957
FXUS66 KPQR 221013
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
313 AM PDT TUE SEP 22 2026
SYNOPSIS
BROAD UPPER LEVEL TROUGHING OVER THE GULF OF ALASKA WILL
MAINTAIN DRY SOUTHWEST FLOW ALOFT OVER NORTHWEST OR AND SOUTHWEST WA
THROUGH THURSDAY MORNING, BRINGING MAINLY DRY WEATHER AND SLIGHTLY
COOLER THAN NORMAL HIGH TEMPERATURES IN THE MID 60S TO LOWER 70S.
TROUGHING OVER THE GULF OF ALASKA DEEPENS EARLY THURSDAY AND BEGINS
PROGRESSING EASTWARD TOWARDS THE PACIFIC NORTHWEST. CONFIDENCE IS NOW
HIGH THIS TROUGH WILL MOVE INLAND LATE IN THE WEEK, BRINGING
WIDESPREAD RAIN TO THE ENTIRE AREA LATE THURSDAY INTO FRIDAY. WEAK
HIGH PRESSURE BUILDS IN BEHIND THE TROUGH ON SATURDAY, BRINGING DRY
WEATHER. CHANCES FOR SHOWERS INCREASE AGAIN SUNDAY INTO MONDAY, BUT
ONLY UP TO 10-30%.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
THE SHORT TERM FORECAST
IS HIGHLIGHTED BY MAINLY DRY WEATHER WITH SLIGHTLY COOLER THAN
AVERAGE TEMPERATURES. STARTING OFF WITH EARLY TUESDAY MORNING,
SATELLITE AND SURFACE WEATHER OBSERVATIONS DEPICTED WIDESPREAD LOW
CLOUDS EXPANDING ACROSS NEARLY ALL OF SOUTHWEST WA AND NORTHWEST OR
FROM THE COAST TO THE CASCADES. A BAND OF HIGH CLOUDS ASSOCIATED WITH
A WEAK UPPER LEVEL IMPULSE WAS ALSO EVIDENT OVER THE AREA. GIVEN
MOSTLY CLOUDY CONDITIONS ARE EXPECTED FOR MUCH OF THE DAY,
TEMPERATURES WILL REMAIN SLIGHTLY BELOW AVERAGE FOR THIS TIME OF YEAR
WITH HIGHS MAINLY IN THE MID 60S TO LOWER 70S OVER THE LOWLANDS.
SIMILAR CONDITIONS ARE EXPECTED ON WEDNESDAY GIVEN LITTLE CHANGE IN
THE WEATHER PATTERN, ALBEIT A DEGREE OR TWO COOLER. WILL NOTE THERE
IS A 10-20% CHANCE FOR LIGHT RAIN SHOWERS OVER THE SOUTH WA/NORTH OR
COAST AND WILLAPA HILLS WEDNESDAY MORNING AS A VERY WEAK SURFACE
FRONT MOVES INLAND AND DECAYS. THE REST OF SOUTHWEST WA AND NORTHWEST
OR SHOULD STAY DRY THROUGH WEDNESDAY NIGHT. -23
LONG TERM...THURSDAY THROUGH MONDAY NIGHT
WEATHER CONDITIONS BEGIN
TO CHANGE CONSIDERABLY THURSDAY INTO FRIDAY AS A BROAD UPPER LEVEL
TROUGH OVER THE GULF OF ALASKA DEEPENS AND PROGRESSES EASTWARD OVER
THE PACIFIC NORTHWEST. NOW THAT MODEL ENSEMBLE GUIDANCE IS IN
EXCELLENT AGREEMENT THIS TROUGH WILL MOVE INLAND WITHOUT SIGNIFICANT
DEAMPLIFICATION, CONFIDENCE IS HIGH FOR WIDESPREAD RAIN OVER ALL OF
NORTHWEST OR AND SOUTHWEST WA LATE THURSDAY INTO FRIDAY (80-90%
CHANCE). THE EXACT TIMING RAIN WILL BEGIN REMAINS UNCERTAIN, BUT MOST
GUIDANCE SUGGESTS RAIN WILL BEGIN SOMETIME BETWEEN NOON-11 PM
THURSDAY WITH RAIN BEGINNING CLOSER TO THE START OF THAT RANGE AT THE
COAST/COAST RANGE AND CLOSER TO THE END OF THAT RANGE FOR THE
WILLAMETTE VALLEY, PORTLAND METRO, CASCADES/FOOTHILLS, COLUMBIA RIVER
GORGE, AND COWLITZ VALLEY. RAIN IS EXPECTED TO END FAIRLY QUICKLY
FROM WEST TO EAST FRIDAY EVENING INTO FRIDAY NIGHT AS WEAK HIGH
PRESSURE BUILDS IN BEHIND THE TROUGH.
