753
FXUS66 KPQR 101129
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
429 AM PDT THU SEP 10 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
TEMPERATURES WILL GRADUALLY COOL EACH DAY THURSDAY
THROUGH THE WEEKEND AS ONSHORE FLOW STRENGTHENS AHEAD OF A LOW
PRESSURE SYSTEM SET TO BRING WIDESPREAD RAIN TO THE AREA ON
SATURDAY. SHOWERS DISSIPATE ON SUNDAY, WITH DRY AND MILD
CONDITIONS EXPECTED EARLY NEXT WEEK.
SHORT TERM...THURSDAY MORNING THROUGH SUNDAY
SATELLITE
IMAGERY EARLY THURSDAY MORNING SHOWS MARINE STRATUS HAS FORMED
UNDER ONSHORE (WESTERLY) FLOW ALONG PORTIONS OF THE NW OR AND SW
WA COAST AS A BAND OF MID TO HIGH LEVEL CLOUDS IS SLOWLY PUSHING
SOUTH INTO THE AREA. THIS IS DUE TO A WEAK TROUGH DEEPENING OVER
THE PACNW ALONG WITH A DRY COLD FRONT APPROACHING FROM THE
NORTH. TEMPERATURES TODAY WILL BE RELATIVELY COOLER FROM
YESTERDAY DUE TO THE TROUGHING. THE MID TO HIGH LEVEL CLOUD
BAND WILL SLOWLY SPREAD SOUTH THROUGH THE DAY, THOUGH LANE
COUNTY SHOULD REMAIN MOSTLY SUNNY, SO TEMPERATURES WILL BE
SLIGHTLY WARMER THERE COMPARED TO LOCATIONS TO THE NORTH. EXPECT
HIGH TEMPERATURES BETWEEN 75-85 DEGREES FOR MOST INLAND VALLEY
LOCATIONS AND 65-70 DEGREES AT THE COAST. THE COLD FRONT WILL
PASS THROUGH THE REGION BY TONIGHT AND THE NEXT UPPER LEVEL LOW
WILL BEGIN APPROACHING THE REGION THROUGH FRIDAY, BRINGING MORE
CLOUD COVER AND EVEN COOLER TEMPERATURES ON FRIDAY. HIGH
TEMPERATURES WILL BE IN THE UPPER 60S TO AROUND 70 DEGREES FOR
THE INTERIOR LOWLANDS AND LOW TO MID 60S FOR THE COAST, AROUND
5-10 DEGREES BELOW AVERAGE FOR THIS TIME OF YEAR.
ENSEMBLE GUIDANCE FROM THE GEFS/GEPS/ENS INDICATES THE
AFOREMENTIONED UPPER LEVEL LOW PRESSURE SYSTEM DEEPENS JUST OFF
THE COAST FRIDAY NIGHT INTO EARLY SATURDAY BEFORE SHIFTING EAST
AND MOVING INLAND ON SATURDAY. THIS WEATHER SYSTEM WILL BRING
THE NEXT ROUND OF WIDESPREAD RAIN TO NW OR AND SW WA, THOUGH
SOME UNCERTAINTY REMAINS IN TIMING AS MANY OF THE LATEST
ENSEMBLE GUIDANCE HAS SLOWED THE APPROACH OF THE WEATHER SYSTEM.
RAIN IS FORECAST TO BEGIN SOMETIME SATURDAY MORNING ALONG THE
COAST AND SPREAD INLAND SOMETIME BETWEEN SUNDAY MORNING AND LATE
SATURDAY AFTERNOON. WITH THE SLOWING OF PRECIPITATION ONSET,
RAIN IS NOW EXPECTED TO CONTINUE INTO SATURDAY NIGHT WITH
SHOWERS POSSIBLY CONTINUING THROUGH SUNDAY FOR PORTIONS OF THE
INTERIOR LOWLANDS AND CASCADES. THIS COULD ALSO IMPACT
THUNDERSTORM CHANCES ON SATURDAY. IF THE CORE OF THE LOW
PRESSURE SYSTEM DOESN'T MOVE OVER THE AREA UNTIL LATER ON
SATURDAY AFTER PEAK HEATING, THERE IS LESS CHANCE FOR ENOUGH
CONVECTIVE ABILITY TO DEVELOP, LIMITING THUNDERSTORM CHANCES.
HOWEVER, COLD CORE FUNNEL CLOUDS COULD STILL DEVELOP GIVEN THE
OVERALL PATTERN. ROTATION WITH COLD CORE FUNNEL CLOUDS RARELY
REACHES THE GROUND OR CAUSES IMPACTS, BUT IT IS NOT IMPOSSIBLE.
THEY ARE ALSO NON-MESOCYCLONIC IN NATURE AND CAN FORM WITHOUT
STRONG DEEP-LAYER WIND SHEAR IN PLACE. DESPITE THE MODEL TIMING
DIFFERENCES, AROUND 95% OF MODEL ENSEMBLE GUIDANCE SUGGESTS
MEASURABLE RAIN WILL OCCUR WITH THIS SYSTEM. THE LATEST
FORECAST INDICATES TOTAL RAIN AMOUNTS RANGING BETWEEN 0.1-0.5
INCH FOR MOST LOCATIONS, HIGHEST IN THE CASCADES IN COAST RANGE.
NOTE THIS IS NOT ENOUGH RAIN TO RESULT IN FLOODING IMPACTS.
TEMPERATURES WILL COOL EVEN MORE ON SATURDAY AND NOW LIKELY
REMAINING VERY SIMILAR ON SUNDAY DUE TO CONTINUED CLOUD COVER.
