Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 261028
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
328 AM PDT FRI JUN 26 2015

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL REMAIN OVER THE REGION
THROUGH THE WEEKEND BRINGING HOT WEATHER TO WESTERN WASHINGTON. AN
UPPER LEVEL DISTURBANCE WILL BRING A CHANCE OF THUNDERSTORMS TO
PARTS OF WESTERN WASHINGTON LATE SATURDAY THROUGH SUNDAY. THE UPPER
LEVEL RIDGE WILL WEAKEN EARLY NEXT WEEK WHILE A RETURN TO WEAK
ONSHORE FLOW WILL BRING A LITTLE COOLING TO THE AREA. DRY WEATHER
AND A TREND BACK TO WARMER TEMPERATURES IS POSSIBLE LATER NEXT WEEK.

&&

.SHORT TERM...A STRONG UPPER LEVEL RIDGE WILL REMAIN OVER THE REGION
PRETTY MUCH THROUGH THE NEXT WEEK...KEEPING TEMPERATURES ABOVE
NORMAL. TODAY AND SATURDAY WILL BE HOT WITH 500 MB HEIGHTS UP AROUND
5900 METERS. MODEL GUIDANCE HAS REMAINED FAIRLY CONSISTENT WITH
REGARD TO FORECAST HIGH TEMPERATURES...SHOWING THE HOTTEST
LOCATIONS REACHING THE LOWER TO MID 90S. SATURDAY STILL LOOKS LIKE
THE HOTTEST DAY WITH SOME SPOTS REACHING RECORD HIGH TEMPERATURES
FOR THE DATE. WEAK NW ONSHORE FLOW OVERNIGHT HAS PRODUCED SHALLOW
STRATUS ALONG THE COAST AND PARTWAY THROUGH THE STRAIT OF JUAN DE
FUCA THIS MORNING. THE STRATUS SHOULD HAVE NO REAL IMPACT ON THE
HEAT EXPECTED OVER THE SW INTERIOR AND AROUND THE GREATER PUGET
SOUND REGION TODAY...AND SHOULD BURN OFF QUICKLY OVER THE NEARBY
LAND AREAS.

THE EXCESSIVE HEAT WATCH FOR THE GREATER PUGET SOUND REGION AND SW
INTERIOR HAS BEEN UPGRADED TO A WARNING...FROM THIS AFTERNOON
THROUGH SATURDAY NIGHT. IN ADDITION...A HEAT ADVISORY HAS BEEN ADDED
FOR THE HOOD CANAL AND LOWER CHEHALIS VALLEY ZONES. A KEY FACTOR IN
THESE HEAT EVENTS ARE THE WARM TEMPERATURES OVERNIGHT...WHICH LIMIT
THE AMOUNT OF RELIEF FROM THE HOT DAYTIME READINGS. MANY AREAS WILL
REMAIN IN THE 80S THROUGH 9 PM TONIGHT AND WILL ONLY DROP BELOW 70
AFTER 1 AM. MID AND HIGH LEVEL CLOUDS ARE EXPECTED TO MOVE N OVER W
WA ON SATURDAY WHICH WILL FURTHER SLOW THE RATE OF COOLING SATURDAY
NIGHT. WEAK ONSHORE FLOW ALONG THE COAST AND THE LARGE WATER AREAS
AROUND THE N INTERIOR WILL KEEP THOSE AREAS COOLER THAN THE REST OF
THE INTERIOR...ALTHOUGH THEY WILL STILL HAVE TEMPERATURES WELL ABOVE
NORMAL.

