499
FXUS66 KPQR 140426 AAB
AFDPQR
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PORTLAND OR
926 PM PDT SUN SEP 13 2026
UPDATED AVIATION DISCUSSION
SYNOPSIS
COOLER THAN NORMAL CONDITIONS PERSIST INTO EARLY
NEXT WEEK AS DRIER WEATHER RETURNS ALBEIT WITH AREAS OF MORNING
LOW CLOUDS AND FOG. OUR ATTENTION THEN TURNS TO A RIDGE OF HIGH
PRESSURE BUILDING OVERHEAD MID TO LATE WEEK LEADING TO THE
RETURN OF SUMMER-LIKE TEMPERATURES - HIGHS IN THE 80S ACROSS THE
LOWLANDS. A PERIOD OF ENE FLOW CENTERED AROUND WEDNESDAY AND
THURSDAY LIKELY BRINGS BREEZY EAST WINDS TO THE COLUMBIA RIVER
GORGE, CASCADES, AND ADJACENT FOOTHILLS AS WELL. LOWER FORECAST
CONFIDENCE FRIDAY ONWARD AS THE RIDGE OF HIGH PRESSURE BEGINS TO
BREAK DOWN.
DISCUSSION...NOW THROUGH SATURDAY
A CLOSED UPPER-LEVEL LOW
PRESSURE SYSTEM REMAINS OVERHEAD THIS AFTERNOON AS RAIN SHOWER
ACTIVITY ROTATES INTO THE AREA OUT OF THE N-NW. HEADED INTO THE
EVENING AND OVERNIGHT HOURS CONFIDENCE IS HIGH THIS LOW PRESSURE
CONTINUES TO RACE EASTWARD FOLLOWED BY BUILDING UPPER-LEVEL
HEIGHTS HELPING TO DECREASE LINGERING SHOWERS, LARGELY ENDING
ACROSS THE LOWER ELEVATIONS THIS EVENING, AND AIDING IN A BIT
OF PARTIAL CLEARING. THIS LATTER VARIABLE WILL COME INTO PLAY BY
SUNRISE MONDAY MORNING COMBINING WITH LIGHTER WINDS AND AMPLE
SURFACE MOISTURE TO FACILITATE AREAS OF FOG AND LOW CLOUD
DEVELOPMENT. GIVEN THE LATEST MODEL SOUNDINGS FOR MONDAY
MORNING, WOULD HEDGE TOWARDS A MORE PREVALENT LOW STRATUS/CLOUD
LAYER THAN PROLIFIC FOG.
OVERALL QUIETER AND DRY CONDITIONS ARE ANTICIPATED EARLY NEXT
WEEK WITH WEAK RIDGING BEGINNING TO DEVELOP OFFSHORE MONDAY
FOLLOWED BY AN AMPLIFYING UPPER-LEVEL SHORTWAVE TROUGH DROPPING
SOUTHWARD INTO THE PACIFIC NORTHWEST FROM BRITISH COLUMBIA LATE
TUESDAY. COMPARED TO MONDAY MORNING, THE SUNRISE HOURS TUESDAY
PRESENT A BETTER SET-UP (STRONGER LOW LEVEL INVERSION) FOR
MORNING FOG IN OUR PROTECTED VALLEY AREAS ACROSS THE REGION. FOG
WILL GREATLY REDUCE VISIBILITY WHERE EVER PRESENT. BOTH MONDAY
AND TUESDAY INTERIOR HIGH TEMPERATURES SHOULD REACH INTO THE
UPPER 60S TO LOW 70S, AROUND 5 TO 7 DEGREES BELOW NORMAL FOR
MID-SEPTEMBER. IF YOU'RE A GLUTTON FOR WARMER CONDITIONS YOU
WON'T HAVE TO WAIT LONG FOR THE PROVERBIAL TEMPERATURE PENDULUM
TO SWING THE OTHER DIRECTION.
