Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 071613
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE JUL 7 2015

.SYNOPSIS...THE UPPER RIDGE OVER THE REGION WILL BRING MORE WARM AND
GENERALLY SUNNY WEATHER TO WESTERN WASHINGTON TODAY THROUGH
THURSDAY. AN UPPER TROUGH WILL MOVE INTO THE OFFSHORE WATERS
FRIDAY...APPROACH THE COAST THIS WEEKEND...AND MOVE INLAND MONDAY.
THE RESULT WILL BE A SWITCH TO MORE TYPICAL JULY WEATHER.

&&

.SHORT TERM...WV/VISIBLE SATELLITE IMAGERY SHOWS A CLOSED LOW OFF
THE CA COAST AND A TROUGH OVER S/CENTRAL B.C. PROVIDING MOSTLY DRY
WEATHER OVER WRN WA. CHANGES IN THE UPPER AIR PATTERN ARE HELPING TO
INDUCE LOW LEVEL ONSHORE FLOW. MARINE CLOUDS SPREAD INTO MUCH OF THE
INTERIOR LOWLANDS THIS MORNING FROM AROUND SEATTLE SWD AND NEAR THE
STRAIT AND COAST. THIS SHOULD EASILY BURN OFF BY MIDDAY OVER THE
INTERIOR GIVING FILTERED AFTERNOON SUNSHINE. IT WILL REMAIN HAZY DUE
TO WILDFIRE SMOKE ALOFT MOVING INTO WRN WA THE FROM B.C. AND OTHER
AREAS AROUND THE PAC NW. HIGHS TODAY WILL BE A FEW DEGREE
COOLER...BUT STILL A BIT ABOVE AVERAGE NEAR 80 AROUND PUGET SOUND.
IF SEA-TAC REACHES 80 OR ABOVE TODAY THROUGH THURSDAY...THAT WOULD
TIE THE RECORD FOR THE LONGEST STRETCH ABOVE 80 DEGREES. FRIDAY
WOULD THEN BEAT THE RECORD WHICH IS POSSIBLE.


THE ONLY WEATHER CONCERN TODAY IS THE COVECTION SHOWN BY MODELS OVER
THE N/CENTRAL CASCADES DURING THE AFTERNOON/EVENING. GIVEN THAT THE
HIGHER ELEVATIONS OF THE CASCADES ARE UNDER LESS MARINE
INFLUENCE...SURFACE BASED INSTABILITY COULD BE ENOUGH TO GENERATE
SOME ISOLATED THUNDERSTORMS. THIS IS ALREADY COVERED IN THE
FORECAST.

A STRONG UPPER LEVEL RIDGE WILL SHIFT EWD OVER THE PAC NW TONIGHT
AND WEDNESDAY. THE GFS SHOWS LITTLE CHANGE IN THE UPPER LEVEL
HEIGHTS WITH LIGHT NWLY ONSHORE GRADIENTS. THIS LOW LEVEL FLOW
PATTERN IS FAVORABLE FOR BRING STRATUS FROM THE COAST INTO THE
STRAIT OF JUAN DE FUCA AND WRN PORTIONS OF THE SW INTERIOR. THE
STRATUS DECK IS NOT LIKELY TO REACH PUGET SOUND ALTHOUGH SOME PATCHY
LOW CLOUDS COULD FORM IN PLACE FOR JUST A FEW HOURS. OVERALL...IT
WILL BE A MOSTLY SUNNY DAY WITH PERHAPS SOME HAZE AND SMOKE ALOFT.
WITH LACK OF A STRONG MARINE INFLUENCE ACROSS THE INTERIOR...HIGHS
SHOULD WARM SEVERAL DEGREES...WITH LOW TO MID 80S COMMON AROUND
PUGET SOUND AND THE SW INTERIOR.