MODELS CONTINUE TO SHOW S FLOW ALOFT DEVELOPING ALONG THE W COAST
THIS AFTERNOON...WHICH EVENTUALLY ALLOWS MID AND HIGH LEVEL MOISTURE
TO ADVECT N OVER W WA SATURDAY AND SUNDAY. THE GFS CONTINUES TO BE
THE MOST AGGRESSIVE MODEL WITH THIS MOISTURE...BUT THE NAM IS NOT
FAR BEHIND. CROSS-SECTIONS FROM BOTH MODELS SHOW A SERIES OF SMALL
WEAK SHORTWAVE TROUGHS EMBEDDED IN THE S FLOW WHICH MOVE N ACROSS W
WA. ANY OF THESE LITTLE VORT MAXES COULD BE STRONG ENOUGH TO RELEASE
THE POTENTIAL INSTABILITY IN THE COMBINED HOT AIR MASS AND MID LEVEL
MOISTURE. THE GFS SHOWS THE GREATEST 700 MB-300 MB LAPSE RATES
THROUGH SATURDAY EVENING WHICH THEN LOWER ON SUNDAY. HOWEVER
MORE MOISTURE WILL BE AVAILABLE ON SUNDAY AND THE PASSING SHORTWAVES
COULD BE A LITTLE STRONGER. SO THE CHANCE OF THUNDERSTORMS WILL
STILL EXTEND FROM SATURDAY AFTERNOON INTO SUNDAY EVENING. WITH ONLY
MID AND HIGH LEVEL MOISTURE THIS WEEKEND...RAIN FROM ANY CELLS THAT
DEVELOP WILL BE VERY LIGHT OR NON-EXISTENT. THESE ELEVATED
CONVECTION EVENTS ALSO TEND TO BE GOOD LIGHTNING PRODUCERS WHICH
RAISES THE POTENTIAL FOR WILDFIRES.

TEMPERATURES ON SUNDAY SHOULD BE A LITTLE COOLER THAN
SATURDAY...WITH MOST AREAS DROPPING BACK INTO THE 80S. THE THICKER
MID AND HIGH LEVEL MOISTURE EXPECTED ON SUNDAY SHOULD BE THE MAIN
COOLING FACTOR. THE GFS SHOWS AN INCREASE IN THE ONSHORE FLOW BUT
THE NAM AND ECMWF ARE NOT AS STRONG AND ARE LATE ENOUGH SO THAT THE
COOLING EFFECTS PROBABLY WILL NOT REACH THE INTERIOR BEFORE EVENING.
KAM

.LONG TERM...A MORE SIGNIFICANT UPPER LEVEL SHORTWAVE TROUGH MOVES
NE ACROSS THE AREA MONDAY MORNING...WITH DRIER AND MORE STABLE SW
FLOW ALOFT MOVING OVER W WA BEHIND IT. COOLING ALOFT WITH THE TROUGH
COMBINED WITH INCREASING ONSHORE FLOW SHOULD END THE HOT SPELL. THE
AIR MASS WILL STILL BE WARMER THAN NORMAL SO THE WARMEST MAX
TEMPERATURES WILL STILL REACH THE LOWER TO MID 80S. THE UPPER LEVEL
RIDGE OVER THE REGION WILL GRADUALLY STRENGTHEN AGAIN FROM MIDWEEK
ONWARD...AND LOW LEVEL ONSHORE FLOW BEGINS TO WEAKEN. TEMPERATURES
WILL RISE AGAIN BUT WITH THE MODELS SHOWING MORE INCONSISTENCY IT IS
NOT CERTAIN JUST HOW HOT IT WILL GET. IT DOES LOOK LIKE DAILY MAX
TEMPERATURES WILL STILL BE IN THE 80S AROUND MUCH OF THE INTERIOR.
KAM

&&

.CLIMATE...THE FOLLOWING ARE THE RECORD AND FORECAST HIGH
TEMPERATURES FOR SELECT SITES ON SATURDAY JUNE 27 2015...

LOCATION    RECORD HIGH            FORECAST HIGH

SEA-TAC     88 DEGREES IN 2000     92
OLYMPIA     91 DEGREES IN 2000     94
EVERETT     84 DEGREES IN 2000     85
BELLINGHAM  82 DEGREES IN 2000     84
QUILLAYUTE  86 DEGREES IN 2000     85


IN ADDITION...THE RECORD FOR THE ENTIRE MONTH OF JUNE IN TERMS OF
AVERAGE HIGH TEMPERATURES AT SEA-TAC IS 75.8 DEGREES SET IN 1992.
WITH MOST OF JUNE ALREADY HAVING ABOVE NORMAL HIGH TEMPS...WE ARE ON
TRACK TO SHATTER THIS RECORD WITH THE ANTICIPATED HEAT WAVE OVER THE
NEXT FEW DAYS. MERCER

&&

.AVIATION...AN UPPER RIDGE OVER THE WESTERN UNITED STATES WILL BUILD
A BIT NORTHWARD TODAY WITH WESTERLY FLOW ALOFT. AT THE SURFACE...
NORTHERLY ONSHORE FLOW WILL PREVAIL WITH HIGH PRESSURE OFFSHORE AND
LOWER PRESSURE INLAND. AIR MASS STABLE.

