863
FXUS66 KSEW 151010
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
310 AM PDT SAT AUG 15 2026
SYNOPSIS
THUNDERSTORM POTENTIAL WILL CONTINUE ALONG THE CASCADES
ON SATURDAY, BUT WILL WANE THROUGHOUT THE WEEKEND AS AN UPPER
LEVEL RIDGE STARTS TO BUILDS INTO THE AREA FROM THE SOUTHEAST.
ANOTHER UPPER LEVEL TROUGH WILL MOVE INTO THE REGION EARLY NEXT
WEEK. UNCERTAINTY THEN INCREASES IN THE FORECAST HEADING INTO
MIDWEEK AS GUIDANCE REMAINS SPLIT BETWEEN A WARMER, DRIER PATTERN
AND A COOLER, WETTER ONE.
SHORT TERM /TODAY THROUGH MONDAY/
BROAD UPPER-TROUGHING RESIDES OVER THE PAC COAST THIS MORNING
WHILE UPPER-RIDGING IS POSITIONED ACROSS MUCH OF THE NATION.
IN THE PNW, A WEAK UPPER-LOW WILL INFLUENCE THE WEATHER TODAY AS
THE MAIN HIGHLIGHT ONCE AGAIN IS SHOWERS AND THUNDERSTORM
FORECASTED FOR THE MOUNTAINS. AS A RESULT, ELEVATED FIRE
WEATHER CONDITIONS ARE EXPECTED FOR THE CASCADES.
CURRENTLY, MARINE STRATUS HAS MARCHED WELL INLAND SO FAR THIS
MORNING - STRETCHING FROM THE COAST INTO PUGET SOUND. IT'LL
REMAIN IN PLACE BEFORE GRADUALLY BURNING OFF INTO THE AFTERNOON.
HOWEVER, AFOREMENTIONED THUNDERSTORMS WILL POTENTIALLY EMERGE
THIS AFTERNOON ALONG THE CASCADE CREST AS A SUBTLE SHORTWAVE
WITHIN THE MEAN FLOW TRACKS INTO THE REGION AND PERTURBS THE
ENVIRONMENT. LATEST HREF DEPICTS 500-800 J/KG OF SURFACE CAPE
ALONG THE CASCADES WITH 250-500 J/KG ACROSS THE OLYMPICS. MODEL
DERIVED 700-500 MB LAPSE RATES ARE AROUND 6 C/KM, CONDITIONALLY
UNSTABLE FOR ANY SATURATED AIR PARCELS. THE NBM HAS A 20-30%
CHANCE OF THUNDERSTORMS THIS AFTERNOON INTO THE EVENING AND LESS
THAN 15% ELSEWHERE ACROSS WESTERN WASHINGTON. THE THREAT SHOULD
END TONIGHT BARRING A FEW STRAGGLERS. HIGHS TODAY FOR THE
INTERIOR ARE FORECAST TO RANGE BETWEEN THE MID 70S TO LOWER 80S.
COASTAL AREAS ARE FAVORED TO REMAIN IN THE 60S. OVERNIGHT LOWS
WILL BE IN THE UPPER 40S TO UPPER 50S.
GLOBAL GUIDANCE HAS RIDGING BUILDING INTO THE REGION OUT OF THE
SOUTHEAST ON SUNDAY. SOUTHWEST FLOW ALOFT WILL HELP PUSH SMOKE
EASTWARD AND AWAY FROM THE REGION. A SLIGHT CHANCE (15-20%) OF
THUNDERSTORMS IS FORECAST FOR THE NORTH CASCADES WITH LESSER
PROBABILITIES SOUTHWARD ALONG THE RANGE. MONDAY'S FORECAST IS
QUITE SIMILAR IN REGARDS TO CONVECTION BUT PROBABILITIES SHOULD
REMAIN CAPPED AT 15%, LIKELY DUE TO MORE LARGE-SCALE SUBSIDENCE
PROVIDED BY DIRECT RIDGING OVERHEAD. HIGHS FOR SUNDAY AND
MONDAY IN THE MID 70S TO MID 80S WITH OVERNIGHT LOWS IN THE
LOWER TO UPPER 50S. COASTAL AREAS HIGHS ARE FORECAST IN THE 60S.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
THE FIRST PART OF NEXT WEEK REMAINS TO FOLLOW A RATHER TYPICAL
PATTERN OF ONSHORE LOW-LEVEL FLOW MAINTAINING MORNING CLOUDS, WITH
SOME CLEARING IN THE AFTERNOON. A PASSING TROUGH AROUND TUESDAY
COULD PROVIDE A REINFORCING PUSH OF CLOUDS AND KNOCK TEMPERATURES A
FEW DEGREES COOLER THAN NORMAL. OTHERWISE, ENSEMBLE GUIDANCE BEGINS
TO SPREAD A BIT LARGER TOWARD THE MIDDLE OF NEXT WEEK WITH A FAIRLY
EVEN SPLIT BETWEEN A COOLER TROUGH PATTERN AND A WARMER (NEAR
NORMAL) PATTERN UNDER ZONAL FLOW OR A WEAK RIDGE. IN ANY EVENT,
THERE'S NOT A SIGNIFICANT SIGNAL FOR ANY PRECIPITATION OF NOTE
WITH TEMPERATURES LEANING WARMER THAN AVERAGE.
