487
FXUS66 KSEW 080321
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
821 PM PDT SUN JUN 7 2026
SYNOPSIS
COOL AND UNSETTLED CONDITIONS WILL CONTINUE ACROSS
WESTERN WASHINGTON FOR THE FIRST HALF OF THE WEEK AS A PAIR OF
SYSTEMS MOVE THROUGH THE REGION. A PATTERN SHIFT TOWARD DRY AND
CONSIDERABLY WARMER CONDITIONS IS EXPECTED LATE IN WEEK AS
STRONG HIGH PRESSURE ALOFT BUILDS INTO THE REGION.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
WE'VE GOTTEN A
BRIEF REPRIEVE FROM PRECIPITATION THIS AFTERNOON ACROSS THE AREA
AS WEAK SHORTWAVE RIDGING SLIDES ONSHORE AHEAD OF THE NEXT
APPROACHING SYSTEM. AS MENTIONED IN THE UPDATE THIS MORNING,
MODEL SOLUTIONS ARE TRENDING FURTHER NORTHWARD WITH THE SURFACE
LOW WHICH IMPLIES THAT MUCH OF THE FORECAST AREA WILL SEE A
SOGGY STRETCH OF WEATHER MONDAY AFTERNOON INTO MUCH OF TUESDAY.
UNLIKE THIS PAST SATURDAY, WE'RE LOOKING FOR STRATIFORM PRECIP
TO SPREAD ONSHORE DURING THE DAY MONDAY. BETWEEN MONDAY
AFTERNOON AND TUESDAY MORNING, LOWLAND AREAS FROM AROUND SEATTLE
SOUTHWARD COULD SEE 0.50" TO 0.75" OF RAIN WITH HIGHER AMOUNTS
IN THE CASCADES. SNOW LEVELS WILL BE HIGHER THIS ROUND KEEPING
ANY ACCUMULATING SNOW ONLY IN THE HIGHEST OF ELEVATIONS. ONSHORE
FLOW RAMPS UP ON TUESDAY AS THE TRAILING UPPER TROUGH MOVES
ONSHORE. THIS IS EXPECTED TO GENERATE A FAIRLY POTENT
CONVERGENCE ZONE. AS A WHOLE, CONVECTIVE INDICES ARE PRETTY
MINUSCULE ACROSS THE CWA ON TUESDAY, BUT IT WOULDN'T BE
SURPRISING TO GET THE WELL-KNOWN ONE CLAP WONDER IN THE PSCZ.
TEMPERATURES THROUGHOUT THE SHORT TERM FORECAST WILL REMAIN ON
THE COOL SIDE. AS FOR THE COOL TEMPERATURES: TO QUOTE A SONG
TITLE BY THE SUNDAYS, "HERE'S WHERE THE STORY ENDS".
LONG TERM /WEDNESDAY THROUGH SUNDAY/
AN UPPER LEVEL TROUGH
EXITS THE AREA ON WEDNESDAY MAKING IT SOMETHING OF A
TRANSITIONAL DAY. CLOUDS AND A FEW, MAINLY MOUNTAIN, SHOWERS
WILL BE PRESENT EARLY IN THE DAY. THE TREND TOWARD CLEARING AND
MODEST WARMING WILL BE UNDERWAY BY WEDNESDAY AFTERNOON. AN UPPER
LEVEL RIDGE CENTERED OFFSHORE BEGINS TO BUILD INTO THE REGION
ON THURSDAY. SOME RESIDUAL UPPER TROUGHING OVER THE WESTERN
CANADIAN PROVINCES WILL TEMPER IT'S STRENGTH INITIALLY, BUT ONLY
LOOKS TO TEMPORARILY SLOW WHAT NOW LOOKS LIKE AN INEVITABLE
CLIMB IN TEMPERATURES TO WELL ABOVE SEASONAL NORMALS.
BY THE WEEKEND, A HIGH AMPLITUDE RIDGE IS EXPECTED TO BE CENTERED
JUST OFFSHORE WITH 500 MILLIBAR HEIGHTS OVER WESTERN WASHINGTON IN
THE MID TO UPPER 580S DECAMETERS. NEAR THE SURFACE, THERMALLY
INDUCED LOW PRESSURE WILL EXPAND INTO THE REGION AND THE LOW
LEVEL FLOW IS EXPECTED TO TURN OFFSHORE SATURDAY NIGHT INTO
SUNDAY AS THE THERMAL TROUGH SHIFTS TOWARD THE COAST. BROADLY
SPEAKING, A LARGE PORTION OF THE FORECAST AREA WILL BE LOOKING
AT POTENTIAL HIGH TEMPERATURES IN THE MID 80S TO MID 90S BY THE
EARLY PORTION OF NEXT WEEK. PROBABILISTIC GUIDANCE IS POINTING
TOWARDS LIKELY MODERATE HEATRISK FOR A SUBSTANTIAL PORTION OF
THE LOWLANDS (COAST INCLUDED) BY SUNDAY. RECORD HIGHS FOR SEA-
TAC FOR SUNDAY AND MONDAY ARE WELL WITHIN REACH AT 86 AND 88,
RESPECTIVELY. THE RECORD HIGH ON MONDAY HAS STOOD FOR 63 YEARS.
