903
FXUS66 KSEW 062039
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
139 PM PDT SAT JUN 6 2026
SYNOPSIS
AN UPPER LEVEL TROUGH OVER WESTERN WASHINGTON TODAY WILL SHIFT
EASTWARD TONIGHT. A WEAK UPPER RIDGE WILL PRODUCE A BRIEF DRYING
TREND ON SUNDAY BEFORE A SERIES OF SYSTEMS PRODUCE COOL AND
UNSETTLED CONDITIONS FOR THE FIRST HALF OF THE COMING WEEK. A
PATTERN SHIFT TOWARD DRY AND CONSIDERABLY WARMER CONDITIONS IS
EXPECTED LATE NEXT WEEK AS STRONG HIGH PRESSURE ALOFT BUILDS
INTO THE REGION.
SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/
DAYTIME HEATING COUPLED WITH AN UPPER TROUGH AXIS OVER WESTERN
WASHINGTON WILL PRODUCE SCATTERED SHOWERS, ISOLATED THUNDERSTORMS
AND UNSEASONABLY COOL TEMPERATURES INTO THIS EVENING. THE HIGHER
TERRAIN OF THE CASCADES AND OLYMPICS ABOVE 4500 FEET WILL SEE
SOME LIGHT SNOWFALL, BUT IT IS NOT EXPECTED TO PRODUCE ANY TRAVEL
IMPACTS ACROSS THE PASSES. THE TROUGH WILL SHIFT EASTWARD TONIGHT
AND A WEAK SHORTWAVE RIDGE WILL SLIDE ONSHORE ON SUNDAY ALLOWING
THE AREA TO BRIEFLY DRY OUT THOUGH TEMPERATURES WILL REMAIN BELOW
NORMAL. THE NEXT IN A SERIES OF TROUGHS WILL SPREAD ADDITIONAL
CLOUDS AND SHOWERS INTO THE REGION SUNDAY NIGHT INTO MONDAY.
IT'S EASTWARD PROGRESSION WILL, HOWEVER, BE HINDERED AS A WEAK
SURFACE LOW DEVELOPING OFF THE OREGON COAST SPLITS THE SYSTEM
APART AND TAKES THE FOCUS OF THE BULK OF THE PRECIPITATION INTO
OREGON.
LONG TERM /TUESDAY THROUGH SATURDAY/
THE COOL AND UNSETTLED PATTERN CONTINUES INTO THE MIDDLE OF THE
COMING WEEK AS ANOTHER UPPER TROUGH DIGGING SOUTHWARD ALONG THE
BRITISH COLUMBIA COAST KEEPS SHOWERS AND COOL TEMPERATURES IN
THE FORECAST.
THE NARRATIVE TAKES A DECIDED TURN FROM THAT POINT FORWARD.
ENSEMBLES ARE VIRTUALLY UNANIMOUS THAT WE'LL SEE A SUBSTANTIVE
CHANGE IN THE SYNOPTIC PATTERN HEADING INTO LATE NEXT WEEK AND
THE DAYS THAT FOLLOW. A BUILDING UPPER RIDGE WILL PRODUCE A
WARMING TREND THAT WILL RESULT IN TEMPERATURES CLIMBING BACK TO
JUST ABOVE NORMAL LEVELS SWIFTLY ON THURSDAY. THE CLIMB UPWARD
CONTINUES AS WE ROUND OUT THE WEEK AND LIKELY BEYOND. HIGH
TEMPERATURES BY THE BEGINNING OF NEXT WEEKEND COULD RUN 10 TO 15
DEGREES ABOVE SEASONAL AVERAGES AS ANOMALOUSLY STRONG UPPER
RIDGING TAKES UP RESIDENCE JUST TO OUR WEST.
LONGER TERM GUIDANCE STRONGLY SUGGESTS THAT THE UPWARD TREND IN
TEMPERATURES WILL PERSIST BEYOND THE 7 DAY PERIOD. PROBABILISTIC
HEATRISK SUGGESTS A 90-100% CHANCE OF MINOR HEATRISK ACROSS
MUCH OF THE LOWLANDS BY FRIDAY AND SATURDAY AND A 40-70%
PROBABILITY OF MODERATE HEATRISK ON SATURDAY FOR THE INTERIOR
LOWLANDS OF SOUTH PUGET SOUND AND THE SOUTHWEST INTERIOR. THOUGH
IT'S EARLY YET, CURRENT PROBABILISTIC DATA HAS A CONSIDERABLE
PORTION OF THE CWA LIKELY REACHING MODERATE HEATRISK AS WE ENTER
THE JUNE 14TH/15TH PERIOD WITH POTENTIAL DAYTIME TEMPERATURES
IN THE MID 80S TO MID 90S FOR INTERIOR AREAS FROM SEATTLE
SOUTHWARD. STAY TUNED.
