423
FXUS66 KPQR 192140
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
240 PM PDT SAT SEP 19 2026
SYNOPSIS
SEASONABLY WARM AND DRY WEATHER THIS WEEKEND WILL
TREND TOWARD MORE TYPICAL EARLY FALL WEATHER THROUGH THE
WORKWEEK AS TEMPERATURES COOL AND A WEATHER SYSTEM APPROACHES
FROM THE GULF OF ALASKA. UNCERTAINTY IN THE POSITION OF THIS
SYSTEM LEADS TO LOW CHANCES FOR RAIN BEYOND MIDWEEK.
SHORT TERM...NOW THROUGH TUESDAY NIGHT
GUIDANCE IS IN STRONG
AGREEMENT THAT A BROAD BUT LOW-AMPLITUDE RIDGE WILL STEADILY
SHIFT EASTWARD THROUGH THE MIDDLE OF NEXT WEEK WHILE BEING
REPLACED BY AN UPPER-LEVEL TROUGH DIGGING SOUTHWARD OVER THE
GULF OF ALASKA. AFTER PEAKING ON SUNDAY, UPPER-LEVEL HEIGHTS
AND MID-LEVEL TEMPERATURES WILL BEGIN TO TREND DOWNWARD ON
MONDAY, LEADING TO A GENERAL COOLING TREND ACROSS THE REGION. AT
THE SURFACE, TEMPERATURES WILL REACH SOME 5-10 DEGREES ABOVE
NORMAL INLAND SUNDAY AFTERNOON, NAMELY THE UPPER 70S TO LOW 80S,
WHILE THE COAST REMAINS NEAR NORMAL IN THE 60S. AS ONSHORE FLOW
STRENGTHENS MONDAY THROUGH WEDNESDAY, INLAND TEMPERATURES WILL
STEADILY COOL BE A FEW DEGREES EACH DAY. OTHERWISE, LONGER
NIGHTS AND LIGHT WINDS WILL FAVOR PERIODS OF EARLY MORNING FOG
IN SHELTERED VALLEYS, AND A TYPICAL FALL PATTERN OF LOW CLOUDS
PUSHING INLAND OVERNIGHT AND CLEARING THROUGH THE DAY.
LONG TERM...WEDNESDAY THROUGH SATURDAY
MODEL CONSENSUS
DECREASES BEYOND THE MIDDLE OF THE WEEK AS UNCERTAINTY IN THE
POSITION OF AN UPPER-LEVEL TROUGH DROPPING SOUTHWARD FROM THE
GULF OF ALASKA INCREASES. THIS UNCERTAINTY IS REFLECTED IN THE
INCREASED SPREAD IN POSSIBLE HIGH TEMPERATURES AS WELL AS LOW
CHANCES OF RAIN FROM LATE WEDNESDAY THROUGH FRIDAY, BUT IN
GENERAL, A TROUGH LOCATED CLOSER TO THE COAST WILL FAVOR RAIN
AND COOLER TEMPERATURES WHILE A MORE DISTANT TROUGH WILL
INSTEAD FAVOR DRIER WEATHER AND NEAR-NORMAL TEMPERATURES.
MEAN FORECAST HIGHS FALL TO THE UPPER 60S INLAND AND LOW 60S
ALONG THE COAST BY FRIDAY, SOME 5 DEGREES BELOW NORMAL. HOWEVER
THE 80% CONFIDENCE INTERVAL (THE DIFFERENCE BETWEEN THE 10TH
AND 90TH PERCENTILES OF THE FORECAST DISTRIBUTION) NEARLY
DOUBLES IN WIDTH FROM 2 DEGREES F ON THE COAST AND 4-6 DEGREES
F INLAND ON WEDNESDAY TO 4 DEGREES F ON THE COAST AND 6-10
DEGREES F INLAND ON FRIDAY. IN GENERAL, RAINFALL CHANCES WILL
ALSO INCREASE AS THE TROUGH APPROACHES. THERE IS GOOD AGREEMENT
IN THE LOCATION OF AN INITIAL PASSING SHORTWAVE ON WEDNESDAY,
WITH RAINFALL CHANCES OF ONLY 10-15% ALONG THE SOUTH WASHINGTON
AND FAR NORTH OREGON COASTS WITH HIGHER CHANCES FARTHER NORTH
ON THE OLYMPIC PENINSULA. THURSDAY INTO FRIDAY, ABOUT ONE
QUARTER OF ENSEMBLE MEMBERS FAVOR THE COOLEST AND WETTEST
SCENARIO, RESULTING IN FAIRLY WIDESPREAD 15-25% CHANCES FOR
RAIN TO END THE WORKWEEK. -36
AVIATION...THROUGH 18Z SUNDAY
SATELLITE IMAGERY AND TERMINAL
OBSERVATIONS AS OF LATE SATURDAY MORNING DEPICTS WIDESPREAD STRATUS
ACROSS NORTHWEST OREGON, BRINGING IFR/MVFR CIGS TO MOST TERMINALS.
