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 280511
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1011 PM PDT SAT JUN 27 2015

.SYNOPSIS...STRONG HIGH PRESSURE ALOFT WILL REMAIN OVER THE REGION
THROUGH SUNDAY. THE AIR MASS WILL BECOME MORE MOIST AND UNSTABLE
ON SUNDAY FOR A RISK OF THUNDERSTORMS...ESPECIALLY SUNDAY NIGHT. A
WEAK LOW PRESSURE SYSTEM ALOFT WILL MOVE ACROSS THE AREA ON MONDAY
FOR SOME COOLING...AND WILL BE FOLLOWED BY ANOTHER WEAK SYSTEM ON
TUESDAY.

&&

.SHORT TERM...
SO FAR...TSTMS HAVE REMAINED WELL OUTSIDE THE CWA. LATEST GUIDANCE
FROM THE MODELS AND SPC INDICATED THAT THE RISK OF TSTMS OVER THE
AREA THE REST OF TONIGHT WAS VERY LOW OR NONEXISTENT. THEREFORE...
THE FORECAST WAS UPDATED TO REMOVE THE THREAT OF TSTMS FOR
TONIGHT. EXPECT OCCASIONAL MID AND/OR HIGH CLOUDS TO MOVE ACROSS
THE CWA FROM THE SOUTHWEST OVERNIGHT.

IT APPEARED THAT THE BEST CHANCE OF TSTMS WILL BE SUNDAY NIGHT
WHEN AN UPPER TROF APPROACHES FROM THE SOUTHWEST. IT ALSO LOOKED
LIKE THE BEST CHANCE OF TSTMS WILL BE OVER THE INTERIOR...EAST OF
THE OLYMPIC RANGE SUNDAY NIGHT.

MEANWHILE...STRONG HIGH PRESSURE ALOFT WILL PREVAIL OVER THE
REGION THROUGH SUNDAY FOR ANOTHER VERY WARM DAY ACROSS MUCH OF THE
CWA. ALTHOUGH...TEMPS WILL LIKELY BE A FEW DEGREES COOLER DUE TO
AN INCREASE IN MID AND HIGH CLOUDS. THIS WILL BE OFFSET BY HIGHER
DEW POINTS...SO IT WILL FEEL MORE UNCOMFORTABLE OR MUGGY ON SUNDAY
COMPARED TO TODAY.

A WEAKENING UPPER LEVEL TROUGH WILL APPROACH THE CWA FROM THE
SOUTHWEST SUNDAY NIGHT. ANTICIPATE THE FLOW ALOFT TO STRENGTHEN
FROM THE SOUTH AND ADVECT IN ADDITIONAL MOISTURE AND INSTABILITY.
CONSEQUENTLY...AS MENTIONED EARLIER...IT APPEARED THAT SUNDAY
NIGHT WILL PROBABLY BE THE MOST ACTIVE PERIOD TSTM-WISE. THE
MODELS ALSO APPEARED WETTER THAN THE PREVIOUS RUNS...AND WERE
SPITTING OUT QUARTER INCH AMOUNTS OVER THE CASCADES SUNDAY NIGHT.

THE UPPER TROF WILL MOVE ACROSS THE REGION ON MON AND THIS WILL
SERVE TO SHUNT THE RISK OF TSTMS EAST OF THE CWA DUE TO INCREASED
WESTERLY FLOW ALOFT. IT ALSO APPEARED THAT A FAIRLY STRONG MARINE
PUSH WILL BE UNDERWAY ON MON...SO TEMPS ON MON SHOULD BE
NOTICEABLY COOLER THAN ON SUNDAY. THE LATEST GFS MOS GUIDANCE
HAD A HIGH OF 78 DEGREES AT KSEA...WHICH IS COOLER THAN CURRENTLY
FORECAST.

ANOTHER UPPER LEVEL TROF WILL MOVE ACROSS THE AREA ON TUE. TEMPS
ON TUE SHOULD BE SIMILAR TO MON OR A LITTLE COOLER.

.LONG TERM FROM THE PREV DISCUSSION...
EXTENDED MODELS HAVE BEEN CONSISTENT WITH AN UPPER LEVEL RIDGE
BUILDING OVER THE AREA WEDNESDAY THROUGH FRIDAY WITH 500 MB
HEIGHTS NEAR 590 DM...FOR WELL ABOVE NORMAL TEMPS AGAIN DURING
THIS PERIOD. ON SATURDAY THE 4TH...THERE ARE A FEW DIFFERENCES BUT
IT LOOKS LIKE IT MIGHT COOL OFF A BIT FOR SLIGHTLY MORE
COMFORTABLE TEMPERATURES DEPENDING ON THE TRACK OF AN UPPER LEVEL
LOW OR SHORTWAVE TROUGH TO OUR NORTH. JSMITH

&&

.AVIATION...AN UPPER RIDGE WILL BE CENTERED OVER IDAHO WITH
SOUTHERLY FLOW ALOFT FOR WESTERN WASHINGTON THROUGH SUNDAY. LOW
LEVEL NORTHWEST FLOW WILL TURN MORE SOUTHWESTERLY ON SUNDAY. AIR
MASS GENERALLY DRY AND SLIGHTLY UNSTABLE EAST OF PUGET SOUND.

