522
FXUS66 KSEW 151056
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
356 AM PDT WED APR 15 2026
SYNOPSIS
A COLD FRONT CONTINUES TO SHIFT EASTWARD TODAY, WITH STEADY SNOW
COMING TO AN END IN THE CASCADES. HOWEVER, EXPECT WIDESPREAD
SHOWERS WEDNESDAY ACROSS THE AREA IN THE COOL, UNSTABLE POST-
FRONTAL AIR MASS. A FEW ISOLATED THUNDERSTORMS ARE POSSIBLE THIS
AFTERNOON. DRIER BUT COOL CONDITIONS THEN DEVELOP LATER THIS
WEEK UNTIL THE NEXT FRONTAL SYSTEM APPROACHES THE REGION
OFFSHORE THIS WEEKEND.
SHORT TERM /TODAY THROUGH FRIDAY/
A COLD FRONT PASSED THROUGH WESTERN WASHINGTON YESTERDAY
EVENING/THIS MORNING. THIS IS BEING DRIVEN BY AN UPPER LEVEL
LOW/TROUGH THAT WILL DIG SOUTHWARD TODAY ACROSS THE STATE. THE RADAR
REMAINS ACTIVE THIS MORNING WITH PRECIPITATION CONTINUING IN THE
LOWLANDS AND CASCADES THIS MORNING. A CONVERGENCE ZONE IS KEEPING
SHOWERS GOING BETWEEN SEATTLE AND EVERETT. SNOW HAS BEEN FALLING AT
ALL OF THE CASCADE PASSES, AND THE SURFACE TEMPERATURES UP THERE
HAVE BEEN JUST BELOW FREEZING. THE WINTER STORM WARNING WILL
CONTINUE THROUGH 11 PM THIS EVENING, WITH A COUPLE ADDITIONAL ROUNDS
OF SNOW EXPECTED THROUGH THE DAY TODAY. A COUPLE OF THE SNOW-BANDS
LATER MAY BE ABLE TO PRODUCE HEAVIER SNOW RATES.
FOR THE REMAINDER OF THE AREA TODAY, THE COLD AIR ALOFT WITH THE
TROUGH SINKING OVER WILL CREATE AN UNSTABLE AIRMASS FOR A CHANCE OF
CONVECTION TODAY. SPC HAS THE COASTAL AREAS IN A GENERAL RISK OF
THUNDER TODAY, ALTHOUGH THE THUNDER RISK WILL ENCOMPASS THE ENTIRE
COVERAGE AREA TODAY. THE RISK IS CAPPED AT 30% (WITH THE COASTLINE
AND INTERIOR/PUGET SOUND AREAS HAVING THE BEST CHANCE OF SEEING
THUNDER). THESE SHOWERS/THUNDERSTORMS ARE EXPECTED TO BE SCATTERED
IN NATURE, WITH ANY BREAKS OF SUN DURING THE MORNING ABLE TO ADD TO
THE 200-300 J/KG OF CAPE IN PLACE. THE WINDOW FOR THUNDER WILL BE
FROM LATE MORNING THROUGH EARLY EVENING. THE MAIN CONCERNS ARE
LIGHTNING, AND DOWNPOURS CONTAINING HEAVY RAIN AND GRAUPEL/SMALL
HAIL. NO ORGANIZED SEVERE WEATHER IS EXPECTED. HIGHS TODAY REMAIN
COOL - UPPER 40S TO LOW 50S IN THE LOWLANDS, AND 30S/40S IN THE
MOUNTAINS. WINDS WILL REMAIN LIGHT OUT OF THE WEST 5-10 MPH.
