977
FXUS66 KPQR 180041
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
440 PM PST WED DEC 17 2025
SYNOPSIS
A STRONG FRONTAL SYSTEM WITH AN ASSOCIATED ATMOSPHERIC
RIVER WILL ARRIVE EARLY THURSDAY, PERSISTING THROUGH THURSDAY NIGHT.
THERE IS INCREASING CONFIDENCE FOR WIDESPREAD MINOR TO MODERATE
RIVER FLOODING, ALONG WITH PERIODS OF CASCADE SNOW, AND ANOTHER
ROUND OF GUSTY WINDS. RAIN PERSISTS THROUGH EARLY NEXT WEEK.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
SCATTERED SHOWERS WILL
GRADUALLY DECREASE ACROSS THE AREA FROM SOUTH TO NORTH THROUGH THIS
EVENING. THE RELATIVELY CALM WEATHER WILL BE SHORT LIVED, HOWEVER,
AS THE NEXT SYSTEM ARRIVING EARLY THURSDAY IS EXPECTED TO BE RATHER
ROBUST. MULTIPLE WEATHER HAZARDS HAVE BEEN ISSUED, WITH HIGHEST
CONCERNS FOCUSED ON HEAVY RAINFALL, FLOODING, WINDS AND POTENTIAL
ASSOCIATED IMPACTS.
A STRONG TO POTENTIALLY EXTREME ATMOSPHERIC RIVER IS EXPECTED TO
BRING HEAVY RAINFALL TO NORTHWEST OREGON AND SOUTHWEST WASHINGTON.
THE EXACT POSITION OF THE AXIS OF HIGHEST IVT VALUES, AND ASSOCIATED
HEAVY RAINFALL, WILL CONTINUE TO FLUCTUATE SLIGHTLY NORTH OR SOUTH,
BUT LATEST MODEL RUNS HAVE REMAINED FAIRLY CONSISTENT. ENSEMBLE IVT
FORECASTS FROM THE CW3E INDICATE FAIRLY HIGH CONFIDENCE OF THIS
SYSTEM PERSISTING WITHIN THE STRONG AR CATEGORY (750-1000 KG/M/S)
DURING A PERIOD OF 12-18 HOURS. AND, ALTHOUGH THE FLOW IS EXPECTED
TO GENERALLY TURN SOUTHWESTERLY, THERE WILL STILL BE SOME WESTERLY
COMPONENT INITIALLY ALLOWING FOR THE BAND OF MOISTURE TO REMAIN AN
AREA FOR AN EXTENDED PERIOD OF TIME. SO, STEADY RAIN WILL BEGIN TO
SPREAD ACROSS THE AREA EARLY THURSDAY MORNING, WITH HEAVIEST
PRECIPITATION EXPECTED THURSDAY AFTERNOON INTO THURSDAY NIGHT.
LATEST RAINFALL ACCUMULATION FORECASTS HAVE INCREASED SLIGHTLY, WITH
HIGHEST QPF VALUES LIKELY SITTING ACROSS THE CENTRAL OREGON COAST
RANGE INTO THE CENTRAL AND NORTHERN OREGON CASCADES AND FOOTHILLS.
THIS IS HIGHLIGHTED WELL BY THE ECMWF EXTREME FORECAST INDEX (EFI)
FOR QPF GREATER THAN 0.8. THERE IS ALSO HIGH CONFIDENCE (75-85%
CHANCE) OF 2+ INCHES OF RAINFALL OCCURRING WITHIN A 24-HR PERIOD
ACROSS THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY. TO UNDERSTAND THE
SPREAD OF UNCERTAINTY THAT EXISTS IN TERMS OF THE RANGE OF POSSIBLE
RAINFALL AMOUNTS, TAKE AN EXAMPLE AT SALEM, OR: THE REASONABLE LOW
END AMOUNT IS AROUND 1.5 INCHES, WHILE THE "WORST CASE" SCENARIO
SHOWS A 10% CHANCE OF EXCEEDING 4 INCHES IN 24-HOURS. TO PUT THAT
INTO PERSPECTIVE, THE ALL-TIME 24-HR RAINFALL RECORD AT THE SALEM
AIRPORT WAS 4.44" IN NOVEMBER OF 1996. RAINFALL AMOUNTS OF THESE
RATES CAN PRODUCE LOCALIZED FLOODING ALONG CREEKS AND URBAN AREAS.
