Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 270547 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
1047 PM PDT FRI JUN 26 2015

CORRECTED A MINOR TYPO IN THE SECOND PARAGRAPH OF THE SHORT TERM
SEGMENT.

.SYNOPSIS...STRONG HIGH PRESSURE ALOFT WILL RESULT IN A VERY WARM
SPELL THIS WEEKEND. SOUTHERLY FLOW ALOFT WILL ALSO BRING IN AN
UNSTABLE AIR MASS...LEADING TO A RISK OF THUNDERSTORMS. A WEAK LOW
PRESSURE SYSTEM ALOFT WILL MOVE ACROSS THE AREA ON MONDAY. THIS
WILL CAUSE THE FLOW ALOFT TO BECOME WESTERLY...THUS ENDING THE
THUNDERSTORM THREAT. TEMPERATURES WILL REMAIN ABOVE NORMAL.

&&

.SHORT TERM...
A STRONG UPPER LEVEL RIDGE CENTERED OVER THE SOUTHERN GREAT BASIN
WILL DOMINATE THE WEATHER PATTERN OVER WESTERN WA THROUGH SUNDAY.
500 MB HEIGHTS OVER THE CWA WILL BE IN THE 587 TO 590 DAM RANGE ON
SATURDAY. THIS COMBINED WITH LOW LEVEL NORTHERLY FLOW AND LACK OF
STRATUS WILL RESULT IN RECORD OR NEAR RECORD TEMPS. THE NORTHERLY
FLOW WILL PROBABLY PREVENT TEMPS FROM REALIZING THEIR TRUE
POTENTIAL OVER THOSE AREAS EXPOSED TO NORTHERLY BREEZES COMING
OFF THE WATER.

500 MB HEIGHTS WILL LOWER SLIGHTLY ON SUNDAY. THIS COMBINED WITH
AN INCREASE IN PRIMARILY MID AND HIGH CLOUDS WILL RESULT IN SOME
COOLING BUT THIS WILL BE OFFSET BY AN INCREASE IN SURFACE DEW
POINTS...WHICH WILL MAKE IT FEEL MORE UNCOMFORTABLE OR MUGGY.
THUS...THE EXCESSIVE HEAT WARNING WILL PROBABLY NEED TO BE EXTENDED
THROUGH SUNDAY EVENING.

A WEAKENING UPPER TROF WILL APPROACH THE PACIFIC NORTHWEST DURING
THE DAY SUNDAY...AND WILL MOVE ACROSS THE CWA ON MON. THE MAIN
IMPACT THIS SYSTEM WILL HAVE ON OUR WEATHER WILL BE TO INITIATE A
SHALLOW ONSHORE PUSH. TEMPS ON MON SHOULD BE A LITTLE COOLER THAN
ON SUNDAY...ALTHOUGH SOME MODELS WERE SUGGESTING THAT TEMPS ON
MON WILL BE SIMILAR TO SUNDAY.

CONCERNING TSTMS...NWS DOPPLER RADARS AND LIGHTNING DATA SHOWED A
CLUSTER OF TSTMS OVER NORTHERN OREGON AT THIS TIME. THE TSTMS
SHOULD REMAIN SOUTH OF THE CWA. THE PRIMARY CONCERN IN THE NEAR
TERM WAS THE SURFACE PRESSURE RISES TO OUR SOUTH. THERE IS A
POSSIBILITY THAT THIS COULD RESULT IN A STRATUS SURGE NORTHWARD
ALONG THE COAST. IF THIS DOES HAPPEN...IT WILL PROBABLY NOT MAKE
IT TOO FAR NORTH.

MEANWHILE...IT LOOKS LIKE THE BEST CHANCE OF TSTMS SATURDAY
AFTERNOON WILL BE OVER THE CASCADES BUT CANNOT COMPLETELY RULE OUT
AN ISOLATED TSTM OR TWO OVER THE EASTERN PORTION OF THE PUGET
SOUND REGION. THE TSTMS WILL LIKELY BE HIGH-BASED AND PRODUCE
LITTLE OR NO RAINFALL.

SOUTHERLY FLOW ALOFT WILL CONTINUE THROUGH SUNDAY...WHICH WILL
ADVECT MORE MID LEVEL MOISTURE ACROSS THE CWA. SUNDAY WILL LIKELY
BE THE MOST ACTIVE DAY TSTM-WISE. THE HIGHEST THREAT AREAS WILL BE
THE MOUNTAINS. THIS WILL ONLY SERVE TO EXACERBATE THE WILDFIRE
THREAT.

