078
FXUS66 KPQR 301715
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1015 AM PDT SUN AUG 30 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
A SHORTWAVE RIDGE OF HIGH PRESSURE WILL BRING A
BRIEF PERIOD OF DRY AND WARM CONDITIONS WITH MOSTLY SUNNY SKIES
THROUGH MONDAY. A SIGNIFICANT PATTERN CHANGE WILL SEE COOLER
TEMPERATURES, WIDESPREAD RAIN CHANCES, AND A 5-15% CHANCE FOR
THUNDERSTORMS TUESDAY THROUGH THE END OF THE WORKWEEK, WITH
WEDNESDAY AND THURSDAY EXPECTED TO BE THE WETTEST DAYS. WARMER
AND DRIER CONDITIONS MAY RETURN BY THE WEEKEND.
SHORT TERM...TODAY THROUGH TUESDAY
A SHORTWAVE RIDGE LOOKS
TO BUILD OVER THE REGION THROUGH MONDAY. THIS WILL RESULT IN A
BRIEF WARMING AND DRYING TREND THROUGH THE FIRST PART OF THIS
WEEK. DAYTIME HIGHS TODAY ARE EXPECTED TO WARM UP INTO THE MID
TO UPPER 70S FOR INTERIOR VALLEYS, MID TO UPPER 60S ALONG THE
COAST AND LOW TO UPPER 70S FOR THE CASCADES. AS FOR MONDAY,
DAYTIME HIGHS WILL WARM FURTHER INTO THE UPPER 70S TO MID 80S
FOR INTERIOR VALLEYS, MID 60S TO LOWER 70S ALONG THE COAST AND
UPPER 70S TO MID 80S FOR THE CASCADES. MONDAY WILL BE THE
WARMEST DAY OF THE WEEK AS THE RIDGE REACHES ITS PEAK. AS
TUESDAY APPROACHES, THE SHORT WAVE RIDGE WILL GET DISPLACED BY A
SERIES OF UPPER LEVEL LOWS/TROUGHS DIVING SOUTHWARD OUT OF THE
GULF OF ALASKA. THESE INCOMING SYSTEMS WILL BRING ABOUT A
SIGNIFICANT COOL AND MOIST PATTERN FOR THE PAC NW FOR TUESDAY.
THE FIRST OF TWO LOWS WILL SWING DOWN FROM THE GULF OF ALASKA
AND TRACK TOWARDS OR/CA BORDER. THIS WILL BRING WIDESPREAD CLOUD
COVER, COOLER DAYTIME HIGHS AND ABOUT A 35-75% CHANCE FOR LIGHT
SHOWERS ON THROUGH TUESDAY NIGHT. DAYTIME HIGHS ON TUESDAY LOOK
TO BE AROUND 5-10 DEGREES COOLER THAN MONDAY WITH HIGHS IN THE
UPPER 60S TO MID 70S FOR INTERIOR VALLEYS, MID 50S TO MID 60S
ALONG THE COAST AND UPPER 60S TO MID 70S FOR THE CASCADES.
GIVEN THE POSITION OF THIS TROUGH, THIS WILL RESULT IN SOUTHERLY
FLOW ALOFT WHICH IS A FAVORABLE PATTERN FOR THUNDERSTORMS IN
OUR REGION. HOWEVER, THERE IS A LOT OF UNCERTAINTY AS TO HOW
MUCH INSTABILITY WILL ACCOMPANY THE TUESDAY/TUESDAY NIGHT
SYSTEM. MODEL SOUNDINGS ARE CURRENTLY SHOWING MINIMAL MOST
UNSTABLE, CONVECTIVE AVAILABLE POTENTIAL ENERGY (MUCAPE), WITH
VALUES MAXING OUT AROUND 100-150 J/KG OVER THE CASCADES. FOR
NOW, THERE IS ABOUT A 5-15% CHANCE FOR THUNDERSTORMS ACROSS THE
REGION ON TUESDAY INTO TUESDAY NIGHT. -42
LONG TERM...WEDNESDAY THROUGH SATURDAY
WEDNESDAY INTO EARLY
THURSDAY IS SHAPING UP TO BE MORE SIGNIFICANT, AS THE STRONGER
OF THE TWO SYSTEMS MOVE INTO THE PAC NW. THE ASSOCIATED FRONT
WITH THIS SYSTEM SWINGS THROUGH ON WEDNESDAY, BRINGING MORE
WIDESPREAD RAIN, COOLER TEMPERATURES, AND BREEZIER SOUTHERLY
WINDS. CHANCES FOR EXCEEDING 1 INCH OF RAIN IN 48 HOURS BETWEEN
5 AM WEDNESDAY TO 5 AM FRIDAY ARE AROUND 75-90% ACROSS THE CWA,
WITH THE HIGHEST CHANCES ALONG THE COAST, COAST RANGE, AND
CASCADES. CHANCES FOR EXCEEDING 2 INCHES DURING THIS SAME
TIMEFRAME ARE AROUND 25-40% FOR THESE HIGHER TERRAIN FEATURES,
AND 10-20% ALONG THE I-5 CORRIDOR.
