569
FXUS66 KPQR 052159
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
259 PM PDT FRI SEP 5 2025
SYNOPSIS
AFTER A COUPLE ROUNDS OF ISOLATED TO SCATTERED
THUNDERSTORMS THIS WEEKEND, PARTICULARLY OVER THE CASCADES,
EXPECT A CONSIDERABLY COOLER AND WETTER WEATHER PATTERN EARLY
NEXT WEEK.
SHORT TERM...THROUGH SUNDAY NIGHT
WATER VAPOR SATELLITE
IMAGERY REVEALS A SHORTWAVE TROUGH OVER THE NORTHEAST PACIFIC
AND AN ELONGATED AND HIGH AMPLITUDE SHORTWAVE RIDGE OVER THE
NORTHERN ROCKY MOUNTAINS. THIS HAS PLACED THE REGION UNDER LARGE
SCALE SOUTHERLY FLOW ALOFT. A SUBTLE SHORTWAVE TROUGH PIVOTING
NORTHWARD IN THIS FLOW ACROSS WESTERN OREGON HAS RESULTED IN A
NUMBER OF SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPING AHEAD OF
IT THIS MORNING. THESE WILL CONTINUE TO LIFT NORTHWARD INTO
WESTERN WASHINGTON AND POINTS OFFSHORE. SUBSIDENCE BEHIND THIS
FEATURE IS TEMPORARILY SUPPRESSING SURFACE BASED CONVECTION
OVER THE CASCADES, BUT WITH FURTHER SURFACE HEATING AND LARGE
SCALE LIFT AHEAD OF THE NEXT EMBEDDED SHORTWAVE TROUGH, HIGH
RESOLUTION MODELS SUGGEST CONVECTION WILL BEGIN FIRING OVER
SOUTHERN OREGON AND THE CENTRAL OREGON CASCADES BETWEEN 3-5PM.
WHAT HAPPENS THEREAFTER REMAINS UNCERTAIN. HIGH RESOLUTION
MODELS SUGGEST A VARIETY OF SCENARIOS. SOME SUGGEST STORMS WILL
REMAIN CONFINED TO THE CASCADES AND THEN DIE BEFORE THEIR
REMNANTS SPREAD NORTHWESTWARD OVER THE WILLAMETTE VALLEY.
MEANWHILE, SOME MEMBERS OF THE HREF AND REFS SUGGEST ISOLATED TO
SCATTERED ELEVATED STORMS WILL TRAVERSE THE REGION LATER THIS
EVENING INTO THE EARLY MORNING HOURS ON SATURDAY.
MODELS AND THEIR ENSEMBLES ARE IN GOOD AGREEMENT THE NEXT
EMBEDDED SHORTWAVE TROUGH CURRENTLY SLIDING EASTWARD TOWARDS
NORTHERN CALIFORNIA WILL BEGIN ROUNDING THE PARENT TROUGH AND
WILL SLIDE NORTHWARD ACROSS WESTERN OREGON AND WASHINGTON ON
SATURDAY. THIS SHOULD RESULT IN ANOTHER ROUND OF SHOWERS AND
THUNDERSTORMS DEVELOPING ACROSS THE CASCADES WITH A 15-25%
CHANCE OF A THUNDERSTORM IMPACTING ANY GIVEN SITE WEST OF THE
CASCADES ON SATURDAY AS AT LEAST A FEW ELEVATED THUNDERSTORMS
ARE LIKELY TO COME WESTWARD OFF THE CASCADES ON SATURDAY. SUNDAY
SHOULD SEE ANOTHER ROUND OF SHOWER AND THUNDERSTORMS DEVELOP
OVER THE CASCADES, BUT COVERAGE APPEARS LESS THAN TODAY AND
SATURDAY. TEMPERATURES APPEAR MOST LIKELY TO END UP NEAR
SEASONAL AVERAGES THIS WEEKEND.
LONG TERM...MONDAY THROUGH FRIDAY
WPC CLUSTER ANALYSIS SHOWS
THAT GLOBAL ENSEMBLE SYSTEMS ARE IN BROAD AGREEMENT THE
AFOREMENTIONED SHORTWAVE TROUGH OVER THE NORTHEAST PACIFIC WILL
SETTLE INTO THE PACIFIC NORTHWEST EARLY NEXT WEEK. THIS WILL
BRING A COUPLE DAYS OF WELL BELOW AVERAGE TEMPERATURES AND
SHOWERY WEATHER. ENSEMBLES ARE IN GENERAL AGREEMENT THE HIGHEST
PRECIPITATIONS AMOUNTS TO FALL BETWEEN MONDAY AND TUESDAY NIGHT
WILL BE ACROSS SOUTHEASTERN THIRD OF THE CWA, PARTICULARLY OVER
THE LANE AND LINN COUNTY CASCADES, WHICH IS GOOD NEWS FOR
REDUCING FIRE DANGER IN THE DRIEST PART OF THE AREA. IN GENERAL,
IT APPEARS WE SHOULD BEGIN TO DRY OUT MID TO LATE WEEK, BUT
UNCERTAINTY AROUND HOW QUICKLY THE AFOREMENTIONED SHORTWAVE
TROUGH LINGERS OVER THE PACIFIC NORTHWEST AND/OR HOW QUICKLY THE
NEXT FALL-LIKE STORM SYSTEM APPROACHES THE REGION, RESULTS IN
MENTIONABLE POPS THROUGH THE END OF NEXT WEEK.
