028
FXUS66 KPQR 022151
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
251 PM PDT WED SEP 2 2026
SYNOPSIS
A FRONTAL SYSTEM WILL BRING WIDESPREAD RAIN, BREEZY
WINDS FROM THE SOUTH, AND A 15-20% CHANCE FOR THUNDERSTORMS
TODAY. RAIN CONTINUES TOMORROW WITH A 20-30% CHANCE FOR
THUNDERSTORMS. ANY PASSING THUNDERSTORMS MAY PRODUCE LIGHTNING,
HEAVY RAIN, GUSTY ERRATIC WINDS, SMALL HAIL, AND/OR A FUNNEL
CLOUD. CHANCES FOR LINGERING SHOWERS CONTINUE THROUGH THE
WEEKEND WITH COOLER THAN AVERAGE TEMPERATURES. DRIER CONDITIONS
EARLY NEXT WEEK.
SHORT TERM...TODAY THROUGH FRIDAY NIGHT
RADAR, SATELLITE,
AND SURFACE OBSERVATIONS AS OF LATE WEDNESDAY MORNING DEPICTS
WIDESPREAD RAIN ACROSS NORTHWEST OREGON AND SOUTHWEST WASHINGTON
AS OUR FIRST FALL-LIKE FRONTAL SYSTEM PUSHES THROUGH THE
REGION. AS THE FRONT SWINGS THROUGH, EXPECT RAIN TO PERSIST
TODAY ALONG WITH BREEZY WINDS FROM THE SOUTH/SOUTHWEST. BUOY
OBSERVATIONS HAVE BEEN SHOWING WIND GUSTS PEAKING AROUND 35-45
MPH OVER THE MARINE WATERS WITH THE FRONTAL PASSAGE, SO EXPECT
SIMILAR GUSTS ALONG THE IMMEDIATE COAST. AS THE FRONT MOVES
INLAND, WE'LL ALSO SEE WINDS INCREASE ALONG THE I-5 CORRIDOR AND
INTERIOR VALLEYS, BUT NOT AS STRONG AS THE COAST. PRESSURE
GRADIENTS ARE NOT LOOKING AS TIGHT, SO WE'LL LIKELY (80% CHANCE)
EXPERIENCE PEAK GUSTS BETWEEN 20-35 MPH FOR INTERIOR LOCATIONS.
CAN'T RULE OUT A LOW CHANCE (10%) FOR ISOLATED GUSTS UP TO
35-40 MPH ALONG THE I-5 CORRIDOR.
THE OTHER THREAT FOR TODAY IS A SLIGHT CHANCE (15-20%) FOR
THUNDERSTORMS. LOOKING AT SATELLITE IMAGERY AS OF 11:30 AM,
CONDITIONS ARE CLEARING UP BEHIND THE FRONT ABOUT 75 MILES
OFFSHORE. IT APPEARS THERE'S SUBSIDENCE BEHIND THE FRONT WITH A
LOT OF DRY AIR. EVEN FURTHER BEHIND THIS POCKET OF DRY AIR
AROUND 180 MILES OFFSHORE, WE START TO SEE SOME INSTABILITY WITH
POPCORN CUMULUS CLOUDS. HOWEVER, RADAR CURRENTLY SHOWS NO
INDICATION OF THUNDERSTORMS IN THAT POST-FRONTAL REGION
OFFSHORE. LOOKING AHEAD AT THIS AFTERNOON ONCE WE TURN POST-
FRONTAL, IF WE GET ENOUGH CLEARING AND HEATING TODAY, WE COULD
SEE SOME ISOLATED THUNDERSTORMS POP-UP. IT WILL ULTIMATELY
DEPEND ON HOW MUCH HEATING WE GET. IF WE DON'T CLEAR OUT UNTIL
LATE THIS AFTERNOON OR EVENING, THEN CONFIDENCE FOR
THUNDERSTORMS WILL BE LOW. IF A THUNDERSTORM DOES PASS OVER AN
AREA, IT MAY PRODUCE LIGHTNING, HEAVY DOWNPOURS, GUSTY ERRATIC
WINDS, SMALL HAIL, AND/OR A FUNNEL CLOUD.
