788
FXUS66 KPQR 021820
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1120 AM PDT WED SEP 2 2026
.UPDATED AVIATION DISCUSSION.
SYNOPSIS
AN UNUSUALLY STRONG SERIES OF SYSTEMS, BY EARLY
SEPTEMBER STANDARDS, TAKES AIM AT THE PACIFIC NORTHWEST OVER THE
NEXT 36-48 HOURS. THESE SYSTEMS LOOK TO BRING WIDESPREAD
RAINFALL, LOCALLY BREEZY/GUSTY WINDS, AND A 15-30% CHANCE FOR
POP-UP THUNDERSTORMS, WITH HIGHER CHANCES ON THURSDAY.
CONDITIONS TREND SLIGHTLY DRIER BY LATE THURSDAY/FRIDAY AND
CONTINUE INTO THE WEEKEND. HOWEVER, COOLER THAN NORMAL
TEMPERATURES AND SHOWER CHANCES PERSIST.
SHORT TERM...TODAY THROUGH THURSDAY NIGHT
TODAY IS SHAPING
UP TO BE MORE EVENTFUL FOR THE PAC NW AS A MUCH STRONGER UPPER
LEVEL LOW DROPS SOUTH ALONG THE WESTERN CANADA COAST. EARLY
MORNING OBSERVATIONS VIA RADAR SHOW PRECIPITATION WELL OFFSHORE
AND IS THE HARBINGER OF A COLD FRONT THAT IS SLOWLY MOVING
EASTWARD. EXPECT CONDITIONS TO BECOME MUCH WETTER, COOLER, AND
WINDIER AS THE DAY PROGRESSES ACROSS THE CWA. RAIN IS EXPECTED
TO REACH THE COAST EARLY THIS MORNING, REACHING THE INTERIOR
LOWLANDS AND CASCADES BY MID-MORNING. SOUTHERLY WINDS ALSO
INCREASE DURING THIS TIME WITH THE STRONGEST WINDS EXPECTED
ALONG THE COAST, MOST LIKELY BETWEEN 35-45 MPH BUT THERE IS A
15-30% CHANCE FOR ISOLATED GUSTS OF 50 MPH OR GREATER THROUGH
THIS AFTERNOON. WHILE WIND GUSTS ARE NOT EXPECTED TO REACH
WARNING CRITERIA ALONG THE COAST, THIS WILL BE THE STRONGEST
WINDS OBSERVED IN SEVERAL MONTHS SO IT IS POSSIBLE TREES OR
BRANCHES THAT HAVE WEAKENED OR DIED MAY COME LOSE WITH THESE
WINDS. INLAND GUSTS WILL PEAK AROUND 30 MPH WITH ISOLATED GUSTS
UP TO 40 MPH WITH LITTLE TO NO IMPACT EXPECTED, STILL VIGILANCE
SHOULD BE MAINTAINED.
THIS SYSTEM WILL BRING THE MOST SIGNIFICANT WIDESPREAD RAINFALL
SINCE THE SPRING WITH A 85-95% CHANCE FOR 48 HOUR RAINFALL TOTALS
OF AT LEAST 1 INCH BY FRIDAY MORNING. CHANCES FOR 2 INCHES OR
MORE DURING THE SAME TIME FRAME ARE 20-50% AND ARE CONFINED TO
THE COAST AND COAST RANGE ALONG WITH THE SOUTHWEST WA CASCADES.
THERE IS ALSO A SLIGHT CHANCE FOR EMBEDDED THUNDERSTORMS
TOMORROW AFTERNOON, MAINLY ACROSS THE COAST RANGE, WILLAMETTE
VALLEY AND PORTLAND METRO. DAYTIME HIGHS EXPECTED TO BE IN THE
LOW TO MID 60S FOR INLAND VALLEYS, MID 50S TO MID 60S FOR THE
COAST AND LOW TO UPPER 50S FOR THE HIGHER TERRAIN IN THE COAST
RANGE AND CASCADES.
THERE A RELATIVE LULL IN PRECIPITATION IS EXPECTED OVERNIGHT
WITH SCATTERED SHOWERS LINGERING. HOWEVER, WIDESPREAD PRECIPITATION
RETURNS THURSDAY MORNING AS THE SURFACE LOW CONTINUES TO SLOWLY
TRACK ALONG THE WA THEN OR COASTS. IN THE POST FRONTAL ENVIRONMENT,
SHOWER ACTIVITY WILL INCREASE ALONG WITH A BETTER CHANCE FOR
THUNDERSTORMS ACROSS THE ENTIRE AREA. CAPE IS EXPECTED TO BE
BETWEEN 150-250 J/KG DURING THE AFTERNOON ALONG WITH COOLER
TEMPERATURES IN THE UPPER LEVELS WILL SUPPORT A 20-30% CHANCE
FOR THUNDERSTORMS. THE OVERALL STORM ENVIRONMENT LOOKS TO FAVOR
POP-CORN STORMS THAT WILL BE CAPABLE OF SOME LIGHTNING, GUSTY
WINDS AND SMALL HAIL. IN ADDITION, COLD AIR ALOFT WILL ALSO PUT
INTO PLAY THE POTENTIAL DEVELOPMENT OF COLD CORE FUNNEL CLOUDS.
/42-19
LONG TERM...FRIDAY THROUGH WEDNESDAY
CHANCES FOR SHOWERS AND
THUNDERSTORMS CONTINUE FRIDAY AND THE WEEKEND AS THE
AFOREMENTIONED, UPPER LEVEL LOW WEAKENS BUT REMAINS OVER THE
REGION. CAPE WILL BE ON THE RELATIVELY LOWER SIDE, AROUND
100-200 J/KG EACH AFTERNOON FRIDAY THROUGH SUNDAY, WITH CIN
INCREASING EACH DAY. INCREASING CIN WILL LOWER THUNDERSTORM
CHANCES EACH AFTERNOON. TEMPERATURES TREND WARMER FRIDAY THROUGH
SUNDAY AS A SHORT-WAVE RIDGE QUICKLY BUILDS OVER THE REGION.
EXPECT DAYTIME HIGHS TO WARM INTO THE MID TO UPPER 70S BY THE
MIDDLE OF NEXT WEEK AS CLOUD COVER BECOMES MORE BROKEN AND LESS
OVERCAST. DRIER, MORE BENIGN CONDITIONS ARE EXPECTED TO RETURN
EARLY NEXT WEEK AS SHORTWAVE RIDGING DEVELOPS ACROSS THE PACNW.
/42-19
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
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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