588
FXUS66 KPQR 021923
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1223 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 18Z THURSDAY
A FRONTAL SYSTEM MOVING INTO
THE PACIFIC NORTHWEST HAS SPREAD RAINFALL TO ALL TERMINALS LATE
THIS MORNING LEADING TO A MIX OF VFR TO MVFR CONDITIONS. AS
RAINFALL RATES PEAK MIDDAY INTO THE AFTERNOON HOURS, VIS/CIGS ARE
EXPECTED TO DEGRADE FURTHER INTO MVFR. HOWEVER, ONCE THE FRONT
PASSES (22Z-01Z) PREVAILING VFR CONDITIONS RETURN. SHOWER ACTIVITY
BEHIND THE MAIN BAND OF RAINFALL BEGINS RATHER SPARSE IN COVERAGE
LATE THIS AFTERNOON AND EVENING 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 10-20% CHANCE FOR
THUNDERSTORMS LATE THIS AFTERNOON THROUGH THURSDAY MORNING AND
BEYOND - HIGHEST PROBABILITIES AT THE COAST. 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 WHILE
SITTING REACHING INTO THE 25-30 KNOT RANGE AT THE COAST. ONCE
THE FRONT PASSES, EXPECT WINDS TO GAIN A TEMPORARY WESTERLY
COMPONENT WHILE DECREASING BEFORE INLAND SITES SEE A SLIGHT UPTICK
IN WINDS AGAIN OVERNIGHT INTO THURSDAY MORNING.
KPDX AND APPROACHES...VFR CONDITIONS HAVE QUICKLY TRENDED TO MVFR
MIDDAY INTO THE EARLY AFTERNOON AS RAINFALL RATES PEAK. EXPECT
WINDS TO INCREASE OVER THE NEXT SEVERAL HOURS AS WELL WITH PEAK
GUSTS AROUND 20-23 KNOTS BETWEEN 21-23Z OUT OF THE SOUTH. ONCE
THE FRONT PASSES AROUND 23Z-00Z CIGS/VIS TREND BACK TO VFR WITH
ONLY A 10-15% CHANCE FOR MVFR CONDITIONS THEREAFTER - WINDS
DECREASE AS WELL. -99
MARINE
AN ACTIVE WEATHER PATTERN CONTINUES THROUGH THE
MIDDLE OF THE WEEK AS A SERIES OF SYSTEMS MOVES INTO THE PAC NW.
A BROAD AREA OF LOW PRESSURE DROPPING FROM THE GULF OF ALASKA
TOWARD THE OREGON AND WASHINGTON COASTS WILL DRIVE A STRONG
FRONTAL BOUNDARY ACROSS ALL WATERS THROUGH THE LATE AFTERNOON,
WHICH WILL RESULT IN STRENGTHENING WINDS AND BUILDING SEAS
ACROSS THE WATERS. SOUTH TO SOUTHWEST WINDS WILL REACH 20-35 KT
WITH FREQUENT GUSTS OF 40-45 KT EARLY THIS MORNING THROUGH THE
LATE AFTERNOON. THE STRONGEST GUSTS WILL MOST LIKELY OCCUR
BETWEEN 8 AM AND NOON PDT BEYOND 30 NM FROM THE COAST, AND
BETWEEN 10 AM AND 3 PM WITHIN 30 NM. WHILE NOT EXPECTED TO BE
PERSISTENT OR WIDESPREAD, THERE ARE 20-40% CHANCES OF ISOLATED
STORM-FORCE GUSTS WITHIN 20 NM AS THE FRONT MOVES ONTO THE COAST
LATE THIS MORNING/AFTERNOON. AS SUCH WILL MAINTAIN THE CURRENT
SUITE OF GALE WARNINGS ACROSS ALL WATERS UNTIL AT LEAST 5 PM PDT
TODAY.
SEAS REMAIN LARGELY WIND-DRIVEN, BUILDING TOWARDS TO 10-14 FT.
BEHIND THE FRONT, A FRESH WEST/NORTHWEST SWELL OF 7-9 FT WILL
ARRIVE, AND HELP TO MAINTAIN SEAS AROUND 9-11 FT THROUGH MUCH OF
THURSDAY. THESE STEEP SEAS MAY REQUIRE SMALL CRAFT OR HAZARDOUS
SEAS ALERTS IF CONFIDENCE IN THEIR TIMING, OCCURRENCE, AND
PERSISTENCE INCREASES. THERE WILL ALSO BE 15-30% CHANCES FOR
ISOLATED TO SCATTERED THUNDERSTORMS ON THURSDAY, WHICH WILL BE
CAPABLE OF PRODUCING GUSTY AND ERRATIC WINDS, SMALL HAIL, AND
LIGHTNING.
WHILE RELATIVELY ACTIVE WEATHER WITH LINGERING RAIN SHOWERS WILL
CONTINUE INTO THE WEEKEND, MARINE CONDITIONS WILL TEND TO SUBSIDE
AS WINDS AND SEAS EASE AFTER THURSDAY. FAIRLY BENIGN WINDS OF
5-15 KT AND SEAS OF 4-6 FT ARE EXPECTED BY THE WEEKEND AND INTO
EARLY NEXT WEEK. /42-36
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...GALE WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR PZZ210-251>253-
271>273.
WWW.WEATHER.GOV/PORTLAND
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