615
FXUS66 KSEW 121538
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
838 AM PDT SAT SEP 12 2026
UPDATE
NO MAJOR UPDATES TO THE FORECAST TODAY. SHOWERS AND
THUNDERSTORMSARE STILL FORECAST FOR LATE THIS AFTERNOON
THROUGH EARLY SUNDAY AS THE SYSTEM MOVES ACROSS THE AREA. A FEW
ISOLATED STRIKES HAVE BEEN OBSERVED OVER THE COASTAL WATERS THIS
MORNING. SEE BELOW FOR AN UPDATE TO THE AVIATION DISCUSSION. 62
SYNOPSIS
UNSETTLED WEATHER WILL MOVE INTO WESTERN WASHINGTON THIS
WEEKEND WITH RAIN, SHOWERS, AND THE POTENTIAL FOR THUNDERSTORMS.
DRIER CONDITIONS ARE EXPECTED TO RETURN BY MONDAY, WITH
TEMPERATURES GRADUALLY WARMING BACK UP THROUGHOUT THE COURSE OF
THE WEEK.
SHORT TERM /TODAY THROUGH MONDAY/
AN UPPER-LOW IS CURRENTLY POSITIONED OVER THE OFFSHORE WATERS
THIS MORNING. IT'LL TRACK INLAND AS THE DAY PROGRESS BRINGING
WIDESPREAD RAIN, SHOWERS AND A 15-25% CHANCE OF THUNDERSTORMS.
THE NBM HAS HIGHEST PROBABILITY OF LIGHTNING OCCURING OVER THE
OLYMPIC PENINSULA AND SOUTHWEST INTERIOR WHERE HREF SURFACE
BASED CAPE HAS 250-500 J/KG PRESENT. RAINFALL IS FORECAST TO
ARRIVE TOWARDS THE LATE AFTERNOON-EVENING HOURS ON SATURDAY BUT
CAN'T RULE OUT A FEW SHOWERS BEFOREHAND. THE ACTIVITY WILL
PERSIST OVERNIGHT SATURDAY INTO SUNDAY MORNING BEFORE
CONDITIONS TREND DRIER BY SUNDAY EVENING THOUGH, CAN'T RULE OUT
LINGERING SHOWERS OVER THE CASCADES. 24 HOUR PRECIPITATION
PROBABILITIES GREATER 2.00" RANGE BETWEEN 50-80% ACROSS THE
CENTRAL AND SOUTHERN CASCADES THROUGH SUNDAY NIGHT.
PROBABILITIES GREATER THAN 1.00" RANGE ANYWHERE FROM 30-60%
ACROSS THE PUGET SOUND LOWLANDS INTO THE SOUTHWEST INTERIOR.
AREAS NORTHWARD TOWARDS BELLINGHAM WON'T BE AS WET. WINDS THIS
WEEKEND SHOULD BE GENERALLY BENIGN BUT CAN'T RULE OUT LOCAL
GUSTS UPWARDS OF 20-25 MPH. HIGH TEMPERATURES WILL REMAIN IN THE
UPPER 60S TO AROUND 70, WITH LOWS IN THE MID 50S.
EXPECT CONDITIONS TO DRY OUT AREA WIDE THROUGH THE DAY ON
MONDAY WITH TEMPERATURES REMAINING THE SAME AS THE PREVIOUS
DAYS. THE UPPER-LOW WILL BE WELL EAST OF THE AREA, NEAR THE
NORTHERN GREAT PLAINS BY MONDAY EVENING. WE'LL BE LEFT IN A
REGIME OF NORTHWESTERLY FLOW ALOFT AS A STOUT UPPER-RIDGE
POSITIONS OVER THE GULF OF ALASKA.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
ANOTHER TROUGH WILL PASS THROUGH EARLY TUESDAY, HOWEVER MOISTURE
DOESN'T APPEAR TO BE ABUNDANT WITH THIS FEATURE. WEDNESDAY IS
WHERE THE MODELS HAVE AN UPPER LEVEL HIGH BUILDING OVER THE
PACIFIC, WITH A SPLIT DIFFERENCE AS TO HOW LONG THE HIGH REMAINS
OFFSHORE GOING INTO LATE NEXT WEEK. REGARDLESS, MOST WILL SEE A
WARM UP ALONG WITH CONTINUED DRY WEATHER. HIGHS IN THE LOWLANDS
WILL LIKELY CLIMB BACK INTO THE MID/UPPER 70S (WITH PERHAPS A
FEW 80S).
