943
FXUS66 KSEW 202150
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
250 PM PDT MON JUL 20 2026
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
STRONG HIGH PRESSURE BUILDING OVER THE REGION WITH DRY
CONDITIONS IN PLACE. WITH LIGHT NORTHERLY FLOW OVER THE REGION
IN THE LOWER LEVELS, EXPECT VFR CONDITIONS UNDER VARIABLE HIGH
CIRRUS AND SOME ENTRAINED SMOKE OVERHEAD THROUGH THE PERIOD.
WINDS INCREASE A BIT THROUGH THE EVENING, BEFORE GOING LIGHT OR
CALM OVERNIGHT. LIFR STRATUS WILL RETURN ALONG THE IMMEDIATE
COASTLINE TONIGHT BEFORE CLEARING OUT TUESDAY MORNING. NORTHERLY
SURFACE WINDS AGAIN INCREASE TUESDAY THROUGH MUCH OF THE REGION.
INCREASING WILDFIRE SMOKE ACROSS NORTHWEST WA MAY BEGIN TO
LIMIT BOTH HORIZONTAL AND SLANT-RANGE VISIBILITY BY THIS
AFTERNOON.
KSEA...WEST/NORTHWEST SURFACE WINDS THIS AFTERNOON WILL EASE
OVERNIGHT, BEFORE INCREASING AGAIN TUESDAY AFTERNOON. VFR
CONDITIONS CONTINUE WITH HIGH CLOUDS AND OCCASIONAL SMOKE ALOFT,
BUT CEILINGS AND REDUCTIONS IN VISIBILITY AT THE SURFACE ARE
NOT EXPECTED THROUGH THE PERIOD.
MARINE
HIGH PRESSURE WILL REMAIN SITUATED INLAND AS A LOW PRESSURE
SYSTEM STALLS OVER THE OFFSHORE WATERS, MAINTAINING
NORTHWESTERLY FLOW OVER THE OUTER WATERS THROUGH THE FIRST HALF
OF THE WEEK. STRONGER ONSHORE FLOW WILL RESUME BY LATE THURSDAY,
BRINGING POTENTIAL FOR SMALL CRAFT WESTERLY PUSHES THROUGH THE
STRAIT OF JUAN DE FUCA DAILY THEREAFTER HEADING INTO THE
WEEKEND.
SEAS WILL GENERALLY REMAIN BETWEEN 5 TO 7 FEET THROUGH THE
WEEK.
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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