STRATUS AT THE COAST AND PARTIALLY INLAND DOWN THE STRAIT INTO
NORTHERN PUGET SOUND AND INTO THE SOUTHWEST INTERIOR THROUGH THE
CHEHALIS GAP SHOULD BURN BACK TO THE COAST LATE THIS MORNING AND
PROBABLY BURN OFF EVEN AT THE COAST THIS AFTERNOON. ONSHORE FLOW
WILL BE A LITTLE WEAKER TONIGHT WHICH SUGGESTS EVEN LESS STRATUS
SATURDAY MORNING.

KSEA...GENERALLY CLEAR THROUGH TONIGHT. STRATUS IS NOT EXPECTED TO
AFFECT THE TERMINAL THIS MORNING. NORTHERLY WIND 5-10 KNOTS.
SCHNEIDER

&&

.MARINE...NORTHERLY LOW LEVEL ONSHORE FLOW WILL PREVAIL FOR THE NEXT
COUPLE DAYS WITH SMALL CRAFT ADVISORY NORTHWEST WINDS FOR THE
COASTAL WATERS AT TIMES. THERE WILL ALSO BE SMALL CRAFT ADVISORY
WEST WINDS IN THE CENTRAL AND EASTERN STRAIT AND NORTHERLY WINDS IN
PUGET SOUND THIS EVENING. LOW LEVEL FLOW WILL BECOME MORE SOUTHERLY
SUNDAY AND MONDAY...THEN MORE NORTHERLY AGAIN ON TUESDAY. SCHNEIDER

&&

.FIRE WEATHER...WITH DEVELOPING HOT AND UNSTABLE CONDITIONS BY
SATURDAY...WILL ISSUE A FIRE WEATHER WATCH THIS AFTERNOON FOR DRY
UNSTABLE AIR MASS STARTING SATURDAY AFTERNOON INTO SUNDAY NIGHT FOR
THE MOUNTAINS. AFTER REVIEWING THE FORECAST SOUNDINGS FOR THE
LOWLANDS...A LOW LEVEL TEMPERATURE INVERSION EXISTS WELL INTO
SUNDAY...DAMPENING THE UNSTABLE CONDITIONS BELOW ABOUT 2000 FEET.
YET A NICE THERMAL BELT BETWEEN ABOUT 2K AND 4K DEVELOPS IN THE
MOUNTAINS.

THE OTHER ISSUE IS THE POTENTIAL FOR DRY LIGHTNING AS SOUTHERLY FLOW
DEVELOPS BY SATURDAY. ALL THE INCOMING MOISTURE FROM THE SOUTH IS
ABOVE 10K FT. WILL THERE BE A TRIGGERING MECHANISM TO SET OFF THE
CONVECTION. THE DEVIL IS IN THE DETAILS. CLEARLY THE PROGS HAVE AN
EJECTING SHORTWAVE SET TO ROLL THROUGH THE REGION FROM THE SOUTH ON
SUNDAY. YET WILL ANYTHING SET OFF CONVECTION BEGINNING SATURDAY
AFTERNOON OR NIGHT. LIGHTNING COULD BE ANYWHERE IN WESTERN
WASHINGTON. SO MAY NEED TO EXTEND THE FIRE WEATHER WATCH TO THE
LOWLANDS LATER ONCE MORE INFORMATION ABOUT THE LIGHTNING THREAT AND
EXTENT BECOMES MORE CLEAR.

FUEL CONDITIONS THROUGHOUT WESTERN WASHINGTON ARE BEYOND CRITICAL
VALUES - QUITE DRY. SO FOR THE FIRE AND EMERGENCY RESPONSE
COMMUNITY...READINESS TO RESPOND TO ANY FIRE STARTS - LIGHTNING OR
FIREWORKS OR OTHER SOURCES - IS IMPERATIVE. BUEHNER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FIRE WEATHER WATCH - ZONES 652 661 658 AND 659

     EXCESSIVE HEAT WARNING FOR THE GREATER PUGET SOUND REGION AND
     THE SOUTHWEST INTERIOR FRIDAY AFTERNOON THROUGH SATURDAY NIGHT.

     HEAT ADVISORY FOR HOOD CANAL AND THE LOWER CHEHALIS VALLEY
     FRIDAY AFTERNOON THROUGH SATURDAY NIGHT.

PZ...SMALL CRAFT ADVISORY COASTAL WATERS...CENTRAL AND EAST STRAIT
     OF JUAN DE FUCA...AND PUGET SOUND AND HOOD CANAL.


&&

$$

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






























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