502
FXUS66 KSEW 181537
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
837 AM PDT SAT JUL 18 2026
SYNOPSIS
WEAK UPPER LEVEL TROUGH OVER THE AREA TODAY WILL MOVE NORTHEAST
SUNDAY. SEASONABLE TEMPERATURES OVER THE WEEKEND WITH SOME
MORNING CLOUDS. HIGH PRESSURE BUILDS OVER WESTERN WASHINGTON
MONDAY WITH THE RIDGE REMAINING IN PLACE THROUGH WEDNESDAY
GIVING THE INTERIOR MUCH ABOVE NORMAL TEMPERATURES. RIDGE
WEAKENS THURSDAY WITH AN UPPER LEVEL TROUGH APPROACHING FRIDAY
BRINGING COOLER TEMPERATURES TO THE REGION.
SHORT TERM /TODAY THROUGH MONDAY/
NO MAJOR UPDATES HAVE BEEN MADE THIS MORNING. SEE BELOW FOR AN
UPDATED AVIATION DISCUSSION.
WEAK UPPER LEVEL TROUGH HANGING OVER THE AREA TODAY WITH LIGHT
FLOW IN THE LOWER LEVELS. WITHOUT ANY RIDGE BUILDING/SUBSIDENCE
WILL HAVE TO RELY ON THE MID JULY SUN TO DISSIPATE THE STRATUS.
STRATUS LAYER NOT VERY THICK, 1000 FEET OR LESS IN MOST PLACES,
MAKING FOR A LATE MORNING/MIDDAY BREAKOUT OVER THE INTERIOR.
STRATUS HANGING TOUGHER ALONG THE COAST INTO THE AFTERNOON
HOURS. HIGHS MID 60S ALONG THE COAST AND 70S OVER THE INTERIOR.
WEAK UPPER LEVEL TROUGH OVER THE AREA TONIGHT LIFTING NORTHEAST
SUNDAY. MARINE LAYER NOT AS THICK SUNDAY MORNING WITH LESS
MORNING CLOUD COVER AND MORE SUNSHINE BY LATE MORNING. HIGHS
WARMING A LITTLE, NEAR 70 ALONG THE COAST AND MID 70S TO MID 80S
OVER THE INTERIOR. LOWS TONIGHT IN THE 50S.
UPPER LEVEL RIDGE WELL TO THE SOUTHEAST BEGINNING TO BUILD BACK
TO THE NORTHWEST TOWARDS WESTERN WASHINGTON. 500 MB HEIGHTS
RISING INTO THE MID 580 DMS MONDAY WITH 500 MB TEMPERATURES
WARMING TO PLUS 18 TO 20C BY 00Z TUESDAY. LOW LEVEL FLOW TURNING
LIGHT OFFSHORE. HIGHS WARMING INTO THE 80S AND LOWER 90S OVER
THE INTERIOR WITH 70S TO LOWER 80S FOR THE COAST.
MINOR HEATRISK OVER THE WEEKEND WITH MODERATE HEATRISK OVER MOST
OF THE INTERIOR MONDAY. FELTON
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
MODELS IN GOOD AGREEMENT WITH THE UPPER LEVEL RIDGE REMAINING
OVER WESTERN WASHINGTON THROUGH WEDNESDAY. HIGH IN THE 80S TO
LOWER 90S OVER THE INTERIOR WITH 70S TO LOWER 80S ALONG THE
COAST. NOT EXPECTING ANY RECORD HIGHS WITH THE MUCH ABOVE NORMAL
TEMPERATURES. SEATTLE RECORDS TUESDAY AND WEDNESDAY BOTH FROM
2006 ( 97 TUESDAY AND 96 WEDNESDAY ). LOWS IN THE 50S AND LOWER
60S.
MODERATE HEATRISK FOR THE INTERIOR FOR BOTH DAYS WITH A 30-50%
CHANCE OF MAJOR HEATRISK FOR THE CENTRAL AND SOUTHERN PUGET
SOUND.
UPPER LEVEL RIDGE WEAKENING THURSDAY WITH THE LOW LEVEL FLOW
GOING LIGHT ONSHORE. HIGHS MUCH COOLER ON THE COAST, MID 60S TO
LOWER 70S. FOR THE INTERIOR 5 TO 10 DEGREES OF COOLING WITH HIGHS
IN THE UPPER 70S TO UPPER 80S.
