AFTERNOON WITH THE TRAILING UPPER LEVEL TROUGH MOVING OVER WESTERN
WASHINGTON EARLY THIS EVENING. HIGH TEMPERATURES WILL BE ON THE COOL
SIDE WITH THE CLOUDS AND SHOWERS AROUND...3 TO 5 DEGREES BELOW
NORMAL. UPPER LEVEL RIDGING WILL BE REBUILDING OVER THE REGION BY
SUNDAY MORNING. I HELD ON TO THE LOW CHANCE OF SHOWERS FOR SUNDAY
MORNING...BUT IT SHOULD BE A DRY DAY WITH PARTLY SUNNY SKIES AND
TEMPERATURES REBOUNDING TO NEAR SEASONAL NORMALS. I NUDGED THE
EXPECTED HIGHS FOR SUNDAY UP A FEW DEGREES FROM THE PREVIOUS
FORECAST.

THE UPPER RIDGE AXIS WILL BE OVER THE AREA SUNDAY NIGHT WITH 500 MB
HEIGHTS AT OR ABOVE 570 DAM. THE RIDGE AXIS SHIFTS EAST OF THE
CASCADES ON MONDAY...BUT HEIGHTS ONLY FALL SLOWLY. DESPITE ONSHORE
FLOW...INTERIOR AREAS FROM SEATTLE SOUTHWARD HAVE A GOOD SHOT AT
REACHING 70 DEGREES OR BETTER MONDAY AFTERNOON. THE MODELS HAVE
PUSHED THE ARRIVAL OF THE NEXT SYSTEM BACK BY 6 TO 12 HOURS. I
SCALED BACK POPS MONDAY AFTERNOON AND EVENING. MOST INTERIOR AREAS
SHOULD BE DRY MONDAY EVENING...WITH RAIN CHANCES INCREASING LATE
MONDAY NIGHT AS AN UPPER LEVEL TROUGH AND ASSOCIATED FRONT PUSH
SOUTHEASTWARD INTO THE AREA. THIS WILL BEGIN WHAT COULD BE AN
EXTENDED PERIOD OF UNSEASONABLY COOL TEMPERATURES AND OCCASIONALLY
SHOWERY WEATHER MUCH OF NEXT WEEK.


.LONG TERM...THE EXTENDED MODELS ARE IN GENERALLY GOOD AGREEMENT
WITH THE ARRIVAL OF A RATHER DEEP UPPER LEVEL TROUGH ON TUESDAY THAT
SETTLES OVER THE PACIFIC NORTHWEST ON WEDNESDAY. AS PREVIOUSLY
DISCUSSED...THIS WILL LEAD TO SHOWERY AND COOL WEATHER WITH RATHER
LOW SNOW LEVELS FOR LATE MAY. THE MODELS QUICKLY DIVERGE WITH THE
EVOLUTION OF THE TROUGH AS WE GET INTO THE LATER HALF OF NEXT WEEK.
THE CANADIAN TAKES A CLOSED LOW CENTER INTO NORTHERN CALIFORNIA BY
LATE THURSDAY. THE EURO TAKES THE BASE OF THE TROUGH INTO THE
NORTHERN GREAT BASIN DURING THE SAME PERIOD WHILE GFS KEEPS THE LOW
CENTER RIGHT OVER WESTERN WASHINGTON. ALL OF THE MODELS KEEP A BROAD
TROUGH OVER THE WEST COAST INTO LATE NEXT WEEK...BUT HAVE
SIGNIFICANTLY DIFFERENT IDEAS WITH THE TRACKS OF DISTURBANCES
ROTATING THROUGH IT. CONFIDENCE IN ANY LEVEL OF DETAIL FOR THE
BEGINNING OF THE HOLIDAY WEEKEND FORECAST IS VERY LOW AT THIS TIME.
NO SIGNIFICANT CHANGES WERE MADE TO THE EXTENDED FORECAST OVERNIGHT.

