994
FXUS66 KSEW 201543
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
843 AM PDT SAT JUN 20 2026
SYNOPSIS
HIGH PRESSURE ALOFT WILL BRIEFLY WEAKEN OVER WESTERN WASHINGTON
TODAY AS AN UPPER TROUGH MOVES ACROSS BRITISH COLUMBIA. UPPER
LEVEL RIDGING WILL REBUILD INTO THE REGION SUNDAY THROUGH
TUESDAY FOR A SIGNIFICANT WARMING TREND. THE RIDGE WILL BEGIN TO
WEAKEN BY THE MIDDLE OF THE COMING WEEK FOR COOLER CONDITIONS. A
FRONTAL SYSTEM COULD BRING THE REGIONS FIRST CHANCE OF RAIN IN
MORE THAN TWO WEEKS BY THE END OF NEXT WEEK.
SHORT TERM /TODAY THROUGH MONDAY/
NO MAJOR FORECAST UPDATES HAVE BEEN MADE THIS MORNING.
WIDESPREAD MARINE STRATUS CLOUDS WILL LINGER THROUGH AROUND MID
MORNING BEFORE BREAKING OUT FOR A CLEAR AFTERNOON. SEE BELOW FOR
THE PREVIOUS DISCUSSION AND AN UPDATED AVIATION SECTION.
A WEAK SYSTEM PASSING WELL NORTH OF THE AREA THIS MORNING HAS
INDUCED A DECENT ONSHORE PUSH WITH COOLER MARINE AIR POURING
INLAND. WE'LL SEE AREAS OF MORNING LOW CLOUDS GETTING AT LEAST
PART WAY INLAND AND MOST INTERIOR LOCATIONS WILL SHAVE 7 TO 10
DEGREES OFF THEIR HIGH TEMPERATURES OVER YESTERDAYS READINGS.
THE COOLING TREND WILL BE SHORT-LIVED.
UPPER LEVEL RIDGING WILL BEGIN TO REBUILD INTO THE AREA ON
SUNDAY. OUR BRIEF FLIRTATION WITH LOW LEVEL ONSHORE FLOW WILL
REVERT TO NORTHERLY SUNDAY AFTERNOON THEN TURN VERY WEAKLY
OFFSHORE SUNDAY NIGHT INTO EARLY MONDAY AS THERMALLY INDUCED LOW
PRESSURE AT THE SURFACE EXPANDS NORTHWARD INTO WESTERN
WASHINGTON ONCE AGAIN. THIS WILL LEAD TO A PRETTY GOOD SPIKE IN
HIGH TEMPERATURES FOR MONDAY WITH MUCH OF THE PUGET SOUND
LOWLANDS SEEING HIGHS IN THE 80S TO AROUND 90 IN THE SOUTHWEST
INTERIOR. COASTAL HIGH TEMPERATURES ON MONDAY ARE FAR LESS
CERTAIN. A NUMBER OF MODELS SUGGEST THE THERMAL TROUGH WILL BE
ORIENTED JUST INLAND FROM THE COAST. THIS MAKES THE FORECAST
FROM THE 50TH PERCENTILE NBM (NEAR 80 AT HOQUIAM) USED IN THE
FORECAST A BIT SUSPECT. IN ANY CASE, MODERATE HEATRISK REMAINS
THE CENTRAL STORY FOR THE INTERIOR LOWLANDS ON MONDAY.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
AN UPPER LEVEL RIDGE REMAINS OVER THE AREA INTO TUESDAY, BUT THE
LOW LEVEL FLOW WILL BE WEAKLY ONSHORE. THIS WILL COOL THE
COAST, BUT THE NBM SEEMS TO DISCOUNT THIS REALITY. THE THERMAL
TROUGH REMAINS IN PLACE ACROSS THE INTERIOR LOWLANDS WHERE MOST
LOCATIONS AWAY FROM THE WATER WILL BE WELL INTO THE 80S AND
LOWER 90S WITH WIDESPREAD MODERATE HEATRISK.
UPPER LEVEL RIDGING IS EXPECTED TO BEGIN TO WEAKEN AS WE MOVE
BEYOND THE MIDDLE OF NEXT WEEK. THIS WILL LEAD TO A DOWNWARD
TREND IN TEMPERATURES. ENSEMBLES GENERALLY AGREE THAT ANOMALOUS
UPPER TROUGHING WILL TAKE UP RESIDENCE OVER THE REGION BY THE
END OF NEXT WEEK. THOUGH THEY DISAGREE SOMEWHAT ON THE OVERALL
STRENGTH OF THE TROUGH, THE BIGGER STORY IS THE INTRODUCTION OF
WESTERN WASHINGTON'S FIRST CHANCE AT MEASURABLE PRECIPITATION IN
MORE THAN TWO WEEKS.