NOT A LOT OF CONSISTENCY IN THE SOLUTIONS FOR FRIDAY. THE
OPERATIONAL ECMWF HAS THE MUCH WEAKENED REMNANTS OF WHAT IS NOW
TROPICAL STORM ELIDA JUST OFFSHORE. THE GFS HAS A WEAK TROUGH
MOVING THROUGH WITH INCREASING LOW LEVEL ONSHORE FLOW. THE BLEND
JUST HAS A CONTINUATION OF THE WEAK MARINE PUSH THAT STARTED
THURSDAY. CONFIDENCE LOW SO WILL TREND THE FORECAST TOWARDS
CLIMATOLOGY WITH HIGHS MID 60S COAST AND 70S INLAND. FELTON
AVIATION
WESTERLY FLOW ALOFT WILL CONTINUE ACROSS WESTERN
WASHINGTON TODAY AS AN UPPER TROUGH OVER SOUTHERN BRITISH COLUMBIA
GRADUALLY PROGRESSES EASTWARD. BROKEN MVFR TO IFR CIGS ACROSS THE
AREA THIS MORNING WILL START TO ERODE LATER THIS MORNING, GIVING WAY
TO VFR CONDITIONS FOR THE AFTERNOON AND EVENING. ANOTHER ROUND OF
STRATUS IS ON TRACK TO REDEVELOP AND PUSH INLAND ONCE AGAIN TONIGHT
INTO SUNDAY MORNING. IT WILL MOST LIKELY REMAIN JUST WEST OF THE
METRO AREA, BUT THERE IS A 25-30% CHANCE OF SEEING MVFR OR LOWER
CIGS IN THE SEATTLE METRO FROM AROUND 12-17Z SUN. WINDS REMAIN WEST
TO NORTHWEST ALONG THE COAST, WITH WINDS IN THE INTERIOR TURNING
FROM LIGHT SOUTH TO NORTHERLY 5-10 KT BY THIS EVENING. A FEW GUSTS
TO 15 KT WILL BE POSSIBLE AT CLM THIS EVENING.
KSEA...IFR CIGS UNDER BROKEN STRATUS SHOULD BEGIN TO ERODE AFTER 18-
19Z THIS MORNING, GIVING WAY TO VFR CONDITIONS THROUGH THE REST OF
THE DAY. ANOTHER ROUND OF LOW CEILINGS WILL BE POSSIBLE WITH A 20-
25% CHANCE OF SEEING MVFR OR LOWER CONDITIONS BETWEEN 12Z-17Z SUN.
SURFACE WINDS LIGHT S/SW WILL VEER W/NW 5 TO 8 KNOTS THIS AFTERNOON
THEN NORTHERLY TONIGHT.
27/62
MARINE
A BROAD SURFACE RIDGE CENTERED WELL OFFSHORE WILL EXPAND
EASTWARD THIS WEEKEND. THIS WILL INCREASE ONSHORE FLOW SOMEWHAT
LATER TODAY INTO TONIGHT WITH SMALL CRAFT ADVISORY WESTERLIES
DEVELOPING IN THE CENTRAL/EAST STRAIT AS WELL AS GUSTY
NORTHWESTERLIES AND CHOPPY SEAS FOR THE OUTER COASTAL WATERS.
THERMALLY INDUCED SURFACE LOW PRESSURE IS EXPECTED TO DEEPEN ACROSS
THE INTERIOR OF WESTERN WASHINGTON MONDAY THROUGH WEDNESDAY. THIS
WILL LEAD TO VARYING DEGREES OF ONSHORE FLOW INTO THE MIDDLE PORTION
OF THE COMING WEEK.
27
FIRE WEATHER
FIRE WEATHER CONCERNS INCREASING AS HIGH TEMPERATURES WARM TO
MUCH ABOVE NORMAL THE FIRST PART OF NEXT WEEK. WHILE THE LOW
LEVEL FLOW DOES NOT GO OFFSHORE FOR A PROLONGED PERIOD OF TIME
RELATIVE HUMIDITY VALUES IN THE AFTERNOON WILL DROP BELOW 30% IN
THE FOOTHILLS AS WELL AS THE CENTRAL AND SOUTHERN PUGET SOUND
MONDAY THROUGH WEDNESDAY. THE VERY WARM AND DRY CONDITIONS
BEGINNING MONDAY HAS THE POTENTIAL FOR INCREASING FIRE ACTIVITY
FROM ANY NEW LIGHTNING STARTS FROM THURSDAY'S CONVECTION. FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 1 AM PDT
SUNDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 11 AM 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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