206
FXUS66 KSEW 140409
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
909 PM PDT THU AUG 13 2026
SYNOPSIS
SHOWERS AND THUNDERSTORMS WILL CONTINUE OVER THE MOUNTAINS
THIS AFTERNOON AND FRIDAY AFTERNOON UNDER THE INFLUENCE OF AN
UPPER LEVEL TROUGH. SOUTHWEST FLOW ALOFT WILL DEVELOP OVER THE
WEEKEND, BRINGING SOME WARMING AHEAD OF ANOTHER WEAK TROUGH AT
THE BEGINNING OF NEXT WEEK THAT WILL LIKELY BRING SLIGHTLY
COOLER AND UNSETTLED CONDITIONS.
SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/
CONVECTION CONTINUES OVER THE NORTHERN CASCADES THIS EVENING.
EXPECT THUNDERSTORM ACTIVITY TO CONTINUE SUBSIDING INTO TONIGHT.
OTHERWISE NO MAJOR UPDATES TO THE FORECAST. REFER TO AN UPDATED
AVIATION DISCUSSION.
AN UPPER LEVEL TROUGH WILL REMAIN IN PLACE OVER WESTERN
WASHINGTON INTO FRIDAY. THIS TROUGH WILL HELP THE AIR MASS
BECOME UNSTABLE THIS AFTERNOON AND EVENING OVER THE CASCADES AND
THE OLYMPICS, ESPECIALLY THE HIGHER TERRAIN. WE'LL CONTINUE TO
SEE CHANCES FOR SCATTERED CONVECTION THIS AFTERNOON AND EVENING,
PRIMARILY FOR AREAS IN THE CASCADES AND OLYMPICS. IN ANY
THUNDERSTORM THAT DEVELOPS, WE COULD SEE THE POTENTIAL FOR
ABUNDANT LIGHTNING, ERRATIC WIND GUSTS UP TO 40 MPH, AND
LOCALIZED WETTING RAINS THAT COULD PRODUCE AND ELEVATED RISK OF
BURN SCAR DEBRIS FLOWS. ADDITIONALLY, A RED FLAG WARNING REMAINS
IN EFFECT THIS EVENING FOR THOSE AFOREMENTIONED AREAS. FOR MORE
INFORMATION ABOUT FIRE WX CONDITIONS, SEE THE .FIRE WEATHER
SECTION DOWN BELOW.
GENERALLY, WE'LL SEE HIGH TEMPERATURES THIS AFTERNOON IN THE
UPPER 70S TO LOWER 80S IN SPOTS WITH A MIX OF SUN AND HAZE.
ONSHORE FLOW WILL CONTINUE TONIGHT AND INTO FRIDAY MORNING, WITH
A SHALLOW MARINE LAYER MOVING INLAND BY THE MORNING. HIGH
TEMPERATURES ON FRIDAY WILL BE SLIGHTLY COOLER, IN THE UPPER 70S
FOR MOST LOCATIONS. THE ATMOSPHERE WILL CONTINUE TO REMAIN
UNSTABLE FRIDAY AFTERNOON - WHICH WILL LEAD TO ANOTHER CHANCE OF
SCATTERED THUNDERSTORMS, PRIMARILY IN THE CASCADES AND OLYMPICS.
A FIRE WEATHER WATCH IS IN EFFECT FOR THOSE AREAS - PRIMARILY
FOR LIGHTNING AND GUSTY OUTFLOW WINDS.
WEAK RIDGING WILL INFLUENCE THE AREA HEADING INTO SATURDAY,
WHICH WILL LEAD TO GENERALLY WARM AND DRY CONDITIONS. A FEW
SHOWERS MAY STILL BE POSSIBLE IN THE CASCADES, BUT OVERALL A
TYPICAL SUMMER DAY WITH HIGH TEMPERATURES IN THE LOW 80S.
LONG TERM /SUNDAY THROUGH THURSDAY/
WARM AND DRY CONDITIONS CONTINUING ON SUNDAY WITH HIGH
TEMPERATURES IN THE LOWER 80S. UPPER LEVEL TROUGHING LOOKS TO
MAINTAIN INFLUENCE OVER THE AREA THROUGH MIDWEEK, ALLOWING FOR
ONSHORE FLOW IN VARIABLE STRENGTHS THROUGHOUT THE WEEK.
UNSETTLED AND COOLER CONDITIONS THROUGH THE REMAINDER OF THE
WEEK, WITH HIGH TEMPERATURES IN THE MID 70S.
MAZURKIEWICZ
AVIATION
INTERIOR TERMINALS VFR THIS EVENING AND IFR/LIFR ALONG
THE COAST. THUNDERSTORM ACTIVITY CONTINUES FOR THE CASCADES THIS
EVENING, BUT IS EXPECTED TO STAY AWAY FROM THE MAIN TERMINALS.