AVIATION
UPPER LEVEL LOW NEAR 45N/130W THIS MORNING WILL
SLOWLY MOVE EAST INTO OREGON TONIGHT THEN MOVE INTO EASTERN
WASHINGTON SUNDAY. SOUTHWESTERLY FLOW ALOFT THIS MORNING
BECOMING SOUTHEASTERLY THIS AFTERNOON AND EASTERLY OVERNIGHT
INTO SUNDAY MORNING. ONSHORE FLOW IN THE LOWER LEVELS.
VFR CEILINGS TODAY INTO TONIGHT. MVFR CEILINGS DEVELOPING FROM
ABOUT KPAE SOUTH SUNDAY MORNING CONTINUING THROUGH THE DAY WITH
RAIN. THERE IS A 10% OF THUNDERSTORMS ACROSS THE REGION TONIGHT.
KSEA...VFR CEILINGS TODAY INTO TONIGHT. MVFR CEILINGS DEVELOPING
AROUND 09Z SUNDAY CONTINUING INTO SUNDAY AFTERNOON. VARIABLE
WIND 5 KNOTS OR LESS BECOMING SOUTHWEST 6 TO 10 KNOTS AROUND
00Z. 33/FELTON
MARINE
A BROAD 1010 MB LOW OVER THE COASTAL WATERS TODAY WILL WEAKEN
AND MOVE SOUTH INTO OREGON TONIGHT. WEAK LOW PRESSURE REMAINING
OVER THE WATERS SUNDAY. HIGH PRESSURE WILL BUILD OVER THE
COASTAL WATERS MONDAY AND REMAIN OVER THE AREA THROUGH
WEDNESDAY.
INCREASING ONSHORE FLOW LATER TODAY WITH SMALL CRAFT ADVISORY
WESTERLIES IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA
TONIGHT. SEAS REMAINING IN THE 3 TO 5 FOOT RANGE OVER THE INNER
COASTAL WATERS AND 4 TO 6 FOOT RANGE OVER THE OUTER COASTAL
WATERS INTO THE MIDDLE OF NEXT WEEK. FELTON
FIRE WEATHER
ONSHORE MOISTURE WILL INCREASE THIS WEEKEND AS A TROUGH MOVES ACROSS
WESTERN WASHINGTON. THE INITIAL PRECIPITATION SATURDAY AFTERNOON
WILL BE MORE SHOWERY (WITH A 15-25% CHANCE OF THUNDER, HIGHEST
PROBS OVER THE OLYMPICS), BUT COVERAGE WILL BECOME MORE
STRATIFORM LATE SATURDAY NIGHT INTO SUNDAY, INCREASING THE
CHANCES OF A WETTING RAIN FOR MOST (ESPECIALLY THE SOUTH
CASCADES). AS A RESULT, THE FIRE WEATHER CONCERNS WILL REMAIN
MINIMAL GOING THROUGH THE WEEKEND AND EARLY NEXT WEEK. HIGH
PRESSURE WILL BUILD IN SOUTH B.C. BY MIDWEEK, WITH LOWER
PRESSURE OFFSHORE AT THE SURFACE. THE PATTERN WILL BECOME DRIER
WITH WARMER TEMPERATURES, AND ADDITIONALLY SOME MODELS ARE
SHOWING BRIEF BREEZY EAST TO SOUTHEAST WINDS WEDNESDAY
EVENING/THURSDAY MORNING. A FEW CASCADE LOCATIONS MAY SEE RH
VALUES DIP INTO THE 20S, THOUGH THERE REMAINS SOME UNCERTAINTY
IN THE ENSEMBLES AT THIS TIME AS TO HOW STRONG AND LONG THE HIGH
PRESSURE WILL REMAIN LATE NEXT WEEK.
HPR/41
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 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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