526
FXUS66 KPQR 131642
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
942 AM PDT SAT SEP 13 2025
SYNOPSIS
SHALLOW MARINE STRATUS AND/OR FOG THIS MORNING
SHOULD CLEAR OUT BY THE EARLY AFTERNOON. THE NEXT FRONTAL SYSTEM
ARRIVES TONIGHT INTO SUNDAY, BRINGING WIDESPREAD RAIN SHOWERS.
CONDITIONS DRY OUT AND WARM UP AGAIN EARLY NEXT WEEK WITH THE
POTENTIAL FOR OFFSHORE WINDS MONDAY NIGHT THROUGH TUESDAY.
ANOTHER WEAK FRONT RETURNS ONSHORE FLOW AND PRECIPITATION
CHANCES MID-WEEK.
SHORT TERM...NOW THROUGH MONDAY NIGHT
SATELLITE IMAGERY AS
OF EARLY SATURDAY MORNING DEPICTS PATCHY, SHALLOW MARINE STRATUS
ALONG THE COAST, LOWER COLUMBIA RIVER VALLEY, AND COAST RANGE
LOWLAND VALLEYS. THE AXIS OF AN UPPER LEVEL SHORTWAVE RIDGE IS
CURRENTLY CENTERED OVER THE PACIFIC NORTHWEST, WHICH ALLOWING
FOR A MUCH SHALLOWER MARINE LAYER COMPARED TO PREVIOUS NIGHTS.
THIS IS PRETTY EVIDENT FROM THE LATEST SURFACE OBSERVATIONS
ALONG THE CENTRAL OREGON COAST WHERE CLOUD CEILINGS ARE AROUND
100 FT OR LESS, ESSENTIALLY BECOMING FOG AND REDUCING VISIBILITY
TO 1/2 MILE OR LESS. IF YOU'LL BE DRIVING IN FOG THIS MORNING,
ESPECIALLY ALONG THE COAST, SLOW DOWN, USE YOUR LOW BEAM
HEADLIGHTS, AND KEEP YOUR DISTANCE FROM OTHER VEHICLES.
LATER THIS MORNING AROUND 4-7 AM, MODEL SOUNDINGS SUGGEST THAT
SHALLOW STRATUS WILL ALSO DEVELOP ACROSS THE WILLAMETTE VALLEY
AND SOUTHWEST WASHINGTON LOWLANDS AS THE SURFACE MOISTENS UNDER
THE NIGHTTIME INVERSION. GRADUAL CLEARING OF LOW STRATUS AND/OR
FOG SHOULD BEGIN AROUND 9-11 AM AS DAYTIME HEATING PROGRESSES
AND LEADS TO BETTER MIXING OF THE LOWER ATMOSPHERE. WE SHOULD
SEE MOSTLY SUNNY SKIES BY THE EARLY AFTERNOON WITH HIGH
TEMPERATURES IN THE UPPER 70S TO LOW 80S ACROSS INTERIOR
VALLEYS AND 60S ALONG THE COAST. BY THIS 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 RAIN SHOWERS ARE
LIKELY (70-80%) BY SUNDAY MORNING AS A SHORTWAVE TROUGH AND
ACCOMPANYING COLD-FRONT SWINGS 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 FORECAST TO BE IN THE 0.10-0.20" RANGE
ACROSS MOST INTERIOR VALLEYS, 0.20-0.40" ALONG THE COAST, AND
0.30-0.50" 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. SHORTWAVE RIDGING
RETURNS ON MONDAY AS WILL DRIER CONDITIONS AND CLEARING SKIES
BY MONDAY AFTERNOON. -ALVIZ/SCHULDT
LONG TERM...TUESDAY THROUGH FRIDAY
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.
AFTERNOON HIGHS ON TUESDAY ARE FORECAST IN THE MID 80S ACROSS
MOST INTERIOR VALLEYS WITH UPPER 60S TO LOW 70S ALONG THE COAST.
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 -5 MB PRESSURE GRADIENT FROM
KTTD TO KDLS TUESDAY MAY YIELD 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. THIS OFFSHORE FLOW PATTERN LOOKS
BRIEF AT LEAST, SINCE THE THERMAL TROUGH BREAKS DOWN TUESDAY
NIGHT INTO WEDNESDAY AND RETURNS WESTERLY ONSHORE FLOW.