GREATER RAINFALL AMOUNTS ARE EXPECTED IN THE HIGHER TERRAIN, WITH 2-
DAY TOTALS POTENTIALLY EXCEEDING 10 INCHES, WITH MOST AREAS WITHIN
THE HIGHER TERRAIN OF NW OREGON SEEING 5-8 INCHES OF RAINFALL.
LANDSLIDES ARE POSSIBLE ON STEEP TERRAIN, AND RIVER RISES ARE
EXPECTED AND IS DISCUSSED IN THE HYDROLOGY SECTION BELOW.
WHILE WINDS ARE NOT EXPECTED TO BE AS STRONG OR IMPACTFUL AS THE
STORM THAT OCCURRED LAST NIGHT, DO EXPECT TO SEE AT LEAST BREEZY
SOUTH TO SOUTHWEST WINDS INCREASING THROUGH THURSDAY AFTERNOON
ACROSS MUCH OF THE AREA. THERE IS A HIGH WIND WATCH FOR THE CENTRAL
OREGON COAST AND COAST RANGE FOR WIND GUSTS UP TO 60 MPH POSSIBLE.
HAVE ALSO ISSUED WIND ADVISORIES THROUGH INTERIOR VALLEYS AND
CASCADE FOOTHILLS, AS WELL AS NORTHERN PORTIONS OF THE COASTAL
MOUNTAINS, FOR WINDS GUSTING UP TO 35-45 MPH. WITH VERY SATURATED
SOILS, COULD SEE A FEW MORE DOWNED TREES AND POWER OUTAGES. HIGHEST
WINDS ARE EXPECTED ACROSS SOUTHERN PORTIONS OF THE AREA, WHERE THE
925 MB JET SETS UP AT AROUND 60-70 KT OVER THE CENTRAL OREGON COAST,
LIKELY DEVELOPING A COASTAL JET BY LATE THURSDAY MORNING. WINDS
INLAND ARE LESS LIKELY TO MIX DOWN, BUT STILL LIKELY TO BE BREEZY
THURSDAY AFTERNOON.
THURSDAY MORNING WILL ALSO FEATURE A QUICK BURST OF SNOW FOR THE
CASCADES, AND POTENTIALLY IN THE HIGHER TERRAIN ABOVE 1500 FT OF THE
UPPER HOOD RIVER VALLEY. OVERRUNNING PRECIPITATION AHEAD OF THE WARM
FRONT COULD PRODUCE 3-6 INCHES OF SNOWFALL DURING A 6-HR PERIOD AT
CASCADE PASS LEVEL, WHILE 1-2 INCHES IS MOST LIKELY NEAR PARKDALE.
HAVE ISSUED WINTER WEATHER ADVISORIES FOR THESE AREAS THROUGH LATE
THURSDAY MORNING, UNTIL THE WARM FRONT LIFTS NORTH AND SNOW LEVELS
QUICKLY RISE BACK TO AROUND 7500-8000 FT.
BY FRIDAY, THE MAIN AXIS OF PRECIPITATION IS EXPECTED TO SLIDE SOUTH
INTO SOUTHWEST OREGON, THOUGH THERE MAY BE SOME LINGERING HEAVIER
RAIN OVER THE CENTRAL OR CASCADES. SCATTERED SHOWERS WILL CONTINUE
WITH LIGHTER RAINFALL ON FRIDAY, BUT RIVERS ARE EXPECTED TO CONTINUE
TO RISE. SNOW LEVELS WILL DROP AGAIN THROUGH FRIDAY NIGHT, LIKELY TO
AROUND 2000-2500 FT LATE. WILL SEE ANOTHER ROUND OF SNOW SHOWERS FOR
THE CASCADE PASSES, WITH HIGHEST AMOUNTS EXPECTED ACROSS THE SOUTH
WASHINGTON CASCADES. /DH
LONG TERM...SATURDAY THROUGH TUESDAY
NO SIGNIFICANT CHANGES TO
THE LONG TERM DISCUSSION: THE WEEKEND WILL FEEL LIKE THE CALM AFTER
THE STORM. WE WILL STILL SEE CONTINUED RAINFALL BUT IT WILL BE MORE
CLIMATOLOGICALLY NORMAL. SOUTH TO SOUTHWESTERLY FLOW WILL ALSO BRING
BREEZY CONDITIONS TO INTERIOR VALLEYS AND EVEN THE COLUMBIA RIVER
GORGE. THE COMPONENT ABOUT SATURDAY TO KEEP AN EYE ON IS THAT WE
WILL SEE CONTINUED FLOODING FROM THE RISING THAT OCCURRED ON
THURSDAY AND FRIDAY. MANY RIVERS ARE FORECAST TO BE IN A FLOOD STAGE
ON THAT DAY.