AVIATION
A NEARLY STATIONARY UPPER LEVEL TROUGH WILL MAINTAIN SOUTHWESTERLY
FLOW ALOFT TODAY, WHICH WILL MAINTAIN SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS ALONG THE CASCADE CREST. STRATUS CONTINUES TO PUSH
INLAND EARLY THIS MORNING, WITH THE STRATUS LIKELY TO PUSH IN
FARTHER COMPARED TO THE PAST FEW DAYS. OVERALL THIS MORNING'S
CEILINGS HAVE BEEN TRENDING HIGHER WITH LESS VIS ISSUES, AS WELL.
CEILINGS SHOULD REMAIN LOW-END MVFR TO IFR, WITH FAVORED LOCATIONS
REACHING LIFR AT TIMES. CONTINUING LIGHT WINDS EARLY THIS MORNING
SHOULD HELP TO MAINTAIN HIGHER VISIBILITY BUT LIMITATIONS ARE STILL
POSSIBLE. VFR CONDITIONS ARE EXPECTED ONCE THE STRATUS DISSIPATES,
BUT MODELS ARE HINTING AT A LATER CLEAR-OUT TIMING, POTENTIALLY AS
LATE AS 18-20Z ACROSS THE INTERIOR. THE COAST WILL LIKELY NOT FULLY
CLEAR OUT IN THE AFTERNOON BEFORE STRATUS REBUILDS TONIGHT INTO
SUNDAY MORNING.
LIGHT WEST TO SOUTHWEST WINDS WILL INCREASE IN THE AFTERNOON.
WINDS LOOK TO SWITCH TO NORTHWESTERLY THROUGH THE CENTRAL PUGET
SOUND TERMINALS AFTER AROUND 23Z SAT - 02Z SUN AND EASE LATE TONIGHT.
KSEA...IFR CIGS EARLY THIS MORNING AS THE STRATUS BUILDS IN. MODELS
ARE INDICATING A LATER CLEAR OUT TIME, POSSIBLY BY 19-20Z LATE THIS
MORNING. VFR CONDITIONS FOLLOW UNTIL THE NEXT ROUND OF STRATUS
RETURNS EARLY SUNDAY MORNING. WINDS REMAIN PREDOMINANTLY OUT OF THE
SOUTHWEST 4-8 KT, BUT MAY ATTEMPT TO TURN MORE WEST TO NORTHWEST
BETWEEN AROUND 02-06Z SUN. 62
MARINE
HIGH PRESSURE WILL REMAIN WELL OFF THE COAST OF CALIFORNIA TODAY,
KEEPING WINDS LIGHT OVER THE COASTAL WATERS.
NORTHWESTERLY WINDS WILL BEGIN TO RESUME SUNDAY AS HIGH PRESSURE
REBUILDS OF THE COAST OF BRITISH COLUMBIA. THE HIGH WILL STRENGTHEN
AS IT SHIFTS SOUTHWARD OFF THE PACIFIC NORTHWEST COAST, MAINTAINING
NW WINDS INTO NEXT WEEK. SEAS LOOK TO REMAIN BETWEEN 3-6 FT THROUGH
NEXT WEEK.
DIURNALLY DRIVEN WESTERLY WINDS WILL CONTINUE TO OCCUR EACH
AFTERNOON AND EVENING IN THE STRAIT OF JUAN DE FUCA THROUGH THIS
WEEKEND AND INTO EARLY NEXT WEEK WITH GUSTS REACHING SMALL CRAFT
ADVISORY CRITERIA AT TIMES. THE WESTERLY PUSHES LOOK TO START TO
WEAKEN BY THE MIDDLE OF NEXT WEEK. 62
FIRE WEATHER
ELEVATED FIRE WEATHER CONDITIONS WILL CONTINUE ACROSS THE CASCADES
INTO SATURDAY WITH CHANCES OF THUNDERSTORMS POSSIBLE AGAIN ALONG
THE CASCADE CREST ON SATURDAY AFTERNOON AND EVENING. OVERALL
CHANCES FOR CONVECTION WILL DECREASE THROUGH THE WEEKEND, HOWEVER,
AS AN UPPER LEVEL RIDGE STARTS TO BUILD INTO THE AREA FROM THE
SOUTHEAST. BY SUNDAY, EXPECT CONVECTION TO MAINLY BE CONFINED TO
THE CASCADE CREST AND AREAS EAST OF THE CREST. ANOTHER UPPER
LEVEL TROUGH WILL MOVE INTO THE AREA NEXT WEEK AND COULD BRING
SOME ADDITIONAL ELEVATED FIRE WEATHER CONCERNS TO WESTERN
WASHINGTON AT TIMES.
14/41
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT EARLY THIS MORNING FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 5 AM PDT
SUNDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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