Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 261039
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
339 AM PDT SUN JUL 26 2015

.SYNOPSIS...AN UPPER LEVEL TROUGH WILL BRING KEEP SHOWERS OVER
WESTERN WASHINGTON THROUGH TONIGHT WITH A CHANCE OF THUNDERSTORMS
THIS AFTERNOON AND EVENING. SHOWERS WILL DIMINISH LATE TONIGHT INTO
EARLY MONDAY MORNING AS THE UPPER LEVEL TROUGH SHIFTS EAST OF THE
CASCADES. A BROAD UPPER LEVEL RIDGE WILL BUILD OVER THE REGION
TUESDAY AND LINGER THROUGH THE REMAINDER OF THE WEEK KEEPING
CONDITIONS DRY AND WARM.

&&

.SHORT TERM...THE UPPER LEVEL MOVING SOUTH AND EAST ALONG THE SPINE
OF BRITISH COLUMBIA WILL SAG SOUTH OVER WESTERN WASHINGTON TODAY.
THE WEAK CONVERGENCE ZONE THAT FORMED EARLIER THIS EVENING HAS ALL
BUT FALLEN APART AS OF 10Z...WITH A FEW LINGERING LIGHT SHOWERS
ALONG THE SNOHOMISH AND KING COUNTY LINE.

TODAY THE FOCUS REMAINS ON MORE WIDESPREAD SHOWERS AND THE POTENTIAL
FOR THUNDERSTORMS OVER THE AREA AS THE MAIN UPPER LEVEL TROUGH MOVES
OVERHEAD AND AN EMBEDDED SHORTWAVE ROTATES ONSHORE THIS AFTERNOON.
EXPECT LIFT AND UPPER LEVEL DYNAMICS WITH BOTH OF THESE FEATURES TO
ENHANCE INSTABILITY IN AN ALREADY SATURATED AIR MASS. MODELS
CONTINUE TO HIGHLIGHT LIFTED INDICES DROPPING SUNDAY AFTERNOON
ESPECIALLY THE SW INTERIOR AND PUGET SOUND. IN ADDITION...SIMILAR
POTENTIAL FOR THE CENTRAL AND NORTH WASHINGTON COAST WARRANTIED
EXTENDING THE CHANCE OF THUNDERSTORMS THERE DURING THE AFTERNOON
HOURS AS THE UPPER LEVEL SHORTWAVE MOVES ONSHORE. MODELS SHOW THE
SHOWERS DIMINISHING SUNDAY EVENING WITH ONLY LINGERING SHOWERS OVER
THE CASCADES AS THE MAIN UPPER LEVEL TROUGH SHIFTS EAST OF THE AREA.

FLOW ALOFT WILL TRANSITION TO NORTHERLY HELPING DRY THE REGION AHEAD
OF AN THE UPPER LEVEL RIDGE THAT WILL BUILD OVER THE REGION FROM THE
WEST. ONSHORE FLOW MONDAY NIGHT WILL SUPPORT AREAS OF STRATUS OVER
THE INTERIOR FOR A MOSTLY CLOUDY START TO TUESDAY WITH MORNING
CLOUDS CLEARING TO MOSTLY SUNNY SKIES AND WARMER TEMPERATURES. HIGHS
ON WILL WARM TO THE 70S TO LOWER 80S.

.LONG TERM...THE BROAD UPPER LEVEL RIDGE WILL BUILD OVER THE WESTERN
US BY FRIDAY...KEEPING UPPER LEVEL HEIGHTS OVER THE PACIFIC
NORTHWEST HIGH THROUGH THE END OF THE WEEK. EXPECT TEMPERATURES TO
WARM 4 TO 5 DEGREES A DAY WEDNESDAY AND THURSDAY...WITH LIGHT
OFFSHORE FLOW HELPING THURSDAY END UP AS THE WARMEST DAY OF THE
WEEK. AFTERNOON TEMPERATURES THURSDAY WILL CREEP INTO THE LOW 90S
OVER THE SOUTH INTERIOR AND AS FAR NORTH AS THE SEATTLE METRO AREA.
CONDITIONS WILL REMAIN SLIGHTLY COOLER...BUT STILL WARM AND DRY
THROUGH THE WEEKEND.

&&

.AVIATION...AN UPPER LEVEL TROUGH OVER THE PAC NW WILL SLOWLY SHIFT
E OF THE REGION TONIGHT. LIGHT WLY FLOW ALOFT BECOMING LIGHT-
MODERATE NW FLOW ALOFT DURING THE EVENING. THE AIR MASS IS MOIST AND
SOMEWHAT UNSTABLE WITH SCATTERED SHOWERS THIS MORNING. THE PUGET
SOUND CONVERGENCE ZONE WILL REMAIN SOMEWHAT ACTIVE OVER SNOHOMISH
COUNTY THIS MORNING WITH LIGHT RAIN AT TIMES AND LOW MVFR CIGS
AFFECTING KPAE. ELSEWHERE...CIGS WILL BE MORE VARIABLE THIS MORNING
WITH AREAS OF MVFR OR LOW VFR STRATUS. INSTABILITY WILL INCREASE
SUBSTANTIALLY THIS AFTERNOON/EARLY EVENING WITH A CHANCE OF TSTMS.
MODEL GUIDANCE SUGGESTS THE CONVERGENCE ZONE MAY ALSO INTENSIFY THIS
AFTERNOON AND SHIFT SWD INTO KING/NRN PIERCE COUNTIES...THEN
GRADUALLY DISSIPATING. BKN-OVC STRATUS/CUMULUS W/ BASES 3-4K FT WILL
PREVAIL DURING THE AFTERNOON.

KSEA...SW WIND TO 5 KT...RISING TO 5 TO 10 KT DURING THE
MORNING...THEN A SHIFT TO N-NW LATE THIS AFTERNOON OR EARLY EVENING.
MVFR CIGS LIKELY AT TIMES BETWEEN 12Z-18Z...THEN MOSTLY ABOVE 3K FT.
 25 PERCENT CHANCE OF TSTMS AT THE TERMINAL THIS AFTERNOON/EARLY
EVENING. WILL MAINTAIN THE VCTS IN THE TAF GIVEN THE UNCERTAINTY.
DTM

&&

.MARINE...ONSHORE FLOW WILL DOMINATE THE PATTERN THROUGH TUESDAY.
SMALL CRAFT WINDS ARE LIKELY IN THE CENTRAL AND EASTERN STRAIT
DURING THE EVENING AND EARLY MORNING HOURS THROUGH THE PERIOD.
ONSHORE FLOW WILL WEAKEN AND TURN MORE NORTHERLY WEDNESDAY AND
THURSDAY AS A THERMAL TROUGH BUILDS NORTH ALONG THE COAST. DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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