Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 250415
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT FRI JUL 24 2015

.SYNOPSIS...A LARGE UPPER LEVEL TROUGH WILL REMAIN OVER THE REGION
THROUGH THIS WEEKEND...BRINGING MOSTLY CLOUDY SHOWERY AND COOL
WEATHER TO WESTERN WASHINGTON. THE TROUGH WILL MOVE EAST ON MONDAY
ALLOWING TEMPERATURES TO WARM AND THE SHOWER ACTIVITY TO END. AN
UPPER LEVEL RIDGE WILL BRING DRY WEATHER AND A WARMING TREND TO THE
AREA THE REST OF NEXT WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS W WA COVERED IN CLOUDS THIS
EVENING...BUT WITH SOME BREAKS OVER CENTRAL PUGET SOUND. AT 03Z/8 PM
A VERY WEAK COLD FRONT EXTENDED FROM S VANCOUVER ISLAND ACROSS THE
OLYMPICS TO RIGHT AROUND HOQUIAM...WITH SCATTERED LIGHT SHOWERS
SHOWING UP ON RADAR JUST AHEAD OF THE FRONT. THESE SHOWERS WILL
PROBABLY SPREAD SLOWLY E OVER THE PUGET SOUND LOWLANDS THIS EVENING
FOR SOME SPOTTY LIGHT RAIN. POPS LOOK GOOD FOR TONIGHT WITH CHANCE
POPS OVER THE INTERIOR LOWLANDS AND LIKELY POPS OVER THE COAST AND
MOUNTAINS.

THE LARGE UPPER LEVEL TROUGH JUST OFFSHORE WILL MAINTAIN MOIST SW
FLOW ALOFT OVER W WA SATURDAY AND SATURDAY NIGHT AS IT MOVES SLOWLY
TOWARD THE AREA. NO SIGNIFICANT SHORTWAVE TROUGHS APPEAR TO BE
CROSSING THE AREA DURING THIS PERIOD. WITH THE MOIST AIR MASS AND
WEAK LIFT FROM THE TROUGH THERE WILL STILL BE A CHANCE OF SHOWERS
BUT THE LOWLANDS SHOULD BE MORE DRY THAN WET. SHOWERS ARE LIKELY
OVER THE MOUNTAINS.

THE CENTER OF THE MAIN TROUGH WILL MOVE RIGHT ACROSS W WA ON
SUNDAY...AT THE SAME TIME AS A SMALL EMBEDDED SHORTWAVE TROUGH IS
ROTATING AROUND THE S PART OF THE MAIN TROUGH. THIS WILL ENHANCE THE
LIFT OVER W WA...AND THE MODELS HAVE BEEN CONSISTENTLY SHOWING MORE
PRECIP ON SUNDAY ALONG WITH HIGHER POPS. BOTH THE GFS AND NAM
CONTINUE TO SHOW NEGATIVE LIFTED INDICES OVER JUST ABOUT ALL OF W WA
SUNDAY AFTERNOON...WITH -2 TO -3.5 READINGS OVER THE SW INTERIOR AND
THE S PART OF PUGET SOUND. A NAM HIGH RESOLUTION SOUNDING FOR SUNDAY
AFTERNOON SHOWS A VERY MOIST AND UNSTABLE AIR MASS. THERE WILL BE
LOTS OF CLOUD COVER AROUND SO THE EXTRA BOOST FROM SOLAR HEATING
WILL MUCH WEAKER...THUS THE INSTABILITY FROM THE TROUGH WILL HAVE TO
BE ENOUGH TO TRIGGER ANY THUNDERSTORMS. THE CURRENT FORECAST HAS
THIS COVERED WITH A CHANCE OF THUNDERSTORMS IN THE AFTERNOON.

THE UPPER LEVEL TROUGH WILL CONTINUE MOVING EAST AND WILL BE OVER E
WA BY 12Z MONDAY. DRIER N FLOW ALOFT WILL SPREAD OVER W WA ALLOWING
SHOWERS TO END BY MONDAY MORNING. MORNING CLOUDS SHOULD GIVE WAY TO
A MOSTLY SUNNY AFTERNOON WITH TEMPERATURES NEAR NORMAL. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 315 PM AFD...THE UPPER
RIDGE FLATTENS A BIT DURING THE WEEK BUT 500MB HEIGHTS OVER
WASHINGTON REMAIN HIGH...IN THE 580S. HAVE KEPT THE FORECAST SUNNY
WITH MORNING LOW CLOUDS NEAR THE COAST. HIGHS WILL BE IN THE 80S
WITH THURSDAY LOOKING LIKE THE WARMEST DAY AT THIS POINT. IT APPEARS
THE WEATHER WILL BE BACK TO THE SUMMERY PATTERN OF THE LAST COUPLE
OF MONTHS. BURKE

&&

.AVIATION...A TROUGH OF LOW PRESSURE WILL SETTLE OVER THE PAC NW
THROUGH THE WEEKEND. THE ASSOCIATED SURFACE FRONT IS CURRENTLY
PUSHING THROUGH PUGET SOUND AT 9 PM PDT AND WILL BE OVER THE
CASCADES BY MIDNIGHT. LIGHT TO MODERATE WLY FLOW ALOFT. GENERALLY
STABLE AND BECOMING MOIST THIS EVENING AT ALL LEVELS. AREAS OF RAIN
ACROSS WRN WA WILL DECREASE TO SCATTERED SHOWERS LATER TONIGHT. CIGS
WILL BE VARIABLE WITH IFR AT TIMES ALONG THE COAST/STRAIT...AND
AREAS OF MVFR OVER THE INTERIOR AFFECTING ALL TERMINALS. CIGS MAY
LOWER LATER TONIGHT AND SATURDAY MORNING WITH LOW MVFR BECOMING MORE
WIDESPREAD. CIGS SHOULD IMPROVE TO MOSTLY VFR BY SATURDAY AFTERNOON.

KSEA...A FRONT IS CURRENTLY MOVING PAST THE TERMINAL AT 9 PM PDT.
WINDS HAVE SHIFTED MORE SWLY AND WILL CONTINUE IN THE 10 TO 20 KT
RANGE...THEN EASING LATER TONIGHT. VFR CIGS WITH LIGHT RAIN AT
TIMES...THEN MVFR BECOMES MORE LIKELY LATER TONIGHT AND SATURDAY
MORNING. CIGS WILL IMPROVE TO VFR SATURDAY AFTERNOON. DTM

&&

.MARINE...A FRONT OVER THE INLAND WATERS WILL MOVE E OVER THE
CASCADES BY MIDNIGHT. ONSHORE FLOW WILL PREVAIL SATURDAY THROUGH
WEDNESDAY WITH HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND.
THIS WILL KEEP SMALL CRAFT ADVISORY WINDS GOING IN THE CENTRAL AND
EASTERN STRAIT THROUGH SATURDAY EVENING...POSSIBLY EASING FOR A TIME
ON SATURDAY. THERE WILL LIKELY BE AT SMALL CRAFT ADVISORY WEST WINDS
IN THE CENTRAL AND EASTERN STRAIT EACH EVENING ON SUNDAY AND MONDAY
AS WELL. DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA
     THROUGH 11 AM PDT SATURDAY EVENING.

&&

$$

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