AS MOIST ZONAL FLOW THEN CONTINUES THROUGH THE WEEKEND,
PERSISTENT LOWLAND RAIN AND HIGH ELEVATIONS SNOW CHANCES ALSO
CONTINUE. WHILE THE DETAILS REMAIN RELATIVE LOW CONFIDENCE,
CURRENT LONG-RANGE GUIDANCE DOES NOT FAVOR ANOTHER HIGH-END
RAINFALL EVENT THROUGH THE MIDDLE OF NEXT WEEK. BUT DON'T LET
THAT CATCH YOU OFF OF YOUR FEET. 500 MB HEIGHTS AND OTHER
SYNOPTIC FEATURES ARE SUGGESTING A BROAD TROUGH TAKING OVER
MUCH OF THE NORTHEAST PACIFIC. THIS TROUGH IS ASSOCIATED WITH A
COLD WRAPPED LOW THAT WILL PRODUCE WEAK IMPULSES. THESE
DISTURBANCES WILL THEN PUSH OVER THE REGION. WHILE NOT WELL
REALIZED AT THIS TIME, RAIN WILL PERSIST THROUGH TUESDAY. -27/36
AVIATION
GENERALLY VFR CONDITIONS WITH LINGERING RAIN SHOWERS
THROUGH WEDNESDAY NIGHT. THERE'S A 10-20% CHANCE OF ISOLATED
THUNDERSTORMS THROUGH 03Z THURSDAY, NOT HIGH ENOUGH PROBABILITY TO
INCLUDE IN THE TAFS. ANY STRONG SHOWER OR THUNDERSTORM COULD
PRODUCE GUSTY AND ERRATIC WINDS, HEAVY RAIN, AND SMALL HAIL. SOUTH
TO SOUTHWEST WINDS GENERALLY LESS THAN 12 KTS EXCEPT FOR
OCCASIONAL GUSTS UP TO 20 KTS ALONG THE COAST.
CONDITIONS BEGIN TO DEGRADE AFTER 08-12Z FRIDAY AS A STRONG
ATMOSPHERIC RIVER APPROACHES, BRINGING HEAVY RAIN AND INCREASED
WINDS FROM THE SOUTHWEST TO NORTHEAST. CEILINGS AND VISIBILITIES
WILL FALL TO MVFR CONDITIONS INLAND AND IFR/LIFR CONDITIONS
ALONG THE COAST AS THE HEAVY RAIN REACHES EACH TERMINAL. SOUTH
WINDS INCREASE 15-19Z THURSDAY WITH GUSTS UP TO 35-45 KT ALONG
THE COAST, EXCEPT UP TO 50 KTS AT KONP, AND 30-40 KTS INLAND.