FORECAST RAIN TOTALS WITH THIS SYSTEM HAVE INCREASED TO 0.3-1.0
INCHES, WITH THE HIGHEST TOTALS IN THE MOUNTAINS AND THE LOWEST
TOTALS IN THE WILLAMETTE VALLEY, COWLITZ VALLEY, AND PORTLAND METRO.
CHANCES FOR RAIN TOTALS OVER 1 INCH RANGE BETWEEN 15-35% IN THE
WILLAMETTE VALLEY, COWLITZ VALLEY, AND PORTLAND METRO TO 35-55% FOR
THE COAST, COAST RANGE, AND WESTERN SLOPES OF THE CASCADES. IT
APPEARS THE ONLY WAY LOCATIONS IN THE WILLAMETTE VALLEY, COWLITZ
VALLEY, OR PORTLAND METRO COULD SEE RAIN AMOUNTS THAT HIGH IS IF
HEAVIER SHOWERS AND THUNDERSTORMS HIT A GIVEN AREA ON FRIDAY.
CONFIDENCE IN THE THUNDERSTORM POTENTIAL ON FRIDAY REMAINS LOW,
HOWEVER PROBABILITIES FOR THUNDER HAVE INCREASED SLIGHTLY TO 20-25%.
LREF GUIDANCE CURRENTLY SUGGESTS LIMITED INSTABILITY WITH SBCAPE
VALUES MOST LIKELY PEAKING AROUND 50-150 J/KG WITH A 10% CHANCE FOR
VALUES AS HIGH AS 250-300 J/KG. THE LATTER WOULD ONLY OCCUR IF THERE
ARE SUFFICIENT BREAKS OF SUN FRIDAY MORNING INTO THE AFTERNOON TO
ALLOW FOR ENOUGH SURFACE HEATING TO STEEPEN LAPSE RATES. IF BREAKS OF
SUN DO OCCUR, THEN THE POTENTIAL FOR HEAVIER SHOWERS AND LOW-TOPPED
THUNDERSTORMS WOULD INCREASE FRIDAY AFTERNOON. GIVEN WHAT APPEARS TO
BE A DECENT WIND SHEAR PROFILE IN PLACE AT THAT TIME (0-3 KM SHEAR
VALUES AROUND 20-30 KT), ANY STRONGER SHOWER OR THUNDERSTORM WOULD
HAVE THE POTENTIAL TO PRODUCE GUSTY OUTFLOW WINDS. EVEN AWAY FROM
CONVECTION, ENVIRONMENTAL SURFACE WINDS LOOK TO BE RATHER BREEZY WITH
WIND GUSTS MOST LIKELY PEAKING WITHIN THE 20-30 MPH RANGE. IN FACT,
THE NBM IS SHOWING A 5-15% CHANCE FOR MAX WIND GUSTS AS HIGH AS 40
MPH OR STRONGER ON FRIDAY. WHILE WIND GUSTS OF THIS MAGNITUDE ARE
UNLIKELY TO OCCUR, IT IS WORTH MENTIONING AS THESE WIND SPEEDS WOULD
BE ENOUGH TO RESULT IN MINOR TREE DAMAGE AND ISOLATED POWER OUTAGES
GIVEN LEAVES ARE STILL ON TREES.
THOSE HOPING FOR DRY WEATHER COME SATURDAY ARE IN LUCK, AS MODELS
REMAIN IN GOOD AGREEMENT FOR HIGH PRESSURE BEHIND THE TROUGH. AS
SUCH, CHANCES FOR RAIN ON SATURDAY ARE LESS THAN 10%. CHANCES FOR
SHOWERS INCREASE SLIGHTLY SUNDAY INTO MONDAY, BUT ONLY UP TO 10-30%.
