092
FXUS66 KSEW 310321
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
821 PM PDT SAT AUG 30 2025
SYNOPSIS
AN UPPER LEVEL LOW OFF THE COAST WILL CONTINUE TO KEEP
TEMPERATURES SEASONABLE THIS WEEKEND, WITH SLIGHT CHANCES FOR
SHOWERS THROUGH SUNDAY AND PERHAPS A THUNDERSTORM OVER THE NORTH
CASCADES LATE SUNDAY NIGHT. UPPER LEVEL RIDGING RETURNS MONDAY,
BRINGING ANOTHER ROUND OF HOT AND DRY CONDITIONS WITH WELL ABOVE
NORMAL TEMPERATURES ARE EXPECTED BY MID-WEEK.
SHORT TERM /TONIGHT THROUGH TUESDAY/
NO SIGNIFICANT CHANGES
MADE TO THE FORECAST THIS EVENING. THE PREVIOUS DISCUSSION CAN BE
FOUND BELOW ALONG WITH UPDATES TO THE AVIATION SECTION:
WITH LITTLE CHANGE IN THE OVERALL PATTERN FOR SUNDAY, EXPECT A
SIMILAR DAY WITH MOSTLY CLOUDY SKIES THROUGH MUCH OF THE MORNING
AND EARLY AFTERNOON, WITH PERHAPS A FEW ISOLATED SHOWERS IN THE
MORNING. HIGHS WILL BE IN THE MID 90S TO NEAR 80, AND 60S AND 70S
ALONG THE COAST. LOWS IN THE 50S TO NEAR 60 IN THE METRO.
THE UPPER LEVEL LOW, WHILE NOT MOVING MUCH, WILL APPROACH JUST
EAST ENOUGH BY SUNDAY, WHICH WILL PLACE A WEAK JET STREAK OVER
THE AREA; THE LEFT-EXIT REGION BEING OVER THE NORTHERN CASCADES.
ELEVATED INSTABILITY WILL BE PRESENT, BUT THE SURFACE WILL BE
WELL-CAPPED. THIS COULD BE ENOUGH LIFT TO SEE A FEW ISOLATED
THUNDERSTORMS, THOUGH MOISTURE CONTENT IS LOW. CONFIDENCE IS ALSO
FAIRLY LOW, BUT HAVE ADDED A 15% CHANCE FOR ISOLATED THUNDERSTORMS
ACROSS THE CASCADES LATE SUNDAY NIGHT INTO MONDAY MORNING.
GOING INTO NEXT WEEK, A BUILDING UPPER LEVEL RIDGE ACROSS THE
INTERMOUNTAIN WEST WILL PUSH THE UPPER LOW BACK TO THE
WEST/NORTHWEST, SENDING IT UP INTO THE GULF OF ALASKA. THIS WILL
ALLOW FOR TEMPERATURES TO START TO WARM UP THROUGH THE FIRST HALF
OF THE WEEK. MONDAY LOOKS TO BE AROUND 80 THROUGH THE LOWLANDS
WITH 70S ALONG THE COAST AS THE DAY STARTS CLOUDY THEN CLEARS FOR
THE AFTERNOON. LESS CLOUDS TO START TUESDAY SHOULD ALLOW FOR HIGHS
TO REACH INTO THE MID 80S, WITH 90S STARTING TO SHOW UP IN THE
CASCADE VALLEYS. LOW TEMPERATURES WILL START TO CLIMB, WITH LOWS
AROUND 60 ACROSS THE METRO AND LOW TO MID 60S FOR SOME OF THE
CASCADE VALLEYS. HERE IS WHEN WE WILL START TO SEE AREAS OF
MODERATE (ORANGE) HEATRISK, WITH MAJOR (RED) HEATRISK FOR THE
CASCADE VALLEYS.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
AS THE UPPER LEVEL LOW
RETROGRADES TO THE NORTHWEST, IT MAY BE ABLE TO PULL IN A WEAK
SHORTWAVE TROUGH UP FORM NORTHERN CALIFORNIA ACROSS THE PACIFIC
NORTHWEST ON WEDNESDAY. WILL HAVE TO WATCH CLOSELY TO SEE HOW THIS
PATTERN PROGRESSES. GOING INTO THURSDAY AND FRIDAY IS WHEN WE
START TO SEE THE RIDGE BREAK DOWN. CURRENTLY, WEDNESDAY AND
THURSDAY LOOK TO BE THE WARMEST DAYS, WITH MORE UNCERTAINTY AS TO
HOW FAST WE COOL OFF FRIDAY INTO NEXT WEEKEND BUT A RETURN TO MORE
SEASONABLE TEMPERATURES IS EXPECTED.