KPDX AND APPROACHES...VFR THROUGH WEDNESDAY NIGHT. SHOWERY
CONDITIONS PERSIST THROUGH THE DAY WITH WEST TO SOUTHWESTERLY
WINDS. GUSTS UP TO 20 KTS POSSIBLE THROUGH 02Z FRI. DETERIORATING
CONDITIONS EXPECTED AFTER 12-14Z THU AS HEAVY RAIN SPREADS TO THE
AREA. MVFR CIGS AND VIS LIKELY WITH HEAVY RAIN WITH A 50-60%
CHANCE OF IFR CIGS AFTER 18Z THU. WINDS ALSO INCREASE AFTER 16-18Z
THU, BECOMING SOUTH TO SOUTHEAST WITH GUSTS UP TO 25-30 KTS. -03
MARINE
WIND GUSTS HAVE DECREASED BY WEDNESDAY AFTERNOON WITH
GUSTS BELOW 20 KTS. SEAS STILL REMAIN ELEVATED AROUND 13 TO 15 FT
AT 10 TO 11 SECONDS BUT ARE EXPECTED TO DECREASE TO AROUND 11 TO
13 FEET OVERNIGHT. A HAZARDOUS SEAS WARNING REMAINS IN EFFECT
THROUGH 4 AM THURSDAY. THESE CONDITIONS WON'T LAST LONG AS THE
NEXT WEATHER SYSTEM BEGINS IMPACTING THE WATERS EARLY THURSDAY
MORNING. WINDS WILL QUICKLY RAMP UP AFTER 4 TO 6 AM WITH
WIDESPREAD SOUTH TO SOUTHWEST GALE FORCE WIND GUSTS THROUGH THE
DAY, DECREASING AFTER 7 TO 10 PM. A COASTAL JET IS FORECAST TO
DEVELOP SOUTH OF ROCKAWAY BEACH WITH GUSTS UP TO 55 KTS POSSIBLE
UP TO 10-20 NM WEST OF THE COASTLINE. A GALE WATCH HAS BEEN ISSUED
FOR ALL MARINE ZONES EXCEPT FOR PZZ252 AND 253, FOR WHICH A STORM
WATCH HAS BEEN ISSUED. BOTH WATCHES ARE FROM 4 AM THROUGH 10 PM ON
THURSDAY. SEAS WILL ALSO REBUILD TO AROUND 15 TO 16 FT AT 10 TO 11
SECONDS, EXCEPT LOCALLY UP TO 17 TO 19 FEET IN VICINITY OF THE
COASTAL JET. THERE'S ALSO A 15-25% CHANCE OF SEAS REACHING OR
EXCEEDING 20 FEET IN THE VICINITY OF THE COASTAL JET. -03
HYDROLOGY
POTENTIAL FOR RIVER FLOODING IS HIGHEST ON
THURSDAY AND FRIDAY DUE TO THE ABUNDANT RAINFALL FROM AN
ATMOSPHERIC RIVER. HEAVIEST RAINFALL OCCURS FOR A RELATIVELY
SHORT PERIOD OF TIME FROM THURSDAY THROUGH THURSDAY NIGHT. THE
ALREADY SATURATED SOILS AND HIGH RIVERS COMBINED WITH THE
INCOMING WELL ABOVE NORMAL RAINFALL HAS RESULTED IN AN ELEVATED
RISK FOR FLOODING LATE THIS WEEK. AS IS TYPICAL IN ATMOSPHERIC
RIVERS, THE HIGHEST RAINFALL TOTALS ARE LIKELY TO BE OVER AREAS
OF TERRAIN INCLUDING THE COAST RANGE AND CASCADES, WHILE LESSER
TOTALS CAN BE EXPECTED ACROSS INLAND VALLEYS. NONETHELESS,
RAINFALL IS LIKELY TO BE MEASURED IN INCHES ACROSS MOST OF THE
REGION. ONE DIFFERENCE BETWEEN THE LAST SERIES OF ARS AND THE
ONE ARRIVING ON THURSDAY IS THE PLACEMENT OF HIGHEST RAINFALL
TOTALS. THIS NEXT SYSTEM FAVORS A MORE SOUTHERN MAXIMUM, AND
THUS AREAS THAT PREVIOUSLY MISSED THE HEAVIEST RAIN WILL SEE THE
HIGHER ACCUMULATIONS THIS TIME AROUND.
DUE TO THE LACK OF OBSERVED RAIN, PARTICULARLY IN LANE COUNTY,
SOME BASINS WILL BE MORE CAPABLE OF HANDLING HEAVY RAINFALL
WITHOUT EXPERIENCING FLOODING. OTHER AREAS TO THE NORTH WITHIN
THE COAST RANGE IN LINCOLN, TILLAMOOK, BENTON, POLK, YAMHILL,
AND WASHINGTON COUNTIES MAY SEE MORE OVERLAP BETWEEN RECENTLY
OBSERVED HEAVY RAINFALL AND ADDITIONAL HIGH TOTALS WITH THIS
UPCOMING SYSTEM. SIMILARLY, RIVER BASINS COVERING THE CENTRAL OR
CASCADES IN LANE AND LINN COUNTIES MAY HAVE A SLIGHTLY MORE
OPTIMISTIC OUTLOOK THAN NORTH INTO MARION AND CLACKAMAS
COUNTIES, BUT THAT DOES NOT MEAN FLOODING CANNOT HAPPEN IN ALL
OF THE AFOREMENTIONED AREAS. LUCKILY, WHERE RAINFALL HAS SO FAR
BEEN THE HEAVIEST ACROSS SOUTHWESTERN WASHINGTON AND FAR
NORTHWESTERN OREGON MAY SEE THE LOWEST TOTALS FROM THIS SYSTEM,
ALTHOUGH EVEN 1-2 INCHES OF RAIN OVER 24 HOURS MAY BE ENOUGH TO
CAUSE ADDITIONAL FLOODING IN THESE VERY SATURATED AREAS.