27

&&

.AVIATION...A COLD FRONT WILL CROSS THE REGION TODAY FOR ADDITIONAL
SHOWERS. THE AIR MASS IS MOIST AND UNSTABLE WITH WESTERLY FLOW
ALOFT. MVFR CIGS ARE POSSIBLE WITH HEAVIER SHOWERS. SHOWERS WILL
MAINLY AFFECT THE CASCADES TONIGHT AS THE UPPER LEVEL TROUGH SHIFTS
EAST OF THE CASCADES. 33

KSEA...SHOWERS WILL INCREASE THIS MORNING AS A COLD FRONT APPROACHES
AND MOVES INLAND. SHOWER ACTIVITY WILL DECREASE TONIGHT AS THE UPPER
LEVEL TROUGH EXITS. THE SURFACE FLOW WILL REMAIN SOUTHERLY. 33

&&

.MARINE...A COLD FRONT WILL CROSS THE REGION TODAY...WITH ONSHORE
FLOW INCREASING TONIGHT. THE CENTRAL AND EASTERN STRAIT OF JUAN DE
FUCA MAY SEE SMALL CRAFT ADVISORY WINDS. HIGH PRES OVER THE NE PAC
WILL MAINTAIN NORTH/NORTHWESTERLY FLOW SUN AND MON. ANOTHER FRONT
WILL ARRIVE ON TUE. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 180455
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
955 PM PDT FRI MAY 17 2013

.SYNOPSIS...A WEAK COLD FRONT AND AN UPPER TROUGH WILL MOVE INLAND
SATURDAY GIVING A COOL SHOWERY DAY. AN UPPER RIDGE WILL BUILD
OFFSHORE SUNDAY AND MOVE INLAND MONDAY FOR WARMER AND MOSTLY DRY
WEATHER. A DEEP UPPER LOW WILL REACH THE AREA TUESDAY AND LINGER
THROUGH MIDWEEK FOR SHOWERY AND UNSEASONABLY COOL WEATHER. SOME
IMPROVEMENT IS POSSIBLE BY MEMORIAL DAY WEEKEND.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLOUDY SKIES OVER MOST OF
WESTERN WASHINGTON THIS EVENING. WEAK UPPER LEVEL TROUGH MOVED INTO
THE AREA IN THE AFTERNOON HOURS TRIGGERING SOME SHOWERS BY LATE IN
THE AFTERNOON. MOST OF THE SHOWER ACTIVITY HAS COME TO AN END OVER
THE AREA OR WILL COME TO AN END BEFORE MIDNIGHT. THE EXCEPTION IS
OVER ISLAND...SAN JUAN AND WESTERN SKAGIT AND WHATCOM COUNTY WHERE
WEAK CONVERGENCE WILL KEEP THE SHOWERS GOING PAST MIDNIGHT.
TEMPERATURES AT 9 PM WERE IN THE 50S.

SATELLITE IMAGERY ALSO SHOWS WEAK COLD FRONT OFFSHORE NEAR 130W AT
04Z. CLOUD TOP TEMPERATURES ARE NOT WARMING AS THE FRONT APPROACHES
THE COAST INDICATING THAT THE SYSTEM IS NOT WEAKENING. THE UPPER
LEVEL TROUGH BEHIND THE FRONT WILL DIG SOUTH A BIT ON SATURDAY WITH
THE JET AIMED AT SOUTHERN OREGON/NORTHERN CALIFORNIA. THIS WILL SLOW
DOWN THE EASTWARD MOVEMENT OF THE SYSTEM AND WEAKEN IT AS IT MOVES
INLAND ON SATURDAY. EVEN WITH THE FRONT WEAKENING EXPECT LIGHT
PRECIPITATION ALONG THE COAST FOR MOST OF THE DAY WITH MORE SPOTTY
PRECIPITATION OVER THE INTERIOR. HIGHEST POPS OVER THE INTERIOR IN
THE AFTERNOON VERSUS THE MORNING HOURS STILL LOOK GOOD. FRONT
DISSIPATES OVER THE AREA LATE IN THE DAY WITH THE UPPER LEVEL TROUGH
EAST OF THE CASCADES BY 06Z. THIS WILL BRING ABOUT AN END TO MOST OF
THE SHOWER ACTIVITY.

