680
FXUS66 KSEW 151653
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
953 AM PDT WED JUL 15 2026
UPDATE
NO CHANGES MADE IN THIS MORNING'S UPDATE. THE PREVIOUS
DISCUSSION REMAINS BELOW ALONG WITH AN UPDATED AVIATION SECTION.
SYNOPSIS
WARM AND DRY CONDITIONS AGAIN TODAY WITH HIGH PRESSURE OVER WESTERN
WASHINGTON. WIDESPREAD SHOWERS AND THE THREAT FOR THUNDERSTORMS
RETURNS THURSDAY AS A LOW PRESSURE SYSTEM PASSES THROUGH, EXITING
THE REGION THIS WEEKEND. HIGH PRESSURE BUILDS OVER THE AREA NEXT
WEEK, BRINGING A RETURN TO WARM AND DRY WEATHER.
SHORT TERM /TODAY THROUGH FRIDAY/
SATELLITE SHOWS SOME MARINE STRATUS PRESENT OVER THE SOUTHERN TWO-
THIRDS OF THE COASTLINE GRADUALLY SEEPING EASTWARD...ALTHOUGH ITS
EXTENT IS STILL SOMEWHAT LIMITED. THE NORTHERN THIRD OF THE
COASTLINE SEES SOME STRATUS AS WELL, BUT COVERAGE IS PATCHY AND
REMAINS FAIRLY STATIONARY. OTHERWISE, A BAND OF HIGH CLOUDS IS
PASSING OVER THE AREA WITH SOME BREAKS HERE AND THERE.
WARM AND DRY CONDITIONS ON TAP AGAIN TODAY AS THE UPPER LEVEL RIDGE
AXIS BEGINS TO SHIFT INTO THE GREAT PLAINS. LATEST MODELS ARE TRYING
TO TAKE INTO ACCOUNT SOME POTENTIAL INFLUENCE FROM THE UPPER LEVEL
LOW OVER THE COASTAL WATERS WHEN IT COMES TO DETERMINING THE DAYTIME
HIGH TEMP FOR TODAY...BUT ANY COOLING WOULD ONLY BE A DEGREE OR TWO
DIFFERENT FROM HIGHS YESTERDAY. THUS, NO CHANGE EXPECTED TO HEATRISK
OVER THE AREA WITH MOST OF W WA EXPECTED TO REMAIN AT MINOR/YELLOW
ALTHOUGH SOME SCATTERED AREAS OF MODERATE/ORANGE ARE EXPECTED IN
SOME VALLEYS. THE LARGEST AREA OF MODERATE/ORANGE HEATRISK REMAINS
CONSISTENT WITH PRIOR FORECASTS, GENERALLY ALONG THE I-5 CORRIDOR
FROM THE SEATTLE METRO AREA DOWN INTO TACOMA.
RAINFALL WITH THE INCOMING UPPER LOW LOOKS TO BE SPLIT INTO TWO
WAVES WITH THE FIRST STARTING LATE TONIGHT AND PRIMARILY FOCUSED ON
THE CASCADES. THE SECOND WAVE ENTERS INTO THE CWA THURSDAY MORNING
AND SPREADS FROM SW TO NE OVER THE AREA THROUGHOUT THE DAY. THIS
SECONDARY WAVE POSES THE HIGHER THUNDERSTORM POTENTIAL OF THE TWO
AND, UNLIKE MODEL OUTPUT FROM 24 HOURS AGO, THE THUNDER THREAT NO
LONGER SEEMS TO BE ATTACHED TO TERRAIN...PUTTING THE LOWLANDS INTO A
SLIGHT CHANCE FOR THUNDERSTORMS AS WELL. DAYTIME HIGHS THURSDAY
REMAIN A BIT OF A CHALLENGE, AS EASTERLY FLOW DURING THE OVERNIGHT
HOURS WEDNESDAY COULD PLAY A ROLE IN KEEPING TEMPS A LITTLE HIGHER
THAN WHAT WOULD NORMALLY BE THE CASE. THE TIMING OF THE CHANGEOVER
FROM OFFSHORE FLOW TO ONSHORE FLOW STILL LOOKS FAVORABLE TOWARD THE
COOLER SOLUTIONS AND AS SUCH HIGHS ARE EXPECTED TO DIP DOWN INTO THE
LOWER TO MID 70S FOR THE INTERIOR LOWLANDS, LOWER TO MID 60S ALONG
THE COAST.