TOMORROW, THE UPPER-LEVEL LOW ASSOCIATED WITH TODAY'S SYSTEM
WILL MOVE OVERHEAD OF THE PACIFIC NORTHWEST. THIS WILL LEAD TO
COOLER TEMPERATURES ALOFT AND INCREASE ATMOSPHERIC INSTABILITY.
HREF GUIDANCE IS SHOWING MUCAPE VALUES ANYWHERE BETWEEN 100-500
J/KG ACROSS THE REGION TOMORROW. THIS INSTABILITY, ALONG WITH
GOOD LIFT AND MOISTURE FROM THE OVERALL UPPER-LEVEL LOW, WILL
SUPPORT A 20-30% CHANCE FOR THUNDERSTORMS THURSDAY
AFTERNOON/EVENING. EXPECT THE SAME IMPACTS LISTED ABOVE FOR ANY
PASSING THUNDERSTORMS. AGAIN, WITH EVEN COOLER AIR ALOFT ON
THURSDAY, AN ISOLATED COLD-CORE FUNNEL CLOUD CAN'T BE RULED OUT
(5-10% CHANCE). BY FRIDAY, THE UPPER-LEVEL LOW CONTINUES TO SIT
OVERHEAD, MAINTAINING CHANCES FOR LINGERING SHOWERS AND ANOTHER
15-20% CHANCE FOR AFTERNOON THUNDERSTORMS.
AS MENTIONED BEFORE, THIS SYSTEM IS A SOAKER AND IS BRINGING THE
FIRST SUBSTANTIAL RAINFALL OF THE SEASON. CHANCES FOR 48-HOUR
RAIN TOTALS EXCEEDING 1 INCH BETWEEN 5 AM WEDNESDAY AND 5 AM
FRIDAY ARE 85-95+% ALONG THE COAST, AND 50-75% ACROSS INTERIOR
VALLEYS INCLUDING THE I-5 CORRIDOR. WHILE THIS WET WEATHER WON'T
BE A "FIRE SEASON ENDER," IT WILL DEFINITELY SLOW DOWN FIRE
SEASON. -10
LONG TERM...SATURDAY THROUGH TUESDAY
OVER THE WEEKEND, THE
MAJORITY OF ENSEMBLE MEMBERS CONTINUE TO SHOW BROAD UPPER-LEVEL
TROUGHING OVER THE PACIFIC NORTHWEST. HOWEVER, THERE IS
UNCERTAINTY WITH WHETHER OR NOT WE REMAIN DRY OR CONTINUE WITH
LINGERING SHOWERS. WHILE 60% OF ENSEMBLE MEMBERS SUGGEST SHOWERS
CONTINUING OVER THE REGION SATURDAY-SUNDAY, THE OTHER 40% KEEP
US DRY. WHAT WE CAN SAY WITH HIGHER CONFIDENCE IS THAT THIS
UPPER-LEVEL LOW WILL MAINTAIN BELOW-AVERAGE 500 MB HEIGHTS AND
KEEP HIGH TEMPERATURES SLIGHTLY COOLER THAN AVERAGE FOR THIS
TIME OF YEAR. EARLY NEXT WEEK, THE MAJORITY OF ENSEMBLE MEMBERS
SHOW THE UPPER LOW WEAKENING AND BEGINNING TO MOVE EASTWARD.
THIS WOULD FAVOR DRIER CONDITIONS, BUT THERE REMAINS UNCERTAINTY
WITH HOW MUCH HIGH PRESSURE WILL RE-BUILD OVER OUR AREA, AND
HOW WARM/DRY WE GET. -10
AVIATION...THROUGH 00Z FRIDAY
THIS AFTERNOON A FRONTAL BOUNDARY
CONTINUES TO PROGRESS THROUGH WESTERN OREGON AND SOUTHWEST
WASHINGTON WITH A LARGELY MVFR CONDITIONS. ONCE THE FRONT PASSES
(00-02Z) PREVAILING VFR CIGS/VIS LIKELY RETURN FOR INLAND SITES.
