969
FXUS66 KPQR 231123 AAB
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
400 AM PDT WED SEP 23 2026
SYNOPSIS
SEASONABLY COOL AND DRY WEATHER CONTINUES THOUGH THURSDAY
MORNING/AFTERNOON BEFORE A LOW PRESSURE SYSTEM MOVES ONSHORE THURSDAY
EVENING/NIGHT. CONFIDENCE IS HIGH THIS SYSTEM WILL BRING WIDESPREAD
RAIN AND INCREASING WINDS TO ALL OF NORTHWEST OREGON AND SOUTHWEST
WASHINGTON LATE THURSDAY INTO FRIDAY, HOWEVER EXACT RAIN AMOUNTS AND
PEAK WIND SPEEDS REMAIN UNCERTAIN. HIGH CONFIDENCE FOR A RETURN TO
DRY WEATHER ON SATURDAY AND SUNDAY AS HIGH PRESSURE BUILDS BACK IN.
CHANCES FOR RAIN THEN RETURN TO THE FORECAST ON TUESDAY.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
RADAR, SATELLITE, AND
SURFACE WEATHER OBSERVATIONS FROM EARLY WEDNESDAY MORNING DEPICTED A
SHOWED A WEAK COOL FRONT MOVING TOWARDS THE COAST. THIS DECAYING
FRONT WILL BRING A 20-30% CHANCE FOR LIGHT RAIN SHOWERS ALONG THE
SOUTH WA/FAR NORTH OR COAST AND WILLAPA HILLS THIS MORNING, INCLUDING
IN ASTORIA. A NARROW BAND OF LIGHT RAIN SHOWERS WAS ALREADY BEING
OBSERVED ON RADAR AROUND 10-30 MILES OFFSHORE ALONG THIS FRONTAL
BOUNDARY AS OF 330 AM PDT WEDNESDAY. THE REST OF SOUTHWEST WA AND
NORTHWEST OR WILL REMAIN DRY THROUGH TODAY AND TONIGHT WITH HIGH
TEMPERATURES AROUND 70 DEGREES INLAND AND 60S AT THE COAST.
DRY CONDITIONS WILL CONTINUE THURSDAY MORNING AND MOST LIKELY
THURSDAY AFTERNOON AS WELL, BUT WITH INCREASING CLOUDS AHEAD OF AN
INCOMING LOW PRESSURE SYSTEM THAT WILL IMPACT THE AREA BEGINNING
SOMETIME THURSDAY EVENING/NIGHT AND CONTINUING THROUGH FRIDAY
AFTERNOON/EVENING. CONFIDENCE IS HIGH THIS SYSTEM WILL BRING A
WIDESPREAD SOAKING RAIN TO ALL OF NORTHWEST OREGON AND SOUTHWEST
WASHINGTON LATE THURSDAY INTO FRIDAY (90-100% CHANCE), ALONG WITH
INCREASING WINDS AND EVEN A 10-20% CHANCE OF THUNDERSTORMS. ALTHOUGH
CONFIDENCE IS HIGH CONDITIONS WILL BECOME COOL AND WET, EXACT RAIN
TOTALS AND PEAK WIND SPEEDS REMAIN UNCERTAIN, WITH EXACT WIND SPEEDS
BEING MOST UNCERTAIN.