A NOTICEABLE WARM-UP BEGINS WEDNESDAY INTO THURSDAY AS THE THE
RIDGE OF HIGH PRESSURE OFFSHORE BEGINS TO EXERT MORE INFLUENCE
OVER THE PACIFIC NORTHWEST WHILE THE PREVIOUSLY MENTIONED
SHORTWAVE FROM TUESDAY TRANSITIONS INTO A CLOSED LOW AND SETS UP
OVER NORTHERN CALIFORNIA - THIS'LL COME INTO PLAY TO AID
EASTERLY FLOW. DETERMINISTIC AND ENSEMBLE GUIDANCE ARE STILL IN
GOOD AGREEMENT SHOWING MAXIMUM TEMPERATURES IN THE UPPER 70S TO
MID 80S ACROSS THE INTERIOR VALLEYS MIDWEEK, HIGHEST ON
THURSDAY. FOR THURSDAY AFTERNOON SPECIFICALLY, THE NBM ONLY
SHOWS A 10-20% CHANCE FOR HIGH TEMPERATURES TO MEET OR EXCEED 90
DEGREES IN THE NORTHERN WILLAMETTE VALLEY (LOWER PROBABILITIES
ELSEWHERE) WHICH IS A DECREASE FROM PREVIOUS FORECAST CYCLES. SO
AT LEAST IT APPEARS TEMPERATURES WON'T GET TOO WARM MIDWEEK,
BUT THEY'LL STILL BE RUNNING 6-12 DEGREES ABOVE CLIMATOLOGY.
BEYOND THE INCREASE IN TEMPERATURES, THE LARGE SCALE PATTERN
FAVORS BROAD SCALE ENE WINDS THROUGHOUT THE DEPTH OF THE
ATMOSPHERE IN ADDITION TO A NEAR SURFACE THERMAL TROUGH SURGING
NORTHWARD. THE STRONGEST EASTERLY WINDS CURRENTLY APPEAR MOST
LIKELY WEDNESDAY INTO THURSDAY MORNING, WITH GUSTS OF 20-30 MPH
AND ISOLATED GUSTS NEAR 30-40 MPH IN WIND-PRONE AREAS OF THE
COLUMBIA RIVER GORGE, CASCADES AND ADJACENT FOOTHILLS. THE
HIGHER TERRAIN OF THE COAST RANGE COULD BECOME SIMILARLY BREEZY
AS WELL. THIS COMBINATION OF WARMER TEMPERATURES, SOMEWHAT
LOWER HUMIDITY (30-35%) AND WINDS MAY PRODUCE A PERIOD OF
ELEVATED FIRE-WEATHER CONCERNS. WE'LL CONTINUE TO CLOSELY
MONITOR THE EVOLUTION OF THE WEATHER PATTERN MIDWEEK.
COME FRIDAY INTO SATURDAY FORECAST UNCERTAINTY INCREASES
NOTABLY AS ENSEMBLES STRUGGLE TO HANDLE THE PROGRESSION OF THE
LARGE SCALE UPPER-LEVEL PATTERN. LOOKING AT FRIDAY, AROUND
60-70% OF ENSEMBLE MEMBERS HAVE THE RIDGE AXIS EITHER OVERHEAD
TO CLOSE ENOUGH FOR A REPEAT OF MID-80 DEGREE HIGH TEMPERATURES
ACROSS THE LOWLANDS, WHILE THE OTHER 30-40% POINT TO A QUICKER
RIDGE PROGRESSION AND THUS TEMPERATURES COOLING BACK INTO THE
70S. A SIMILAR THEME IS SEEN ON SATURDAY AS WELL ALTHOUGH THE
TREND EVEN AMONG THE WARMEST SOLUTIONS IS TOWARDS LOWER
TEMPERATURES, IT'S JUST A MATTER OF HOW LOW. IN ANY CASE DRY
WEATHER IS FAVORED (80-90%) TO PREVAIL THROUGH THE LATE WEEK AND
EARLY WEEKEND TIME PERIOD. -99
AVIATION...THROUGH 06Z TUESDAY
DRY, NORTHWESTERLY FLOW ALOFT
TONIGHT INTO MONDAY AS AN UPPER LEVEL LOW DEPARTS THE REGION.