UPPER LEVEL RIDGE OFFSHORE BUILDING INLAND ON SUNDAY. SURFACE
GRADIENTS REMAINING ONSHORE BUT 00Z MODEL RUNS HAVE 500 MB HEIGHTS
570 DM PLUS BY THE AFTERNOON HOURS. STILL A CHANCE OF AN ISOLATED
SHOWER EARLY SUNDAY MORNING. DAYTIME HIGHS SHOULD RECOVER BACK TO
NEAR NORMAL.

RIDGE SHIFTING TO THE EAST ON SUNDAY WITH SOUTHWESTERLY FLOW ALOFT
OVER THE AREA. WEAK ONSHORE PRESSURE GRADIENTS CONTINUE BUT THE
PRECIPITATION ASSOCIATED WITH A COOL UPPER LEVEL LOW APPROACHING THE
AREA STILL WELL OFFSHORE AT 00Z TUESDAY. WARMEST LOCATIONS ON MONDAY
SHOULD CREEP BACK INTO THE LOWER 70S. CURRENT FORECAST LOOKS A
LITTLE ON THE COOL SIDE FOR SUNDAY AND MONDAY. WILL LET THE MIDSHIFT
MAKE THE FINAL DECISION ON BUMPING THE MAX TEMPS UP A COUPLE OF
DEGREES BOTH DAYS. NO UPDATE THIS EVENING. FELTON


.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. THE UPEPR LOW DEEPENS AND
MOVES TO JUST OFF THE COAST ON TUESDAY. THE GFS AND EURO AGREE ON
THIS. THEN BOTH MODELS MOVE THE UPPER LOW INLAND AND KEEP IT MORE OR
LESS OVER THE AREA WEDNESDAY AND THURSDAY...ALTHOUGH BY THURSDAY THE
TRACKS ARE DIVERGING SIGNIFICANTLY. THE GFS MOVES THE LOW NORTH AND
THE EURO MOVES IT SOUTH...THEREBY MAKING FRIDAY A DRIER AND WARMER
DAY COMPLETELY BY COINCIDENCE.

IF THE MODELS ARE RIGHT...TUESDAY THROUGH THURSDAY ARE GOING TO BE
COOL AND SHOWERY DAYS. HIGHS MAY NOT GET OUT OF THE 50S. THERE COULD
BE SNOW SHOWERS IN THE MOUNTAINS WITH THE SNOW LEVEL DIPPING TO 3000
FEET OR SO. CONFIDENCE IS NOT PARTICULARLY HIGH IN ANY DETAILS. FOR
INSTANCE...THE ENSEMBLE GFS SOLUTIONS SHOW KSEA HIGHS ON TUESDAY
RANGING FROM 55 TO 68. HOWEVER IT SEEMS LIKELY THERE WILL BE SOME
VERY COOL DAYS WITH SHOWERS...PROBABLY MIXED IN WITH SOME PARTLY
SUNNY DAYS. BURKE

&&

.AVIATION...AN UPPER LEVEL TROUGH OVER THE PAC NW WILL MAINTAIN
ISOLATED TO SCATTERED SHOWERS ACROSS WESTERN WA TONIGHT. THE FLOW
ALOFT IS LIGHT WESTERLY. SHOWERS WILL INCREASE IN COVERAGE SAT
MORNING AS A COLD FRONT MOVES INLAND. ONSHORE FLOW WILL INCREASE
BEHIND THIS FRONT SAT NIGHT. 33

KSEA...ISOLATED LIGHT SHOWERS WILL REMAIN IN THE VICINITY
TONIGHT...WITH SOUTHERLY FLOW AT THE SURFACE. SHOWERS WILL INCREASE
ON SAT AS A COLD FRONT MOVES INLAND. 33

