898
FXUS66 KSEW 210325
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
825 PM PDT MON JUL 20 2026
UPDATE
HAZY CONDITIONS ARE LEADING TO A PICTURESQUE SUNSET THIS
EVENING. CURRENTLY, MOST WILDFIRE SMOKE REMAINS ALOFT WITH ONLY
LOCALIZED AREAS OF MODERATE AIR QUALITY OBSERVED ACROSS WESTERN
WASHINGTON. FOR TONIGHT, DRY WEATHER REMAINS IN THE FORECAST AS
HIGH-LEVEL CLOUD COVERAGE STREAMS OVERHEAD. CAN'T RULE OUT THE
DEVELOPMENT OF MARINE STRATUS OVERNIGHT BUT THIS ACTIVITY WILL
LIKE REMAIN ALONG THE COAST. OVERNIGHT LOWS ARE TO RANGE
BETWEEN THE MID 50S TO LOWER 60S WITH URBAN CENTERS BEING THE
WARMEST. THE PREVIOUS DISCUSSION REMAINS BELOW ALONG WITH AN
UPDATED MARINE/AVIATION SECTION:
SYNOPSIS
A WARMING AND DRYING TREND WILL CONTINUE ACROSS WESTERN
WASHINGTON THROUGH THE MIDDLE OF THE WEEK, WITH TEMPERATURES
REACHING THE LOW 90S FOR MANY LOWLAND AREAS TUESDAY AND
WEDNESDAY. ONSHORE FLOW WILL INCREASE DURING THE LATTER HALF OF
THE WEEK, BRINGING COOLER TEMPERATURES WITH CHANCES FOR SHOWERS
AND MORNING LOW CLOUDS.
SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/
AN UPPER LEVEL RIDGE WILL CONTINUE TO BUILD OVER THE GREAT BASIN
THROUGH THE MIDDLE OF THE WEEK, WITH A LOW PRESSURE SYSTEM
SITUATED OFFSHORE. THIS WILL MAINTAIN SOUTHERLY FLOW ALOFT OVER
WESTERN WASHINGTON, PULLING IN WARMER AIR THROUGH WEDNESDAY.
TEMPERATURES TODAY ARE ON TRACK TO PEAK WELL INTO THE 80S ACROSS
MUCH OF THE LOWLANDS, WITH FURTHER WARMING BRINGING TEMPERATURES
CLOSER TO 90 DEGREES ON TUESDAY. BY WEDNESDAY, MANY AREAS EAST
AND SOUTH OF THE PUGET SOUND WILL SEE HIGH TEMPERATURES PEAKING
IN THE LOW TO MID 90S, WHICH MAY RESULT IN THE WARMEST DAY OF
THE YEAR SO FAR. THIS WILL ALSO CORRESPOND TO WIDESPREAD AREAS
OF BOTH MODERATE (ORANGE) AND MAJOR (RED) HEATRISK ON TUESDAY
AND WEDNESDAY, WHICH REFLECTS AN INCREASED RISK OF HEAT-RELATED
ILLNESS TO THOSE WITHOUT ACCESS TO COOLING OR HYDRATION. A HEAT
ADVISORY REMAINS IN EFFECT FOR ALL INLAND LOWLAND AREAS FROM
TUESDAY MORNING TO WEDNESDAY EVENING.
IN ADDITION TO THE HEAT, NORTHERLY FLOW AT TIMES WILL PULL
WILDFIRE SMOKE FROM BRITISH COLUMBIA INTO WHATCOM AND SKAGIT
COUNTIES, AND AN AIR QUALITY ALERT HAS BEEN ISSUED BY THE
NORTHWEST CLEAN AIR AGENCY. WEAK EASTERLY FLOW TONIGHT INTO
TUESDAY WILL ALSO BRING WILDFIRE SMOKE FROM EASTERN WASHINGTON
WEST OF THE CREST TONIGHT INTO TUESDAY. 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.
