288
FXUS66 KSEW 210952
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
252 AM PDT SUN JUN 21 2026
SYNOPSIS
A BUILDING UPPER LEVEL RIDGE WILL BRING A RETURN OF WARMER
TEMPERATURES AND CONTINUED DRY CONDITIONS. THE DRY CONDITIONS
WILL ELEVATE FIRE WEATHER CONCERNS THROUGH MIDWEEK. THE RIDGE
WILL WEAKEN LATE THIS WEEK AND A FRONTAL SYSTEM IS EXPECTED TO
BRING COOLER TEMPERATURES AND MEASURABLE PRECIPITATION TO MOST
OF THE AREA BY THE END OF WEEK.
SHORT TERM /TODAY THROUGH TUESDAY/
ONSHORE FLOW IS WEAKENING ACROSS THE AREA EARLY THIS MORNING. AS
A RESULT, LOW CLOUD COVERAGE WILL BE LESS EXTENSIVE ACROSS THE
INTERIOR AND WILL BURN BACK TO THE COAST EARLIER THAN YESTERDAY.
THIS ALONG WITH AN UPPER RIDGE REBUILDING BACK INTO THE REGION
WILL GIVE HIGH TEMPERATURES ACROSS WESTERN WASHINGTON A NUDGE
UPWARD SEVERAL DEGREES THIS AFTERNOON. THE WARMING TREND KICKS
INTO HIGH GEAR ON MONDAY AS 500 MILLIBAR HEIGHTS APPROACH THE
580 DECAMETER THRESHOLD AND THERMALLY INDUCED LOW PRESSURE AT
THE SURFACE EXPANDS INTO THE REGION. MUCH LIKE YESTERDAY, MOST
OF THE MODELS KEEP THE AXIS OF THE THERMAL TROUGH OVER THE
INTERIOR WITH LIGHT ONSHORE GRADIENTS. THE 50TH PERCENTILE NBM
USED IN THE FORECAST LARGELY REMAINS DISCONNECTED FROM THIS FACT
AND CONTINUES TO SUGGEST WARMER TEMPERATURES FOR THE COAST THAN
WHAT ARE LIKELY TO OCCUR FOR BOTH MONDAY AND TUESDAY. AS FOR
THE INTERIOR, IT'LL WARM WELL INTO THE 80S AWAY FROM THE WATER
BOTH MONDAY AND TUESDAY WITH SOME LOCATIONS IN THE SOUTHWEST
INTERIOR GETTING INTO THE LOWER 90S. MODERATE HEATRISK IS
EXPECTED DURING THIS TIME FOR MOST OF THE INTERIOR LOWLANDS AND
A HEAT ADVISORY REMAINS IN EFFECT BEGINNING MIDDAY MONDAY.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
THE THERMAL TROUGH SHIFTS EAST OF THE CASCADES BY TUESDAY NIGHT
INDUCING A PRETTY GOOD ONSHORE PUSH. AS IT OFTEN DOES, THE NBM
DOES NOT ADEQUATELY WEIGH THE COOLING EFFECT THIS WILL HAVE AND
IS LIKELY AROUND 10 DEGREES TOO WARM FOR SEATTLE METRO AND OTHER
INTERIOR LOCATIONS ON WEDNESDAY AFTERNOON.
THE UPPER RIDGE FLATTENS AND WEAKENS WEDNESDAY INTO THURSDAY
SETTING THE STAGE FOR THE PREVIOUSLY ADVERTISED ARRIVAL OF SOME
PRECIPITATION AT THE CONCLUSION OF THE WEEK. ENSEMBLES ARE IN
GOOD AGREEMENT THAT MOST OF THE AREA WILL SEE SOME MEASURABLE
PRECIPITATION BY LATER FRIDAY INTO SATURDAY AS AN UPPER TROUGH
AND ASSOCIATED FRONT REACH THE AREA. WE'RE LIKELY TO SEE
SEVERAL CONSECUTIVE DAYS OF BELOW NORMAL TEMPERATURES AS
WELL...SOMETHING WE HAVEN'T EXPERIENCED IN A COUPLE WEEKS.
27
AVIATION
VFR ACROSS THE MAJORITY OF TERMINALS, WITH THE EXCEPTION OF THE
COAST, WHERE IT IS MVFR DUE TO MARINE STRATUS. WITH A WEAKER ONSHORE
PUSH, PROBABILITIES FOR MVFR CIGS ACROSS THE INTERIOR TERMINALS HAS
GENERALLY BEEN TRENDING DOWNWARDS FOR THE MAJORITY TERMINALS, WITH
CURRENT PROBABILITIES AT 20% OR LESS. HOWEVER, GUIDANCE DOES
HIGHLIGHT MODERATE CONFIDENCE (50-65%) FOR MVFR CIGS FOR THE KITSAP
PENINSULA AND STRAIT OF JUAN DE FUCA BETWEEN 10Z-19Z. IN ADDITION,
THERE'S A CHANCE FOR IFR AND LIFR CIGS AT THESE TWO LOCATIONS; IFR
CHANCES RANGE BETWEEN 40-60% AND LIFR BETWEEN 30-40%. THERE'S ALSO A
CHANCE FOR IFR/LIFR CIGS ALONG THE COAST, BUT PROBABILITIES ARE
TRENDING LOWER AROUND 20-35%. IMPROVEMENT FOR THE AFFECTED TERMINALS
IS EXPECTED AFTER 18Z-19Z. ANOTHER ROUND OF MVFR CIGS POSSIBLE
TONIGHT/MONDAY MORNING. LATEST GUIDANCE SUGGESTS A 60-80% CHANCE FOR
THE COASTLINE AFTER 03Z AND A 30-50% CHANCE OF IFR CIGS AFTER 07Z.