THIS IS DUE TO UNCERTAINTY IN THE EXACT STRENGTH AND TRACK OF THE
SURFACE LOW RESPONSIBLE FOR THE ABRUPT CHANGE TO COOL AND WET
WEATHER. THE 00Z/SEPTEMBER 23RD ITERATION OF THE GFS ENSEMBLE
SUGGESTS A 1000-1005 MB CLOSED SURFACE LOW WILL MOST LIKELY TRACK
SOMEWHERE BETWEEN MANZANITA, OR AND OCEAN CITY, WA. THE 00Z EURO
ENSEMBLE SHOWS EVEN MORE MODEL SPREAD, SUGGESTING THE SURFACE LOW
COULD DEEPEN ANYWHERE BETWEEN 995-1005 MB AND TRACK SOMEWHERE BETWEEN
FLORENCE, OR AND PACIFIC BEACH, WA. ENSEMBLE GUIDANCE SHOWING A
STRONGER SURFACE LOW WITH A CENTRAL PRESSURE DOWN TO 995-1000 MB
DEPICTS HIGHER MAX WIND GUSTS ALONG THE SOUTH SIDE OF THE LOW CENTER
DUE TO THE DEVELOPMENT OF A POTENTIAL STING JET. IF THE LOW DOES
BECOME THIS DEEP WHILE ALSO TRACKING TOWARDS THE CENTRAL OR NORTHERN
OREGON COAST OR FAR SOUTH WASHINGTON COAST, THEN A SMALL AREA OF
STRONG WIND GUSTS OVER 50-55 MPH WOULD BE POSSIBLE SOMEWHERE ALONG
THE IMMEDIATE COAST, WHICH WOULD RESULT IN A LOCALIZED AREA OF DOWNED
TREES AND POWER OUTAGES. FORTUNATELY, THE PROBABILITY FOR WIND GUSTS
OVER 50 MPH IS LOW (5-15% ALONG THE IMMEDIATE COAST AND 0-1% INLAND),
AS MOST ENSEMBLE GUIDANCE SUGGESTS A WEAKER 1000-1005 MB LOW WITH
WIND GUSTS PEAKING CLOSER TO 25-35 MPH AT THE COAST AND 20-30 MPH
INLAND, EXCEPT 35-40 MPH OVER HIGHER TERRAIN IN THE COAST RANGE AND
CASCADES. CHANCES FOR MAX WIND GUSTS OVER 40 MPH RANGE FROM 25-45% AT
THE COAST TO 15-30% OVER THE WILLAMETTE VALLEY AND PORTLAND METRO.
WHILE WIND SPEEDS OF THIS MAGNITUDE ARE LESS IMPACTFUL FOR COASTAL
COMMUNITIES, INLAND AREAS COULD SEE SOME TREES OR BRANCHES COME DOWN
WHERE WINDS ARE STRONGEST GIVEN LEAVES ARE STILL ON TREES.
ASIDE FROM THE SYNOPTIC SCALE AND MESOSCALE WINDS ASSOCIATED WITH
THIS LOW, THERE IS ALSO A THREAT FOR GUSTY OUTFLOW WINDS AND HEAVY
RAINFALL RATES ASSOCIATED WITH STRONGER SHOWERS OR THUNDERSTORMS
FRIDAY AFTERNOON. THIS IS WHEN COOLER AIR ALOFT BEHIND A COLD FRONT
ASSOCIATED WITH THE INCOMING SURFACE LOW WILL MATERIALIZE OVER THE
AREA, SUPPORTING SHALLOW CONVECTION ON FRIDAY. THE OCCURRENCE AND
COVERAGE OF ANY THUNDERSTORMS WILL HINGE ON THE TIMING OF THIS
FRONTAL PASSAGE AND HOW MANY BREAKS OF SUN OCCUR FRIDAY MORNING/EARLY
AFTERNOON, IF ANY. IF THE FRONT MOVES THROUGH FASTER THAN WHAT MOST
GUIDANCE SUGGESTS (E.G. EARLY FRIDAY MORNING INSTEAD OF FRIDAY
AFTERNOON), THEN THERE WOULD BE A BETTER CHANCE FOR EARLIER AND MORE
WIDESPREAD SUN BREAKS. THIS WOULD ALLOW FOR MORE SURFACE-BASED
INSTABILITY TO DEVELOP IN THE AFTERNOON WITH SUBSEQUENT ISOLATED TO
SCATTERED THUNDERSTORM DEVELOPMENT. HOWEVER, MOST GUIDANCE SUGGESTS
THE MAIN COLD FRONT WILL MOVE THROUGH FRIDAY AFTERNOON FOLLOWING A
WET
AND CLOUDY MORNING. THIS MEANS THUNDERSTORMS ARE UNLIKELY TO OCCUR,
AND THE LATEST NBM BACKS THIS UP AS CHANCES HAVE LOWERED TO 10-20%
WITH THE LATEST ITERATION. THAT SAID, EVEN STRONGER SHOWERS WITHOUT
THE PRESENCE OF LIGHTNING WILL HAVE THE POTENTIAL TO MIX DOWN
STRONGER WINDS ALOFT AND CAUSE HIGHLY LOCALIZED WIND DAMAGE.