THE TROUGH MOVES OUT GOING INTO THURSDAY. NORTH FLOW BEHIND THE
TROUGH WILL BRING IN COOLER CANADIAN AIR INTO THE REGION. CONDITIONS
WILL BE DRY GOING INTO THURSDAY/FRIDAY. MAIN CONCERN WILL BE THE
POTENTIAL FOR ANY FOG/FROST/FREEZE CONDITIONS NEXT COUPLE MORNINGS
TO FINISH THE WEEK. MITIGATING FACTORS WILL BE THE POTENTIAL FOR
SOME CLOUD COVERAGE OVERNIGHT, BOUNDARY LAYER CONDITIONS AND THE WET
GROUNDS FROM RECENT RAINS MAY FAVOR SOME PATCHY FOG DEVELOPMENT IN
SPOTS. LIGHT TO CALM WINDS AND ANY CLEARING THAT DOES TAKE PLACE
WILL ALLOW TEMPERATURES TO FALL INTO THE LOW 30S AND UPPER 20S
THURSDAY AND FRIDAY MORNING. PROBABILITIES FOR A HARD FREEZE ARE
GREATEST IN THE CHEHALIS VALLEY/SOUTH INTERIOR AREAS, WITH REMAINING
LOWLAND AREAS MORE LIKELY TO SEE FROST AT THIS POINT. IF
FROST/FREEZE CONDITIONS DO FORM, IT WILL BE IMPORTANT TO PROTECT ANY
PLANTS/CROPS OUTSIDE SUSCEPTIBLE TO THE COLD CONDITIONS.
HPR
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
ENSEMBLE GUIDANCE CONTINUES TO BRING THE NEXT LOW PRESSURE
SYSTEM SOUTH FROM THE GULF OF ALASKA OFFSHORE PAST THE REGION
THIS WEEKEND. THERE REMAINS A SIGNIFICANT SPREAD IN THE
EASTWARD EXTENT OF THE ASSOCIATED FRONT ACROSS THE REGION, WHICH
WOULD IMPACT THE POTENTIAL FOR ADDITIONAL RAINFALL THIS WEEKEND.
WHILE THERE REMAINS SOME MENTION ACROSS MOST OF THE AREA, THE
CHANCES REMAIN HIGHEST ACROSS THE OLYMPIC PENINSULA AND
COASTLINE. REGARDLESS, THIS LOOKS TO BE A WEAKER SYSTEM THAN
THE CURRENTLY PASSING FRONT AND A MORE SEASONABLE AIR MASS WITH
LOWLAND TEMPERATURES RETURNING TO THE 60S AND SNOW LEVELS
RETURNING BACK ABOVE THE CASCADE PASSES.
12
AVIATION
A COLD FRONT MOVED THROUGH THE TERMINALS THIS MORNING, WITH A POST-
FRONT CONVERGENCE ZONE PRODUCING ADDITIONAL SHOWERS IN PUGET SOUND.
THE SHOWERS WERE ROTATING AROUND AN ANTI-CYCLONIC MESO-LOW, WITH
SOME OUTFLOW TURNING THE WINDS NORTHEASTERLY AT KSEA AND KBFI THIS
MORNING. THE CONVERGENCE ZONE IS EXPECTED TO LAST THROUGH 16-18Z,
WITH WINDS TURNING BACK TO THE SOUTHWEST 4-8 KT. CEILINGS THIS
MORNING HAVE RANGED BETWEEN MVFR/VFR, BUT WILL TREND TOWARDS VFR
THROUGH THE DAY. A TROUGH WILL DIG SOUTHWARD TODAY, WITH NORTH FLOW
INCREASING LATE TONIGHT/THURSDAY ALOFT. BREAKS IN THE CLOUDS WITH
SUN TODAY WILL HELP DESTABILIZE THE ATMOSPHERE FOR CONVECTION DURING
THE DAY. THERE IS A 20-30% CHANCE OF THUNDER IN THE TERMINALS THIS
AFTERNOON (MOST LIKELY WINDOW IS FROM 20Z-00Z THIS AFTERNOON DENOTED
WITH PROB30). CLOUD TOPS ON ANY STORMS ARE LIKELY TO REMAIN UNDER
20,000 FT. COVERAGE WILL BE SCATTERED IN NATURE. MAIN CONCERNS ARE
LIGHTNING, HEAVY DOWNPOURS THAT MAY CONTAIN GRAUPEL/SMALL HAIL, AND
GUSTY/VARIABLE OUTFLOW WINDS. CONDITIONS WILL DRY GOING INTO
THURSDAY WITH AN INCREASED LIKELIHOOD OF MVFR CEILINGS THURSDAY
MORNING. WINDS BECOME LIGHT OUT OF THE NORTHWEST TONIGHT/THURSDAY
LESS THAN 5 KT.