ADDITIONALLY, SMOKE FROM FIRES WILL PRIMARILY REMAIN ELEVATED OVER
THE TERMINALS, BUT AREAS NEAR FIRES WILL SEE POOR SURFACE
VISIBILITIES. ANOTHER MARINE PUSH IS EXPECTED FOR FRIDAY MORNING.
SLIGHT INCREASE IN PROBABILITIES FOR IFR/LIFR CONDITIONS. IFR
PROBABILITIES CURRENTLY AROUND 40-60% AND LIFR AROUND 20-40%. SOME
AREAS OF FOG CAN'T BE RULED OUT WITHIN THE MARINE PUSH. IMPROVEMENT
TO VFR EXPECTED FOR INTERIOR TERMINALS AFTER 17Z. CALM TO LIGHT
NORTHWEST WINDS TONIGHT WILL INCREASE OUT OF THE WEST/SOUTHWEST ON
FRIDAY TO 5-10 KT.
KSEA...VFR CONDITIONS THIS EVENING. PROBABILITIES FOR IFR/LIFR
CONDITIONS HAVE TRENDED SLIGHTLY UPWARDS. LATEST PROBABILITIES HINT
AT A 30-50% CHANCE FOR IFR CIGS AND 20-40% CHANCE FOR LIFR CIGS
BETWEEN 13Z-15Z. IMPROVEMENT TO VFR I THE AFTERNOON. LIGHT NORTHWEST
WINDS WILL SHIFT SOUTHWESTERLY FRIDAY MORNING, INCREASING TO 4-7 KT.
29
MARINE
HIGH PRESSURE REMAINS IN THE NORTHEAST PACIFIC THROUGH FRIDAY. AN
UPPER LEVEL LOW WILL CUT SOUTHWARD OVER THE WATERS THIS WEEKEND
WHICH WILL PUSH THE HIGH TOWARDS THE SOUTH. THE HIGH PRESSURE WILL
REBUILD AGAIN OVER THE COASTAL WATERS EARLY NEXT WEEK. MAIN CONCERN
REMAINS THE DIURNAL WESTERLY PUSHES THROUGH THE STRAIT OF JUAN DE
FUCA, WITH PROBABILITIES FOR WINDS AND/OR GUSTS OVER 20 KT REMAINING
LOW UNTIL FRIDAY AND SATURDAY EVENING.
SEAS NEXT 7 DAYS WILL REMAIN AT 3-6 FT.
HPR
FIRE WEATHER
FIRE WEATHER CONCERNS REMAIN ELEVATED TO CRITICAL AT TIMES
THROUGH FRIDAY NIGHT. AIR MASS HAS ALREADY BECAME UNSTABLE OVER
THE HIGHER TERRAIN THIS AFTERNOON AND WILL CONTINUE THROUGH THE
EARLY EVENING HOURS WITH CHANCES OF THUNDERSTORMS AND SHOWERS
LIKELY, PRIMARILY IN THE CASCADES AND OLYMPICS. A RED FLAG
WARNING IS IN EFFECT THROUGH 9PM. IN ANY THUNDERSTORM THAT
DEVELOPS, WE COULD SEE THE POTENTIAL FOR ABUNDANT LIGHTNING,
ERRATIC WIND GUSTS UP TO 40 MPH, AND LOCALIZED WETTING RAINS.
ADDITIONALLY, A FIRE WEATHER WATCH HAS BEEN ISSUED FOR FRIDAY
AFTERNOON AND EVENING, FOR ANOTHER ROUND OF CONVECTION ACROSS
THE CASCADES AND OLYMPICS - PRIMARILY FOR LIGHTNING AND GUSTY
OUTFLOW WINDS.
UPPER LEVEL TROUGH REPLACED BY AN UPPER LEVEL RIDGE OVER THE
WEEKEND LESSENING BUT NOT ELIMINATING THE CHANCES FOR CONVECTION
OVER THE MOUNTAINS ESPECIALLY THE CASCADES. ANOTHER UPPER LEVEL
TROUGH MOVING INTO THE AREA NEXT WEEK WILL ONCE AGAIN INCREASE
FIRE WEATHER CONCERNS.
FELTON/MAZURKIEWICZ
SEW WATCHES/WARNINGS/ADVISORIES
WA...FIRE WEATHER WATCH FROM FRIDAY AFTERNOON THROUGH FRIDAY
EVENING FOR EAST PORTION OF THE OLYMPIC MOUNTAINS-WEST
PORTION OF THE OLYMPIC MOUNTAINS-WEST SLOPES OF THE
CENTRAL CASCADES GENERALLY ABOVE 1500 FEET-WEST SLOPES OF
THE NORTH CASCADES GENERALLY ABOVE 1500 FEET.
PZ...NONE.
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