&&

.MARINE...ONSHORE FLOW WILL CONTINUE ACROSS WESTERN WA TONIGHT. A
COLD FRONT WILL CROSS THE REGION ON SAT FOR INCREASING WINDS.
HIGHEST WINDS WILL BE FOUND THROUGH THE STRAIT OF JUAN DE FUCA -
SMALL CRAFT ADVISORY WINDS ARE LIKELY. HIGH PRES OVER THE NE PAC
WILL MAINTAIN ONSHORE FLOW SUN AND MON. ANOTHER FRONT WILL ARRIVE ON
TUE. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 172202
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT FRI MAY 17 2013

.SYNOPSIS...AN UPPER TROUGH WILL ARRIVE MOVE INLAND SATURDAY GIVING
A COOL SHOWERY DAY. AN UPPER RIDGE WILL BUILD OFFSHORE SUNDAY AND
MOVE INLAND MONDAY FOR WARMER AND MOSTLY DRY WEATHER. A DEEP UPPER
LOW WILL REACH THE AREA TUESDAY AND LINGER THROUGH MIDWEEK FOR
SHOWERY AND UNSEASONABLY COOL WEATHER. SOME IMPROVEMENT IS POSSIBLE
BY MEMORIAL DAY WEEKEND.

&&

.SHORT TERM...CLOUDS PERSISTED LONGER OVER INLAND AREAS TODAY AS A
RAIN BAND SLOWLY MOVED NORTH. MEANWHILE WHAT WAS SUPPOSED TO BE AN
AREA OF PARTIAL CLEARING TO THE WEST QUICKLY FILLED IN WITH CUMULUS
AND SCATTERED SHOWERS. HIGH TEMPERATURES WILL TOP OUT IN THE LOW
60S...UPPER 50S NORTH. THERE WILL LIKELY BE SOME BREAKS IN THE
CLOUDS TONIGHT THAT ALLOW TEMPERATURES TO FALL TO NEAR 50 DEGREES.

A SIGNIFICANT UPPER TROUGH WILL MOVE ONTO THE COAST SATURDAY MORNING
THEN INLAND SATURDAY AFTERNOON. SHOWERS SHOULD BE MORE NUMEROUS WITH
THIS UPPER TROUGH...ESPECIALLY DURING THE 18Z-03Z PERIOD. THE CLOUDS
AND SHOWERS WILL DAMPEN TEMPERATURES FURTHER WITH HIGHS LUCKY TO
MAKE IT TO 60 DEGREES...AND PLENTY OF HIGHS IN THE 50S ARE LIKELY ON
THE COAST AND OVER THE NORTH.

AN UPPER RIDGE OF HIGH PRESSURE WILL BUILD OFF THE COAST SATURDAY
NIGHT AND SUNDAY. CONDITIONS SHOULD DRY AND THERE SHOULD BE AT LEAST
SOME CLEARING SUNDAY AFTERNOON...WITH HIGHS IN THE LOW TO MID 60S
OVER INLAND AREAS. DRY WEATHER IS LIKELY TO CONTINUE INTO MONDAY BUT
BY MONDAY AFTERNOON A DEEP UPPER TROUGH APPROACHING FROM THE
NORTHWEST WILL BEGIN TO AFFECT THE WEATHER. HAVE PUT A CHANCE OF
SHOWERS ON THE COAST AND OVER THE NORTH MONDAY AFTERNOON. CLOUDS
WILL BE INCREASING AND TEMPERATURES WILL BE NOTICEABLY LOWER IN THE
NORTH. SOUTHERN INLAND AREAS WILL PROBABLY HAVE LOTS OF HIGHS IN THE
60S AS THE CLOUDS WILL REACH THERE LAST. BURKE

