688
FXUS66 KSEW 270405
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
905 PM PDT FRI JUN 26 2026
UPDATE
LATEST RADAR IMAGERY SHOWS THE CONVERGENCE ZONE
FORMING OVER THE NORTH END OF THE PUGET SOUND. WINDS HAVE
STARTED TO SLACK FOR THE NIGHT, BUT CAN BE ELEVATED DUE TO THE
RAIN SHOWER ACTIVITY. RAIN SHOWER ACTIVITY WILL SLOWLY MOVE
NORTHEAST THROUGH THE NIGHT INTO THE NORTH CASCADES. THE ZONE
WILL STAY AROUND THROUGH THE EARLY MORNING AND THEN CLEARING.
OTHERWISE, THE MAIN 7 DAY FORECAST IS ON TRACK. AVIATION
DISCUSSION HAS BEEN UPDATED. SEE PREVIOUS DISCUSSION BELOW
SYNOPSIS
AN ELONGATED UPPER-LEVEL LOW OFFSHORE SE AK TO VANCOUVER ISLAND
WILL CONSOLIDATE AND EVOLVE TO BE OFFSHORE THE WA COAST TONIGHT.
ITS ATTENDANT SURFACE LOW WILL BE WEAKENING AS IT EVOLVES EAST
INTO BC WITH A BROADER LOW DEVELOPING NEAR THE NORTHERN
CONTINENTAL DIVIDE. THIS UPPER-LEVEL LOW WILL SETTLE IN THE
WESTERN CONUS THIS WEEKEND WITH SLOW EASTWARD MOVEMENT ACROSS
THE PACIFIC NW-NORTHERN ROCKIES WITH THE JET STREAM SOUTH OF WA.
MEANWHILE, STRENGTHENING UPPER-LEVEL HIGH PRESSURE WILL BUILD
SATURDAY-SUNDAY IN THE EASTERN NORTH PACIFIC WITH A BUILDING
SURFACE HIGH IN THE OFFSHORE WATERS. THIS AMPLIFIED PATTERN IS
EXPECTED TO PERSIST WITH RIDGING WEST AND TROUGHING EAST BEFORE
THE NEXT UPPER-LEVEL DISTURBANCE DROPS SOUTHWARD INTO WA LATE
WEDNESDAY-THURSDAY.
SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/
PREVIOUS DISCUSSION:
LATEST DAY CLOUD PHASE RGB SHOWS A FEW AREAS OF CLUMPING-
AGITATED CU WITH EVIDENCE OF GLACIATING CLOUD TOPS ACROSS
NORTHERN INTERIOR, MORE SCARCE SOUTH OVER KING AND PIERCE
COUNTY. LATEST WATER VAPOR IMAGERY SHOWS MULTIPLE EMBEDDED
DISTURBANCE WITH THE COMPLEX LOW OFFSHORE BC WITH ITS PRIMARY
SHORTWAVE ROTATING EASTWARD OVER VANCOUVER ISLAND AND ANOTHER
MOVING IN SOUTHEAST OR. PRIMARY CONCERNS REVOLVE AROUND
LIGHTNING RISK THIS EVENING.
LATEST WOFS RUNS CONTINUE TO SUPPORT A LOW NON-ZERO CHANCE THAT
BEARS WATCHING WITH RESPECT TO LIGHTNING. THIS COULD BE
ATTRIBUTABLE TO A NORTHERLY DEVELOPING CONVERGENCE ZONE FOCUSED
WESTERN SKAGIT AND WHATCOM BEFORE DRIFTING SOUTH AFTER 00-03Z
TODAY INTO WESTERN SNOHOMISH. THIS FORCING AND ENHANCED LIFT
WILL COMBINE WITH MARGINAL INSTABILITY WITH MUCAPES PER REFS AND
HREF AROUND 200-300 J/KG IN THE WESTERN INTERIOR. LATEST WOFS
SHOW A LOW FLASH EXTENT DENSITY SIGNAL BASED ON THE 90TH %TILE
AND ENS MAX FORECASTS ACROSS WHATCOM AND SKAGIT THROUGH ITS RUN
ENDING AT 01Z. WOFS ENS MAX SHOWS A FEW SIMULATED STORMS
FORECASTING LIGHTNING ALONG THE WESTERN SLOPES OF THE
CENTRAL/NORTHERN WA CASCADES, ALBEIT LOWER CHANCE/”WORST CASE.”