THE TSTM THREAT WILL END ON MON DUE TO THE WESTERLY FLOW ALOFT
BECOMING ESTABLISHED OVER THE AREA. TEMPS WILL REMAIN ABOVE
NORMAL.

.LONG TERM FROM THE PREVIOUS DISCUSSION...
MODELS WERE IN GOOD AGREEMENT THAT THE UPPER RIDGE WILL BUILD
STRONGER ON TUESDAY AND PERSIST THROUGH THE END OF NEXT WEEK.
THIS WILL ALLOW FOR A GRADUAL WARMING TREND AND PERSISTENT DRY
CONDITIONS. HIGH TEMPERATURES ARE EXPECTED TO REMAIN WELL ABOVE
AVERAGE THROUGH THE WEEK. SOME MODELS WERE SUGGESTING ANOTHER BOUT
OF EXCESSIVELY HOT WEATHER IS POSSIBLE TOWARD THE FORTH OF JULY
HOLIDAY WEEKEND. FORECASTS SHOULD BE MONITORED GIVEN THE DRY
CONDITIONS AND ELEVATED FIRE POTENTIAL. MERCER

&&

.AVIATION...AN UPPER RIDGE WILL BE OVER THE AREA THROUGH SATURDAY
WITH WEST/SOUTHWEST FLOW ALOFT AND LOW LEVEL NORTHWESTERLY FLOW. AIR
MASS STABLE...BECOMING UNSTABLE EAST OF PUGET SOUND SATURDAY
AFTERNOON. SKIES WILL BE GENERALLY CLEAR THROUGH SATURDAY. THERE
MIGHT BE SOME PATCHY LOW CLOUDS OR FOG NEAR THE COAST AND OVER THE
SOUTHEAST INTERIOR FOR A FEW HOURS SATURDAY MORNING.

KSEA...A FEW HIGH CLOUDS. OTHERWISE CLEAR. NORTHERLY WIND 5-10
KNOTS. SCHNEIDER

&&

.MARINE...NORTHWESTERLY ONSHORE FLOW WILL PREVAIL THROUGH SATURDAY
WITH HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. THIS WILL
GIVE SMALL CRAFT ADVISORY NORTHWEST WINDS FOR THE COASTAL WATERS AND
SMALL CRAFT ADVISORY WEST WINDS FOR THE STRAIT THIS EVENING. LOW
LEVEL FLOW WILL TURN MORE SOUTHWESTERLY SUNDAY AND MONDAY...THEN
SWITCH TO NORTHWESTERLY AGAIN TUESDAY AND WEDNESDAY. SCHNEIDER

&&

.FIRE WEATHER FROM THE PREV DISCUSSION...
WITH A GREATER LIKELIHOOD OF ABUNDANT LIGHTNING SPREADING OVER
MUCH OF THE LOWLANDS OF WESTERN WASHINGTON...WILL ISSUE A FIRE
WEATHER WATCH FOR SATURDAY NIGHT INTO SUNDAY EVENING. THANKS TO
THE DRY CONDITIONS...ANY LIGHTNING ORIENTED FIRE STARTS HAVE THE
POTENTIAL TO GROW RAPIDLY IN THIS CONDUCIVE ATMOSPHERE. THE DEVIL
WILL BE IN THE DETAILS. ANY UPPER LEVEL TRIGGERING MECHANISM CAN
SET OFF THE CONVECTION. NEED TO MONITOR THE DEVELOPING SITUATION
IN NORTHERN CALIFORNIA AND OREGON TONIGHT TO GET A BETTER FEEL FOR
WHAT MAY TRANSLATE FURTHER NORTH SATURDAY.

WILL CONTINUE THE WATCH FOR THE MOUNTAINS GIVEN DEVELOPING HOT AND
UNSTABLE AIR MASS SITUATION. THE NICE THERMAL BELT BETWEEN ABOUT 2K
AND 4K IN THE MOUNTAINS REMAINS ON TRACK.

AS NOTED EARLIER...FUEL CONDITIONS THROUGHOUT WESTERN WASHINGTON -
FROM THE CASCADES TO THE COAST - 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

&&

.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     91
OLYMPIA     91 DEGREES IN 2000     94
EVERETT     84 DEGREES IN 2000     85
BELLINGHAM  82 DEGREES IN 2000     84

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...EXCESSIVE HEAT WARNING IN EFFECT TIL 5 AM PDT SUNDAY FOR MUCH
     OF THE PUGET SOUND REGION.

     FIRE WEATHER WATCHES ARE IN EFFECT FOR THE ENTIRE CWA BEGINNING
     SATURDAY AFTERNOON.

PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS AND
     CENTRAL/EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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