579
FXUS66 KSEW 160328
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
828 PM PDT WED JUL 15 2026
SYNOPSIS
WIDESPREAD SHOWERS AND THE THREAT FOR THUNDERSTORMS RETURNS ON
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.
UPDATE
THUNDER ACTIVITY HAS EASED NOW THAT THE SUN IS SETTING AND THE
FIRST IMPULSE HAS MOVED NORTHWARD INTO BRITISH COLUMBIA.
ANOTHER SHORTWAVE IMPULSE IS ON TRACK TO MOVE THROUGH THE LOW
AND INTO THE AREA EARLY TOMORROW MORNING AND THROUGH THE FIRST
HALF OF THE DAY. EYES WILL BE ON THE NORTHERN COAST RANGE IN
OREGON FOR DEVELOPMENT BETWEEN 5-8 AM THURSDAY MORNING AS THE
BEST CHANCES FOR STORMS WILL BE WEST OF THE METRO AND ACROSS THE
OLYMPIC PENINSULA. THE PREVIOUS DISCUSSION FOLLOWS, AS WELL AS
UPDATES TO THE AVIATION PORTION. 62
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
BROAD UPPER-RIDGING EXISTS OVER MUCH OF CONUS AT THIS TIME.
IT'S INFLUENCE HAS BEEN BEEN FELT ACROSS W WA DUE IN PART TO THE
RECENTLY OBSERVED WELL ABOVE-NORMAL TEMPERATURES THE LAST
COUPLE OF DAYS. UPSTREAM, AN UPPER-LOW IS POSITIONED JUST
OFFSHORE OF THE PNW. ITS GENTLE PROGRESSION LANDWARD WILL BE
RESPONSIBLE TO THE UPCOMING PATTERN CHANGE AS THUNDERSTORMS
ALONG THE OR AND WA CASCADE CREST THIS AFTERNOON IS A SIGN OF
WHAT'S TO COME.
TONIGHT, THE AFOREMENTIONED UPPER-LOW WILL SPREAD MOIST,
DIFFLUENT SOUTHERLY FLOW ALOFT ACROSS W WA INTO THE EARLY
MORNING HOURS ON THURSDAY. WITH OROGRAPHIC ENHANCEMENT - THE
FIRST WAVE OF RAIN AND SHOWERS WILL TRACK ALONG THE CASCADES
AFTER MIDNIGHT. HI-RES GUIDANCE (REFS) IS INDICATING SUFFICIENT
MID-LEVEL INSTABILITY WITH 7-8 C/KM DURING THE ONSET OF
PRECIPITATION ALONG WITH A COUPLE HUNDRED J/KG OF CAPE. THE NEXT
IMPULSE LOOKS TO ARRIVE BY MID-MORNING ALONG THE COAST AND
OLYMPIC PENINSULA. NBM 12-HOUR PROBABILITIES OF THUNDER ENDING
A 11 PM THURSDAY RANGE BETWEEN 20-30% ACROSS ALL OF W WA
INCLUDING THE LOWLANDS WITH THE HIGHEST PROBABILITIES ALONG THE
OLYMPIC PENINSULA. THUNDERSTORMS MAY PRODUCE SMALL HAIL, GUSTY
WINDS, AND ADDITIONAL FIRE STARTS AS A RED FLAG WARNING HAS
BEEN ISSUED - MORE DETAILS ARE PROVIDED IN THE FIRE WEATHER
SECTION BELOW.
THE UPPER-LOW WILL LIFT INTO BC ON FRIDAY AS CONDITIONS TREND
DRIER. WHILE SOME LOW-END CHANCE TO SLIGHT CHANCE POPS WILL
LINGER OVER THE NORTHERN THIRD OF THE CWA, GENERALLY DRY
CONDITIONS ARE EXPECTED. COOLER TEMPERATURES ON THURSDAY WITH
HIGHS MOSTLY IN THE LOWER TO MID 70S FOLLOWED BY A WARM UP INTO
FRIDAY WITH HIGHS IN THE MID 70S TO NEAR 80 F. OVERNIGHT LOWS
ARE FORECAST INTO THE 50S.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
SAGGY TROUGHING OVER THE REGION THIS WEEKEND BUT MID-LEVEL
HEIGHTS ARE SLATED TO RISE. AS A RESULT, CONDITIONS WILL REMAIN
DRY AND TREND WARMER BUT MINOR HEATRISK IS EXPECTED. HOWEVER,
UPPER-RIDGING WILL BUILD INTO THE AREA ON MONDAY WITH WIDESPREAD
MODERATE/ORANGE CONDITIONS WITH SOME ISOLATED SPLOTCHES OF
MAJOR/RED. THE HEAT NOW LOOKS TO POTENTIALLY STICK AROUND INTO
MIDWEEK WITH NOMINAL COOLING ACROSS THE INTERIOR.
