Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 051558
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SUN JUL 5 2015

.SYNOPSIS...THE STREAK OF WARM WEATHER WILL CONTINUE THROUGH
WEDNESDAY OR THURSDAY. COOLER WEATHER WILL ARRIVE LATE IN THE WEEK
AS AS AN UPPER TROUGH NEARS THE AREA AND ONSHORE FLOW INCREASES.

&&

.SHORT TERM...HIGHS WILL BE IN THE 80S TO MID 90S ACROSS WESTERN WA
TODAY. A HEAT ADVISORY IS IN EFFECT FOR THE MAIN WRN WA SEA-TAC
URBAN AREA. THERE IS A PATCH OF FOG AND LOW CLOUDS ON THE COAST THIS
MORNING BUT IT SHOULD BURN OFF QUICKLY. AN AREA OF SMOKE IS DRIFTING
SOUTH FROM A FOREST FIRE IN THE MOUNTAINS OF BRITISH COLUMBIA. FOR
MON AND TUE SOME LOW LEVEL ONSHORE FLOW WILL RETURN BUT MARINE LAYER
STRATUS AND FOG SHOULD BE CONFINED TO THE COAST AND TEMPS WILL
REMAIN WELL ABOVE NORMAL...EXCEPT ALONG THE OCEAN BEACHES WHERE
HIGHS SHOULD RANGE FROM THE 60S RIGHT ON THE BEACH TO THE 70S A FEW
MILES INLAND.

.LONG TERM...A WEAK UPPER RIDGE WILL MOVE OVER THE AREA ON
WEDNESDAY. THIS WILL CAUSE HIGHS TO WARM A FEW DEGREES. A COOLING
TREND SHOULD BEGIN ON THURSDAY AS AN UPPER TROUGH SLOWLY MOVES
OVER THE PACIFIC NORTHWEST. HIGHS SHOULD COOL TO NEAR NORMAL
FRIDAY AND SATURDAY. THERE SHOULD ALSO BE MORE CLOUDS AND MAYBE
EVEN A FEW SHOWERS. SCHNEIDER

&&

.AVIATION...A STRONG UPPER LEVEL RIDGE IS OVER THE NE PAC TODAY WITH
N/NW FLOW ALOFT OVER WESTERN WA. THE AIR MASS IS DRY. THERE IS
PATCHY STRATUS ALONG THE CENTRAL COAST THAT WILL BURN OFF LATE THIS
MORNING WITH OFFSHORE FLOW. OTHERWISE VFR CONDITIONS ARE EXPECTED
TODAY. 33

KSEA...VFR CONDITIONS TODAY WITH N WINDS AT THE SURFACE TO 12 KT. 33

&&

.MARINE...THERMALLY INDUCED TROUGH OF LOW PRES ALONG THE WA COAST
WILL RESULT IN OFFSHORE FLOW ACROSS THE AREA TODAY. THE TROUGH WILL
WEAKEN TONIGHT THEN SHIFT EAST OF THE CASCADES ON MONDAY FOR A
RETURN OF ONSHORE FLOW. ONSHORE FLOW WILL CONTINUE THROUGH THE
MIDDLE OF THE WEEK. THE STRONGEST WINDS WILL OCCUR OVER THE CENTRAL
AND EAST STRAIT OF JUAN DE FUCA DURING THE AFTERNOON AND EVENING
HOURS. 33


&&

.FIRE WEATHER...NORTHEAST PRESSURE GRADIENTS APPEARED TO BE PEAKING
THIS MORNING...WITH THE BELLINGHAM-WILLIAMS LAKE B.C. GRADIENT AT
-10.3 MB AS OF 8 AM. THIS KIND OF GRADIENT BRINGS FRASER-OUTFLOW
STYLE WINDS...EXCEPT THIS WIND IN THE SUMMER IS HOT AND DRY.
OBSERVING SITES AROUND WESTERN WHATCOM COUNTY HAVE STARTED THE
MORNING OFF WITH MODERATE BREEZES AND RELATIVE HUMIDITY BELOW 30
PERCENT. OVER THE NEXT FEW HOURS...THESE KIND OF CONDITIONS WILL
EXPAND OUT ACROSS THE SAN JUAN ISLANDS AND THE NORTHWEST OLYMPIC
PENINSULA. NE WINDS WILL TAKE HOT TEMPERATURES ALL THE WAY TO THE
COAST TODAY...WITH FORKS EXPECTING A HIGH TEMPERATURE OF 94 DEGREES
TODAY. MARBLEMOUNT IN THE NORTH CASCADES MAY ALSO HAVE A FEW HOURS
OF NE WIND AND LOW HUMIDITY AS WELL. FOR THE AFOREMENTIONED AREAS...
THE MOST CRITICAL COMBINATION OF WIND AND HUMIDITY COMING LATE THIS
MORNING. A MODERATE NORTH BREEZE WILL THEN DEVELOP AROUND MID-DAY
FROM THE ADMIRALTY INLET AREA SOUTHWARD THROUGH THE PUGET SOUND
LOWLANDS...FOCUSING ON THE KITSAP PENINSULA. WITH RELATIVE HUMIDITY
DROPPING INTO THE VERY DRY 15-30 PERCENT RANGE THIS AFTN...EVEN A
MODERATE BREEZE OF 10-15 MPH WILL REALLY PUSH GRASS FIRES ALONG
QUICKLY...ESPECIALLY WHERE WIND AND SLOPE ALIGN. A RED FLAG WARNING
IS IN EFFECT TODAY TO HIGHLIGHT THE SAFETY CONCERNS BROUGHT ABOUT BY
THE MODERATE BREEZES AND VERY LOW HUMIDITY.

LASTLY...THE MID-LEVEL HAINES INDEX WILL BE IN THE 5-6 RANGE THIS
AFTERNOON. THIS INDICATES A DRY AND UNSTABLE AIR MASS IN THE 850-700
MB LAYER. FIRES BURNING AT ELEVATIONS ABOVE ABOUT 2000 FEET UNDER
SUCH CONDITIONS CAN BECOME ROWDY AND PLUME-DOMINATED.HANER

&&

.CLIMATE...THERE HAVE BEEN FOUR CONSECUTIVE DAYS WITH HIGHS OF 90
DEGREES OR ABOVE AT SEATAC THROUGH SATURDAY...JULY 4. THE RECORD
FOR CONSECUTIVE DAYS WITH A HIGH AT OR ABOVE 90 DEGREES IS FIVE.
THIS WAS SET IN AUGUST OF 1981. IT IS ALMOST CERTAIN WE WILL TIE
THIS RECORD TODAY WITH A FORECAST HIGH OF 95. THERE IS A CHANCE WE
WILL BREAK THE RECORD ON MONDAY WHEN THE HIGH WILL BE NEAR 90
AGAIN. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...HEAT ADVISORY IN EFFECT FOR
PARTS OF THE PUGET SOUND REGION UNTIL 9 PM MONDAY.

     RED FLAG WARNING IN EFFECT TIL 5 PM TODAY FOR FIRE WEATHER
ZONES 650...653...654...AND 656.

PZ...NONE.

$$

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