275
FXUS66 KPQR 130445
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
945 PM PDT FRI SEP 12 2025
SYNOPSIS
A BRIEF WARMING TREND CONTINUES THROUGH THE FIRST
HALF OF THE WEEKEND AS DRY CONDITIONS PREVAIL. HOWEVER, THIS
BREAK APPEARS SHORT-LIVED AS OUR NEXT FRONTAL SYSTEM ARRIVES
SATURDAY NIGHT INTO SUNDAY BRINGING WIDESPREAD LIGHT RAINFALL.
CONDITIONS DRY OUT AND WARM UP AGAIN EARLY NEXT WEEK WITH THE
POTENTIAL FOR OFFSHORE WINDS MONDAY NIGHT THROUGH TUESDAY.
SHORT TERM...NOW THROUGH SUNDAY NIGHT
LATE THIS AFTERNOON
CLEARING HAS FINALLY OVERTAKEN THE PORTLAND/VANCOUVER METRO DOWN
THROUGH THE WILLAMETTE VALLEY AND INTO THE CASCADES AS WITH
TEMPERATURES LIKELY TOPPING OUT IN THE LOW TO MID 70S WHERE THIS
CLEARING IS PRESENT. THE AXIS OF A TRANSITORY UPPER-LEVEL RIDGE
OF HIGH PRESSURE IS EXPECTED TO PASS OVERHEAD TONIGHT FAVORING
AN EVEN SHALLOWER MARINE LAYER HEADED INTO SATURDAY MORNING.
MODELS SUGGEST THAT LOW STRATUS AND FOG LIKELY RE-DEVELOPS
ACROSS THE WILLAMETTE VALLEY AND SOUTHWEST WASHINGTON LOWLANDS
AS THE SURFACE MOISTENS UNDER THE NIGHTTIME INVERSION, BUT AGAIN
IN WEAKER/THINNER STATE THAN PAST NIGHTS. THIS WILL LEAD TO A
QUICKER CLEARING SATURDAY MORNING AND THUS HIGHER TEMPERATURES
(UPPER 70S TO NEAR 80) SATURDAY AFTERNOON ACROSS THE INTERIOR
VALLEYS. BY SATURDAY EVENING, THE AFOREMENTIONED SHORTWAVE RIDGE
PROGRESSES EASTWARD WITH INCREASING CLOUD COVER ACROSS THE AREA
AS THE NEXT FRONTAL SYSTEM APPROACHES.
COOLER TEMPERATURES AND WIDESPREAD LIGHT RAINFALL IS LIKELY
(70-80%) BY SUNDAY MORNING AS A SHORTWAVE TROUGH AND
ACCOMPANYING COLD-FRONT SWING THROUGH WESTERN OREGON AND
SOUTHWEST WASHINGTON. WHILE PRECIPITATION ALONG THE IMMEDIATE
FRONTAL BOUNDARY MAY BE MORE STRATIFORM IN NATURE, RAINFALL
QUICKLY TRANSITIONS TO LINGERING SHOWERS BY THE MIDDAY HOURS.
FORECAST RAINFALL TOTALS FROM LATE SATURDAY EVENING THROUGH
SUNDAY EVENING ARE PROJECTED TO BE IN THE 0.10-0.30" RANGE
ACROSS MOST INTERIOR VALLEYS, 0.20-0.40" ALONG THE COAST, AND
0.30-0.60" ACROSS THE COAST RANGE, WILLAPA HILLS, AND CASCADES
WITH THE HIGHEST RELATIVE AMOUNTS ON THE WESTERN SLOPES OF THESE
TERRAIN FEATURES. HOWEVER, CONFIDENCE IN THESE TOTALS ARE ONLY
MODERATE AS OVER THE PAST SEVERAL MODEL RUNS GUIDANCE HAS SLOWLY
BEEN TRENDING DOWNWARD WITH OUR STORM TOTALS AS IS OFTEN THE
CASE FOR THESE EARLY FALL SYSTEMS. THAT'S NOT TO SAY LARGE
SWATHS OF THE REGION WON'T GET ANY RAIN AT ALL, BUT AMOUNTS
OUTSIDE OF THE WEST SLOPES OF THE COAST RANGE APPEAR RATHER
LIGHT. BY SUNDAY EVENING, THE FRONT FURTHER WEAKENS AND RAPIDLY
EXITS TO THE EAST ALLOWING ANY LINGERING SHOWER ACTIVITY TO