THE UPPER LOW THEN MAKES LIKE A DINE AND DASH, EJECTING QUICKLY OUT
OF THE AREA FRIDAY AND TAKING THE MAJORITY OF ITS MOISTURE WITH IT.
WHILE SOME LOW-END CHANCE TO SLIGHT CHANCE POPS WILL LINGER OVER THE
NORTHERN THIRD OF THE CWA, GENERALLY DRY CONDITIONS ARE EXPECTED,
WHILE DAYTIME HIGHS BEGIN THEIR REBOUND AS MID TO UPPER 70S ARE
QUICK TO RETURN TO THE INTERIOR LOWLANDS.
18
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
ALTHOUGH UPPER LEVEL TROUGHING WILL BE PRESENT OVER THE AREA FRIDAY
NIGHT AND INTO THE WEEKEND, THE BUILDING RIDGE OVER THE EASTERN
PACIFIC WILL BE THE DRIVING FORCE IN W WA WEATHER, RETURNING WARM
AND DRY CONDITIONS TO THE AREA AS THIS FEATURE GRADUALLY SLIDES
EASTWARD THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. THIS WILL
BE MOST OBVIOUS IN THE STEEP WARMING TREND IN DAYTIME HIGHS DURING
THE LONG TERM PERIOD WITH TEMPS RANGING IN THE UPPER 70S TO LOWER
80S SATURDAY /MID 60S TO NEAR 70 ALONG THE COAST/, LOWER TO MID 80S
SUNDAY /LOWER 70S ALONG THE COAST/ AND UPPER 80S TO LOWER 90S /MID
70S TO NEAR 80 ALONG THE COAST/ ON MONDAY. THIS WILL RATCHET UP
HEATRISK OVER THE AREA DURING THIS TIME FRAME. SATURDAY REMAINS IN
WIDESPREAD MINOR/YELLOW WITH LARGER SWATHS OF MODERATE/ORANGE
BECOMING PRESENT FOR SUNDAY. MONDAY SEES WIDESPREAD MODERATE/ORANGE
CONDITIONS WITH SOME ISOLATED SPLOTCHES OF MAJOR/RED. THE POTENTIAL
FOR A MARINE PUSH TUESDAY COULD KEEP THIS THREAT LIMITED TO ONE DAY
AS DAYTIME HIGHS RETREAT A HANDFUL OF DEGREES.
18
AVIATION
WIDESPREAD VFR CONDITIONS WILL CONTINUE ACROSS MUCH OF
THE AIRSPACE THROUGHOUT THE PERIOD, EXCEPTING THE PACIFIC COAST. LOW
MARINE STRATUS WILL YIELD PERSISTENT RESTRICTED CIGS AT COASTAL
TERMINALS INCLUDING KHQM , WITH HIGH CONFIDENCE (75% OR GREATER
CHANCE) IN IFR OR LOW-END MVFR (BELOW 1.5 KFT) CIGS THROUGH AT LEAST
17Z. DIURNAL MIXING WILL SEE SKIES TREND CLEARER THROUGH THE
LATE MORNING AND EARLY AFTERNOON, WITH VFR CONDITIONS FAVORED
(50% CHANCES OR HIGHER) AT KHQM BY 19Z WED. LIGHT AND VARIABLE
WINDS EARLY THIS MORNING WILL BUILD TO 5-10 KT OUT OF THE NORTH
TO NORTHWEST AT MOST TERMINALS, AND 10-15 KT ALONG THE COAST
SOUTH OF CAPE ELIZABETH, BEFORE EASING AFTER 00-03Z THU.