.LONG TERM...THE UPEPR LOW DEEPENS AND MOVES TO JUST OFF THE COAST
ON TUESDAY. THE GFS AND EURO AGREE ON THIS. THEN BOTH MODELS MOVE
THE UPPER LOW INLAND AND KEEP IT MORE OR LESS OVER THE AREA
WEDNESDAY AND THURSDAY...ALTHOUGH BY THURSDAY THE TRACKS ARE
DIVERGING SIGNIFICANTLY. THE GFS MOVES THE LOW NORTH AND THE EURO
MOVES IT SOUTH...THEREBY MAKING FRIDAY A DRIER AND WARMER DAY
COMPLETELY BY COINCIDENCE.

IF THE MODELS ARE RIGHT...TUESDAY THROUGH THURSDAY ARE GOING TO BE
COOL AND SHOWERY DAYS. HIGHS MAY NOT GET OUT OF THE 50S. THERE COULD
BE SNOW SHOWERS IN THE MOUNTAINS WITH THE SNOW LEVEL DIPPING TO 3000
FEET OR SO. CONFIDENCE IS NOT PARTICULARLY HIGH IN ANY DETAILS. FOR
INSTANCE...THE ENSEMBLE GFS SOLUTIONS SHOW KSEA HIGHS ON TUESDAY
RANGING FROM 55 TO 68. HOWEVER IT SEEMS LIKELY THERE WILL BE SOME
VERY COOL DAYS WITH SHOWERS...PROBABLY MIXED IN WITH SOME PARTLY
SUNNY DAYS. BURKE

&&

.AVIATION...A WEAK TROUGH WAS GIVING SCATTERED SHOWERS ACROSS
WESTERN WA THIS AFTERNOON. A STRONGER FRONT WILL REACH WESTERN WA
SATURDAY AND A MORE ORGANIZED BAND OF PRECIP SHOULD MOVE THROUGH
WESTERN WA OVER THE COURSE OF THE DAY. THE AIR WILL REMAIN MOIST AND
SLIGHTLY UNSTABLE. LIGHT SW FLOW ALOFT.

KSEA...SCATTERED SHOWERS AND SLY BREEZE TONIGHT...MORE PRECIP ON
SATURDAY WITH THE NEXT FRONT.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE. A WEAK SURFACE TROUGH
DISSIPATED OVER WESTERN WA TODAY. A FRONT JUST OUTSIDE OF 130W THIS
AFTERNOON WILL MOVE OVER WESTERN WA SATURDAY...THE WIND OVER THE
COASTAL WATERS SATURDAY MORNING SHOULD BE SOUTH OR SE AROUND 20KT.
BEHIND THE FRONT WLY FLOW WILL CONTINUE SAT NITE THROUGH SUNDAY
NIGHT...WITH SMALL CRAFT ADVISORY LEVEL WLY WINDS LIKELY IN THE
STRAIT IN THE EVENINGS. ANOTHER WEATHER SYSTEM WILL REACH THE AREA
MON NIGHT OR TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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

000
FXUS66 KSEW 171533
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 AM PDT FRI MAY 17 2013

.SYNOPSIS...A WEAK UPPER TROUGH WILL MOVE INTO WESTERN WASHINGTON
TODAY...PRODUCING SOME SHOWERS BUT ALLOWING SUN BREAKS. A STRONGER
TROUGH WILL ARRIVE SATURDAY FOR A SHOWERY COOLER DAY. AN UPPER RIDGE
WILL BUILD OFFSHORE SUNDAY AND MOVE INLAND MONDAY FOR WARMER AND
MOSTLY DRY WEATHER. A DEEP UPPER LOW WILL REACH THE AREA TUESDAY AND
LINGER THROUGH MIDWEEK FOR SHOWERY AND UNSEASONABLY COOL WEATHER.

