701
FXUS66 KSEW 211729
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1029 AM PDT TUE JUL 21 2026
SYNOPSIS
AN UPPER LEVEL RIDGE IS CENTERED WELL TO THE SOUTHEAST OF THE
AREA EXTENDING BACK OVER WESTERN WASHINGTON THROUGH WEDNESDAY.
SOUTHWESTERLY FLOW ALOFT CONTINUES WITH HIGH CLOUDS MOVING
THROUGH AT TIMES. IN THE LOWER LEVELS, LIGHT FLOW CONTINUES
WITH A THERMALLY INDUCED SURFACE TROUGH BOUNCING BACK AND FORTH
BETWEEN THE COAST AND THE INTERIOR. A PATTERN CHANGE ARRIVES
WEDNESDAY NIGHT INTO THURSDAY WITH SHOWER CHANCES INCREASING AND
SOME POTENTIAL FOR THUNDERSTORMS. AN UPPER LEVEL TROUGH MOVES
OVER WESTERN WASHINGTON WITH LOW LEVEL ONSHORE FLOW FRIDAY
THROUGH THE FIRST PART OF NEXT WEEK FOR A ROUND OF SEASONABLE
TEMPERATURES.
SHORT TERM /TODAY THROUGH THURSDAY/
SATELLITE IMAGERY SHOWS HIGH CLOUDS OVER MOST OF THE AREA EARLY
THIS MORNING WITH PATCHY LOW CLOUDS AND FOG ALONG THE COAST.
HIGH CLOUDS KEEPING TEMPERATURES MILD OVERNIGHT WITH MOST PLACES
IN THE LOWER TO MID 60S AT 3 AM/10Z.
UPPER LEVEL RIDGE CENTERED WELL TO THE SOUTHEAST EXTENDING BACK
OVER WESTERN WASHINGTON THROUGH WEDNESDAY. SOUTHWESTERLY FLOW
ALOFT SENDING HIGH CLOUDS THROUGH THE AREA AT TIMES. THERMALLY
INDUCED SURFACE TROUGH ALONG THE COAST THIS MORNING WILL SHIFT
INLAND THIS AFTERNOON, RETREAT BACK TO THE COAST TONIGHT THEN
MOVE INLAND AGAIN WEDNESDAY AFTERNOON. TEMPERATURES ALOFT
WARMING WITH THE 850 MB TEMPERATURES PEAKING IN THE PLUS 22C TO
24C RANGE WEDNESDAY AFTERNOON. ALL THIS ADDS UP TO A PAIR OF
HOT DAYS FOR WESTERN WASHINGTON WITH NEAR RECORD BREAKING HIGH
TEMPERATURES AND MAXIMUM LOW TEMPERATURES. HIGHS TODAY IN 80S TO
MID 90S OVER THE INTERIOR WARMING A COUPLE OF DEGREES WEDNESDAY
INTO THE MID 80S TO NEAR 100. HIGHS ON THE COAST IN THE MID 70S
TO MID 80S BOTH DAYS. LOWS IN THE LOWER TO MID 60S INLAND AND
MID 50S ALONG THE COAST.
A HEAT ADVISORY WILL GO INTO EFFECT THIS MORNING AT 10 AM/17Z
AND REMAIN IN EFFECT UNTIL AT LEAST 11 PM WEDNESDAY EVENING.
IN ADDITION TO THE HEAT, NORTHERLY FLOW AT TIMES WILL PULL
WILDFIRE SMOKE FROM BRITISH COLUMBIA INTO WHATCOM AND SKAGIT
COUNTIES. AN AIR QUALITY ALERT HAS BEEN ISSUED BY THE NORTHWEST
CLEAN AIR AGENCY. WEAK EASTERLY FLOW TODAY WILL ALSO BRING
WILDFIRE SMOKE FROM EASTERN WASHINGTON WEST OF THE CREST. WHILE
INCOMING WILDFIRE SMOKE MAY CAUSE LOCALIZED DEGRADATIONS IN AIR
QUALITY AT TIMES OVER THE MOUNTAINS, THE SMOKE IS NOT EXPECTED
TO MIX DOWN INTO THE LOWER LEVELS AND IS FAVORED TO STAY EAST OF
THE SEATTLE METRO.
CHANGES IN THE PATTERN WEDNESDAY NIGHT INTO THURSDAY WITH
REMNANTS OF TROPICAL STORM ELIDA MOVING THROUGH THURSDAY
MORNING CREATING A CHANCE OF SHOWERS. IN ADDITION TO THE
POSSIBLE SHOWERS LOW LEVEL FLOW TURNING ONSHORE PRODUCING MUCH
COOLER HIGH TEMPERATURES. AFTER LOWS IN THE LOWER TO MID 60S
AGAIN THURSDAY MORNING FOR THE INTERIOR HIGHS COOLING TO THE
70S AND LOWER 80S. FOR THE COAST, LOWS IN THE MID 50S AND HIGHS
IN THE MID 60S.