TOTAL NBM SPREAD FOR TEMPERATURES RANGES IS FAIRLY LOW FOR BOTH
DAYS, WITH HIGHS MOST LIKELY RANGING BETWEEN THE UPPER 50S AND
UPPER 60S (80% CHANCE) FOR THE INTERIOR LOWLANDS. -03/23
LONG TERM...MONDAY THROUGH WEDNESDAY
THE LONG TERM FORECAST
IS HIGHLIGHTED BY DRY CONDITIONS AND THE CONTINUATION OF BELOW
AVERAGE TEMPERATURES, ALBEIT A BIT WARMER THAN WHAT IS EXPECTED
ON SATURDAY. THE VAST MAJORITY (>90%) OF ENSEMBLE GUIDANCE
SUGGESTS THE UPPER LEVEL LOW OVER THE AREA WILL CONTINUE TO PUSH
EASTWARD AND MOVE TOWARDS THE NORTHERN PLAINS LATE SUNDAY INTO
EARLY NEXT WEEK. A WEAKER SECONDARY TROUGH ON THE BACKSIDE OF
THIS LOW LOOKS TO REMAIN OVER OREGON AND WASHINGTON THROUGH AT
LEAST TUESDAY. ON MONDAY, NBM TEMPERATURE SPREAD RANGES FROM
THE MID 60S TO UPPER 70S FOR THE INTERIOR LOWLANDS, WITH LOW
70S BEING THE MOST LIKELY OUTCOME. SPREAD INCREASES A BIT ON
TUESDAY, AS HIGHS COULD RANGE ANYWHERE FROM THE MID 60S TO THE
MID 80S. BY WEDNESDAY, UNCERTAINTY INCREASES IN THE OVERALL
PATTERN AS AROUND 50-60% OF ENSEMBLE MEMBERS SUGGEST THE LOW
PRESSURE WEAKENING OVER THE PACNW WITH HIGH PRESSURE OVER THE
SOUTHERN US TRYING TO PUSH NORTHWEST INTO THE AREA, ALLOWING FOR
WARMING TEMPERATURES. THE OTHER 40-50% OF GUIDANCE SUGGEST SOME
LEVEL OF TROUGHING REMAINING OVER THE PACNW, WHICH WOULD KEEP
TEMPERATURES ON THE COOLER SIDE. THE TOTAL TEMPERATURE SPREAD
INDICATES HIGHS COULD RANGE ANYWHERE FROM LOW 70S TO UPPER 80S.
OVERALL, THERE ARE NO SIGNS OF ANY HIGH IMPACT WEATHER ON THE
HORIZON. -03/23
AVIATION...THROUGH 12Z FRIDAY
AT 11Z THU, WIDESPREAD VFR
CONDITIONS AT INLAND TERMINALS THROUGH THE PERIOD WHILE LOW CLOUD
COVERAGE IS PRODUCING MVFR/IFR VIS/CIGS AT MOST COASTAL TERMINALS.
KAST IS FORECAST TO FALL TO MVFR/IFR CONDITIONS BY 12-13Z THU. LOW
CLOUDS OVER THE COAST WILL THEN TEND TO DECREASE IN COVERAGE THROUGH
THURSDAY AFTERNOON, THOUGH AREAS FROM KTMK NORTHWARD ARE MORE LIKELY
TO MAINTAIN MVFR CIGS THROUGH MUCH OF THE DAY. INCREASING HIGH CLOUD
COVERAGE IS EXPECTED FROM NORTH TO SOUTH THROUGH THE PERIOD. VFR
CONDITIONS EXPECTED THROUGH THE MAJORITY OF THE PERIOD FOR INLAND
TERMINALS, THOUGH CHANCES FOR MVFR/IFR CIGS INCREASE AROUND 12Z THU
FOR TERMINALS AROUND AND NORTH OF KUAO. LIGHT NORTH TO NORTHWEST
WINDS WILL BUILD TO 5-10 KT INLAND AND 10-15 KT WITH GUSTS AS HIGH
AS 20-25 KT ALONG THE COAST BY THURSDAY AFTERNOON, BECOMING LIGHT
AFTER 04-06Z FRI.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGHOUT THE PERIOD
WITH INCREASING COVERAGE OF HIGH CLOUDS TODAY. CHANCES FOR MVFR CIGS
INCREASE NEAR THE END OF THE PERIOD AROUND 12Z FRI. NORTHWEST WINDS
OF LESS THAN 5 KT WILL RISE TO NEAR 10 KT BY AFTER 21-23Z THU,
DECREASING BY 06Z FRI. -03
MARINE
HIGH PRESSURE OFFSHORE WILL MAINTAIN PREDOMINATELY
NORTHERLY WINDS ACROSS ALL WATERS THROUGH AT LEAST FRIDAY.
BREEZY NORTH WINDS WITH GUSTS UP TO 25 KT AT TIMES ARE POSSIBLE
THROUGH THIS EVENING. A SMALL CRAFT ADVISORY REMAINS IN EFFECT
FOR ALL ZONES EXCLUDING THE COLUMBIA RIVER BAR FROM 5 AM TO 8 PM
PDT TODAY. SEAS 6 TO 8 FT THROUGH FRIDAY WITH PERIOD OF 9 TO 11
SECONDS. ANOTHER WEAKER SYSTEM IS EXPECTED TO APPROACH THE
COASTAL WATERS FROM THE NORTH LATE FRIDAY INTO SATURDAY. THIS
WILL RESULT IN A SOUTHERLY WIND SHIFT ALONG WITH SEAS SUBSIDING
TOWARDS 4 TO 6 FT AND GUSTS BELOW 20 KTS. -03
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR PZZ251>253-
271>273.
WWW.WEATHER.GOV/PORTLAND
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