&&

.SHORT TERM...WESTERN WASHINGTON HAS EXTENSIVE CLOUD COVER TODAY AS
AN UPPER LEVEL TROUGH SETTLES OVER THE AREA. THERE ARE SOME BREAKS
IN THE CLOUDS OFFSHORE SO SUN BREAKS IN THE AFTERNOON SEEM LIKE A
GOOD BET. A BAND OF SHOWERS IS MOVING NORTH THROUGH THE SEATTLE
METRO AREA THIS MORNING AND SCATTERED SHOWERS ARE MOVING ASHORE.
HIGH TEMPERATURES TODAY WILL BE ON THE COOL SIDE...IN THE LOW 60S.

A MORE ORGANIZED SYSTEM ASSOCIATED WITH A SHORT WAVE WILL ARRIVE
SATURDAY. POPS SHOULD BE AT LEAST IN THE LIKELY CATEGORY AND
CONDITIONS WILL REMAIN MOSTLY CLOUDY AND COOL. SUNDAY LOOKS DRIER AS
THE UPPER TROUGH MOVES AWAY TO THE EAST AND HEIGHTS REBOUND. ONSHORE
SURFACE FLOW MAY KEEP TEMPERATURES IN THE LOW 60S. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE UPPER RIDGE WILL BE WELL EAST
OF THE CASCADES MONDAY...AND A DEEP UPPER LOW WILL START DIGGING
SOUTHEAST TOWARD THE REGION ACROSS SOUTHEAST ALASKA AND THE NORTHERN
BRITISH COLUMBIA COAST. IT SHOULD BE A DRY AND PARTLY SUNNY DAY FOR
WESTERN WASHINGTON.

THE UPPER LOW WILL DIG INTO WESTERN WASHINGTON OR ITS OFFSHORE
WATERS TUESDAY AFTERNOON OR TUESDAY NIGHT AND LINGER OVER THE
PACIFIC NORTHWEST THROUGH WEDNESDAY NIGHT. THIS FEATURE WILL BRING
SHOWERY AND UNSEASONABLY COOL WEATHER...AND THE SNOW LEVEL WILL
PROBABLY FALL TO AROUND 3000 FT.

THE UPPER LOW WILL PROBABLY START SHIFTING EAST OF THE AREA
THURSDAY...BUT IT LOOKS LIKE WE ARE STARTING TO SEE A TREND IN THE
MODELS THAT KEEPS THE LOW IN THE VICINITY OF THE FORECAST AREA A BIT
LONGER. TIMING THE DEPARTURE OF THESE UPPER LOWS IS ALWAYS UNCERTAIN
IN THE FORECAST DAY 5 TO 7 RANGE...AND THEY HAVE A TENDENCY TO HANG
AROUND LONGER THAN INITIALLY EXPECTED. FOR NOW THE FORECAST FOR
MARGINAL IMPROVEMENT ON THURSDAY LOOKS FINE.   MCDONNAL

&&

.AVIATION...A WEAK TROUGH IS MOVING THROUGH WESTERN WASHINGTON
TODAY. A STRONGER FRONT WILL REACH WESTERN WA SATURDAY MORNING.
SCATTERED SHOWERS TODAY SHOULD END TONIGHT...AND THEN A MORE
ORGANIZED BAND OF PRECIP SHOULD REACH THE COAST BY DAYBREAK
SATURDAY...SPREADING INLAND BY MIDDAY. THE AIR WILL REMAIN MOIST AND
SLIGHTLY UNSTABLE TODAY...THERE MAY BE A LITTLE TEMPORARY DRYING OF
THE AIR TONIGHT BEFORE THE NEXT SYSTEM ARRIVES SAT.

KSEA...SCATTERED SHOWERS AND A SSW BREEZE AROUND 10KTS.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE...MOST AREAS OUGHT TO HAVE A
BREEZE UP TO ABOUT 15 KNOTS TODAY AS A TROUGH BREAK UP OVER WESTERN
WA. A STRONGER SYSTEM WILL REACH THE AREA SATURDAY...AND THEN
ANOTHER FRONT WILL REACH THE AREA MON NIGHT OR TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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