THURSDAY AFTERNOON TO FRIDAY, THE UPPER-LEVEL TROUGH MOVES
DIRECTLY OVERHEAD AND WE TRANSITION INTO A POST-FRONTAL
ENVIRONMENT WITH LINGERING SHOWERS. GIVEN THAT THERE WILL BE
COOLER AIR ALOFT, THIS WILL FAVOR INCREASING ATMOSPHERIC
INSTABILITY AND THUS CHANCES FOR THUNDERSTORMS. THERE IS AROUND
A 15-20% CHANCE FOR THUNDERSTORMS ON THURSDAY FOLLOWING THE
INITIAL FRONTAL PASSAGE. ANY PASSING THUNDERSTORMS MAY PRODUCE
LIGHTNING, HEAVY RAIN, ERRATIC WINDS, AND SMALL HAIL. OVERALL,
WHILE THE UPCOMING RAIN WILL NOT QUITE YET BE A "FIRE SEASON
ENDER," IT WILL DEFINITELY SLOW DOWN FIRE SEASON AND HELP PUT A
DAMPER ON ONGOING WILDFIRES. -42/10
AVIATION...THROUGH 18Z MONDAY
VFR CONDITIONS FAVORED ACROSS
THE AIRSPACE THROUGHOUT THE PERIOD. LINGERING LOW CLOUDS LATE
THIS MORNING WILL MIX OUT, YIELDING LARGELY CLEAR SKIES BY 21Z
SUN. NORTH TO NORTHWEST WINDS WILL RISE TO 5-10 KT INLAND AND
10-15 KT WITH GUSTS AS HIGH AS 20-25 KT ALONG THE COAST AND IN
THE SOUTHERN WILLAMETTE VALLEY THIS AFTERNOON, THEN EASE TO 5 KT
OR LESS AFTER 03-06Z MON. LIGHT OFFSHORE (NORTH TO NORTHEAST)
FLOW OVERNIGHT WILL LIMIT CHANCES FOR MVFR CIGS BENEATH LOW
CLOUDS TO 20-30% ALONG THE COAST AND IN THE WILLAMETTE VALLEY.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGHOUT THE
PERIOD. LOW CLOUDS THIS MORNING WILL TEND TO CLEAR AND NORTHWEST
WINDS WILL BUILD TO 5-10 KT BY THE EARLY AFTERNOON. WINDS EASE
BELOW 5 KT TONIGHT, WITH LOW CHANCES, ONLY 10%, FOR MVFR CIGS IF
LOW CLOUD COVERAGE IS HIGHER THAN EXPECTED. -36
MARINE
A SHORTWAVE UPPER-LEVEL RIDGE WILL BUILD OVER THE
WATERS THROUGH TUESDAY. THIS MAINTAIN NORTH/NORTHWEST WINDS THAT
WILL SLOWLY STRENGTHEN AS THE RIDGE BUILDS, REACHING DIURNAL
PEAKS AROUND 10-15 KT SUNDAY AND MONDAY AFTERNOONS. BY TUESDAY,
A MORE ROBUST UPPER-LEVEL TROUGH DIGGING OVER THE NORTHEAST
PACIFIC WILL RESULT IN A SOUTHERLY WIND SHIFT ACROSS ALL WATERS
BY TUESDAY MORNING. LARGELY WIND-DRIVEN SEAS THROUGH THIS PERIOD
WILL PERSIST AROUND 4-6 FT.
AS THE AFOREMENTIONED TROUGH AND ASSOCIATED FRONTS APPROACH THE
COAST TUESDAY INTO WEDNESDAY, WILL BRING INCREASING SOUTHERLY
WINDS WITH GUSTS UP TO 35 KT POSSIBLE. IF THE FORECAST TRENDS
CONTINUE, A GALE WATCH MAY BE ISSUED. SEAS WILL SIMILARLY BUILD
TOWARDS 10-12 FT AS WINDS INCREASE ALONG WITH A FRESH SWELL.
TOWARDS THE LATTER PART OF THE UPCOMING WEEK, EXPECT WINDS AND
SEAS TO EASE. -42
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page