680
FXUS66 KSEW 201704
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1004 AM PDT MON JUL 20 2026
SYNOPSIS
UPPER LEVEL RIDGE CENTERED WELL TO THE SOUTHEAST EXTENDING BACK
OVER WESTERN WASHINGTON THROUGH WEDNESDAY. SOUTHWESTERLY FLOW
ALOFT WITH HIGH CLOUDS MOVING THROUGH AT TIMES. IN THE LOWER
LEVELS LIGHT FLOW WITH A THERMALLY INDUCED SURFACE TROUGH
BOUNCING BACK AND FORTH BETWEEN THE COAST AND THE INTERIOR.
PATTERN CHANGE WEDNESDAY NIGHT INTO THURSDAY WITH THE REMNANTS
OF TROPICAL STORM ELIDA MOVING THROUGH PRODUCING A CHANCE OF
SHOWERS. UPPER LEVEL TROUGH OVER WESTERN WASHINGTON WITH LOW
LEVEL ONSHORE FLOW FRIDAY THROUGH THE WEEKEND FOR A ROUND OF
SEASONABLE TEMPERATURES.
SHORT TERM /TODAY THROUGH WEDNESDAY/
THE LATEST FORECAST REMAINS ON TRACK THIS MORNING WITH NO
UPDATES. UPPER LEVEL RIDGE CENTERED WELL TO THE SOUTHEAST
EXTENDING BACK OVER WESTERN WASHINGTON THROUGH WEDNESDAY. 500 MB
HEIGHTS IN THE MID TO UPPER 580 DMS. IN THE LOWER LEVELS
THERMALLY INDUCED SURFACE TROUGH DEVELOPING OVER THE AREA TODAY.
THE TROUGH WILL BOUNCE BACK AND FORTH BETWEEN THE COAST AND THE
INTERIOR THROUGH WEDNESDAY RETREATING BACK TO THE COAST IN THE
OVERNIGHT HOURS AND MOVING INLAND DURING THE DAYTIME. MODEL 850
MB TEMPERATURES IN THE PLUS 16C TO PLUS 20C RANGE TODAY SLOWLY
WARMING TO PLUS 22C TO PLUS 24C WEDNESDAY AFTERNOON. WARMING
TREND THE NEXT THREE DAYS OVER THE INTERIOR. HIGHS TODAY IN THE
80S, 80S TO LOWER 90S TUESDAY AND 80S TO MID 90S WEDNESDAY.
ALONG THE COAST WITH THE THERMALLY INDUCED SURFACE TROUGH
DRIFTING INLAND DURING THE DAY HIGHS IN THE MID 70S TO LOWER 80S
TODAY AND TUESDAY. A LITTLE COOLER WEDNESDAY WITH THE THERMALLY
INDUCED TROUGH INLAND, IN THE 70S.
A HEAT ADVISORY HAS ALREADY BEEN ISSUED FOR TUESDAY MORNING
THROUGH WEDNESDAY EVENING. IN ADDITION TO THE VERY WARM DAYTIME
TEMPERATURES WITH HIGH CLOUDS MOVING THROUGH AT TIMES MORNING
LOWS WILL BE ELEVATED AS WELL, IN THE MID 50S TO MID 60S.
PROBABLY WILL NOT SET ANY RECORD HIGH MINIMUM TEMPERATURES (
SEATTLE RECORDS 66 TUESDAY AND 68 WEDNESDAY BOTH SET IN 2006 )
BUT IT WILL BE CLOSE.
WITH THE LOW LEVEL FLOW TURNING NORTHERLY AT TIMES THIS WILL
PULL DOWN SOME WILDFIRE SMOKE FROM CANADA THE NEXT THREE DAYS.
MOST OF THE SMOKE IS EXPECTED TO REMAIN A BIT ELEVATED KEEPING
AIR QUALITY FROM DETERIORATING TOO MUCH. THE EXCEPTION TO THIS
WILL BE NEAR THE CASCADE CREST IN THE CENTRAL AND NORTHERN
CASCADES WHERE OVERNIGHT EASTERLY WINDS COULD PULL IN THICKER
SMOKE FROM THE FIRES ALONG THE EAST SLOPES OF THE CASCADES.
HIGHS IN SEATTLE FORECASTED TO BE IN THE 90S BOTH TUESDAY AND
WEDNESDAY. THE LAST TIME SEATTLE DID NOT GET AT LEAST ONE 90
DEGREE PLUS DAY IN JULY WAS 2017 ( THERE WERE 5 90 DEGREE PLUS
DAYS IN AUGUST 2017 AND 2 MORE IN SEPTEMBER ). BEFORE THIS
CURRENT STREAK OF 8 JULYS IN A ROW WITH AT LEAST ONE 90 DEGREE
PLUS DAY THE LONGEST STREAK WAS ONLY 4 YEARS ( 1958-1961 AND
1970-1973 ).