TEMPERATURES WILL LIKELY STAY COOLER THAN AVERAGE OVER THE WEEKEND
WITH HIGHS IN THE 60S. IT IS ALSO WORTH MENTIONING OVERNIGHT LOWS
WILL TREND CHILLIER, ESPECIALLY IN THE UPPER HOOD RIVER VALLEY WHERE
MORNING LOWS MAY GET COLD ENOUGH TO SUPPORT FROST SATURDAY MORNING
AND SUNDAY MORNING; THIS IS WHEN THE NBM IS SHOWING A 30-50% CHANCE
FOR MORNING LOWS OF 37 DEGREES OR COLDER IN THE PARKDALE AREA AND
10-15% CHANCE NEAR ODELL. -23
AVIATION...THROUGH 06Z WEDNESDAY
AT 10Z TUESDAY, STRATUS
REMAINED IN PLACE ALONG THE COAST AND HAD FILLED IN OVER THE
WILLAMETTE VALLEY AND GREATER PORTLAND METRO AREA, RESULTING IN A
MIX OF IFR TO MVFR CEILINGS ALONG THE COAST, AND LOW-END VFR TO
MVFR CEILINGS INLAND. BY SUNRISE, CEILINGS WILL LIKELY (60-80%
CHANCE) DROP TO 1500-2500 FT AT ALL INLAND TERMINALS WITH MVFR
CONDITIONS PREVAILING THROUGH AT LEAST 19-21Z TUESDAY. DURING THE
~12-16Z TIME PERIOD, CHANCES FOR IFR CONDITIONS HOLD AROUND
15-20%, HIGHEST AT KTTD AND KEUG. AFTER 21Z TUESDAY, VFR FLIGHT
CONDITIONS ARE EXPECTED TO RETURN AS LOWER CLOUDS SCATTER OUT. THAT
SAID, CONFIDENCE IN THE EXACT TIMING OF THIS IMPROVEMENT IS ONLY
LOW TO MODERATE AT THIS TIME. WINDS WILL STAY FAIRLY LIGHT,
GENERALLY LESS THAN 5-10 KNOTS.
KPDX AND APPROACHES...A BROKEN STRATUS DECK WITH CEILINGS AROUND
4500 FT REMAINED IN PLACE AT THE KPDX TERMINAL AS OF 10Z TUESDAY,
WITH SCATTERED CLOUDS AS LOW AS 2500 FT FROM TIME TO TIME. BY 12-13Z
TUESDAY, EXPECT A MORE SOLID STRATUS DECK TO DEVELOP AROUND 2500
FT, BRINGING MVFR FLIGHT CONDITIONS. CONDITIONS TREND BACK TO VFR
TUESDAY AFTERNOON, MOST LIKELY SOMETIME BETWEEN 20-22Z. CONFIDENCE
IS LOW REGARDING THE EXACT TIME VFR CONDITIONS WILL RETURN,
ASSUMING MVFR CEILINGS DO DEVELOP LATER THIS MORNING. -99/23
MARINE
HIGH PRESSURE WILL MAINTAIN PREDOMINATELY NORTHERLY
WINDS ACROSS THE WATERS THROUGH AT LEAST WEDNESDAY NIGHT. AN
EXCEPTION WOULD BE TUESDAY AFTERNOON TO WEDNESDAY MORNING, WHEN
WINDS MAY TURN MORE WESTERLY TO SOUTHWESTERLY FOR THE WATERS
NORTH OF CAPE FALCON WITH THE PASSAGE OF A WEAK FRONT. WINDS
BECOME NORTHEASTERLY OVER THE WATERS FOR A BRIEF PERIOD OF TIME
THURSDAY MORNING AND EARLY AFTERNOON AHEAD OF AN APPROACHING
FRONTAL SYSTEM. THIS FRONTAL SYSTEM WILL MOVE OVER THE COASTAL
WATERS LATE THURSDAY INTO FRIDAY, BRINGING INCREASING
NORTHWESTERLY WINDS AND RAIN. THIS FRONT WILL BE RELATIVELY
STRONGER THAN THE FRONTAL PASSAGE TUESDAY AFTERNOON INTO WEDNESDAY
MORNING, AND CHANCES FOR SMALL CRAFT ADVISORY LEVEL WIND GUSTS OF
21 KT OR STRONGER HAVE INCREASED TO 60-80% WITH THIS SYSTEM. THE
HIGHEST PROBABILITIES ARE OVER THE NORTHERN WATERS TO THE NORTH OF
THE COLUMBIA RIVER BAR. IN FACT, THERE IS EVEN A 15-25% CHANCE FOR
MAX WIND GUSTS OF 34 KT OR STRONGER, AS SOME GUIDANCE SUGGESTS A
STRONGER AREA OF LOW PRESSURE IS POSSIBLE OVER THE COASTAL WATERS
WITH THIS SYSTEM. HOWEVER, THE MOST LIKELY OUTCOME IS FOR A
RELATIVELY WEAKER LOW WITH PEAK GUSTS SOMEWHERE IN THE 20-25 KT
RANGE.
SEAS WILL MOST LIKELY RANGE BETWEEN 6 AND 9 FT THROUGH FRIDAY,
BUT ARE NOT EXPECTED TO BE PARTICULARLY STEEP AT ANY POINT IN TIME
DUE TO DOMINANT WAVE PERIODS OF 10 TO 13 SECONDS. HOWEVER, THERE
IS A 15-20% CHANCE SEAS WILL PEAK AT 10 FT OR HIGHER LATE THURSDAY
NIGHT INTO FRIDAY. THIS WOULD ONLY OCCUR IF THE AFOREMENTIONED
AREA OF LOW PRESSURE COMES IN STRONGER THAN WHAT MOST GUIDANCE
SUGGESTS. -23
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