AVIATION
AT 21Z FRI, MAINLY VFR CONDITIONS OBSERVED ACROSS NW
OREGON AND SW WASHINGTON. THE ONLY EXCEPTION IS MARINE STRATUS
LINGERING ALONG THE CENTRAL OREGON COAST. THIS STRATUS COULD
CONTINUE DISSIPATING WITH KONP LIFTING TO MVFR OR EVEN BRIEFLY
VFR OVER THE NEXT FEW HOURS, BUT IT WILL QUICKLY BEGIN SPREADING
NORTH ALONG THE COAST AGAIN AFTER 00Z SAT WITH MAINLY IFR/LIFR
CEILINGS EXPECTED AT KAST BY 02-04Z SAT. IFR/LIFR CEILINGS
EXPECTED TO CONTINUE ALONG THE COAST FOR THE MAJORITY OF THE TAF
PERIOD, LIKELY LIFTING TO MVFR/VFR AGAIN AFTER 19-21Z SAT. ONSHORE
FLOW WILL PUSH STRATUS INLAND THROUGH COAST RANGE GAPS AND ALONG
THE COLUMBIA RIVER TONIGHT. THERE'S A 40-70% CHANCE OF MVFR
CEILINGS AT MOST INLAND TERMINALS, EXCEPT FOR 60-80% CHANCE AT
KEUG, BEGINNING BETWEEN 10-14Z SAT. CONDITIONS INLAND EXPECTED TO
LIFT TO VFR AFTER 18-20Z SAT.
LINGERING SHOWERS FROM THIS MORNING'S DISTURBANCE ARE MOVING
NORTHWEST THROUGH SW WASHINGTON. BEHIND THIS, ANOTHER ROUND OF
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS IS EXPECTED AFTER
21-22Z FRI. WHILE MODELS INDICATE THIS SECOND ROUND INDICATES
STORMS WILL BEGIN OVER THE CASCADES, THERE IS THE POTENTIAL FOR
THEM TO PUSH INTO THE WILLAMETTE VALLEY AND SW WASHINGTON AGAIN.
HOWEVER, CONFIDENCE IN PLACEMENT/TIMING REMAINS TOO LOW TO INCLUDE
TAFS, BUT WILL REEVALUATE FOR THE 00Z SAT TAF PACKAGE. BRIEF
PERIODS OF HEAVY RAIN COULD RESULT IN MVFR/IFR CONDITIONS.
PDX AND APPROACHES...PREVAILING VFR CONDITIONS BEFORE A 40-60%
CHANCE OF MVFR CEILINGS RETURNS AFTER 12-14Z SAT, CLEARING TO VFR
BY 18-21Z. THERE IS ALSO A 15-20% CHANCE FOR ANOTHER ROUND OF
ISOLATED SHOWERS OR THUNDERSTORMS TO IMPACT THE TERMINAL AFTER
22Z FRIDAY THROUGH THE EVENING AND OVERNIGHT HOURS. -SCHULDT/HEC
MARINE
THERE'S A 15-20% CHANCE OF SHOWERS AND THUNDERSTORMS
CONTINUING OVER THE WATERS THIS EVENING. AN AREA OF LOW PRESSURE
WILL MOVE THROUGH THE WATERS THIS WEEKEND, WHICH WILL FACILITATE A
SWITCH TO SOUTHERLY WINDS ON SATURDAY. THESE SOUTHERLY WINDS WILL
PERSIST THROUGH MONDAY AND TUESDAY BEFORE TURNING NORTHERLY AGAIN
ON WEDNESDAY AS HIGH PRESSURE RETURNS TO THE WATERS. SEAS WILL
GENERALLY HOLD IN THE 3-5 FT RANGE INTO EARLY NEXT WEEK. THERE IS
A 25-40% CHANCE OF COMBINED SEAS CLIMBING ABOVE 5 FT DURING THE
MIDDLE NEXT WEEK WITH THOSE PROBABILITIES CLIMBING TO 60-70% BY
THE END OF NEXT WEEK. -SCHULDT/HEC
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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