Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 160447
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
945 PM PDT WED APR 15 2015

.SYNOPSIS...AN UPPER LEVEL RIDGE AND SURFACE HIGH WILL REMAIN OVER
WESTERN WASHINGTON THROUGH THURSDAY FOR DRY WEATHER. A WARM FRONT
OVER BRITISH COLUMBIA WILL BRING CLOUDS TO THE NORTH PART TONIGHT.
THE RIDGE WILL BUILD NORTHWARD THURSDAY...BRINGING WARMER WEATHER
AND MORE SUNSHINE. A WEAK UPPER LEVEL TROUGH WILL BRING CLOUDS OVER
THE AREA FRIDAY...AND A CHANCE OF SHOWERS TO THE NORTH COAST AND
NORTH CASCADES FRIDAY AFTERNOON AND EVENING. A STRONGER UPPER LEVEL
RIDGE WILL BRING SUNNY WARMER WEATHER SATURDAY AFTERNOON THROUGH
TUESDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS FLAT UPPER LEVEL RIDGE OVER
WESTERN WASHINGTON THIS EVENING. WARM FRONT WELL TO THE NORTH OF THE
AREA WITH HIGH CLOUDS ASSOCIATED WITH THE FRONT OVER THE NORTHERN
PORTION OF THE AREA. WITH THE LACK OF CLOUD COVER A WIDE VARIETY OF
TEMPERATURES AT 9 PM ACROSS THE AREA...UPPER 30S TO MID 50S.

NO CHANGES IN THE FORECAST TONIGHT WITH THE 00Z MODELS SHOWING THE
RIDGE HOLDING IN PLACE THROUGH THURSDAY KEEPING THE WARM FRONT NORTH
OF THE AREA. SURFACE GRADIENTS TRENDING OFFSHORE TONIGHT WILL SWITCH
BACK AROUND TO NORTHWESTERLY ONSHORE ON THURSDAY. TEMPERATURES ALOFT
WARMING UP WITH THE 850 MB TEMPS NEAR 0 THIS EVENING WARMING TO
AROUND PLUS 5C BY 00Z FRIDAY. WITH PLENTY OF SUNSHINE THIS WILL
RESULT IN ABOUT 5 DEGREES OF WARMING VERSUS TODAY. LOWER TO MID 60S
WILL BE COMMON OVER THE INTERIOR.

SOME CHANGES TAKING PLACE THURSDAY NIGHT WITH THE RIDGE AXIS
SHIFTING EAST. UPPER LEVEL TROUGH OFFSHORE NEAR 130W BY 12Z FRIDAY.
NOT CLOSE ENOUGH TO PROVIDE ANY WEATHER TO THE AREA. EXPECT LOWS IN
THE UPPER 30S TO MID 40S.

UPPER LEVEL TROUGH MOVING INTO WESTERN WASHINGTON ON FRIDAY BUT THE
TROUGH IS FAIRLY WEAK...500 MB HEIGHTS ONLY LOWER INTO THE MID TO
UPPER 560 DMS. SURFACE GRADIENTS TURN ONSHORE IN THE MORNING BUT
WITH THE WEAK LIFT ASSOCIATED WITH THE TROUGH THE ONLY CHANCES FOR
SHOWERS LOOK TO BE ALONG THE NORTH COAST...OLYMPICS AND NORTH
CASCADES. EVEN WITH THE TROUGH OVERHEAD MOS GUIDANCE FOR FRIDAY A
COUPLE OF DEGREES WARMER VERSUS THURSDAY.

TROUGH MOVING EAST OF THE AREA FRIDAY NIGHT WITH AN UPPER LEVEL
RIDGE BUILDING QUICKLY OFFSHORE. SURFACE GRADIENTS GO NORTHWESTERLY
FRIDAY NIGHT AND REMAIN NORTHWESTERLY THROUGH SATURDAY MORNING.
MODEL BOUNDARY LEVEL RH SATURATED SATURDAY MORNING. WITH THE
NORTHWESTERLY SURFACE GRADIENTS EXPECT THIS LAYER TO BE QUITE
SHALLOW. CURRENT FORECAST HAS SOME CLOUD COVER OVER THE INTERIOR
SATURDAY MORNING. IF THE MODEL TRENDS CONTINUE LOOK FOR THE THIS TO
BE TAKEN OUT OF THE FORECAST. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. LONG RANGE MODELS START
BREAKING THE RIDGE DOWN STARTING SUNDAY...WHILE IT REMAINS OVER THE
REGION. BY TUESDAY AFTERNOON...WITH THE RIDGE AXIS OVER THE ID
PANHANDLE...A LARGE UPPER LEVEL TROUGH WILL HAVE FORMED JUST
OFFSHORE. S FLOW ALOFT WILL DEVELOP OVER W WA WITH MOISTURE
INCREASING AT SOME POINT. MODELS ARE STRUGGLING WITH CONSISTENCY
REGARDING THE STRUCTURE OF THE TROUGH AND WHEN AND HOW MUCH MOISTURE
WILL MOVE N OVER W WA. FOR NOW THE FORECASTS FOLLOW A ROUGH BLEND OF
THE GFS AND ECMWF WITH A CHANCE OF SHOWERS OVER W WA TUESDAY NIGHT
AND WEDNESDAY. KAM

&&

.AVIATION...AN UPPER LEVEL RIDGE OVER THE PAC NW WILL MAINTAIN DRY
AND STABLE WEATHER ACROSS WESTERN WA TONIGHT THROUGH THURSDAY. THE
FLOW ALOFT IS WESTERLY. VFR CONDITIONS WILL PREVAIL. 33

KSEA...FEW-SCT CIRRUS CLOUDS ALOFT WITH VFR CONDITIONS. LIGHT N/NE
WINDS AT THE SURFACE. 33

&&

.MARINE...HIGH PRESSURE OVER WESTERN WA WILL BRING GENERALLY LIGHT
WINDS THROUGH THURSDAY. MEANWHILE...WEST SWELL WILL INCREASE TO
10 FT TONIGHT AND A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE OUTER
COASTAL WATER ZONES. ONSHORE FLOW WILL INCREASE ON FRIDAY AS A COLD
FRONT CROSSES WESTERN WA. SMALL CRAFT ADVISORY WINDS ARE LIKELY FOR
THE COASTAL WATERS AND THE STRAIT OF JUAN DE FUCA. NORTHERLY FLOW
WILL DEVELOP ON SATURDAY AS LOW PRES FORMS ALONG THE COAST.
NORTHERLY FLOW WILL CONTINUE THROUGH EARLY NEXT WEEK. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY OUTER COASTAL WATERS FOR HAZARDOUS SEAS.

&&

$$

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