LONG TERM /THURSDAY THROUGH MONDAY/
THE REMNANTS OF TROPICAL STORM ELIDA WILL MEANDER NORTHWARD LATE
WEDNESDAY INTO THURSDAY, AND WHILE CONFIDENCE IS LOW, THIS MAY
PRODUCE ISOLATED THUNDERSTORMS OVER HIGHER ELEVATIONS. INCREASED
ONSHORE FLOW BY FRIDAY WILL BRING IN MORE SEASONABLE
TEMPERATURES IN THE UPPER 70S TO THE REGION, WITH A RETURN TO
MORNING LOW CLOUDS AND AFTERNOON SUNBREAKS. MODELS STRUGGLE TO
COME INTO AGREEMENT OVER THE POTENTIAL FOR ANY INCOMING SHOWERS
IN THE LONG TERM, WITH ENSEMBLES MAINTAINING CHANCES FOR SHOWERS
OVER THE NORTHERN OLYMPIC PENINSULA AND NORTHERN INTERIOR
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.
15
AVIATION
SOUTHWEST FLOW ALOFT WILL CONTINUE THROUGH TUESDAY WITH
A STRONG UPPER RIDGE OVER THE ROCKIES AND WEAK TROUGHING WELL
OFFSHORE. THE LOW LEVEL FLOW IS LIGHT NORTHERLY OR WEAKLY OFFSHORE.
VFR THIS EVENING WITH HIGH CLOUDS. WILDFIRE SMOKE ALOFT ACROSS
NORTHWEST WA MAY LIMIT BOTH HORIZONTAL AND SLANT-RANGE VISIBILITY AT
TIMES INTO TUESDAY. LOW LIFR STRATUS IS EXPECTED TO REACH HQM FOR A
SHORT DURATION EARLY TUESDAY MORNING (MAINLY BETWEEN 09-16Z).
OTHERWISE VFR CONDITIONS ELSEWHERE WITH HIGH CLOUDS AT TIMES. LIGHT
WINDS TONIGHT WILL INCREASE FROM THE W/NW TUESDAY AFTERNOON.
KSEA...VFR WITH HIGH CLOUDS AT TIMES. SURFACE WINDS LIGHT NORTHERLY
GENERALLY BELOW 5 KTS THROUGH TUESDAY MORNING, BECOMING NW AT 5 TO
8 KTS TUESDAY AFTERNOON. JD
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.
27
FIRE WEATHER
ELEVATED FIRE WEATHER CONCERNS WILL CONTINUE THROUGH WEDNESDAY
DUE TO VERY WARM AND DRY CONDITIONS. MINIMUM RELATIVE HUMIDITIES
WILL FALL AS LOW AS 20% TO 30% ON TUESDAY AND WEDNESDAY, WITH
DRIER LOCATIONS ACROSS THE SOUTHERN PUGET SOUND POTENTIALLY
BOTTOMING OUT IN THE TEENS. IN ADDITION, A THERMAL TROUGH WILL
BUILD ALONG THE COAST TODAY AND WILL SHIFT INLAND DURING THE
DAYTIME HOURS AND BACK ALONG THE COAST OVERNIGHT EACH DAY
THROUGH WEDNESDAY. WHILE A LARGE DEGREE OF UNCERTAINTY REMAINS
OVER THE TRACK OF INCOMING SHOWERS AND THUNDERSTORMS, THE
POTENTIAL FOR STORMS COMING IN FROM THE SOUTH LATE WEDNESDAY
INTO THURSDAY POSE A RISK OF ELEVATED FIRE WEATHER CONDITIONS,
AS ADDITIONAL IGNITIONS FROM LIGHTNING CANNOT BE RULED OUT.
ONSHORE FLOW WILL INCREASE BY FRIDAY, BRINGING COOLER
TEMPERATURES AND BETTER OVERNIGHT RH RECOVERIES THROUGH THE
WEEKEND.
15
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 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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