KSEA...VICINITY SHOWERS WITH A CONVERGENCE ZONE TO CONTINUE THROUGH
LATE THIS MORNING. BRIEF NE WINDS WITH THIS FEATURE WILL SWITCH TO
THE SW 4-8 KT AROUND 16-18Z (FEW GUSTS UP TO 20 KT BEFORE THE
SWITCH). MVFR CEILINGS IMPROVING TO VFR THIS MORNING, WITH MVFR
LIKELY THURSDAY MORNING. SHOWERS TO CONTINUE THROUGH THE DAY AND A
30% CHANCE OF THUNDER (MOST LIKELY WINDOW IS FROM 21Z-00Z). DRIER
CONDITIONS INTO THURSDAY MORNING. LIGHTNING, GRAUPEL/DOWNPOURS, AND
VARIABLE BREEZY WINDS ARE POSSIBLE WITH STORMS IN/NEAR THE TERMINAL.
WINDS TO BECOME LIGHT UNDER 5 KT LATER THIS EVENING (BRIEF VARIABLE
PERIOD POSSIBLE FROM 22Z-02Z).
HPR
MARINE
WINDS HAVE PEAKED OVER THE WATERS THIS MORNING IN THE WAKE OF
THE PASSING COLD FRONT. WIDESPREAD SHOWERS CAN BE EXPECTED
THROUGH THE DAY WITH A FEW STRONGER ONES POTENTIALLY BRINGING
LIGHTNING AND STRONGER WIND GUSTS. MEANWHILE, SEAS REMAIN 7 TO
12 FT OVER THE COASTAL WATERS AS THEY INCREASE TODAY. EVEN IF
SHORT OF 10 FT, CONDITIONS WILL BE RATHER STEEP WITH A DOMINANT
PERIOD AROUND 8 SECONDS OVER THE COASTAL WATERS.
CONDITIONS BEGIN TO SUBSIDE LATER IN THE WEEK WITH WEAK HIGH
PRESSURE BUILDING OVER THE WATERS THURSDAY THROUGH SATURDAY. THE
NEXT FRONT WILL APPROACH THE WATERS OVER THE WEEKEND BRINGING
ANOTHER ROUND OF GUSTY WINDS AND BUILDING SEAS OVER THE WATERS
INTO THE WEEKEND.
12
HYDROLOGY
NO RIVER FLOODING IS EXPECTED DURING THE NEXT SEVEN DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...WINTER STORM WARNING UNTIL 11 PM PDT THIS EVENING FOR CASCADES
OF PIERCE AND LEWIS COUNTIES-CASCADES OF SNOHOMISH AND
NORTHERN KING COUNTIES-CASCADES OF SOUTHERN KING COUNTY-
CASCADES OF WHATCOM AND SKAGIT COUNTIES.
PZ...SMALL CRAFT ADVISORY UNTIL 10 AM PDT THIS MORNING FOR GRAYS
HARBOR BAR.
SMALL CRAFT ADVISORY UNTIL 5 AM PDT THURSDAY 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-COASTAL WATERS FROM POINT GRENVILLE
TO CAPE SHOALWATER 10 TO 60 NM-COASTAL WATERS FROM POINT
GRENVILLE TO CAPE SHOALWATER OUT 10 NM.
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