KSEA...HIGH CONFIDENCE IN VFR CONDITIONS CONTINUING THROUGHOUT THE
PERIOD. LIGHT SOUTHWEST WINDS OF 5 KT OR LESS EARLY THIS MORNING
WILL SHIFT OUT OF THE NORTHWEST AND BUILD TO 6-10 KT BY 21Z WED,
VEERING FURTHER OUT OF THE NORTH THROUGH THE AFTERNOON, BEFORE
BECOMING LIGHT AND VARIABLE AFTER 06Z THU.
PICARD/MAZURKIEWICZ
MARINE
A WEAK SURFACE LOW WILL MEANDER OVER THE COASTAL WATERS
THROUGH FRIDAY, RESULTING IN NORTHWEST FLOW BACKING OUT OF THE SOUTH
TO SOUTHWEST THURSDAY INTO FRIDAY, BEFORE VEERING BACK OUT OF THE
NORTHWEST BY LATE FRIDAY. DIURNAL WESTERLY FLOW WILL NONETHELESS
CONTINUE THROUGH THE STRAIT OF JUAN DE FUCA, PEAKING EACH AFTERNOON
BUT REMAINING BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH AT LEAST
THE NEXT FEW DAYS. A MORE TYPICAL SUMMERTIME PATTERN RETURNS THIS
WEEKEND WITH NORTHERLY WINDS OVER THE WATERS, AND GUSTS AS HIGH AS
15-25 KT BEYOND 30 NM.
SEAS OF 4-6 FT TODAY BUILD SLIGHTLY TO 5-8 FT TONIGHT INTO THURSDAY
WITH A CONTINUED DOMINANT WEST-NORTHWEST SWELL AT 7-8 SECONDS. SEAS
EASE BACK TO 4-6 FT FRIDAY, BUT STRONGER NORTHWEST WINDS DEVELOPING
THIS WEEKEND WILL SEE 10-30% CHANCES SEAS REACH 8-10 FT, MOST LIKELY
BEYOND 30-40 NM.
PICARD
FIRE WEATHER
WARM TEMPERATURES ARE EXPECTED TO CONTINUE AGAIN TODAY, WITH MINIMUM
RELATIVE HUMIDITY VALUES DIPPING INTO THE UPPER 20% TO LOW 30%
THROUGHOUT WESTERN WASHINGTON. AN ELEVATED FIRE WEATHER PATTERN WILL
SET UP STARTING TONIGHT AND LIKELY CONTINUE THROUGH EARLY NEXT WEEK.
SHOWERS AND THUNDERSTORMS RETURN TO THE FORECAST TONIGHT THROUGH
THURSDAY. THE MAIN CONCERNS WITH THESE STORMS WILL BE DRY LIGHTNING
/STORMS RESULTING IN LESS THAN 0.25 OF AN INCH OF RAINFALL/ AND THE
POTENTIAL FOR STRONG OUTFLOWS BETWEEN 35-50 MPH. STORMS THAT DEVELOP
ON THE WEST SLOPES OF THE OLYMPICS ARE MORE LIKELY TO PRODUCE A
WETTING RAIN (0.25 INCHES OR MORE), WHILE STORMS ALONG THE CASCADES
WILL PRODUCE SUB-WETTING RAIN AMOUNTS OF 0.10-0.20 INCHES. TAKING
ALL OF THAT INTO ACCOUNT, THE INHERITED FIRE WEATHER WATCH REMAINS
IN PLACE STARTING LATE TONIGHT THROUGH THURSDAY EVENING.
FIRE WEATHER CONCERNS LINGER INTO EARLY NEXT WEEK AS A HOTTER AND
DRIER PATTERN SETS UP OVER WESTERN WASHINGTON, POTENTIALLY
INCREASING FIRE ACTIVITY FROM ANY NEW LIGHTNING STARTS FROM
THURSDAY'S CONVECTION.
29/18
SEW WATCHES/WARNINGS/ADVISORIES
WA...FIRE WEATHER WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING
FOR EAST PORTION OF THE OLYMPIC MOUNTAINS-WEST PORTION OF
THE OLYMPIC MOUNTAINS-WEST SLOPES OF THE CENTRAL CASCADES
GENERALLY ABOVE 1500 FEET-WEST SLOPES OF THE NORTH
CASCADES GENERALLY ABOVE 1500 FEET.
PZ...NONE.
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