AT THIS POINT, THE RIVERS WITH THE HIGHEST CHANCES OF REACHING
FLOOD STAGE ARE THOSE WHICH DRAIN THE CENTRAL OREGON COAST
RANGE, INCLUDING THE WILSON, TRASK, SILETZ, AND SIUSLAW DRAINING
TOWARD THE COAST, AND THE MARYS, LUCKIAMUTE, YAMHILL, AND
TUALATIN DRAINING TOWARD THE WILLAMETTE. THE CHANCES FOR THESE
RIVERS TO REACH AT LEAST MINOR FLOOD STAGE ARE 35-75% AT THIS TIME.
THOSE DRAINING TOWARD THE COAST, PARTICULARLY IN LINCOLN AND LANE
COUNTIES WHERE RAINFALL IS LIKELY TO CONTINUE LATER INTO FRIDAY MAY
SEE MINOR TIDAL OVERFLOW AS RIVERS CRESTS COINCIDE WITH HIGH TIDE ON
FRIDAY, THOUGH THIS OCCURRENCE REMAINS LOWER CONFIDENCE. RIVERS
DRAINING THE CASCADES, INCLUDING THE MOHAWK, SANTIAM, PUDDING,
MOLALLA, CLACKAMAS, AND SANDY, HAVE INCREASED WITH CHANCES OF 25-
90%. THESE RIVERS WILL BEGIN TO RISE LATER ON THURSDAY AS HEAVY RAIN
CONTINUES, NOT CRESTING UNTIL FRIDAY IN MOST CASES. LATEST FORECASTS
HAVE INTRODUCED MULTIPLE FLOODS REACHING MODERATE TO MAJOR FLOOD
STAGE, INCLUDING THE MOLALLA RIVER NEAR CANBY, CLACKAMAS RIVER NEAR
ESTACADA, AND THE JOHNSON CREEK NEAR SYCAMORE. THERE IS ALSO
POTENTIAL FOR THE CLACKAMAS NEAR RIVER NEAR OREGON CITY TO REACH
RECORD STAGES IF LATEST RAINFALL FORECASTS REMAIN ON TRACK.
THE WILLAMETTE RIVER MAIN STEM ITSELF ALSO HAS A 5-10% CHANCE OF
REACHING FLOOD STAGE ABOVE WILLAMETTE FALLS, AND SLIGHTLY HIGHER
CHANCES IN TIDALLY-INFLUENCED PORTIONS DOWNSTREAM OF OREGON CITY,
HOWEVER RUNOFF WILL TAKE LONGER TO REACH THE WILLAMETTE AND FLOODING
WOULD BE DELAYED LATER THAN IN ITS TRIBUTARIES. A FLOOD WATCH
REMAINS IN EFFECT ACROSS ALL OF NORTHWESTERN OREGON AND SOUTHWESTERN
WASHINGTON FROM 4 AM THURSDAY THROUGH 4 AM SATURDAY TO HIGHLIGHT
THESE RISKS.
THESE RIVER FORECASTS REMAIN VERY SENSITIVE TO RAINFALL
FORECASTS, AND INTERESTED PARTIES SHOULD EXPECT CHANGES AS THE
EVENT NEARS. THE LATEST RIVER FORECASTS ACROSS THE REGION CAN BE
FOUND AT WWW.WATER.NOAA.GOV/WFO/PQR.
PQR WATCHES/WARNINGS/ADVISORIES
OR...HIGH WIND WATCH FROM THURSDAY MORNING THROUGH THURSDAY EVENING
FOR ORZ103-107.
WIND ADVISORY FROM 8 AM TO 7 PM PST THURSDAY FOR ORZ105-114>118-
123>125.
WINTER WEATHER ADVISORY FROM 4 AM TO 10 AM PST THURSDAY FOR
ORZ121-126-127.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST THURSDAY FOR WAZ211.
PZ...HAZARDOUS SEAS WARNING UNTIL 4 AM PST THURSDAY FOR PZZ210-
251>253-271>273.
GALE WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR PZZ210-
251-271>273.
STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR
PZZ252-253.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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