SHOWER ACTIVITY BEHIND THE MAIN BAND OF RAINFALL BEGINS RATHER
SPARSE IN COVERAGE LATE THIS AFTERNOON AND EVENING AS WELL BEFORE
INCREASING OVERNIGHT INTO THURSDAY MORNING. IT WORTH NOTING ANY
STRONGER SHOWERS COULD TEMPORARILY KNOCK CIGS/VIS BACK TO MVFR OR
LOWER THIS EVENING THROUGH THURSDAY MORNING. ALSO, THERE IS A
15-25% CHANCE FOR THUNDERSTORMS THURSDAY AFTERNOON AT ALL
TERMINALS.ANY THUNDERSTORMS THAT DEVELOP WILL HAVE THE POTENTIAL
TO PRODUCE LIGHTNING, SMALL HAIL ALONG WITH GUSTY AND ERRATIC
WINDS.
EXPECT SOUTHERLY WINDS JUST AHEAD OF THE FRONTAL BOUNDARY TO PEEK
THIS AFTERNOON WITH GUSTS UP TO 15-25 KNOTS AT INLAND SITES. ONCE
THE FRONT PASSES, EXPECT WINDS TO GAIN A TEMPORARY WESTERLY
COMPONENT WHILE DECREASING BEFORE A SLIGHT UPTICK IN WINDS AGAIN
OVERNIGHT INTO THURSDAY.
KPDX AND APPROACHES...MVFR CONDITIONS ARE IN PLACE THIS AFTERNOON
BUT ONCE THE FRONT PASSES CIGS/VIS TREND BACK TO VFR BY 01-04Z WITH
ONLY A 15-25% CHANCE FOR MVFR CONDITIONS THEREAFTER. EXPECT AN
ISOLATED THUNDERSTORM THREAT THURSDAY AS WELL, MAINLY DURING THE
AFTERNOON HOURS. -99
MARINE
THIS AFTERNOON A FRONTAL BOUNDARY IS QUICKLY PROGRESSING
ACROSS THE WATERS WITH WINDS PEAKING THROUGH 3-5PM BEFORE DROPPING
OFF THIS EVENING - BUOY OBSERVATIONS SHOW GUSTS OF 35-40 KNOTS.
OUR LARGELY WIND DRIVEN SEAS CURRENT SIT AROUND 12-14 FT AT 9-10
SECONDS, LIKELY LEVELING OFF THE NEXT FEW HOURS BEFORE GRADUALLY
DECREASING THIS EVENING AND OVERNIGHT WHILE A FRESH WEST/NORTHWEST
SWELL ARRIVES HELPING TO MAINTAIN SEAS AROUND 9-11 FT THROUGH
MUCH OF THURSDAY. DUE TO THE CONTINUED SEA STATE AND BREEZY WINDS,
A SMALL CRAFT ADVISORY IS IN EFFECT THROUGH THURSDAY AFTERNOON
INTO THE EVENING. THERE'LL ALSO BE 15-30% CHANCE FOR THUNDERSTORMS
TONIGHT THROUGH THURSDAY WITH THE BEST RELATIVE CHANCES THURSDAY
AFTERNOON. ANY OF THESE STORMS WILL BE CAPABLE OF PRODUCING
GUSTY/ERRATIC WINDS, SMALL HAIL, AND LIGHTNING.
WHILE RELATIVELY ACTIVE WEATHER WITH LINGERING RAIN SHOWERS WILL
CONTINUE INTO THE WEEKEND, MARINE CONDITIONS WILL SUBSIDE BY
FRIDAY WITH SEAS HOLDING IN THE 4-6 FT RANGE BY FRIDAY AFTERNOON.
SIMILAR CONDITIONS PERSIST INTO EARLY NEXT WEEK WHILE WINDS
OCCASIONALLY GUST TO 15-20 KNOTS. -99
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...GALE WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR PZZ210-251>253-
271>273.
SMALL CRAFT ADVISORY UNTIL 5 PM PDT THURSDAY FOR PZZ210-251-
252-271-272.
SMALL CRAFT ADVISORY UNTIL 11 PM PDT THURSDAY FOR PZZ253-273.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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