AS FOR THE INTERIOR TERMINALS, CURRENT PROBABILITIES ARE 20% OR LESS
FOR MVFR CIGS. SOUTHERLY SURFACE WINDS THIS MORNING WILL THEN
TRANSITION TO THE NORTH AFTER 17Z-20Z AT 5-10 KT.
KSEA...VFR EARLY THIS MORNING. TODAY'S WEAKER ONSHORE PUSH DOES
HIGHLIGHT THE UNCERTAINTY OF WHETHER THE MARINE STRATUS WILL MAKE IT
TO THE TERMINAL THIS MORNING. CHANCES FOR MVFR CIGS CONTINUE TO
TREND DOWNWARDS, NOW SITTING AROUND 20% BETWEEN 12Z-18Z. OTHERWISE,
VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. SOUTHWESTERLY
WINDS 4-7 KT THIS MORNING, THEN NORTHWESTERLY AFTER 18Z-20Z AT 7-10
KT. NORTHEASTERLY WINDS THIS EVENING 5-8 KT.
29
MARINE
HIGH PRESSURE WILL STRENGTHEN OVER AREA WATERS THROUGH THE MIDDLE OF
THE WEEK. THIS WILL RESULT IN DIURNAL PUSHES THROUGH THE STRAIT OF
JUAN DE FUCA. LATEST GUIDANCE SUGGESTS THE STRONGEST PUSH WILL BE ON
WEDNESDAY. THERE IS INCREASING CONFIDENCE (75-95%) FOR HIGH-END
SMALL CRAFT WINDS THROUGH THE STRAIT. ADDITIONALLY, PROBABILITIES
FOR GALES SLIGHTLY INCREASED TO 25-40%. A WEAKER PUSH OF WESTERLIES
IS EXPECTED ON THURSDAY, WITH A 55-70% CHANCE OF SMALL CRAFT WINDS
AND 15-25% CHANCE FOR GALES. UNSETTLED CONDITIONS RETURN LATE IN THE
WEEK AND HIGH PRESSURE WILL WEAKEN THURSDAY/FRIDAY AS A FRONTAL
SYSTEM MOVES OVER AREA WATERS. HIGH PRESSURE LOOKS TO QUICKLY
REBUILD BEHIND THE FRONT.
COMBINED SEAS BELOW 10 FEET THROUGH EARLY NEXT WEEK. SEAS WILL BEGIN
TO BUILD LATE TUESDAY INTO WEDNESDAY TO 7-10 FT, DECREASING BELOW 10
FT BY THURSDAY. IN ADDITION, SEAS MAY GET STEEP AT TIMES LATE SUNDAY
THROUGH WEDNESDAY OVER SOME PORTIONS OF THE COASTAL WATERS WITH SEAS
HOVERING AROUND 7-9 FT AND A DOMINANT PERIOD AROUND 7-8 SECONDS.
29
FIRE WEATHER
HOT AND DRY WEATHER RETURNS IN EARNEST FOR THE FIRST HALF OF
THE 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.
SEW WATCHES/WARNINGS/ADVISORIES
WA...HEAT ADVISORY FROM 11 AM MONDAY TO 11 PM PDT TUESDAY FOR
EASTERN STRAIT OF JUAN DE FUCA-FOOTHILLS AND VALLEYS OF
THURSTON AND LEWIS COUNTIES-FOOTHILLS AND VALLEYS OF THE
NORTH CASCADES-FOOTHILLS OF THE WESTERN AND SOUTHERN
OLYMPIC PENINSULA-ISLAND COUNTY-LOWER CHEHALIS RIVER
VALLEY-LOWLANDS OF LEWIS AND SOUTHERN THURSTON COUNTIES-
LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN SNOHOMISH
COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-MIDDLE
CHEHALIS RIVER VALLEY-NORTHERN HOOD CANAL-OLYMPIA AND
SOUTHERN PUGET SOUND-PORT TOWNSEND AREA-SAN JUAN COUNTY-
SOUTHERN HOOD CANAL-WILLAPA AND BLACK HILLS.
HEAT ADVISORY FROM 11 AM MONDAY TO 11 PM PDT WEDNESDAY FOR
CITY OF SEATTLE-DOWNTOWN EVERETT / MARYSVILLE AREA-
EASTERN KITSAP COUNTY-EASTSIDE-FOOTHILLS AND VALLEYS OF
CENTRAL KING COUNTY-FOOTHILLS AND VALLEYS OF PIERCE AND
SOUTHERN KING COUNTIES-FOOTHILLS AND VALLEYS OF SNOHOMISH
AND NORTHERN KING COUNTIES-LOWLANDS OF PIERCE AND
SOUTHERN KING COUNTIES-SHORELINE / LYNNWOOD / SOUTH
EVERETT AREA.
PZ...NONE.
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