ANY LIGHTNING IS EXPECTED TO BE INFREQUENT WITH ALL NEIGHBORHOOD
PROBABILITIES SHOWING SCANT CHANCES FOR GREATER THAN > 10
FLASHES. THUS THE MAIN THREAT IS INFREQUENT CG STRIKES, LIKELY
SPORADIC AND ISOLATED FROM AN EMBEDDED STORM, WITH THE LARGER
NEIGHBORHOOD EMPHASIZING WHATCOM AND SKAGIT. THIS SCENARIO IS
BOLSTERED BY LOW 3-HR NBM POT THUNDER (10-15%) AND THE MEAGER
REFS LIGHTNING DENSITY PROB ACROSS THE AFOREMENTIONED NORTHERN
INTERIOR. NSE-WISE, VERY SHALLOW INSTABILITY WITH LIMITED
QUANTITY, IF ANY, TAPPING INTO -10C BASED ON FORECAST SOUNDINGS.
AS SUCH, INCREASED CONFIDENCE IN AN ISOLATED, INFREQUENT
LIGHTNING OUTCOME. WITH LOSS OF DAYTIME HEATING, THREAT FOR
LIGHTNING SHOULD DECLINE AFTER 2-4Z OVER TIME.
OTHERWISE, LARGELY LIGHT PRECIP IS EXPECTED FOR THE
CENTRAL/SOUTH SOUND AND SOUTHERN INTERIOR WITH GREATEST CHANCES
FOR HALF INCH OR MORE FROM REPEATED SHOWERS ACROSS THE OLYMPICS
AND NORTHERN INTERIOR/EVERETT NORTH, AND WEST SLOPES. OF WHICH,
HREF AND REFS LPMM SUPPORT 24-HR TOTALS EXCEEDING 1 INCH IN THE
OLYMPIC PARK AND SLOPES OF THE SNOHOMISH-WHATCOM. 10-20% CHANCE
FOR MORE THAN 1.5” IN ISOLATED SPOTS OF THE HIGHER TERRAIN. A
LARGELY DRYING TREND WILL THEN TAKE HOLD OUTSIDE LOW MOUNTAIN
PRECIP CHANCES THIS WEEKEND AS THE UPPER-LEVEL LOW EVOLVES THE
NORTHWEST CONUS INTO MT. THIS WILL KEEP HIGHS COOLER THAN
NORMAL, GENERALLY READING 4 TO 8 BELOW, WITH LARGELY AVERAGE
HIGHS OUTSIDE THE EASTERN OLYMPICS.
ET
LONG TERM /MONDAY THROUGH FRIDAY/
THE LARGE SCALE PATTERN EARLY MONDAY WILL BE CHARACTERIZED BY A
DEEP UPPER-LEVEL LOW OVER THE NORTHERN HIGH PLAINS AND AMPLIFIED
TROUGH OVER THE WESTERN CONUS WITH AMPLIFIED RIDGE OVER THE
EASTERN NORTH PACIFIC. THIS UNSETTLED COOL PATTERN WILL KEEP
PERIODIC MOUNTAIN PRECIP CHANCE WITH DRIER CONDITIONS LARGELY
OVER THE LOWLANDS/INTERIOR WITH LIMITED CHANGE IN HIGHS AND
LOWS. CONFIDENCE GROWING WITH THE NEXT UPPER-LEVEL TROUGH DIVING
SOUTHEASTWARD INTO THE REGION AROUND THURSDAY BASED ON THE
CLUSTER TOOL (CONFIDENCE 80%). THIS WILL SPREAD PRECIPITATION
ACROSS THE LOWLANDS AND MOUNTAINS, AND PROMOTE A SLIGHT UPTICK
IN HIGHS, ALBEIT STILL READING BELOW NORMAL. LATEST NBM PROBS
SHOW MODEST CHANCES FOR 24-HR QPF GREATER THAN 0.5 INCHES ACROSS
THE OLYMPICS AND CENTRAL/NORTHERN CASCADES ENDING FRIDAY (30% OR
MORE).
ET
AVIATION
RAIN SHOWER ACTIVITY HAS DEVELOPED IN THE CONVERGENT ZONE BY
EVERETT. SHOWERS WILL CONTINUE TO MOVE NORTHEAST TOWARDS THE
CASCADES WITH THE CONVERGENCE ZONE LINGERING UNTIL 15Z SATURDAY
PER THE LATEST HI-RES MODELS. MVFR CHANCES ARE 40-70% CHANCES
WIDE WITH THE COASTAL TERMINALS HAVING 10-40% OF IFR CONDITIONS.