FELTON
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
PATTERN CHANGE BEGINNING WEDNESDAY NIGHT INTO THURSDAY AS THE
REMNANTS OF TROPICAL STORM ELIDA APPROACH THE AREA OFFSHORE.
THURSDAY FORECAST HAS A LOT OF BUST POTENTIAL. ENSEMBLES STILL
SHOWING A FEW MEMBERS WITH THE MOISTURE FROM ELIDA MOVING OVER
WESTERN WASHINGTON THURSDAY PRODUCING SHOWERS. MORE ENSEMBLE
MEMBERS ARE IN THE CAMP THAT THIS WILL JUST BE SOME MIDDLE AND
HIGH LEVEL CLOUDS. EITHER WAY THE LOW LEVEL FLOW TURNS ONSHORE
RESULTING IN SOME COOLING. WILL GO WITH A BIT OF A COMBINATION
OF THE SOLUTIONS DROPPING HIGH TEMPERATURES 5 TO 10 DEGREES
THURSDAY ( WEAK MARINE PUSH SCENARIO ) WITH A SLIGHT CHANCE OF
SHOWERS. BETTER CONSISTENCY IN THE SOLUTIONS FRIDAY INTO THE
WEEKEND WITH UPPER LEVEL TROFINESS OVERHEAD AND LOW LEVEL
ONSHORE FLOW. MORNING CLOUDS AND AFTERNOON SUNSHINE FOR THE
INTERIOR FRIDAY THROUGH SUNDAY. HIGHS NEAR NORMAL, IN THE 70S
INTERIOR AND MID 60S COAST.
FELTON
AVIATION
SOUTHWEST FLOW ALOFT CONTINUES ACROSS THE PACIFIC NORTHWEST WITH
LIGHT NORTHERLY TO NORTHEASTERLY LOW LEVEL FLOW. MARINE STRATUS
HAS PUSHED BACK TO THE COASTLINE, LEAVING HIGH CLOUDS ACROSS THE
REGION. BROKEN TO OVERCAST HIGH CIRRUS WILL REMAIN ACROSS THE
REGION TODAY. INCREASING WILDFIRE SMOKE ACROSS NORTHWEST WA MAY
BEGIN TO LIMIT BOTH HORIZONTAL AND SLANT-RANGE VISIBILITY BY
THIS AFTERNOON. OTHERWISE, EXPECT A RETURN TO MARINE STRATUS
INTO THE IMMEDIATE COASTAL AREAS AGAIN TONIGHT.
KSEA...VFR CONDITIONS CONTINUE TODAY WITH BROKEN HIGH CLOUDS.
NORTH SURFACE WINDS 8-10 KT THIS AFTERNOON AND EVENING, EASING
OVERNIGHT.
MARINE
HIGH PRESSURE WILL REMAIN CENTERED OFFSHORE WITH LOWER PRESSURE
INLAND THROUGH THE WEEK. ONSHORE GRADIENTS WILL EASE THROUGH
THE EARLY PART OF THE WEEK AS THERMALLY-INDUCED LOW PRESSURE
DEVELOPS ACROSS WESTERN WASHINGTON AND OREGON. STRONGER ONSHORE
FLOW AND PUSHES DOWN THE STRAIT LOOK TO RESUME IN THE LATTER
HALF OF THE WEEK AS THE THERMAL TROUGH SHIFTS EASTWARD.
SEAS WILL GENERALLY REMAIN BETWEEN 5 TO 8 FEET THROUGH THE
PERIOD.
FIRE WEATHER
ELEVATED FIRE WEATHER CONCERNS THE NEXT THREE DAYS WITH THE VERY
DRY AND WARM CONDITIONS. MINIMUM RELATIVE HUMIDITY VALUES IN
THE 20 TO 30 PERCENT RANGE, WITH DRIER LOCATIONS IN THE SOUTH
SOUND CAPABLE OF GETTING INTO THE UPPER TEENS. WHILE THERE IS
STILL A LOT OF UNCERTAINTY REGARDING THE LOW PRESSURE SYSTEM OFF
THE COAST FROM WHAT WAS ONCE TROPICAL STORM ELIDA, CHANCES FOR
THUNDERSTORMS LATE IN THE WEEK ARE LOW AT THIS POINT, BUT CANNOT
BE FULLY RULED OUT. ANY THUNDERSTORMS THAT DEVELOP AFTER
ANOTHER ROUND OF HOT AND VERY DRY CONDITIONS POSE A RISK OF
ADDITIONAL IGNITIONS FROM LIGHTNING. FIRE WEATHER CONCERNS EASE
FRIDAY INTO THE WEEKEND WITH COOLER DAYS AND LOW LEVEL ONSHORE
FLOW.
FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...HEAT ADVISORY FROM 10 AM TUESDAY TO 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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