Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 282232
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PDT SUN JUN 28 2015

.SYNOPSIS...A CHANCE OF THUNDERSTORMS REMAINS AHEAD OF A SHORTWAVE
UPPER LEVEL TROUGH MOVING THROUGH THE AREA EARLY MONDAY. TEMPS WILL
MODERATE A BIT AFTER THE TROUGH MOVES THROUGH WITH ONSHORE FLOW AT
THE SURFACE. STARTING WEDNESDAY...UPPER LEVEL HEIGHTS WILL RISE
AGAIN OVER THE AREA FOR MORE VERY WARM TEMPERATURES.

&&

.SHORT TERM...RADAR IMAGERY SHOWS VIRGA AND PRECIPITATION FROM HIGH
BASED CLOUDS OVER WESTERN WASHINGTON RIGHT NOW. VISIBLE SATELLITE
IMAGERY SHOWS THAT MORE MID LEVEL MOISTURE WILL BE ADVECTED INTO OUR
AREA FROM THE SOUTH AHEAD OF A SHORTWAVE TROUGH MOVING THROUGH
MONDAY MORNING. I HAVE LEFT A CHANCE OF THUNDERSTORMS IN THE
FORECAST THROUGH THIS EVENING...EVEN THOUGH THE FORECAST SOUNDINGS
FROM THE WRF GFS 4KM SHOW BUOYANCY AND MU CAPE DECREASING...SINCE
ANY CAPE THAT IS LEFT COULD BE TRIGGERED AGAIN BY THE PASSING
SHORTWAVE. I HAVE KEPT IN ISOLATED THUNDERSTORMS THROUGH MONDAY
MORNING AS WELL FOR MAINLY THE MOUNTAINS.

LOWS TONIGHT WILL REMAIN SOMEWHAT WARM DUE TO THE CLOUD
COVER...ALTHOUGH IN MOST AREAS IT WILL BE COOLER THAN LAST NIGHT
WITH TEMPS FOR THE SEATTLE METRO DROPPING DOWN INTO THE MID 60S.

MONDAY...AFTER THE UPPER LEVEL TROUGH PASSES THROUGH THE UPPER LEVEL
FLOW WILL SWITCH TO MORE WESTERLY. LINGERING SHOWERS ARE POSSIBLE IN
THE MOUNTAINS THROUGH LATE IN THE DAY. TEMPS AT THE SURFACE WILL BE
MODERATED A BIT THANKS TO ONSHORE FLOW SETTING UP DURING THE DAY.
LIGHT ONSHORE FLOW WILL CONTINUE THROUGH TUESDAY AS AN UPPER LEVEL
LOW MOVES THROUGH TO THE NORTH...MODERATING TEMPERATURES EVEN MORE.
HIGH TEMPS IN THE SEATTLE METRO SHOULD DROP TO AROUND 80 BY TUESDAY.

TUESDAY NIGHT THROUGH WEDNESDAY...SURFACE GRADIENTS WILL TURN NWLY
AND AN UPPER LEVEL RIDGE WILL BEGIN TO SET UP OVER THE AREA FOR VERY
WARM TEMPS AGAIN STARTING WEDNESDAY. JSMITH

.LONG TERM...MODELS ARE IN DECENT AGREEMENT THAT 500 MB HEIGHTS WILL
AGAIN RISE TO AROUND 590 DM ON THURSDAY AND FRIDAY...WHICH WILL
RESULT IN WELL ABOVE NORMAL TEMPS FOR WESTERN WASHINGTON.
HOWEVER...SURFACE FLOW REMAINS NWLY WHICH WILL KEEP MOST HIGH TEMPS
FROM BREAKING 90. RECENT LONG TERM MODEL TRENDS HAVE SHOWN HEIGHTS
LOWERING A BIT ON INDEPENDENCE DAY AND SUNDAY FOR SLIGHTLY COOLER
TEMPERATURES. JSMITH

&&

.AVIATION...A HIGH AMPLITUDE UPPER LEVEL RIDGE EXTENDING FROM THE
CANADIAN ROCKIES SOUTHWARD INTO UTAH IS GIVING SLY FLOW ALOFT TO THE
REGION. A TROUGH OF LOW PRES EXTENDS FROM THE NORTHERN CALIFORNIA
COAST INTO THE CENTRAL OREGON OFFSHORE WATERS. THIS TROUGH WILL LIFT
NORTH ACROSS WESTERN WASHINGTON MON MORNING. THE AIR MASS IS
SOMEWHAT UNSTABLE ALOFT.

HIGH-BASED TSTMS THAT MOVED THROUGH THE AREA THIS MORNING HAVE
DISSIPATED. ALL THAT IS LEFT IS AN EXTENSIVE AREA OF MID AND HIGH
LEVEL CLOUDINESS WITH SOME VIRGA. A NEW AREA OF SHOWERS IS
DEVELOPING FROM SOUTH OF KSEA INTO THE CASCADES OF CENTRAL OREGON.
THIS ACTIVITY IS NE OF THE SHORTWAVE TROUGH THAT IS MOVING NE TOWARD
WESTERN WA. THE THREAT OF LIGHTNING WITH THE SHOWERS THIS AFTERNOON
THROUGH TONIGHT WILL BE RATHER LOW W OF THE CASCADES AS THE LOWER
LEVELS HAVE STABILIZED WITH THE MOISTURE ALOFT...SO TSTMS WILL NOT
BE INCLUDED IN THE TERMINAL FORECASTS. BUT IF TSTMS START OCCURING
OVER THE OREGON CASCADES OR THE CASCADES OF SOUTHERN
WASHINGTON...TERMINAL FORECASTS WILL BE AMENDED AS NEEDED. SHOWERS
THAT OCCUR WILL BE LIGHT AND CIGS ARE EXPECTED TO REMAIN ABOVE
FL050.