TAPER OFF OVERNIGHT INTO EARLY MONDAY MORNING. -SCHULDT
LONG TERM...MONDAY THROUGH THURSDAY
SHORTWAVE RIDGING
RETURNS ON MONDAY AS WILL DRIER CONDITIONS AND CLEARING SKIES
BY MONDAY AFTERNOON. THEN COME MONDAY NIGHT INTO TUESDAY THERE
IS HIGH AGREEMENT AMONG ENSEMBLE MEMBERS IN A RETURN TO ABOVE-
AVERAGE 500 MB HEIGHTS AS THE RIDGE AXIS CENTERS OVER THE
PACIFIC NORTHWEST. THIS IS IN ADDITION TO A NEAR SURFACE
THERMAL TROUGH AMPLIFYING ACROSS WESTERN OREGON WITH HIGHER
PRESSURE EAST OF THE CASCADES, LEADING TO AN OFFSHORE FLOW WIND
PATTERN AND A SHARP SPIKE IN HIGH TEMPERATURES. THERE REMAINS
SOME UNCERTAINTY IN THE EXACT PLACEMENT THE THERMAL TROUGH
FEATURE WHICH WOULD DETERMINE THE STRENGTH AND WESTERN EXTENT OF
OFFSHORE WINDS, BUT FOR NOW THEY DON'T APPEAR PARTICULARLY
STRONG. STILL, A -3 TO -5MB GRADIENT FROM KTTD TO KDLS TUESDAY
MAY YIELD AT LEAST BREEZY EAST WINDS THROUGH THE COLUMBIA RIVER
GORGE WITH GUSTS UP TO 25-35 MPH EAST OF TROUTDALE. THIS MONDAY
NIGHT THROUGH TUESDAY PERIOD NEEDS TO BE MONITORED IN THE
COMING DAYS GIVEN AN EXPECTED DROP IN RELATIVE HUMIDITY COMPARED
TO PAST DAYS. FORTUNATELY, WESTERLY FLOW RETURNS TUESDAY NIGHT
INTO WEDNESDAY MORNING MITIGATING ANY FURTHER CONCERNS.
FORECAST CONFIDENCE BEGINS TO DECREASE WEDNESDAY AND THURSDAY AS
ENSEMBLE SYSTEMS STRUGGLE WITH THE EXACT PROGRESSION OF THE
UPPER-LEVEL PATTERN. FOR WEDNESDAY INTO WEDNESDAY NIGHT MOST
ENSEMBLE SYSTEMS DO SHOW A TROUGHING FEATURE MOVING INTO FAR NW
CONUS BUT THERE'S A DECENT SPREAD IN THE LONGITUDINAL PLACEMENT
AND MORESO THE AMPLITUDE OF SAID FEATURE. AT LEAST IN ALMOST
ALL SCENARIOS THE FRONTAL BOUNDARY PAIRED WITH THIS TROUGH
APPEARS TO DETERIORATE BEFORE REACHING OUR AREA. THERE IS A
SLIGHT CHANCE (20-25%) THAT WE COULD SEE SOME LIGHT SHOWERS
MAINLY ALONG THE COAST AND SOUTHWEST WASHINGTON. -SCHULDT/ALVIS
AVIATION
VFR CONDITIONS BENEATH LARGELY CLEAR SKIES INLAND
WILL TREND TO MVFR AS LOW MARINE STRATUS DEVELOPS BY 12-14Z SAT
WITH CALM TO LIGHT AND VARIABLE WINDS. WHILE MVFR CONDITIONS ARE
FAVORED (ABOUT 60% CHANCE), THERE IS A 30-40% CHANCE OF IFR CIGS
AROUND 500 FT OR EVEN, MOST LIKELY AT PORTLAND-AREA AND NORTHERN
WILLAMETTE VALLEY TERMINALS FROM 14-16Z SAT, AS WELL AS A 10%
CHANCE OF VIS RESTRICTED TO 1SM OR LESS WITHIN FOG. FARTHER SOUTH
IN THE WILLAMETTE VALLEY, CHANCES ARE LOWER FOR IFR CONDITIONS OR
FOG. A RELATIVELY SHALLOW MARINE LAYER IS EXPECTED, ALLOWING FOR
AN EARLIER BREAK OUT TO VFR FROM 17-19Z SAT, WITH WINDS BUILDING
OUT OF THE WEST TO SOUTHWEST AT AROUND 5 KT. HIGH CLOUDS BEGIN TO
INCREASE LATE IN THE PERIOD AHEAD OF AN APPROACHING COLD FRONT.