CONDITIONS ARE EXPECTED TO IMPROVE TO MVFR AND THEN VFR
STARTING AT LEAST 17Z. SOUTHERLY WINDS WILL CONTINUE ALONG
PUGET SOUND TERMINALS AND THE COAST, WITH SPEEDS 8-12 KT.
NORTHERLY TO VARIABLE WINDS EXPECTED WITHIN CONVERGENCE ZONE
ACTIVITY.
KSEA...VFR CONDITIONS FOR THE LATE NIGHT AND BECOMING MVFR IN
THE EARLY MORNING. SLIGHT CHANCE (<15%) FOR RAIN SHOWERS BETWEEN
06Z AND 10Z DUE TO THE PROXIMITY OF THE CONVERGENCE ZONE. MODELS
SHOW THE CONVERGENCE ZONE STAYING WELL NORTH OF THE TERMINAL.
THERE ARE HIGHER CHANCES (40-60%) FOR MVFR CONDITIONS BETWEEN
9-17Z THERE IS A SLIGHT CHANCE OF IFR CIGS BETWEEN 12Z-16Z.
IMPROVEMENT TO VFR EXPECTED IN THE AFTERNOON. SOUTHERLY TO
SOUTH-SOUTHWESTERLY WINDS THROUGH THE FORECAST PERIOD.
MARINE
A COLD FRONT CONTINUES TO PUSH INLAND, BRINGING BREEZY WINDS TO
PUGET SOUND AND THE CENTRAL AND EAST PORTIONS OF THE STRAIT. A SMALL
CRAFT ADVISORY CONTINUES FOR THESE LOCATIONS. BROAD HIGH PRESSURE
OVER THE NORTHEAST PACIFIC WILL STARTING BUILDING EASTWARD INTO
WASHINGTON'S WATERS ON SATURDAY. THE DOMINANT WEATHER FEATURE
THROUGH THE MIDDLE OF THE WEEK WILL BE HIGH PRESSURE OVER AREA
WATERS. THIS WILL BRING INCREASED NORTHERLY FLOW OVER THE COASTAL
WATERS WITH INCREASED CHANCES (70-95%) FOR SMALL CRAFT WINDS,
PARTICULARLY OVER THE OUTER COASTAL WATERS. WITH THE PROLONGED
NORTHERLY WINDS OVER THE COASTAL WATERS, SEAS WILL BUILD TO 10-15 FT
THROUGH TUESDAY. A SMALL CRAFT ADVISORY IS SET TO GO INTO EFFECT
SATURDAY AFTERNOON AND WILL LIKELY BE EXTENDED INTO NEXT WEEK. HIGH
PRESSURE WILL WEAKEN ON WEDNESDAY AND SEAS WILL GRADUALLY DECREASE
ON TO 8-11 FT AND LOOK TO FALL BELOW 10 FT IN THE AFTERNOON/EVENING.
IN ADDITION, WEAK HIGH PRESSURE WILL ALSO BRING DIURNAL WESTERLY
PUSHES THROUGH THE STRAIT OF JUAN DE FUCA. LATEST GUIDANCE SUGGESTS
A STRONG PUSH WILL OCCUR SATURDAY EVENING AND LINGER INTO SUNDAY
MORNING, WITH THE LATEST GUIDANCE AT 70-85% CHANCE OF SMALL CRAFT
WINDS.
FIRE WEATHER
LOW CONCERNS OVERALL WITH THREAT TIED TO LOW-END INFREQUENT CG
LIGHTNING POTENTIAL. GREATEST RISK ACROSS WEST SLOPES OF THE
NORTHERN WA CASCADES AND WHATCOM-SKAGIT COUNTIES AS A
CONVERGENCE ZONE SETS UP AND DRIFTS SOUTH EARLY THIS EVENING
INTO SNOHOMISH. OVERALL CONFIDENCE IN OCCURRENCE IS LOW
(10-15%). THREAT WOULD BE TIED TO ANY AREAS THAT DON'T RECEIVE
WETTING RAINS. COOL AND UNSETTLED CONDITIONS CONTINUE TOMORROW.
OVERALL SCANT CONCERNS GOING FORWARD WITH LITTLE LIGHTNING RISK
AND HIGH AFTERNOON HUMIDITY.
ET
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT SATURDAY FOR CENTRAL U.S.
WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 2 PM SATURDAY TO 5 PM PDT SUNDAY 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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