27
AVIATION
AN UPPER TROUGH AXIS OVER THE INTERIOR THIS AFTERNOON WILL SHIFT
EAST OF THE CASCADES TONIGHT. WESTERLY FLOW ALOFT WILL BECOME
NORTH TO NORTHWESTERLY TONIGHT. A COMBINATION OF DAYTIME HEATING
AND COOL TEMPERATURES ALOFT WILL DESTABILIZE THE AIR MASS THIS
AFTERNOON FOR SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. LOW
LEVEL CONVERGENCE WILL ENHANCE THIS ACROSS CENTRAL PUGET SOUND.
SHOWER COVERAGE WILL DIMINISH THIS EVENING. MVFR CEILINGS CAN BE
EXPECTED AROUND HEAVIER SHOWERS AND/OR ISOLATED THUNDERSTORMS.
REMNANT LOW LEVEL MOISTURE AND LIGHT SURFACE WINDS WILL LEAD TO
GREATER COVERAGE OF MVFR CEILINGS ACROSS THE REGION ON SUNDAY
MORNING. THIS WILL GRADUALLY LIFT TO VFR SUNDAY AFTERNOON.
KSEA...TEMPO MVFR CEILINGS EXPECTED AROUND SOME OF THE HEAVIER
SHOWERS TODAY. CONFIDENCE IN THUNDERSTORM ACTIVITY IN THE VICINITY
OF THE TERMINAL REMAINS FAIRLY HIGH. GUSTY AND ERRATIC WINDS
CAN BE EXPECTED AROUND ANY STORMS THAT DO DEVELOP. MORE
PREDOMINANT MVFR CEILINGS ARE EXPECTED SUNDAY AM AS REMNANT LOW
LEVEL MOISTURE REMAINS IN THE AREA. THESE WILL LIFT TO VFR
SUNDAY AFTERNOON. SURFACE WINDS SOUTH TO SOUTHWESTERLY 9 TO 13
KNOTS INTO THE AFTERNOON. THE CONVERGENCE ZONE IS EXPECTED TO
SHIFT INTO THE VICINITY OF THE TERMINAL FOR FEW HOURS THIS
EVENING FOR A BRIEF TO SWITCH TO NW-NE WINDS. WINDS WILL SWITCH
BACK TO PREVAILING SOUTHERLIES AFTER 06Z.
27
MARINE
A WEAK TROUGH OVER THE COASTAL WATERS WILL SHIFT INLAND TONIGHT
AS WEAK HIGH PRESSURE BUILDS JUST OFFSHORE. ANOTHER TROUGH AND
ASSOCIATED FRONTAL SYSTEM WILL APPROACH THE OUTER COASTAL WATERS
SUNDAY EVENING THEN SLOW AND DISSIPATE IN RESPONSE TO A WEAK
SURFACE LOW MOVING TOWARD THE OREGON COAST. ONSHORE FLOW WILL
INCREASE TUESDAY AND WEDNESDAY AS BROAD HIGH PRESSURE GRADUALLY
EXPANDS INTO THE COASTAL AND OFFSHORE WATERS. ONSHORE FLOW WEAKENS
LATE NEXT WEEK AS THERMALLY INDUCED LOW PRESSURE BEGINS TO
EXPAND NORTHWARD ACROSS WESTERN OREGON.
COASTAL SEAS ARE EXPECTED TO REMAIN BELOW 10 FEET THROUGH THE
PERIOD.
27
FIRE WEATHER
ALTHOUGH LIGHTNING WILL BE POSSIBLE TODAY AND RAINFALL AMOUNTS MAY
NOT QUITE MAKE IT UP TO THE 0.25 IN THRESHOLD SEPARATING WET AND DRY
STORMS, MIN RH VALUES EXCEEDING 60 PCT SHOULD LIMIT ANY FIRE WEATHER
CONCERNS TODAY. AS THE GENERALLY TROUGHY PATTERN REMAINS IN PLACE
OVER W WA IN THE FIRST HALF OF THE UPCOMING WEEK, AGAIN, SOME
LIMITING MOISTURE IS EXPECTED TO REMAIN IN PLACE.
AS UPPER LEVEL RIDGING BUILDS INTO THE AREA STARTING THURSDAY,
CONDITIONS, INCLUDING FUELS, WILL NEED TO BE MONITORED AS
TEMPERATURES ARE EXPECTED TO CLIMB TO ABOVE NORMAL VALUES ENTERING
INTO THE WEEK 2 TIME PERIOD.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 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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