KSEA...SOME HIGH CLOUDS AT TIMES THROUGH SUNDAY. NORTHERLY WIND 4-8
KNOTS WILL BECOME LIGHT AFTER MIDNIGHT TONIGHT...THEN SOUTHWEST 4-8
KNOTS SUNDAY. SCHNEIDER

&&

.MARINE...LOW LEVEL NORTHWEST FLOW WILL EASE TONIGHT AND TURN MORE
WEST TO SOUTHWEST SUNDAY AND MONDAY. NORTHWEST WINDS AT DESTRUCTION
ISLAND POPPED UP TO GALE THIS EVENING BUT THE GALE SHOULD BE BRIEF
WITH WINDS EASING LATER THIS EVENING. SMALL CRAFT ADVISORY NORTHWEST
WINDS FOR THE REMAINDER OF THE COASTAL WATERS WILL ALSO EASE LATER
TONIGHT. WESTERLY FLOW THROUGH THE STRAIT WILL REACH HIGH END SMALL
CRAFT ADVISORY LEVELS MONDAY EVENING...WITH GALES POSSIBLE BUT NOT
CURRENTLY INDICATED IN THE FORECAST. LOW LEVEL FLOW WILL TURN MORE
NORTHWESTERLY AGAIN TUESDAY THROUGH THURSDAY. SCHNEIDER

&&

.FIRE WEATHER FROM THE PREV DISCUSSION...
STARTING TO SEE LIGHTNING STRIKES IN PORTIONS OF CENTRAL OREGON...
WHILE THINGS HAVE QUIETED SOME OVER COASTAL WATERS. TEMPS IN
THE UPPER 80S AND INTO THE 90S OVER WESTERN WA CLEARLY SHOWS HOT
AND DRY AIR IN PLACE OVER THE SURFACE. CURRENT MODEL DATA SHOWS
LIFTED INDICIES THIS EVENING EXPECTED TO REACH OVER -10 OVER THE
OLYMPICS AND OVER -8 OVER THE CASCADES...ADVERTISING VERY UNSTABLE
CONDITIONS OVERHEAD. THIS INSTABILITY...COUPLED WITH MOISTURE
MAKING ITS WAY NORTH AS INDICATED BY THE AFOREMENTIONED LIGHTNING
STRIKES...MAKES AN INCREDIBLY STRONG CASE FOR THE CURRENT RED FLAG
WARNING THAT IS OUT. LI VALUES WILL DIMINISH SOME OVERNIGHT...BUT
STILL SEEING VALUES IN THE -5 TO -8 RANGE...INDICATING A GOOD
POSSIBILITY FOR OVERNIGHT THUNDERSTORM ACTIVITY. THE CURRENT HOT
AND DRY CONDITIONS WILL LIMIT THE AMOUNT OF RAINFALL EXPECTED WITH
THESE STORMS...MAKING ANY FUELS THAT GET STRUCK BY LIGHTNING
EXTREMELY PRONE TO IGNITION. LASTLY...IN COORDINATION WITH
OTX...HAVE UPGRADED FIRE WEATHER WATCH IN ZONE 662 TO RED FLAG
WARNING. WITH THUNDERSTORM ACTIVITY EXITING THE WEST SIDE OF THE
CASCADES SUNDAY EVENING...662 BEING THE ONLY FIRE WEATHER ZONE ON
THE EAST SIDE OF THE CREST WILL FALL UNDER THIS LIGHTNING THREAT.
SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...EXCESSIVE HEAT WARNINGS ARE IN EFFECT FOR MUCH OF THE PUGET
     SOUND REGION UNTIL MIDNIGHT SUNDAY.

     RED FLAG WARNINGS ARE IN EFFECT FOR THE ENTIRE CWA...INCLUDING
     THE LAKE CHELAN NATIONAL RECREATION AREA.

PZ...GALE WARNING IN EFFECT TIL 11 PM TONIGHT FOR COASTAL WATERS
     FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING PACIFIC
     COASTAL WATERS.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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.