Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 211655 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
955 AM PDT THU MAY 21 2015

CORRECTED TYPO IN THE MARINE SEGMENT.

.SYNOPSIS...A WEAK WEATHER SYSTEM OVER OREGON WILL SPREAD A CHANCE
OF SHOWERS INTO THE AREA LATER TODAY THROUGH FRIDAY. THERE IS A GOOD
CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS OVER THE MOUNTAINS.
ONSHORE FLOW WILL INCREASE THROUGH FRIDAY WITH MARINE LAYER CLOUDS
SPREADING INLAND TONIGHT. A TYPICAL PATTERN OF MORNING CLOUDS WITH
SOME AFTERNOON SUNSHINE IS LIKELY FOR NEXT WEEK WITH A CHANCE OF
SHOWERS...MAINLY OVER THE MOUNTAINS.

&&

.SHORT TERM...MARINE STRATUS IS IN THE TYPICAL SPOTS...IT IS
OVERCAST ON THE COAST...AND SOME CLOUDS ARE IN THE STRAIT AND
SHALLOW MARINE AIR GAVE SOME FOG AND LOW CLOUDS IN THE SOUTH SOUND
THIS MORNING. THERE IS MORE MOISTURE OVER OREGON NOW...AND SOME OF
THAT WILL PROBABLY WORK NORTH INTO WESTERN WA. THE SOUTHERN HALF OF
THE CASCADES OUGHT TO SEE SHOWERS AND ISOLATED THUNDERSTORMS
BUILDING UP THIS AFTERNOON AND CONTINUING INTO THE EVENING...AND
THAT IS WHERE THE UW WRFGFS HAS THE MOST PRECIP. THAT MODEL ALSO
SHOWS SCATTERED SHOWERS WORKING NORTH OVERNIGHT AND INTO FRIDAY...SO
THERE IS PROBABLY A PRETTY GOOD CHANCE OF SHOWERS DEVELOPING OVER
WRN WA EVEN AS THE STABLE MARINE AIR PUSHES IN OVERNIGHT AND FRIDAY
MORNING. THE FORECAST WILL LIKELY BE PUSHED IN THE DIRECTION OF THE
WRFGFS LATER THIS MORNING. FRIDAY SHOULD BE COOLER WITH MORE CLOUDS
AND THE DEEPER MARINE LAYER. LOW LEVEL ONSHORE FLOW SHOULD CONTINUE
INTO SATURDAY FOR MAINLY CLOUDY SKIES...HIGHS WILL AGAIN BE ONLY IN
THE 60S...AND ANOTHER WEAK UPPER LOW COULD BRING SCATTERED
SHOWERS...WITH BEST CHANCES OVER THE MOUNTAINS.

.LONG TERM...A WEAK UPPER TROUGH OR UPPER LOW WILL REMAIN OVER THE
REGION SUNDAY THROUGH WEDNESDAY WITH CONTINUED MODERATE LOW LEVEL
ONSHORE FLOW. MOST DAYS SHOULD SEE MORNING CLOUDS WITH SOME
AFTERNOON SUNSHINE OVER THE INTERIOR. THERE WILL BE A CHANCE OF
SHOWERS EACH DAY...MAINLY AFTERNOON AND EVENING HOURS OVER THE
MOUNTAINS. SHOWERS LOOK LIKELY MONDAY IN THE NORTH CASCADES.

&&

.AVIATION...A BLOCKING UPPER LEVEL PATTERN WILL REMAIN OVER THE
REGION TODAY. WRN WA WILL BECOME MORE UNDER THE INFLUENCE OF AN
UPPER LOW LATER TONIGHT. CONTD LIGHT AND VARIABLE FLOW ALOFT. THE
LOW LEVEL ONSHORE FLOW WILL STRENGTHEN THIS AFTERNOON. AREAS OF LIFR
CIGS AND MVFR VSBYS THIS MORNING WILL BECOME CONFINED TO THE COAST
BY 2000 UTC.

MEANWHILE...THE AIR MASS WILL CONT TO DESTABILIZE DURING THE DAY
TODAY FOR THE DEVELOPMENT OF TSTMS OVER THE MOUNTAINS. THE TSTMS
SHOULD BE MORE NUMEROUS THIS AFTERNOON COMPARED TO YESTERDAY.
THERE IS A POSSIBILITY THAT A FEW TSTMS COULD DRIFT INTO THE AREA
S OF KOLM LATE THIS AFTERNOON.

KSEA...VFR CONDITIONS WILL PREVAIL THRU THIS EVENING. LOOK FOR
STRATUS OVER THE TERMINAL LATE TONIGHT OR EARLY FRI MORNING.

&&

.MARINE...
THE ONSHORE PRES GRADIENT WILL TIGHTEN DURING THE DAY TODAY. THIS
COMBINED WITH A RELATIVELY LARGE DIFFERENCE BETWEEN THE TEMPERATURES
ON THE COAST AND THE INTERIOR THIS AFTERNOON WILL PROBABLY LEAD TO
GALE FORCE WINDS OVER THE CENTRAL STRAIT OF JUAN DE FUCA THIS
EVENING. THE ONSHORE GRADIENT WILL BE TIGHTER ON FRI BUT TEMPS
OVER THE INTERIOR WILL BE MUCH COOLER...SO CONFIDENCE OF GALE
FORCE WINDS OVER THE STRAIT OF JUAN DE FUCA WAS BECOMING LESS.

MEANWHILE..A 1025 MB HIGH WELL OFFSHORE WILL BRIEFLY STRENGTHEN
TO 1030 MB ON SATURDAY. THE COMBINATION OF HIGH PRES OFFSHORE AND
LOWER PRES INLAND WILL RESULT IN ONSHORE FLOW OF VARYING STRENGTH
THROUGH MON.

&&

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

     GALE WATCH IN EFFECT FROM 6 PM THIS EVENING THROUGH LATE
     TONIGHT FOR THE CENTRAL STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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