SOME LOW STRATUS IS SITTING OVER THE COASTAL WATERS SOUTH OF ABOUT
KHQM. EXPECT THE STRATUS TO MOVE NWD THROUGH THE COASTAL ZONES LATE
TONIGHT AND IN THROUGH THE CHEHALIS GAP TO THE SOUTH PUGET
SOUND...PERHAPS TOUCHING THE KSEA TERMINAL...14Z-17Z TIME FRAME.
WHATEVER STRATUS MOVES INLAND MON MORNING WILL BURN BACK TO THE
COASTLINE BY SHORTLY AFTER 18Z.  ALBRECHT

KSEA...EXPECT HIGH BASED LIGHT SHOWER ACTIVITY THROUGH TONIGHT OR
EARLY MON MORNING. AT THIS TIME ADDITIONAL LIGHTNING IS NOT EXPECTED
AT THE TERMINAL...BUT WILL BE WATCHING SHOWERS THAT ARE DEVELOPING
OVER THE SOUTHERN CASCADES THAT ARE MOVING NWD TOWARD THE TERMINAL.
CIGS WILL REMAIN ABOVE 050. LIGHT NW WIND WILL BECOME SWLY 4-6 KT
AFTER 04Z. ALBRECHT

&&

.MARINE...ONSHORE FLOW WILL GRADUALLY INCREASE TONIGHT THROUGH
MONDAY NIGHT AS HIGH PRES BUILDS OFFSHORE AND LOW PRES REMAINS E OF
THE CASCADES. EXPECT SMALL CRAFT ADVISORY WEST WINDS TO DEVELOP THIS
EVENING IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

ONSHORE FLOW WILL BE A BIT STRONGER LATE MONDAY AFTERNOON INTO
MONDAY NIGHT. EXPECT 20 TO 30 KT W WINDS IN THE CENTRAL AND EAST
STRAIT AND POSSIBLE SMALL CRAFT ADVISORY CONDITIONS IN THE NORTHERN
PORTIONS OF ADMIRALTY INLET AND THE FAR SOUTHERN PORTIONS OF THE
NORTHERN INLAND WATERS.

LOW LEVEL FLOW WILL TURN MORE NORTHWESTERLY TUESDAY THROUGH THURSDAY
WITH SMALL CRAFT ADVISORY CONDITIONS BECOMING MORE LIKELY OVER THE
COASTAL WATERS. WINDS WILL BECOME LIGHTER IN THE INLAND WATERS WED
THROUGH FRI AS A WEAK THERMAL TROUGH DEVELOPS OVER THE WESTERN
WASHINGTON INTERIOR.  ALBRECHT

&&

.FIRE WEATHER...FROM THE RAPID START OF THE MORNING ACTIVITY...A
LULL...AT LEAST IN TERMS OF LIGHTNING STRIKES...SEEMS TO HAVE SET IN
OVER WESTERN WASHINGTON. CURRENT SATELLITE TRENDS SHOW CLOUDINESS
OVER MUCH OF THE AREA AND IF THAT IS THE CASE...CONCERNS START TO
ARISE WITH REGARDS TO HOW MUCH MORE ADDITIONAL CONVECTION...AND THUS
HOW MUCH MORE ADDITIONAL LIGHTNING...CAN BE EXPECTED. MODELS
CONTINUE TO HINT AT INSTABILITY THIS AFTERNOON...BUT FORECAST LIFTED
INDEX VALUES ARE COMING IN LOWER. GETTING THE DISTINCT FEELING THAT
THE MORNING ACTIVITY MAY INDEED HAVE LIMITED ANY ADDITIONAL ACTIVITY
THIS AFTERNOON...BUT CANNOT RULE OUT THE POSSIBILITY OF ISOLATED
STRIKES...ESPECIALLY IN LOCATIONS THAT HAVE CAUGHT A FEW BREAKS IN
THE CLOUDS. WHILE THIS CERTAINLY DOES NOT LIVE UP TO WIDESPREAD
CRITERIA OF RED FLAG WARNING CURRENTLY OUT...MUST ADMIT TO BEING A
BIT GUN SHY ABOUT TAKING IT DOWN. WILL LEAVE CURRENT PRODUCTS UP BUT
WILL UPDATE WORDING TO ILLUSTRATE THE DIMINISHING LIGHTNING
PROSPECTS. THAT SAID...WILL NOT EXTEND WARNING FOR ZONE 662 AT THIS
TIME. WILL WAIT TO SEE HOW THINGS PLAY OUT ON WEST SIDE BEFORE
TAKING ANY ACTION ON OUR ONLY EAST SIDE ZONE. SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...RED FLAG WARNING FOR ALL ZONES.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT.

&&

$$

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









USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.