REGARDLESS OF THE OUTCOME, CONDITIONS WILL DRY OUT QUICKLY FRIDAY
NIGHT AS HIGH PRESSURE BUILDS IN BEHIND THE LOW PRESSURE SYSTEM. NOTE
TOTAL RAIN AMOUNTS WITH THIS SYSTEM SHOULD EXCEED AT LEAST 0.25
INCHES (90-95% CHANCE), WITH A 45-85% CHANCE FOR AMOUNTS OVER 0.75
INCHES. PROBABILITIES ARE HIGHEST IN THE MOUNTAINS. FORTUNATELY,
FLOODING IS NOT EXPECTED WITH THIS SYSTEM GIVEN THE FAST SPEED OF
BOTH THE STRATIFORM PRECIPITATION AHEAD OF THE SYSTEM AND
SHOWERS/POTENTIAL THUNDERSTORMS BEHIND THE SYSTEM. -23
LONG TERM...SATURDAY THROUGH TUESDAY NIGHT
THE WEATHER PATTERN
BECOMES QUIET HEADING INTO THE WEEKEND AS MODEL ENSEMBLE GUIDANCE
REMAINS IN EXCELLENT AGREEMENT FOR A QUICK RETURN TO HIGH
PRESSURE WITH DRY WEATHER. TEMPERATURES WILL LIKELY REMAIN SLIGHTLY
COOLER THAN AVERAGE WITH HIGHS IN THE MID 60S SATURDAY THROUGH
MONDAY, WITH ONLY A 5-10% CHANCE FOR HIGHS NEAR 70 DEGREES OVER
INLAND VALLEYS. CHANCES FOR RAIN HAVE LOWERED AND NOW HOLD OFF UNTIL
TUESDAY, PEAKING NEAR 20-35% TUESDAY EVENING.
MORNING FROST REMAINS POSSIBLE IN THE UPPER HOOD RIVER VALLEY EACH
MORNING SATURDAY THROUGH MONDAY AS LIGHT WINDS AND MOSTLY CLEAR SKIES
WILL ALLOW FOR EXCELLENT RADIATIONAL COOLING OVERNIGHT. THE FROST
POTENTIAL IS MAINLY CONFINED TO THE PARKDALE AND DEE FLAT AREA WHERE
PROBABILITIES FOR LOWS OF 36 DEGREES OR COLDER RANGE ANYWHERE FROM
25-50%. CHANCES NEAR ODELL ARE LOWER AT AROUND 5-10%. -23
AVIATION...THROUGH 06Z THURSDAY
WEST TO SOUTHWEST FLOW ALOFT
WILL PERSIST THROUGH 06Z WEDNESDAY. AS OF 11Z WEDNESDAY, A BROKEN
LOW STRATUS DECK WAS BEGINNING TO EXPAND ALONG THE NORTH COAST,
BRINGING PERIODS OF BROKEN MVFR CEILINGS TO KAST WITH MAINLY VFR
CONDITIONS SOUTH OF KAST. A DECAYING FRONT WAS ALSO BEGINNING TO
APPROACH THE NORTH OREGON COAST, WITH RADAR OBSERVATIONS SHOWING A
VERY NARROW BAND OF LIGHT RAIN ALONG THE FRONTAL BOUNDARY. AS THIS
FRONT MOVES INLAND AND DECAYS BETWEEN 12-18Z WEDNESDAY, KAST MAY SEE
OCCASIONAL LIGHT RAIN (20-30% CHANCE).
CONFIDENCE IN FOG AND LOW STRATUS DEVELOPMENT OVER THE INLAND TAF
SITES IS RELATIVELY LOWER, ESPECIALLY TO THE NORTH OF KSLE. SKIES
REMAINED MOSTLY CLEAR AS OF 11Z WEDNESDAY NORTH OF KSLE, HOWEVER
THERE IS STILL TIME FOR SCATTERED TO BROKEN CEILINGS BELOW 3000 FT
TO DEVELOP OVER THE NORTHERN WILLAMETTE VALLEY AND PORTLAND METRO
AREA. IF LOW STRATUS DOES MATERIALIZE, TIMING WOULD LIKELY BE
BETWEEN 13-18Z WEDNESDAY WITH IMPROVEMENT TO VFR IN THE LATE
MORNING OR EARLY AFTERNOON HOURS. THE PROBABILITY FOR CEILINGS
BELOW 3000 FT PEAK BETWEEN 30-40% AROUND 14-15Z WEDNESDAY AT KPDX,
KTTD, KUAO, AND KHIO. MEANWHILE, KSLE AND KEUG HAVE ALREADY OBSERVED
BRIEF PERIODS OF SHALLOW FOG WITH VISIBILITIES FALLING AS LOW AS
1/4-3/4 SM AT TIMES, BUT WITH VISIBILITIES FLUCTUATING SIGNIFICANTLY
AS FOG STRUGGLES TO DEEPEN AND EXPAND IN COVERAGE. BEYOND 18Z
WEDNESDAY, EXPECT WIDESPREAD VFR CONDITIONS.