THE RETURN OF LOW LEVEL ONSHORE FLOW WILL GET RID OF ANY SMOKE
CONCERNS IN THE LOWER LEVELS. FELTON
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
WEAK UPPER LEVEL LOW THAT IS WHAT WILL BE LEFT OF ELIDA
REMAINING OFFSHORE THURSDAY NIGHT THROUGH FRIDAY NIGHT WITH LOW
LEVEL ONSHORE FLOW. UPPER LEVEL LOW WEAKENING INTO AN UPPER
LEVEL TROUGH AND MOVING THROUGH WESTERN WASHINGTON SATURDAY.
ANOTHER CHANCE FOR SHOWERS AS THE TROUGH MOVES THROUGH THE AREA.
WEAK UPPER LEVEL TROFINESS WITH LOW LEVEL ONSHORE FLOW
CONTINUING SUNDAY AND MONDAY. SEASONABLE TEMPERATURES THROUGH
THE PERIOD WITH HIGHS IN THE 60S ON THE COAST AND 70S INLAND.
LOWS IN THE 50S. FELTON
AVIATION
HIGH PRESSURE ACROSS THE REGION MAINTAINS DRY CONDITIONS. VFR
CONDITIONS CONTINUE ACROSS THE REGION WITH JUST PASSING HIGH
CLOUDS AREA-WIDE AND SOME LINGERING LOW CLOUDS JUST OFFSHORE.
EMBEDDED WILDFIRE SMOKE ALOFT ACROSS PORTIONS OF THE REGION MAY
CONTINUE TO LIMIT BOTH HORIZONTAL AND SLANT-RANGE VISIBILITY
THROUGH EARLY WEDNESDAY.
KSEA...VFR CONDITIONS CONTINUE WITH VARIABLE HIGH CLOUDS WITH
SOME ENTRAINED SMOKE ABOVE THE SURFACE. NO SIGNIFICANT
CEILING/VISIBILITY ISSUES EXPECTED THROUGH THE PERIOD. NORTHERLY
SURFACE WINDS AROUND 5 KT THIS MORNING INCREASING TO 7-8 KT THIS
AFTERNOON AND EVENING.
MARINE
STRONG HIGH PRESSURE IS OFFSHORE WITH A THERMAL TROUGH ALONG
THE WA COAST. OVERALL WINDS ARE GENERALLY LIGHT ACROSS WESTERN
WA WITH SEAS UNDER 6 FT. THE THERMAL TROUGH WILL SHIFT INLAND
WEDNESDAY AND THURSDAY WITH STRONG ONSHORE PUSHES EXPECTED
THROUGH THE STRAIT OF JUAN DE FUCA. 33
FIRE WEATHER
ELEVATED FIRE WEATHER CONCERNS THE NEXT TWO DAYS WITH NEAR
RECORD HIGH TEMPERATURES AND VERY DRY CONDITIONS ESPECIALLY IN
THE AFTERNOON HOURS. MINIMUM RELATIVE HUMIDITIES WILL FALL AS
LOW AS 20% TO 30% BOTH TUESDAY AND WEDNESDAY, WITH DRIER
LOCATIONS ACROSS THE SOUTHERN PUGET SOUND POTENTIALLY BOTTOMING
OUT IN THE TEENS. THERE IS A VERY SLIGHT CHANCE OF
THUNDERSTORMS COMING IN FROM THE SOUTH THURSDAY MORNING WHICH
GIVEN THE WARM AND DRY CONDITIONS COULD CAUSE ADDITIONAL
IGNITIONS FROM LIGHTNING. ONSHORE FLOW WILL INCREASE LATER
THURSDAY BRINGING COOLER TEMPERATURES AND BETTER OVERNIGHT RH
RECOVERIES THROUGH THE WEEKEND INTO THE FIRST PART OF NEXT WEEK
EASING FIRE WEATHER CONCERNS. FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...AIR QUALITY ALERT UNTIL 9 AM PDT WEDNESDAY FOR CASCADES OF
WHATCOM AND SKAGIT COUNTIES-FOOTHILLS AND VALLEYS OF THE
NORTH CASCADES-LOWLANDS OF WESTERN SKAGIT AND
NORTHWESTERN SNOHOMISH COUNTIES-LOWLANDS OF WESTERN
WHATCOM COUNTY.
HEAT ADVISORY UNTIL 11 PM PDT WEDNESDAY FOR CITY OF SEATTLE-
DOWNTOWN EVERETT / MARYSVILLE AREA-EASTERN KITSAP COUNTY-
EASTERN STRAIT OF JUAN DE FUCA-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-FOOTHILLS AND
VALLEYS OF THURSTON AND LEWIS COUNTIES-FOOTHILLS AND
VALLEYS OF THE NORTH CASCADES-FOOTHILLS OF THE WESTERN
AND SOUTHERN OLYMPIC PENINSULA-LAKE CRESCENT AREA
INCLUDING US 101-LOWLANDS OF LEWIS AND SOUTHERN THURSTON
COUNTIES-LOWLANDS OF PIERCE AND SOUTHERN KING 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-SHORELINE /
LYNNWOOD / SOUTH EVERETT AREA-SOUTHERN HOOD CANAL.
PZ...NONE.
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