521
FXUS66 KSEW 110817
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
117 AM PDT SAT JUL 11 2026
SYNOPSIS
AN UPPER LEVEL TROUGH WILL PRODUCE VARYING AMOUNTS OF CLOUD
COVER THROUGH THE WEEKEND ALONG WITH NEAR SEASONAL TEMPERATURES.
HIGH PRESSURE WILL REBUILD INTO THE REGION MONDAY AND TUESDAY
FOR A WARMING TREND. A WEAK SYSTEM MAY BRIEFLY COOL TEMPERATURES
AROUND THE MIDDLE OF THE COMING WEEK BEFORE A LONGER TERM DRY
AND WARM SPELL RETURNS TOWARD NEXT WEEKEND.
SHORT TERM /TODAY THROUGH MONDAY/
A UPPER LEVEL TROUGH JUST OFFSHORE WILL SEND A SERIES OF WEAK
DISTURBANCES ACROSS THE AREA INTO EARLY SUNDAY. FOR THE MOST
PART, DRY CONDITIONS WILL PREVAIL THOUGH A COUPLE LIGHT SHOWERS
WILL BE POSSIBLE AT TIMES ACROSS THE OLYMPIC PENINSULA, NORTH
INTERIOR, AND NORTH CASCADES. TEMPERATURES THROUGH SUNDAY WILL
HOVER WITHIN A COUPLE DEGREES OF SEASONAL NORMALS FOR MOST SPOTS.
THE UPPER TROUGH WILL LIFT BACK INTO BRITISH COLUMBIA LATER ON
SUNDAY AS STRONG UPPER RIDGING CENTERED OVER THE ROCKIES AND
NORTH GREAT PLAINS EXPANDS A LITTLE WESTWARD. WITH WEAKER
ONSHORE FLOW AND MODEST HEIGHT RISES, TEMPERATURES ON MONDAY
WILL EDGE UPWARD SEVERAL DEGREES WITH PLENTY OF SUNSHINE.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
THE DRY AND WARM TREND CONTINUES INTO TUESDAY. LOW LEVEL ONSHORE
FLOW WILL INCREASE A NOTCH OR TWO WHICH WILL COOL COASTAL AREAS
A BIT, BUT INTERIOR TEMPERATURES WILL REMAIN WARM WITH AREAS
AROUND SEATTLE METRO SEEING A 30-50% PROBABILITY OF MODERATE
HEATRISK.
UNCERTAINTY REMAINS IN THE TEMPERATURE TREND FOR THE LATER HALF
OF THE UPCOMING WEEK AS A NUMBER OF ENSEMBLE MEMBERS RETAIN SOME
DEGREE OF UPPER TROUGHING JUST OFFSHORE. BASED ON THE TRENDS OF
THE LAST FEW DAYS, THE MAIN EFFECT OF THIS WEAK TROUGH MAY BE
TO SIMPLY DELAY AN IMPENDING LENGTHY PERIOD OF ABOVE NORMAL
TEMPERATURES THAT MOST GUIDANCE POINTS TOWARD COMMENCING BY NEXT
WEEKEND.
27
AVIATION
VFR CONDITIONS PREVAIL ACROSS THE AIRSPACE WITH MID-LEVEL
BKN/OVC STRATUS AROUND 5500-8000 FT ACROSS MOST OF THE REGION.
LOCATIONS THAT HAVEN'T OBSERVED MID-LEVEL STRATUS ARE EXPECTED
TO SEE IT FORM BY 10-12Z SAT. GUIDANCE HAS ONLY LOW TO MODERATE
CONFIDENCE (20-45% CHANCE) THAT STRATUS WILL DETERIORATE INTO
MVFR/IFR CIGS AT MOST TERMINALS EXCEPT FOR ALONG THE NORTHERN
PUGET SOUND AND OVER TERRAIN WHERE CONFIDENCE INCREASES TO
60-80%. IF MVFR/IFR CIGS DO DEVELOP, IT WOULD BE BY 10-12Z SAT,
IMPROVING TO VFR BY 17-20Z. WINDS GENERALLY REMAIN LIGHT AND
SOUTHWESTERLY, INCREASING TO 8-10 KTS AFTER 18-21Z SAT THROUGH
AROUND 06Z SUN.
KSEA...VFR CONDITIONS PREVAIL. GUIDANCE INDICATES A 20-40% CHANCE OF
MVFR CEILINGS DEVELOPING 10-13Z SAT. IF THEY DO MANIFEST, A RETURN
TO VFR BY 18Z IS FAVORED. SOUTHWEST WINDS CONTINUE BELOW 8 KT. THERE
ARE SIMILAR CHANCES FOR STRATUS REFORMING AROUND 10-12Z SUN.
MARINE
A WEAK SURFACE TROUGH WILL REMAIN OVER THE OFFSHORE WATERS TODAY
BEFORE HIGH PRESSURE BROADLY REBUILDS INTO THE COASTAL AND
OFFSHORE WATERS SUNDAY AND MONDAY AND REMAINS IN PLACE INTO
MIDWEEK. THIS WILL PROMOTE A FAIRLY TYPICAL SUMMER PATTERN WITH
VARYING DEGREES OF ONSHORE FLOW PROMOTING A DIURNALLY DRIVEN
INCREASE IN WESTERLIES THROUGH THE STRAIT OF JUAN DE FUCA NEARLY
DAILY. NORTHWEST WINDS OVER THE COASTAL WATERS ARE LIKELY TO
INCREASE LATER MONDAY INTO TUESDAY AS THERMALLY INDUCED SURFACE
LOW PRESSURE EXPANDING OVER THE INTERIOR OF WESTERN WASHINGTON
TIGHTENS THE ONSHORE GRADIENT.
27
FIRE WEATHER
THE CURRENT ONSHORE PATTERN WILL CONTINUE THROUGH THE WEEKEND
WHICH WILL LEAD TO CONTINUED EXCELLENT NIGHTLY RH RECOVERIES.
THERE'S A 30-40% CHANCE OF RAIN SHOWERS TODAY, MAINLY FOR THE
OLYMPICS AND NORTHERN CASCADES, BUT RAINFALL AMOUNTS DURING
THIS PERIOD WOULD GENERALLY TOTAL LESS THAN 0.10".
A RIDGE OF HIGH PRESSURE REBUILDS INTO THE REGION MONDAY AND
TUESDAY. WHILE THE ONSHORE PATTERN WILL LARGELY REMAIN IN PLACE,
WARMER DAYTIME TEMPERATURES AND CLEAR SKIES WILL LIKELY LEAD TO
RH VALUES DIPPING INTO THE 20-40% PERCENT RANGE, WITH THE
LOWEST VALUES IN THE SOUTH INTERIOR AND CASCADES VALLEYS. THIS
WILL ALLOW FINE FUELS TO CONTINUE TO DRY WITH ELEVATED FIRE
WEATHER CONDITIONS. SOME MODEST COOLING IS SLATED TO ARRIVE BY
THE MIDDLE OF NEXT WEEK, BUT MAY WELL BE SHORT-LIVED.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT EARLY THIS MORNING FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 3 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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