ALONG THE COAST, IFR/LIFR CONDITIONS ARE EXPECTED TO DEVELOP BY
08-09Z SAT AND CONTINUE THROUGH THE OVERNIGHT PERIOD WITH CIGS
NEAR 500 FT, VIS RESTRICTED TO 1SM OR LESS WITHIN FOG/MIST, AND
LIGHT AND VARIABLE WINDS. CONDITIONS WILL BEGIN TO SLOWLY IMPROVE
AFTER 15Z SAT AS WINDS BUILD OUT OF THE SOUTHWEST TO NEAR 10 KT,
WITH MVFR CIGS LIKELY TO PERSIST THROUGH MUCH OF THE DAY. CIGS
WILL TREND DOWN TOWARD IFR LATE IN THE PERIOD WITH 30-40% CHANCES
OF COLD FRONTAL RAIN SHOWERS ARRIVING ARRIVING AFTER 00-03Z SUN.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED TO CONTINUE THROUGH
12-14Z SAT WITH NORTHWEST WINDS OF LESS THAN 5 KT. MVFR CIGS BELOW
2 KFT ARE MOST LIKELY, 50-60% CHANCES, BUT THERE ARE ALSO 30-40%
CHANCES OF IFR CIGS AT 500 FT, AND LESSER (AROUND 10%) IN VIS
BELOW 1SM WITHIN FOG. THE WORST FLYING CONDITIONS ARE EXPECTED
FROM 14-16Z SAT, BEFORE THE ONSET OF MIXING WILL BEGIN TO IMPROVE
VIS AND/OR LIFT CIGS. AN EARLIER BREAK OUT TO VFR IS EXPECTED
THANKS TO A SHALLOW MARINE LAYER, LIKELY BY 18-19Z SAT. WEST WINDS
AROUND 5 KT WILL CONTINUE THROUGH SATURDAY EVENING WITH INCREASING
HIGH CLOUDS LATE AHEAD OF AN APPROACHING COLD FRONT. -PICARD
MARINE
HIGH PRESSURE WILL GIVE WAY TO A LOW PRESSURE SYSTEM
AND ASSOCIATED COLD FRONT APPROACHING THE AREA OVERNIGHT.
VARIABLE WINDS EXPECTED TO BECOME SOUTHERLY LATE THIS EVENING
INTO EARLY SATURDAY MORNING. SEAS 6-8 FEET AT 10-13 SECONDS
EXPECTED THROUGH THE WEEKEND AS A NORTHWESTERLY SWELL MOVES INTO
THE WATERS. WINDS EXPECTED TO INCREASE SATURDAY EVENING TO
10-15 KT WITH GUSTS TO AROUND 20 KT THROUGH SUNDAY MORNING.
HOURLY WIND GUST PROBABILITIES FOR GUSTS OF 21 KT OR GREATER
SATURDAY AFTERNOON THROUGH SUNDAY AFTERNOON ARE REMAIN AROUND
10-35%, WITH THE HIGHEST CHANCE ALONG THE FAR OUTER WATERS. 24
HOUR PROBABILITIES ARE 20-50%, AGAIN HIGHEST FOR THE FAR OUTER
WATERS. GIVEN THE LOW CONFIDENCE IN PERSISTENT GUSTS OF 21 KT OR
GREATER, WILL CONTINUE TO HOLD OFF ON ANY PRODUCTS.
A SMALL CRAFT ADVISORY IS IN EFFECT FROM 6 PM FRIDAY TO 1 AM
SATURDAY FOR THE COLUMBIA RIVER BAR. SEAS AROUND 7 FEET ARE
EXPECTED WITH A STRONG EBB CURRENT OF 5.8 KT WHICH WILL CREATE
ROUGH COLUMBIA RIVER BAR CONDITIONS, HAZARDOUS TO SMALL CRAFT.
NEXT WEEK LOOKS MOSTLY BENIGN. A BUILDING RIDGE OF HIGH PRESSURE
IS EXPECTED TO SUPPORT AN AREA OF THERMAL LOW PRESSURE THAT WILL
INCREASE THE PRESSURE GRADIENT OVER THE WATERS ON TUESDAY. COULD
SEE SOME GUSTS TO AROUND 21 KT DURING THE AFTERNOON AND EVENING
HOURS BUT TO MUCH UNCERTAINTY THIS FAR OUT TO HAVE HIGH
CONFIDENCE. -BATZ
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 1 AM PDT SATURDAY FOR PZZ210.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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