Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 032230
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PDT MON AUG 3 2015

.SYNOPSIS...LOW PRESSURE ALOFT WILL PREVAIL OVER THE PACIFIC
NORTHWEST THROUGH WEDNESDAY. THIS COMBINED WITH ONSHORE FLOW WILL
RESULT IN COOLER CONDITIONS. THERE WILL ALSO BE A THREAT OF
SHOWERS ON WEDNESDAY. WEAK HIGH PRESSURE ALOFT WILL PREVAIL ON
THURSDAY.

&&

.SHORT TERM...
THERE WERE SOME LINGERING CLOUDS OVER THE CASCADES /NEAR THE
CREST/ AND THE COAST THIS AFTERNOON. ELSEWHERE...SKIES WERE
GENERALLY SUNNY. THE SURFACE ONSHORE PRESSURE GRADIENT CONTINUED
TO TIGHTEN THIS AFTERNOON. AT 3 PM PDT...THE KUIL TO KBLI PRESSURE
GRADIENT WAS PLUS 2.8 MB.

AN UPPER TROF THAT WILL BE CENTERED OVER WESTERN CANADA WILL
DOMINATE THE WEATHER PATTERN OVER THE PACIFIC NORTHWEST THROUGH
MIDWEEK. THIS COMBINED WITH MODERATE TO STRONG LOW LEVEL ONSHORE
FLOW WILL RESULT IN COOLER CONDITIONS ACROSS THE CWA. DAYTIME
TEMPS ARE ANTICIPATED TO BE NEAR OR SLIGHTLY BELOW NORMAL TUE AND
WED.

THE UPPER LOW WILL MOVE INTO SOUTHERN BRITISH COLUMBIA ON WED...
AND THIS SHOULD LEAD TO A RISK OF SHOWERS OVER PRIMARILY THE
NORTHERN PART OF THE CWA AND WITHIN THE PUGET SOUND CONVERGENCE
ZONE.

ANTICIPATE THE UPPER TROF TO MOVE INTO THE ROCKIES ON THU. A WEAK
UPPER RIDGE WILL FOLLOW ON ITS HEELS. SKIES WILL LIKELY START OFF
CLOUD OVER MANY PLACES THU MORNING BUT THE CLOUDS SHOULD GIVE WAY
TO MOSTLY SUNNY SKIES IN THE AFTERNOON. THEREFORE...ANTICIPATE
TEMPS TO BE ABOUT NORMAL FOR THIS TIME OF THE YEAR.

.LONG TERM...
WEAK HIGH PRESSURE ALOFT IS ANTICIPATED TO PREVAIL OVER THE REGION
ON FRI. THIS COMBINED WITH WEAK LOW LEVEL ONSHORE FLOW WILL LEAD
TO SLIGHTLY ABOVE NORMAL TEMPS.

BEYOND FRI...THE MEDIUM RANGE SOLUTIONS WERE IN FAIRLY GOOD
AGREEMENT THAT AN UPPER TROF WILL DOMINATE THE WEATHER PATTERN
OVER THE PACIFIC NORTHWEST. THE MAIN DIFFERENCES WERE IN THE
DETAILS. THE MODELS PREDICTED MAX TEMPS APPEARED TOO WARM IN
LIGHT OF THE PATTERN BEING ADVERTISED...THUS TOOK A RISK AND
UNDERCUT GUIDANCE. THE CURRENT FORECAST INDICATED BELOW NORMAL
DAYTIME TEMPS FOR SATURDAY THROUGH MON.

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL APPROACH FROM THE NORTHWEST
TONIGHT AND TUESDAY GIVING W TO SW FLOW ALOFT. A WEAK COLD FRONT
EXTENDING SW FROM CENTRAL BRITISH THROUGH CENTRAL VANCOUVER ISLAND
AND INTO THE PACIFIC WILL MOVE SE THROUGH THE REGION THIS EVENING.
THE MAIN IMPACTS OF THE FRONT WILL BE TO SPREAD A DEEP STRATUS LAYER
INLAND LATE TONIGHT THROUGH TUESDAY MORNING AND INCREASE LOW LEVEL
ONSHORE FLOW.

VISIBLE SATELLITE IMAGERY THIS AFTERNOON SHOWS SOME STRATUS WITH
BASES 015-020 OVER THE WESTERN REACHES OF THE STRAIT OF JUAN DE FUCA
SOUTHWARD OVER THE NORTH COAST AND INTO THE COASTAL WATERS JUST W OF
KHQM. THIS STRATUS WILL SURGE INLAND THIS EVENING AS THE FRONTAL
SYSTEM TO THE NW MOVES ACROSS THE AREA. IN THE INTERIOR...JUST SOME
SCATTERED TO BROKEN CIRRUS TODAY WILL GIVE WAY TO BKN050 THIS
EVENING. STRATUS BASES WILL LOWER TO AROUND 015 LATE TONIGHT AS THE
ONSHORE FLOW INCREASES BEHIND THE FRONTAL SYSTEM. THE STRATUS OVER
THE INTERIOR WILL LIFT TO AROUND BKN035-040 TUESDAY AFTERNOON AND TO
BKN025 OVER THE COASTAL AREAS. ALBRECHT

KSEA...GOOD VFR CONDITIONS WITH ONLY SCATTERED CIRRUS THROUGH ABOUT
04Z THIS EVENING. STRATUS WITH BASES 040-050 WILL DEVELOP AROUND 04Z
THEN CLOUD BASES WILL LOWER TO 015 AFTER 10Z THROUGH ABOUT 17Z TUE.
LIGHT W TO SW WINDS WILL BACK TO SOUTH 5-8 KT AFTER 04Z. ALBRECHT

&&

.MARINE...HIGH PRESSURE WELL OFFSHORE COMBINED WITH LOWER PRESSURE
EAST OF THE CASCADES IS GIVING STRONG ONSHORE FLOW TO THE AREA. THE
ONSHORE FLOW WILL INCREASE SOMEWHAT THIS EVENING AS A WEAK COLD
FRONT EXTENDING SWWD FROM CENTRAL VANCOUVER ISLAND MOVES THROUGH THE
WATERS. ONSHORE FLOW WILL REMAIN STRONG THROUGH WED NIGHT WITH
STRONGEST INFLOW IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA
DURING THE LATE AFTERNOON AND OVERNIGHT HOURS.

A GALE WARNING IS IN EFFECT UNTIL 5 AM PDT TUE FOR THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA. GALES ARE POSSIBLE TUE NIGHT AS
WELL IN THE CENTRAL AND EASTERN STRAIT. SMALL CRAFT ADVISORY NW
WINDS ARE EXPECTED IN ADMIRALTY INLET...WITH STRONGEST WINDS NEAR
THE EAST ENTRANCE TO THE STRAIT.

SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS BEYOND
10 NM FROM THE COASTLINE AS NW PRESSURE GRADIENTS INCREASE THIS
EVENING THROUGH TUESDAY MORNING. WINDS IN THE COASTAL WATERS WILL
RELAX MIDDAY TUESDAY. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING IN EFFECT TIL 5 AM TUESDAY FOR THE CENTRAL AND
 EASTERN STRAIT OF JUAN DE FUCA.

 SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS
 FROM CAPE FLATTERY TO CAPE SHOALWATER FROM 10 NM OUT TO 60
 NM AND THE ADMIRALTY INLET.

&&

$$

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