27
AVIATION
NORTHWEST FLOW ALOFT OVER WESTERN WASHINGTON WILL
BACK TO SOUTHWESTERLY AGAIN TONIGHT AS THE NEXT IN A SERIES OF
UPPER TROUGHS AND ASSOCIATED FRONTAL SYSTEMS APPROACHES THE
AREA. HIGH AND MID LEVEL MOISTURE AHEAD OF THE NEXT SYSTEM WILL
SPREAD ONSHORE THIS EVENING THROUGH TONIGHT. VFR CEILINGS ARE
EXPECTED TO PREVAIL AREAWIDE INTO THIS EVENING. CEILINGS WILL
DETERIORATE BACK TO MVFR IN INCREASING RAIN ALONG THE COAST MID
TO LATE MONDAY MORNING WITH SAID CONDITIONS GRADUALLY SPREADING
TO MOST INTERIOR TERMINALS 21Z MONDAY ONWARD.
KSEA...VFR CEILINGS EXPECTED INTO THIS EVENING WITH CEILINGS
GRADUALLY COMING DOWN OVERNIGHT. MVFR CEILINGS IN RAIN ARE
EXPECTED TO DEVELOP AROUND 21Z MONDAY. SURFACE WINDS S/SW 7 TO
10 KNOTS GRADUALLY EASE THIS AFTERNOON AND VEER LIGHT W/NW FOR A
PERIOD THIS EVENING. WINDS ARE EXPECTED TO BECOME LIGHT E/SE
LATE TONIGHT BEFORE BACKING NORTHERLY 9 TO 14 KNOTS LATE MONDAY
AFTERNOON.
27/MAZURKIEWICZ
MARINE
A SLOW MOVING FRONT AND ASSOCIATED SUB-1000 MILLIBAR
SURFACE LOW WILL MOVE INTO THE COASTAL WATERS LATE TONIGHT AND
EARLY MONDAY THEN GRADUALLY DRAG ONSHORE AND WEAKEN LATE MONDAY
AFTERNOON AND EVENING. ONSHORE FLOW WILL INCREASE BEHIND THIS
SYSTEM ON TUESDAY AND CONTINUE INTO WEDNESDAY AS A SURFACE RIDGE
REBUILDS INTO OFFSHORE AND COASTAL WATERS. ONSHORE FLOW WEAKENS
AND TURNS MORE NORTHERLY LATE IN THE WEEK AS THERMALLY INDUCED
LOW PRESSURE EXPANDS NORTHWARD INTO WESTERN OREGON.
SMALL CRAFT ADVISORY WINDS ARE EXPECTED OVER THE COASTAL WATERS
LATE TONIGHT AND ON MONDAY WITH THE INCOMING FRONT AND SURFACE
LOW. THE ONSHORE FLOW ON TUESDAY LOOKS SUFFICIENT TO GENERATE
SMALL CRAFT ADVISORY WINDS FOR NEARLY ALL OF THE INTERIOR WATERS
AND POSSIBLE GALES IN THE CENTRAL AND EAST STRAIT. ONSHORE FLOW
RELAXES ENOUGH ON WEDNESDAY TO KEEP SMALL CRAFT ADVISORY
WESTERLIES ISOLATED TO THE STRAIT BEFORE QUIETER CONDITIONS TAKE
HOLD ACROSS ALL WATERS AT THE END OF THE WEEK. COASTAL SEAS
ARE EXPECTED TO REMAIN BELOW 10 FEET.
27
FIRE WEATHER
AS UPPER LEVEL RIDGING BUILDS INTO THE AREA
STARTING THURSDAY, CONDITIONS, INCLUDING FUELS, WILL NEED TO BE
MONITORED AS TEMPERATURES ARE EXPECTED TO CLIMB TO ABOVE NORMAL
VALUES BY THE END OF THE EXTENDED FORECAST PERIOD. GIVEN THE
STEEP CLIMB IN TEMPERATURES, EXTRA CAUTION WOULD BE ADVISED IN
ANY PLANNING DURING THIS TIME. CURRENT NBM MINIMUM RELATIVELY
HUMIDITY VALUES ARE RUNNING IN THE 25-35 PERCENT RANGE BY DAY 7
ACROSS PORTIONS OF THE AREA. THESE ARE LIKELY A TAD HIGHER THAN
WHAT WILL TRANSPIRE. IF THE CROSS CASCADE GRADIENT GOES NEGATIVE
BY SUNDAY AS ADVERTISED IN A NUMBER OF MODELS, HUMIDITY VALUES
DROPPING INTO THE TEENS IN THE CASCADES VALLEYS AND PORTIONS OF
THE SOUTHWEST INTERIOR BECOME A DISTINCT POSSIBILITY.
27
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 AM TO 1 PM PDT MONDAY FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT
10 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER OUT 10 NM.
SMALL CRAFT ADVISORY UNTIL 1 PM PDT MONDAY FOR COASTAL WATERS
FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10
TO 60 NM.
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