AVIATION
SOUTHWESTERLY FLOW ALOFT AS AN CUT OFF UPPER LEVEL LOW REMAINS
OFFSHORE. ALL TERMINALS VFR THIS AFTERNOON WILL CONTINUE THROUGHOUT
THE EVENING. DIURNALLY DRIVEN WINDS GENERALLY FROM THE N/NW 5 TO 8
KNOTS WILL CONTINUE THIS EVENING BECOMING LIGHT TO CALM OVERNIGHT.
WINDS WILL THEN SHIFT SOUTHERLY/SOUTHWESTERLY THURSDAY MORNING AND
INCREASE TO 5 TO 10 KT BY THE AFTERNOON. CONDITIONS WILL LOWER
TONIGHT INTO THURSDAY MORNING ALONG THE COAST WITH A RETURN OF
MVFR/IFR MARINE STRATUS STARTING 04-06Z AND CONTINUING THROUGHOUT
MAJORITY OF THURSDAY MORNING.
CONDITIONS OVER THE INTERIOR LOOK TO REMAIN VFR FOR THE MAJORITY OF
THE TAF PERIOD , ALTHOUGH THERE WILL BE INTRODUCTION FOR RAIN
SHOWERS AND A CHANCE OF ISOLATED THUNDERSTORMS ACROSS THE AREA
THROUGH THURSDAY, WHICH COULD LOWER CONDITIONS DOWN TO MVFR/IFR
BRIEFLY IF A SHOWER OR THUNDERSTORM DRIFTED OVER A TERMINAL. LATEST
GUIDANCE SUGGESTS THESE THESE LOWER CEILINGS MAY OCCUR BETWEEN 12Z-
20Z.
KSEA...VFR CONDITIONS AT THE TERMINAL THIS AFTERNOON CONTINUING
THROUGH THE EVENING. LATEST GUIDANCE HIGHLIGHTS MVFR CIGS MAY RETURN
(40%-50% CHANCE) BETWEEN 15Z-20Z AS SHOWER ACTIVITY MOVES THROUGH
THE TERMINAL. NORTHWESTERLY WINDS 5 TO 8 KNOTS WILL SHIFT MORE S/SW
THURSDAY MORNING, MAINTAINING THE SAME SPEEDS. HAVE INTRODUCED VCSH
THROUGHOUT THURSDAY AFTERNOON AS CHANCES FOR SHOWERS CONTINUE TO
REMAIN. THERE IS A SLIGHT CHANCE FOR THUNDERSTORMS TONIGHT
THROUGHOUT THURSDAY, BUT NOT ENOUGH CONFIDENCE TO INCLUDE IT IN THE
TAF AS OF NOW.
MAZURKIEWICZ/29
MARINE
A WEAK SURFACE LOW WILL MEANDER OVER THE COASTAL
WATERS THROUGH FRIDAY WITH VARIABLE CHANGES IN WINDS OVER THE
COASTAL WATERS. DIURNAL WESTERLY FLOW WILL CONTINUE THROUGH THE
STRAIT OF JUAN DE FUCA EACH AFTERNOON BUT CONTINUES TO REMAIN
UNDER SMALL CRAFT ADVISORY CRITERIA AT THIS TIME. A MORE
TYPICAL SUMMERTIME PATTERN RETURNS THIS WEEKEND WITH NORTHERLY
WINDS OVER THE WATERS AND GUSTS UP TO 20 KTS AT TIMES.
COASTAL SEAS 4 TO 6 FEET BUILDING SLIGHTLY TO 5 TO 8 FEET
TONIGHT AND INTO THURSDAY WITH A PERIOD OF 7 TO 8 SECONDS. SEAS
WILL BUILD EVEN FURTHER BEYOND 30-40 NM TO 8 TO 10 FEET OVER THE
WEEKEND, BUT AGAIN WILL REMAIN IN THE OUTER COASTAL WATER ZONE.
FIRE WEATHER
A RED FLAG WARNING IS IN EFFECT FOR THE MOUNTAINS ON THURSDAY.
SHOWERS AND SCATTERED THUNDERSTORMS RETURN TO THE FORECAST
TONIGHT THROUGH THURSDAY EVENING. 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.
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.
SEW WATCHES/WARNINGS/ADVISORIES
WA...RED FLAG WARNING FROM 1 AM TO 11 PM PDT THURSDAY 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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