SOME OF THIS STRATUS IS BEGINNING TO DISSIPATE ALONG THE CASCADE
FOOTHILLS. BASED ON THESE SURFACE OBSERVATIONS AND PIREPS, EXPECT
STRATUS TO COMPLETELY DISSIPATE ACROSS THE WILLAMETTE VALLEY AND
COAST BY 20-21Z SAT AS DAYTIME HEATING PROGRESSES. VFR CONDITIONS
WITH MOSTLY CLEAR SKIES PREVAIL FOR INLAND TERMINALS THROUGH LATE
THIS EVENING, WHILE COASTAL TERMINALS KEEP BRIEF CLEARING THIS
AFTERNOON. THERE IS HIGH CONFIDENCE (>80% CHANCE) THAT IFR/MVFR
MARINE STRATUS RETURNS TO THE COAST AFTER 03-05Z SUN AND PREVAILS
THROUGH THE MORNING.
BETWEEN 12-18Z SUN, THERE IS ALSO A 30-40% CHANCE AT ANY GIVEN HOUR
FOR MVFR STRATUS RETURNING TO VALLEY TERMINALS. NORTHWESTERLY WINDS
GENERALLY UNDER 10 KT TODAY.
KPDX AND APPROACHES...MVFR STRATUS THROUGH 20Z SAT. AFTERWARDS, VFR
CONDITIONS PREVAIL THROUGH LATE TONIGHT. 20-40% CHANCE FOR MVFR
STRATUS RETURNING 12-18Z SUN. NORTHWESTERLY WINDS AROUND 5 KT OR
LESS. -10
MARINE
HIGH PRESSURE OVER THE WATERS WILL MAINTAIN NORTHERLY
WINDS THROUGH THIS WEEKEND. NORTHERLY WINDS STRENGTHEN THIS
AFTERNOON AND EVENING WITH GUSTS UP TO 15 KT, STRONGEST OVER THE
WATERS SOUTH OF CAPE FALCON. NORTHERLY WINDS PEAK IN STRENGTH
SUNDAY AFTERNOON AND EVENING WHEN THERE IS A 50-90% CHANCE FOR
MAXIMUM WIND GUSTS OF 21 KT OR SLIGHTLY STRONGER ACROSS THE
WATERS, WITH THE HIGHEST CHANCES ACROSS THE INNER WATERS OUT TO
10 NM OFFSHORE. GIVEN WIND GUSTS OF THIS MAGNITUDE ARE NOT
EXPECTED TO BE FREQUENT OR WIDESPREAD, SMALL CRAFT ADVISORIES
ARE NOT ANTICIPATED AT THIS TIME. SIGNIFICANT WAVE HEIGHTS WILL
REMAIN AROUND 3 TO 5 FT THROUGH THE WEEKEND, MAINLY DRIVEN BY A
PERSISTENT NORTHWESTERLY SWELL WITH A DOMINANT WAVE PERIOD
BETWEEN 7 TO 8 SECONDS.
NORTHERLY WINDS ARE EXPECTED TO LINGER MONDAY THROUGH WEDNESDAY,
WITH WIND GUSTS GENERALLY STAYING UNDER 20 KT. A LONG PERIOD
WEST-NORTHWESTERLY SWELL IS SET TO ARRIVE EITHER MONDAY
AFTERNOON OR EVENING, PUSHING SEAS UP BY ONE TO TWO FEET.
HOWEVER, SEAS WILL NOT BE PARTICULARLY STEEP AS THE DOMINANT
WAVE PERIOD WITH THIS SWELL WILL BE AROUND 11-13 SECONDS. -10/23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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