249
FXUS66 KSEW 211629
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
929 AM PDT MON APR 21 2025
SYNOPSIS
CONDITIONS WILL BEGIN TO DRY OUT TODAY AS A TROUGH
EXITS. HIGH PRESSURE WILL BRING DRY AND WARMER CONDITIONS
WEDNESDAY AND THURSDAY. PRECIPITATION CHANCES RETURN FRIDAY INTO
THE WEEKEND.
UPDATE
WEAK CONVERGENCE BANDING IS STILL PRESENT ACROSS THE
NORTH INTERIOR THIS MORNING AND SOME VERY WEAK SHOWER ACTIVITY WAS
NOTED ALONG THE SOUTH COAST. THE POP FORECAST WAS ADJUSTED
SLIGHTLY TO ACCOUNT FOR THESE LATEST TRENDS. REGARDLESS, SHOWER
ACTIVITY WILL GRADUALLY TAPER OFF THROUGH THE DAY AND SHOULD BE
LARGELY WRAPPED UP BETWEEN THE 00-03Z TIME FRAME. THE REST OF THE
FORECAST IS ON TRACK AND NO FURTHER UPDATES ARE PLANNED.
-WOLCOTT-
SHORT TERM /TODAY THROUGH WEDNESDAY/
CLASSIC CONVERGENCE ZONE
OVER KING COUNTY OVERNIGHT WITH ONSHORE FLOW AND TROUGHING
OVERHEAD. SO FAR THE CENTRAL CASCADE PASSES LOOK BARE/WET BUT
COULD STILL SEE LIGHT SNOW AT BOTH STEVENS AND SNOQUALMIE PASS
WITH SNOW LEVELS LOWERING TO AROUND 2500 FT. BUT IN GENERAL, THE
CONVERGENCE ZONE WILL FADE THIS MORNING AS THE TROUGH EXITS EAST.
TEMPERATURES WILL TRACK COOLER THAN AVERAGE WITH HIGHS IN THE 50S
TODAY. LOWS WILL DROP INTO THE 30S AND LOWER 40S TONIGHT, WITH
LOWER 30S AROUND THE SOUTH SOUND. THERE'S A LOW CHANCE (10
PERCENT) OF SEEING FREEZING CONDITIONS IN THE SOUTH SOUND. IF SO,
DUE TO CLEARING AND LIGHT WINDS, IT WOULD BE BRIEF IN DURATION.
WE'RE UNDER DRY N/NW FLOW ON TUESDAY WITH HIGH PRESSURE OFFSHORE.
TEMPERATURES ARE A LITTLE WARMER AND IN THE LOWER 60S IN THE
INTERIOR, WITH 50S ELSEWHERE. LOWS WILL BE COOL AND IN THE 30S AND
LOWER 40S AGAIN. THE RIDGE SHIFTS INLAND ON WEDNESDAY FOR SUNNY
SKIES AND HIGHS IN THE 60S THROUGHOUT. 33
LONG TERM /THURSDAY THROUGH SUNDAY/
HIGH PRESSURE BRINGS ONE
MORE DRY AND WARM DAY ON THURSDAY WITH TEMPERATURES PEAKING IN
THE 60S AND 70S. A TROUGH THEN BRINGS SHOWERS AND COOLER
CONDITIONS MOVING INTO FRIDAY. RAIN AND COOLER WEATHER FOLLOWS
INTO THE WEEKEND WITH A BROAD TROUGH OVER THE WEST. SUNDAY IS A
LITTLE DRIER AND WARMER (NEAR NORMAL) AS THE LOW CENTER SHIFTS
TOWARD THE GREAT BASIN. 33
AVIATION
LINGERING SHOWERS AND LOWER CEILINGS REMAIN SPREAD
ACROSS THE REGION THIS MORNING ASSOCIATED WITH RESIDUAL CONVERGENCE
THAT FORMED BEHIND THE LAST DISTURBANCE. EXPECT MVFR CEILINGS AND
RAIN SHOWERS TO CONTINUE IN KING COUNTY AS WELL AS FROM NEAR KFHR
ACROSS TO KBVS AND SOUTH THROUGH KPAE FOR THE NEXT FEW HOURS THIS
MORNING. OTHERWISE, BUILDING HIGH PRESSURE AND SOMEWHAT LIGHT WINDS
WILL PROVIDE FOR SCATTERING THIS AFTERNOON ACROSS THE REGION. LOWER
MVFR CEILINGS LIKELY DEVELOP AGAIN TONIGHT, ESPECIALLY SOUTH AND
SOUTHWEST OF THE SEATTLE AREA TERMINALS.
KSEA...PSCZ SHOWERS HAVE LARGELY FADED OUT BUT EXPECT RESIDUAL
CEILINGS AROUND THE TERMINAL AREA THROUGH AROUND 19-20Z BEFORE
LIFTING AND CONTINUING TO SCATTER. SOUTHERLY WINDS CONTINUE TODAY,
WITH A LIKELY SHIFT TO NORTHERLY WINDS EARLY TUESDAY WITH BUILDING
HIGH PRESSURE. LOW (10-15%) CHANCE OF LOWER MVFR CEILINGS TRYING TO
DEVELOP AROUND 12Z, BUT THESE SHOULD REMAIN WELL SOUTH AND SOUTHWEST
OF THE TERMINAL. 12
MARINE
CONTINUED ONSHORE FLOW CONTINUES BEHIND THE LATEST
DISTURBANCE, WITH LOW-END ADVISORY WINDS LINGERING OVER THE NORTHERN
AND OUTER COASTAL ZONES. LOOK FOR THESE WINDS TO EASE TODAY AND HIGH
PRESSURE TO REBUILD OVER THE COASTAL WATERS THROUGH THE NEXT SEVERAL
DAYS. MEANWHILE, SEAS REMAIN AROUND 8 TO 10 FEET AND RATHER CHOPPY
WITH DOMINANT PERIOD AROUND 8 SECONDS THIS MORNING. IMPACTFUL
WEATHER CONDITIONS ARE NOT EXPECTED THROUGH THE MIDDLE OF THE WEEK
AFTER TODAY AS SEAS DIMINISH AND WINDS EASE. ANOTHER DISTURBANCE
FRIDAY AND SATURDAY WILL BRING ANOTHER ROUND OF BUILDING SEAS AND
POTENTIALLY STRONGER WINDS TO THE LOCAL WATERS. 12
HYDROLOGY
NO RIVER FLOODING IS EXPECTED DURING THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 11 AM PDT THIS MORNING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO
60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE
OUT 10 NM.
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