KPDX AND APPROACHES...VFR CONDITIONS ARE EXPECTED TO PERSIST
THROUGH AT LEAST 12Z WEDNESDAY WITH SCATTERED HIGH CLOUDS. THERE
IS AROUND A 30% CHANCE FOR MVFR STRATUS TO RETURN, MAINLY BETWEEN
13-18Z WED. OTHERWISE, EXPECT VFR TO PERSIST WITH INCREASING HIGH
LEVEL CLOUDS. NORTHWEST WINDS AROUND 3-6 KT ARE EXPECTED THROUGH
THE TAF PERIOD. -23/DH
MARINE
HIGH PRESSURE WILL MAINTAIN NORTHERLY WINDS ACROSS THE
WATERS THROUGH WEDNESDAY NIGHT BEFORE BECOMING NORTHEASTERLY FOR
A PERIOD OF TIME EARLY THURSDAY MORNING THROUGH EARLY THURSDAY
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. THIS SYSTEM
WILL MOVE SOMEWHERE OVER THE COASTAL WATERS LATE THURSDAY INTO
FRIDAY, BRINGING RAPIDLY INCREASING WINDS AND SEAS ALONG WITH
WIDESPREAD RAIN. GUIDANCE HAS NOT COME INTO AGREEMENT YET ON THE
EXACT TRACK AND STRENGTH OF THIS LOW PRESSURE SYSTEM, WHICH MEANS
EXACT WIND SPEEDS AND WAVE HEIGHTS ARE UNCERTAIN THURSDAY NIGHT
INTO FRIDAY.
WITH THAT BEING SAID, CONFIDENCE IS HIGH FOR AT LEAST SMALL CRAFT
ADVISORY LEVEL WIND GUSTS OF 21 KT OR STRONGER WITH THIS SYSTEM
GIVEN PROBABILITIES FOR GUSTS OVER 21 KT HAVE INCREASED TO 80-95%.
IN FACT, CHANCES FOR GALE FORCE WIND GUSTS OF 34 KT OR STRONGER
HAVE ALSO INCREASED AND NOW RANGE BETWEEN 45-55% GIVEN AN
INCREASED POTENTIAL FOR A RELATIVELY STRONG LOW PRESSURE SYSTEM
TRACKING SOMEWHERE OVER THE COASTAL WATERS. POTENTIAL LOW TRACKS
COULD RANGE ANYWHERE FROM OVER THE SOUTHERN WATERS TOWARDS
FLORENCE TO THE NORTHERN WATERS TOWARDS THE COLUMBIA RIVER BAR. A
NARROW BELT OF HIGH WINDS WILL BE POSSIBLE ON THE SOUTH SIDE OF
THIS LOW PRESSURE SYSTEM IF IT RAPIDLY STRENGTHENS AS IT
APPROACHES THE COAST, HOWEVER CONFIDENCE IS LOW REGARDING THE
LOCATION OF THESE HIGHER WINDS IF THEY DO MATERIALIZE. NEVERTHELESS,
THIS HELPS EXPLAIN WHY CHANCES FOR MAX WIND GUSTS OF 48 KT OR
STRONGER ARE NON-ZERO, CURRENTLY RANGING BETWEEN 10-20%.
IF THIS LOW TAKES A FAVORABLE TRACK AND STRENGTHENS AS IT
APPROACHES THE COAST, THEN HAZARDOUS SEAS AS HIGH AS 15-20 FT WOULD
BE POSSIBLE (5-10% CHANCE). IF THE LOW COMES IN WEAKER, PEAK
WINDS WOULD LIKELY RANGE SOMEWHERE BETWEEN 25-35 KT AND SEAS WOULD
LIKELY PEAK CLOSER TO 10-13 FT. THE LATTER IS CURRENTLY THE MOST
LIKELY OUTCOME, HOWEVER THE FORECAST SHOULD BE MONITORED OVER THE
COMING DAYS FOR UPDATES. -23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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