27
AVIATION
MVFR CIGS FOR ALL TERMINALS THIS MORNING EXCEPT FOR KBLI AND
KCLM. BREEZY SOUTHWESTERLY WINDS ARE EXPECTED THROUGH THE
MORNING, EASING UP SOMEWHAT IN THE AFTERNOON TO BELOW 7 KTS. THE
STRATUS IS LIKELY TO LINGER UNTIL AROUND 18Z WHEN A MORE
APPRECIABLE BREAKUP OF THE CLOUDS BEGINS. THEREAFTER, EXPECT A
VFR AFTERNOON AND EVENING. GUIDANCE IS SUGGESTIVE OF ANOTHER
ROUND OF MARINE STRATUS IMPACTING WESTERN WASHINGTON TOMORROW
MORNING (30% LIKELIHOOD OF MVFR FOR INLAND TERMINALS, 50%
LIKELIHOOD FOR THE IMMEDIATE COAST).
KSEA...MVFR AT THE TERMINAL PRESENTLY WITH CIGS HOVERING AROUND
019-020. A BREAKOUT TO VFR CIGS IS STILL FAVORED FOR 18Z,
CONTINUING TO CLEAR THROUGH THE AFTERNOON. SOUTHWEST WINDS 8-10
KTS WILL CONTINUE UNTIL AROUND 21Z, DECREASING TO 7 KTS OR LESS
THEREAFTER. OPTED TO PUT A RETURN TO LOWER CLOUDS AS A SCT025
IN FOR 12Z TOMORROW MORNING AS GUIDANCE SUGGESTS ANOTHER ROUND
OF MARINE STRATUS TO MAKE IT INTO THE SOUND.
21
MARINE
HIGH PRESSURE CONTINUES TO WEAKEN TODAY AS A LOW PRESSURE SYSTEM
MOVES THROUGH BRITISH COLUMBIA. ONCE THE LOW PRESSURE SYSTEM PUSHES
EAST OF THE CASCADES, HIGH PRESSURE WILL QUICKLY REBUILD OVER AREA
WATERS LATE THIS EVENING AND WILL STRENGTHEN THROUGH MIDWEEK. A
FRONTAL SYSTEM WILL APPROACH THE WATERS ON THURSDAY, LEADING TO HIGH
PRESSURE TO WEAKEN.
A SMALL CRAFT ADVISORY CONTINUES THIS MORNING FOR ELEVATED SEAS AND
WINDS. SEAS AND WINDS WILL GRADUALLY SUBSIDE THIS AFTERNOON AND
REMAIN AT 4-7 FT THROUGH MONDAY. GUSTY NORTHWESTERLY WINDS THROUGH
THE STRAIT OF GEORGIA THIS MORNING MAY LEAD TO OCCASIONAL 21 KT OR
GREATER GUSTS OVER THE NORTHERN INTERIOR WATERS. THESE GUSTS ARE
EXPECTED FROM THE SAN JUAN ISLANDS NORTH TO POINT ROBERTS.
MOREOVER, WITH HIGH PRESSURE STRENGTHENING OVER THE WATERS EARLY
NEXT WEEK, INCREASED NORTHERLY FLOW OVER THE COASTAL WATERS WILL
BRING ANOTHER CHANCE FOR SMALL CRAFT WINDS AND SEAS MONDAY THROUGH
MIDWEEK. LATEST PROBABILITIES RANGE BETWEEN 45-70% FOR WINDS 21 KT
OR GREATER. DIURNAL PUSHES THROUGH THE STRAIT OF JUAN DE FUCA WILL
CONTINUE INTO LATE NEXT WEEK. LATEST GUIDANCE SUGGESTS THAT THE BEST
CHANCES FOR FOR SMALL CRAFT WINDS WILL BE WEDNESDAY AND THURSDAY. ON
WEDNESDAY THERE IS A 65-85% CHANCE FOR SMALL CRAFT WINDS AND A
SLIGHT CHANCE (25-35%) OF GALES. THE PUSH ON THURSDAY WILL BE
SLIGHTLY WEAKER, BUT THERE IS MODERATE TO HIGH CONFIDENCE (55-70%)
FOR SMALL CRAFT WINDS, IN ADDITION TO A SLIGHT CHANCE (15-25%) FOR
GALES.
29
FIRE WEATHER
HOT AND DRY WEATHER RETURNS IN EARNEST FOR THE FIRST HALF OF
NEXT WEEK, WITH MINIMUM RELATIVE HUMIDITY VALUES DROPPING INTO
THE 20 PERCENT RANGE OR LESS THROUGH TUESDAY IN THE SOUTH
INTERIOR AND CASCADE VALLEYS. A THERMAL TROUGH DEVELOPING
SLIGHTLY INLAND FROM THE IMMEDIATE COAST ON MONDAY AND TUESDAY
LENDS ITSELF TO A CONDITIONALLY UNSTABLE ATMOSPHERE EARLY IN THE
WEEK. AREA FUELS ARE GETTING MUCH CLOSER TO CRITICAL LEVELS AS
ADDITIONAL WAVES OF HOT AND DRY WEATHER CONTINUES. GRASSES ARE
CURING EXPEDITIOUSLY AND HAVE ALREADY CONTRIBUTED TO A NUMBER OF
ROADSIDE BRUSH FIRES IN RECENT DAYS. PLEASE CONTINUE TO EXERCISE
CAUTION WITH IGNITION SOURCES.
21
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 11 AM PDT THIS MORNING 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 11 PM PDT THIS EVENING 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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