637
FXUS66 KPQR 172120
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
220 PM PDT SAT OCT 17 2026
SYNOPSIS
LARGELY DRY WEATHER EXPECTED THROUGH MIDWEEK WHILE
TEMPERATURES REMAIN ABOVE AVERAGE FOR MID-OCTOBER. A SYSTEM
MOVING SOUTH WELL OFFSHORE IS UNLIKELY TO RESULT IN WIDESPREAD
RAIN, WITH ONLY LOW CHANCES FOR PRECIPITATION ALONG THE COAST.
CHANCES FOR UNSETTLED WEATHER RETURN THURSDAY INTO NEXT WEEKEND.
SHORT TERM...NOW THROUGH MONDAY NIGHT
ZONAL FLOW WILL DEVELOP
OVER THE REGION THROUGH TODAY IN THE WAKE OF A DEPARTING COLD
FRONT EXITING TO THE EAST THROUGH THIS AFTERNOON. FOLLOWING A
FEW DAYS OF UNUSUAL WARMTH, MUCH MORE SEASONABLE BUT STILL ABOVE
NORMAL TEMPERATURES EXPECTED THROUGH THIS WEEKEND AS AFTERNOON
HIGHS REACH THE UPPER 50S TO UPPER 60S. OVERNIGHT TEMPERATURES
WILL ALSO BE SHARPLY COOLER TONIGHT, FALLING TO THE UPPER 30S TO
LOW 40S FOR MOST. THE COLDEST LOCALES ARE LIKELY TO BE IN THE
HOOD RIVER VALLEY, WHERE THERE IS HIGH CONFIDENCE IN MULTIPLE
HOURS OF TEMPERATURES OF 36F OR COLDER WHICH COULD SUPPORT
WIDESPREAD FROST, AND A FROST ADVISORY REMAINS IN EFFECT FOR THE
UPPER HOOD RIVER VALLEY FROM 11 PM PDT THIS EVENING UNTIL 9 AM
PDT SUNDAY. WHILE THERE IS LOWER CONFIDENCE IN THE OCCURRENCE OF
WIDESPREAD FROST, OTHER AREAS WHICH HAVE LOCALLY HIGHER CHANCES
OF FALLING INTO THE MID 30S FOR A FEW HOURS TONIGHT ARE VALLEYS
WITHIN THE NORTH OREGON COAST RANGE INCLUDING THE NEHALEM VALLEY
NEAR VERNONIA AND ALONG OR-18/OR-22 NEAR GRAND RONDE. INCREASING
CLOUD COVER ON SUNDAY NIGHT WILL SEE OVERNIGHT TEMPERATURES
REMAIN A FEW DEGREES WARMER AND RESULT IN LOWER CHANCES FOR
FROST, WITH THE EXCEPTION OF 50-75% CHANCES FOR LOWS IN THE MID
30S IN HIGHEST ELEVATION PORTIONS OF THE UPPER HOOD RIVER
VALLEY NEAR PARKDALE AND DEE.
ON MONDAY, THERE IS GOOD CONSENSUS THAT AN UPPER-LEVEL TROUGH
APPROACHING THE COAST WILL ELONGATE AND PINCH OFF INTO A CLOSED
UPPER LOW WHICH WILL TRACK SOUTH TOWARD CALIFORNIA. AS THE
TROUGH AND ITS ASSOCIATED SURFACE LOW MAKE THEIR CLOSEST
APPROACH, CHANCES FOR RAIN WILL LARGELY REMAIN OFFSHORE, WITH
COASTAL AND COAST RANGE COMMUNITIES SEEING ONLY 5-15% CHANCES
FOR RAIN. RAINFALL AMOUNTS ARE NOT EXPECTED TO BE SIGNIFICANT.
REINFORCING COOL AIR ALOFT WITHIN THE TROUGH WILL CONTINUE TO
PUSH TEMPERATURES DOWNWARD, WITH NEAR-NORMAL HIGHS EXPECTED ON
MONDAY. MONDAY NIGHT WILL BRING MORE WIDESPREAD CHANCES FOR
OVERNIGHT LOWS IN THE MID 30S, TO ADDITIONALLY INCLUDE SOME
CASCADE VALLEYS, PORTIONS OF THE WILLAMETTE VALLEY, AND NORTHERN
LOWLAND AREAS IN CLARK AND COWLITZ COUNTIES.