WEDNESDAY, MOST ENSEMBLE MEMBERS ARE IN AGREEMENT OF AN UPPER
LEVEL TROUGH IN THE NORTHEAST PACIFIC APPROACHING BRITISH
COLUMBIA. A WEAK FRONT ASSOCIATED WITH THIS SYSTEM WILL SWING
THROUGH THE PACIFIC NORTHWEST AND RETURN CHANCES (20-40%) FOR
RAIN SHOWERS, WITH THE HIGHEST CHANCES ALONG THE COAST AND
SOUTHWEST WASHINGTON. FORECAST CONFIDENCE DECREASES THURSDAY TO
FRIDAY AS ENSEMBLE GUIDANCE STRUGGLES WITH THE EXACT
PROGRESSION OF THE UPPER LEVEL PATTERN. MOST ENSEMBLES STILL
MAINTAIN GENERAL TROUGHING OVER THE AREA, HOWEVER, THERE IS HIGH
UNCERTAINTY WITH THE EXACT MAGNITUDE, TRACK, AND TIMING OF THE
TROUGH. -ALVIZ/SCHULDT
AVIATION
CURRENTLY, THERE ARE MIXED FLIGHT CONDITIONS ACROSS
THE AIRSPACE. 16Z SATURDAY SATELLITE AND SURFACE OBSERVATIONS SHOW
MARINE STRATUS BRINGING GENERALLY IFR/LIFR CONDITIONS ALONG THE
COAST, WITH GENERALLY CLEAR SKIES INLAND. HOWEVER, THERE ARE
POCKETS OF IFR CONDITIONS INLAND. AS THE DAY PROGRESSES,
CONDITIONS ARE EXPECTED TO IMPROVE. INLAND LOCATIONS ARE EXPECTED
TO IMPROVE TOWARDS VFR WITH AREAS ALONG THE COAST IMPROVING
TOWARDS MVFR AND THESE CONDITIONS ARE EXPECTED TO PERSIST THROUGH
THE MAJORITY OF THE DAY. COULD ALSO SEE SOME SOUTH/SOUTHWESTERLY
GUSTS ALONG THE COAST UP TO 20 KT FROM 18Z SATURDAY THROUGH 06Z
SUNDAY.
AN INCOMING COLD FRONT AROUND 06Z-08Z SUNDAY, WILL BRING LIGHT
SHOWERS AND MVFR TO LIFR CONDITIONS TO THE COAST. SHOWERS AND
MVFR/IFR CONDITIONS EXPECTED INLAND STARTING AROUND 10Z-12Z
SUNDAY.
KPDX AND APPROACHES...CURRENT IFR CONDITIONS ARE EXPECTED TO
IMPROVE TO VFR BY 18Z SATURDAY IF NOT SOONER. AFTERWARDS, EXPECT
VFR CONDITIONS. AN INCOMING COLD FRONT WILL BRING SHOWERS AND
MVFR/IFR CONDITIONS AT OR NEAR THE TERMINAL AROUND 10Z SUNDAY.
30-45% PROBABILITY FOR IFR CONDITIONS STARTING AROUND 15Z
SUNDAY. /42
MARINE
A COLD FRONT APPROACHES THE WATERS TODAY, MOVING
THROUGH THE WATERS TONIGHT INTO SUNDAY MORNING. SOUTH WINDS
EXPECTED TO INCREASE THIS EVENING TO 10-15 KT WITH GUSTS TO
AROUND 20 KT THROUGH SUNDAY MORNING WITH OCCASIONAL GUSTS UP TO
21-25 KTS FOR THE FAR OUTER WATERS AROUND 50-60 NM AWAY FROM THE
COAST. WITH GUSTS ABOVE 21 KTS NOT EXPECTED TO BE WIDESPREAD,
NO SMALL CRAFT ADVISORY IS BEING ISSUED. SEAS 6-8 FEET AT 10-13
SECONDS EXPECTED THROUGH THE WEEKEND AS A NORTHWESTERLY SWELL
MOVES INTO THE WATERS.
HIGH PRESSURE RETURNS OVER THE WATERS SUNDAY AFTERNOON, SHIFTING
WINDS NORTHERLY AGAIN. PRESSURE GRADIENTS EXPECTED TO TIGHTEN OVER
THE WATERS THROUGH TUESDAY, AND WITH THIS, COULD SEE SOME GUSTS
TO AROUND 21 KT DURING THE AFTERNOON AND EVENING HOURS EACH DAY.
ANOTHER WEAK FRONT IS EXPECTED TO MOVE THROUGH THE WATERS MIDWEEK,
BRIEFLY SHIFTING WINDS WEST TO SOUTHWEST. -HEC
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...DENSE FOG ADVISORY UNTIL 11 AM PDT THIS MORNING FOR PZZ210-
251>253.
WWW.WEATHER.GOV/PORTLAND
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