HIGHS WEDNESDAY AND THURSDAY LOOK TO BE IN THE 80S TO LOW 90S
THROUGH MUCH OF THE INTERIOR, AND APPROACHING 100 IN THE CASCADE
VALLEYS. LOWS WILL BE IN THE UPPER 50S TO LOW 60S, WITH MID TO
UPPER 60S POSSIBLE IN THE CASCADES AND VALLEYS AS THE FLOW LOOKS
TO TURN LIGHT OFFSHORE OVERNIGHT. THIS WILL CORRESPOND TO
WIDESPREAD MODERATE HEATRISK, INCLUDING THE MOUNTAINS, WITH MAJOR
HEATRISK IN THE VALLEYS THROUGH THURSDAY.
62
AVIATION
SOUTHERLY FLOW ALOFT WILL INCREASE INTO SUNDAY AS AN
UPPER LOW OFFSHORE DRIFTS TOWARDS THE COAST. AREAS OF MVFR/IFR
STRATUS WILL REDEVELOP LATE TONIGHT INTO SUNDAY MORNING. CEILINGS
WILL THEN IMPROVE SUNDAY AFTERNOON TO VFR. A FEW SHOWERS MAY DEVELOP
SUNDAY OVER THE OLYMPIC PENINSULA AND INTERIOR AREAS MAINLY NORTH OF
KPAE.
KSEA...VFR CONDITIONS INTO TONIGHT WITH MID AND HIGH CLOUDS AT
TIMES. THE PRESENCE OF THE UPPER TROUGH OFFSHORE COMPLICATES THE
FORECAST IN TERMS OF LOW CEILING DEVELOPMENT ON SUNDAY MORNING.
CONFIDENCE IS CURRENTLY LOW IN ANY IFR CEILINGS AND MAY SCALE BACK
CEILINGS TO A PERIOD OF MVFR SUNDAY MORNING IN THE 06Z TAF ISSUANCE.
SURFACE WINDS LIGHT NORTHERLY SHIFTING W/NW SUNDAY AFTERNOON. 27
MARINE
AN ONSHORE FLOW PATTERN WILL CONTINUE INTO NEXT WEEK.
ONSHORE FLOW WILL VARY IN INTENSITY, WITH WESTERLY PUSHES THROUGH
THE STRAIT OF JUAN DE FUCA EACH EVENING. THERE IS APPROXIMATELY A
30% CHANCE OF SMALL CRAFT ADVISORY WIND GUSTS IN THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA THIS EVENING, AND HAVE HELD OFF ON
ANY SCA GIVEN THE LIMITED CONFIDENCE. HIGHER CONFIDENCE IN SCA WIND
GUSTS SUNDAY EVENING, AND AS A RESULT HAVE ISSUED A SCA FOR THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA DURING THIS PERIOD.
ONSHORE FLOW WILL THEN CONTINUE INTO MIDWEEK.
ALTHOUGH PRIMARILY DRY CONDITIONS ARE EXPECTED, THERE IS LESS THAN A
10% CHANCE OF THUNDERSTORMS INTO SUNDAY AS WELL.
SEAS OF 2 TO 4 FEET FOR THE COASTAL WATERS THROUGH TUESDAY WILL
BUILD TO 4 TO 6 FEET BY MIDWEEK. JD
FIRE WEATHER
A SLIGHT CHANCE OF DRY THUNDERSTORMS IS FORECAST FOR
THE NORTH CASCADES TOMORROW EVENING, WITH AN OUTSIDE CHANCE OF
LINGERING INTO MONDAY. A LOW PRESSURE SYSTEM PARKED OFFSHORE WILL
SEND A WEAK IMPULSE INTO THE AREA, STEEPENING THE LAPSE RATES AND
OFFERING SOME ASCENT, ALTHOUGH WEAK. THERE IS NO SIGNIFICANT SOURCE
OF MOISTURE, INCREASING CONCERN OVER DRY LIGHTNING STRIKES. ANY
STORMS THAT HAPPEN TO DEVELOP WILL BE CAPABLE OF GUSTY AND ERRATIC
WINDS AS A BY-PRODUCT OF THE STEEP LAPSE RATES AND DOWNDRAFT CAPE,
AS WELL AS LIGHTNING ON DRY FUELS. THE PROBABILITIES ARE CAPPED AT
10-15%.
LATER THIS WEEK, TEMPERATURES WILL BE CLIMBING AND HUMIDITY DROPPING
OFF, WITH POOR OVERNIGHT RECOVERIES. TEMPERATURES WILL BE WELL INTO
THE UPPER 80S TO MID 90S, WITH NEAR 100 DEGREES IN THE CASCADE
VALLEYS AS PERIODS OF LIGHT OFFSHORE FLOW DEVELOP DURING THE DAY.
ELEVATED CONCERNS FOR HOT, DRY AND UNSTABLE CONDITIONS WILL PERSIST
THROUGH MUCH OF THE MID TO LATE WEEK PERIOD.
21
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM SUNDAY TO 2 AM PDT MONDAY FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
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