LONG TERM...TUESDAY THROUGH SATURDAY
WHILE THE UPPER LOW
DRIFTS SOUTHWARD OVER CALIFORNIA, HEIGHTS ALOFT REBOUND LOCALLY
AS TRANSIENT UPPER-LEVEL RIDGING DEVELOPS OVERHEAD. THIS WILL
MAINTAIN DRY CONDITIONS THROUGH MIDWEEK AND SUPPORT A WARMING
TREND WITH TEMPERATURES RETURNING TO THE LOW 70S INLAND BY
WEDNESDAY. OVERNIGHT LOWS LOOK TO REMAIN SEASONABLE, YIELDING
NIGHTLY CHANCES FOR FROST WITHIN INLAND VALLEYS.
THROUGH THE LATTER HALF OF THE WORKWEEK, THERE REMAINS DECENT
CONSENSUS AMONG LONG-RANGE ENSEMBLES THAT TROUGHING WILL
REDEVELOP OVER THE GULF OF ALASKA BUT WITH UNCERTAINTY IN ITS
LOCATION AND AMPLITUDE. THE PATTERN NONETHELESS SUPPORTS
MODEST CHANCES FOR RAIN FOR THURSDAY AND FRIDAY, AS WELL AS
FAVORING A RETURN TO SEASONABLE TEMPERATURES EACH DAY. NIGHTLY
CHANCES FOR FROST CONTINUE WITHIN INLAND VALLEYS. -36
AVIATION...THROUGH 18Z SUNDAY
A WEAK COLD FRONT STRADDLING
THE AIRSPACE WILL CONTINUE TO TRACK EASTWARD, EXITING BY THE
EARLY AFTERNOON. VERY LIGHT RAIN SHOWERS WITH LARGELY VFR CIGS
AND SCT LOW CLOUDS AT 1-3 KFT WILL LIKELY PREVAIL THROUGH 20-21Z
SAT. BEHIND THE BOUNDARY, SKIES ARE EXPECTED TO TREND CLEARER
ASIDE FROM SCT HIGH CLOUDS. NORTH TO NORTHWEST WINDS WILL RISE
TO AROUND 10 KT WITH GUSTS UP TO 20 KT ALONG THE COAST THIS
AFTERNOON, AS WELL AS IN THE SOUTHERN WILLAMETTE VALLEY BY THIS
EVENING, AND TO AROUND 5 KT ELSEWHERE.
KPDX AND APPROACHES...VFR CONDITIONS FAVORED TO PREVAIL
THROUGHOUT THE PERIOD WITH LOW CHANCES FOR MVFR CIGS WITH VERY
LIGHT RAIN SHOWERS BEFORE A FRONTAL BOUNDARY EXITS EASTWARD BY
21Z SAT. SCATTERED HIGH CLOUDS OTHERWISE EXPECTED WITH NORTHWEST
WINDS RISING TO AROUND 5 KT THIS AFTERNOON. -36
MARINE
NORTHERLY FLOW CONTINUES THROUGH THE WEEKEND WHILE A
BUILDING MID-PERIOD WEST-NORTHWESTERLY SWELL PUSHES SEAS TO 8-10
FT AT 11-12 SECONDS FROM TONIGHT THROUGH MUCH OF SUNDAY. CHANCES
FOR SEAS HIGHER THAN 10 FT ARE ONLY 5-15% BEYOND 30 NM NORTH OF
CAPE LOOKOUT. THIS SWELL WILL ALSO CONTINUE TO POSE A MODERATE
RISK FOR SNEAKER WAVES ALONG THE COAST; CAUTION SHOULD BE USED BY
THOSE IN OR NEAR THE WATER ALONG BEACHES THROUGH THIS WEEKEND.
ANOTHER WEATHER SYSTEM TRACKING TO THE SOUTH WELL OFFSHORE ON
MONDAY MAY GENERATE A LARGER WESTERLY SWELL YIELDING A PERIOD OF
STEEPER SEAS FROM MONDAY INTO TUESDAY, WITH 20-40% CHANCES OF
SIGNIFICANT WAVE HEIGHTS ABOVE 10 FT, HIGHEST BEYOND 20 NM SOUTH
OF CAPE LOOKOUT. BENIGN CONDITIONS ARE THEN EXPECTED MIDWEEK,
WITH INCREASING CONFIDENCE IN ANOTHER PERIOD OF ACTIVE MARINE
WEATHER LATE IN THE WORKWEEK. -36
PQR WATCHES/WARNINGS/ADVISORIES
OR...FROST ADVISORY FROM 11 PM THIS EVENING TO 9 AM PDT SUNDAY FOR
ORZ121.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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