HIGH PRESSURE SHIFTS A BIT FURTHER EWD ON THURSDAY GIVING LIGHT SLY
FLOW OVER THE PAC NW. THIS MAY ALLOW SOME OF THE MOISTURE OVER
OREGON/CA TO MIGRATE NWD. THERE WILL PROBABLY BE ENOUGH OF A MARINE
INFLUENCE TO INHBIT SURFACE BASED CONVECTION ACROSS THE LOWLANDS.
BUT THE HIGHER ELEVATIONS OF THE CASCADES WILL BE ABOVE THE MARINE
INVERSION AND THUNDERSTORMS COULD POP UP IN THE AFTERNOON. WILL
MAINTAIN THE CHANCE OF THUNDER NEAR THE CREST. NO UPDATES THIS
MORNING. MERCER

.LONG TERM...THE CALIFORNIA UPPER LOW WILL CONTINUE INLAND AS IT
WEAKENS THURSDAY NIGHT AND FRIDAY. ANOTHER UPPER LOW WILL MOVE
INTO THE PACIFIC NORTHWEST OFFSHORE WATERS FRIDAY AND MOVE SLOWLY
INLAND BY MONDAY. THIS WILL BE A PERIOD OF SOMEWHAT STRONGER ONSHORE
FLOW WITH AREAS OF NIGHT AND MORNING LOW CLOUDS GIVING WAY TO
AFTERNOON SUNSHINE. TEMPERATURES SHOULD BE CLOSER TO NORMAL. SOME OF
THE RECENT MODEL RUNS HAVE ALSO STARTED SHOWING AREAS OF
PRECIPITATION OVER THE MOUNTAINS ON SUNDAY AND ACROSS WESTERN
WASHINGTON MORE GENERALLY ON MONDAY AS THE TROUGH MOVES INLAND.
 MCDONNAL

&&

.AVIATION...ONSHORE FLOW OVERNIGHT HAS SPREAD MVFR STRATUS WITH
BASES 010-020 ACROSS MOST OF THE W WA LOWLANDS THIS MORNING. THE
ONLY STRATUS FREE AREAS ARE OVER CENTRAL PUGET SOUND BETWEEN KBFI
AND KAWO...AND THE N INTERIOR AROUND BELLINGHAM AND THE SAN JUANS.
THE STRATUS IS EXPECTED TO BURN OFF ALMOST BACK TO THE COAST BY 19Z.
RESIDUAL SMOKE FROM THE B.C. FOREST FIRES IS STILL PRESENT FROM KPAE
NORTHWARD...BUT IT IS DIFFUSE ENOUGH SO THAT IT IS NOT RESTRICTING
VISIBILITY.

NW ONSHORE FLOW WILL INCREASE AGAIN LATE THIS AFTERNOON AND THIS
EVENING. STRATUS COVERAGE WEDNESDAY MORNING IS EXPECTED TO BE A
LITTLE LESS...ONLY PARTWAY THROUGH THE STRAIT OF JUAN DE FUCA AND E
THROUGH THE CHEHALIS GAP AS FAR AS SW PUGET SOUND AND OVER THE SW
INTERIOR.

KSEA...MVFR STRATUS IS EXPECTED TO BURN OFF AT KSEA BETWEEN 18Z-
19Z...WITH JUST SCT HIGH CLOUDS THE REST OF THIS AFTERNOON AND
EVENING. SURFACE WINDS WILL BE WESTERLY 4-7 KT THROUGH 00Z THEN
SHIFT TO NW 4-7 KT AFTER 00Z. KAM

&&

.MARINE...AN OFFSHORE SURFACE RIDGE COMBINED WITH LOWER PRESSURE
OVER E WA WILL MAINTAIN AN ONSHORE FLOW PATTERN OVER W WA THROUGH
FRIDAY. THE FLOW WILL BE STRONG ENOUGH EACH DAY FOR SCA W WINDS IN
THE CENTRAL AND E STRAIT OF JUAN DE FUCA. THE ONSHORE FLOW TONIGHT
AND WEDNESDAY NIGHT WILL HAVE A NW COMPONENT...WITH SW ONSHORE FLOW
DEVELOPING THURSDAY NIGHT.

A WEAK SURFACE RIDGE WILL FORM ALONG THE WA COAST ON SATURDAY WHICH
WILL KEEP WINDS GENERALLY LIGHT THROUGH THE WEEKEND. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT
ADVISORY IN EFFECT FOR THE CENTRAL AND EASTERN     STRAIT OF JUAN DE
FUCA.

&&

$$

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