PREDOMINATELY VFR CONDITIONS THIS EVENING WITH CIGS AROUND 4-6
KFT, EXCEPT MVFR STRATUS AT THE COAST NEAR KONP. MVFR CIGS AT
COASTAL TERMINALS ARE VERY LIKELY, 80% OR GREATER CHANCES BY 06Z
MON, AS CONTINUED ONSHORE FLOW SEES LOW MARINE CLOUD COVERAGE
INCREASE. MVFR CIGS WILL BE FAVORED AT INLAND TERMINALS BY 12-18Z
MON, WITH CHANCES REACHING 50-70%, HIGHEST ALONG THE LOWER
COLUMBIA RIVER, IN THE PORTLAND AREA, AND IN THE SOUTHERN
WILLAMETTE VALLEY. CHANCES FOR IFR CIGS AT ANY POINT OVERNIGHT ARE
GENERALLY 10-15% OR LESS INLAND BUT 30-40% ALONG THE COAST. HIGH
PRESSURE BEGINNING TO BUILD OFFSHORE WILL FAVOR INCREASED CLEARING
AND IMPROVEMENT TO WIDESPREAD VFR CONDITIONS BY MONDAY AFTERNOON.
SOUTH TO SOUTHWEST WINDS EASE BELOW 5 KT TONIGHT. AS WINDS RISE
TO 5-10 KT THROUGH THE DAY ON MONDAY, FLOW WILL VEER OUT OF THE
NORTH TO NORTHWEST BY THE MID-AFTERNOON.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED TO PREVAIL OVERNIGHT
THROUGH AT LEAST 12Z MONDAY WITH CLOUD BASES AROUND 5 KFT.
CONTINUED ONSHORE FLOW WILL FAVOR LOW MARINE CLOUDS DEVELOPING
EARLY MONDAY MORNING, WITH CHANCES FOR MVFR CIGS INCREASING TO
AROUND 50% BY 13-15Z MON. IMPROVED CLEARING BY MONDAY AFTERNOON
SUPPORT HIGH CONFIDENCE IN A RETURN TO VFR CONDITIONS BY 18-20Z
MON. SOUTH WINDS AROUND 5 KT THIS EVENING EASE TO 3 KT OR LESS
OVERNIGHT, THEN BUILD TO AROUND 5 KT AGAIN WHILE VEERING OUT OF
THE NORTHWEST BY MONDAY AFTERNOON. /DH
MARINE
RAIN SHOWERS END THIS AFTERNOON AS LOW PRESSURE
CONTINUES TO MOVE INLAND. IN ITS WAKE, WEST TO SOUTHWEST WINDS AT
5-10 KT SOUTH OF CAPE FALCON AND 8-12 KT TO THE NORTH WILL EASE
THROUGH TONIGHT AND VEER OUT OF THE NORTH BY MONDAY EVENING AS
HIGH PRESSURE BUILDS OFFSHORE. THE RIDGE WILL CONTINUE TO
STRENGTHEN THROUGH MIDWEEK, WHICH WILL SEE NORTHERLIES SIMILARLY
INTENSIFY TO 15-20 KT WITH GUSTS TO 25 KT BY WEDNESDAY AFTERNOON.
THERE REMAINS A GREATER THAN 50% CHANCE SUSTAINED WINDS PEAK ABOVE
20 KT ON WEDNESDAY TO THE SOUTH OF CAPE FALCON, WITH LOWER
CHANCES, 10-40%, ON BOTH TUESDAY AND THURSDAY. WINDS THEN EASE
INTO NEXT WEEKEND AS HIGH PRESSURE WEAKENS.
SEAS AROUND 5 FT EARLY THIS WEEK WILL SIMILARLY BUILD TO 6-7 FT
AS WINDS STRENGTHEN. A PERSISTENT NORTHWESTERLY SWELL AT 8-9
SECONDS OTHERWISE CONTINUES THROUGH THE WEEK, WITH SEAS EASING
INTO NEXT WEEKEND AS HIGH PRESSURE AND WINDS WEAKEN. -36
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
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