497
FXUS66 KPQR 060448 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
848 PM PST FRI DEC 5 2025
UPDATED AVIATION DISCUSSION.
SYNOPSIS
A STEADY SUCCESSION OF FRONTAL SYSTEMS WILL KEEP
CONDITIONS WET THROUGH THE WEEKEND AND MUCH OF NEXT WEEK. THE
MOST NOTABLE PERIOD CONTINUES TO FOCUS ON MONDAY THROUGH
MIDWEEK, WHEN A PROLONGED ATMOSPHERIC RIVER MAY BRING
SIGNIFICANT RAINFALL AND RISING RIVERS ACROSS SOUTHWEST
WASHINGTON AND NORTHWEST OREGON.
SHORT TERM...NOW THROUGH SUNDAY NIGHT
RADAR IMAGERY
AT 2 PM PST FRIDAY INDICATES RAIN HAS TAPERED OFF ACROSS MOST
OF THE AREA, THOUGH SHOWERS LINGER OVER THE COAST, COAST RANGE,
AND CASCADES INTO TOMORROW. THE FRONT THAT MOVED THROUGH THE
AREA THIS MORNING HAS STALLED OVER THE CASCADES, AND IS EXPECTED
TO MOVE VERY SLOWLY INTO EASTERN OREGON OVERNIGHT AS IT
DECREASES IN STRENGTH. THIS HAS CAUSED TIGHTER PRESSURE
GRADIENTS OVER THE REGION, PRODUCING BREEZY SOUTH TO WESTERLY
WINDS THIS AFTERNOON INTO TONIGHT. EXPECT GUSTS UP TO 25-30 MPH
ACROSS THE WILLAMETTE VALLEY AND UP TO 35-40 MPH IN THE
CASCADES AND COAST RANGE.
SHOWERS LINGER INTO SATURDAY AS A WESTERLY FLOW PATTERN PERSISTS.
ANOTHER FRONTAL WAVE WILL ARRIVE SUNDAY AND BRING YET ANOTHER ROUND
OF STEADY RAINFALL TO THE REGION. ENSEMBLE GUIDANCE SUGGESTS IVT
VALUES WITH SUNDAY'S SYSTEM IN THE 300-500 KG/MS RANGE,
PRODUCING A WIDESPREAD SOAKING. RAINFALL TOTALS FROM SATURDAY
THROUGH SUNDAY ARE CURRENTLY PROJECTED TO FALL IN THE 0.5 TO
1.0 INCH RANGE ACROSS THE INTERIOR LOWLANDS, WITH 1 TO 2.5
INCHES FOR THE COAST AND COAST RANGE. THE CASCADES ARE EXPECTED
TO RECEIVE ROUGHLY 1.25 TO 3.0 INCHES, EXCEPT FOR THE LANE
COUNTY CASCADES WHERE AMOUNTS ARE CLOSER TO 0.5 TO 1.5 INCHES.
WIDESPREAD IMPACTS ARE NOT ANTICIPATED THROUGH SUNDAY; HOWEVER,
IF RAINFALL RATES SUSTAIN AROUND 0.2 TO 0.3 INCHES PER HOUR FOR
SEVERAL HOURS, A FEW FASTER-REPONDING BASINS, SUCH AS THE GRAYS
AT ROSBURG AND THE WILLAPA RIVER, COULD RISE QUICKLY.
LONG TERM...MONDAY THROUGH FRIDAY
ATTENTION THEN TURNS TO THE MONDAY-WEDNESDAY PERIOD, WHERE
ENSEMBLE CONFIDENCE CONTINUES TO INCREASE IN A MULTI-DAY
ATMOSPHERIC RIVER EVENT. OVER THE PAST SEVERAL CYCLES,
ENSEMBLES HAVE BECOME INCREASINGLY CONSISTENT IN HIGHLIGHTING
TWO DISTINCT SURGES OF MOISTURE: ONE CENTERED ROUGHLY ON MONDAY,
AND A SECOND SOMETIME TUESDAY OR WEDNESDAY. BETWEEN THESE
PEAKS, THE MOISTURE FEED IS UNLIKELY TO SHUT DOWN, LEADING TO A
LONG-DURATION EVENT RATHER THAN TWO ISOLATED EPISODES.
THE IVT SPREAD IN ENSEMBLE GUIDANCE HAS SHRUNK SIGNIFICANTLY ON
MONDAY WITH THE FIRST SURGE OF MOISTURE, WITH GEFS AND EURO
ENSEMBLE MEANS AND THEIR HIGH AND LOW END SOLUTIONS PEAKING
WITHIN THE 600-850 KG/MS RANGE. THE ENSEMBLE SPREAD IS STILL
WIDER FOR THE SECOND MOISTURE SURGE, PARTIALLY BECAUSE ENSEMBLES
ARE STILL STRUGGLING TO DETERMINE THE LOCATION OF WHERE IT WILL
FOCUS ALONG THE WA INTO OR COAST ALONG WITH THE TIMING.
ENSEMBLE MEANS ARE CENTERED AROUND THE 700-800 KG/MS RANGE. WITH
THE HIGH ENDS PEAKING AROUND 900-100 KG/MS AND THE LOW END
AROUND 500-650 KG/MS. IN BETWEEN THE PEAKS, THE ENSEMBLE MEANS
INDICATE THE IVT VALUES COULD REMAIN BETWEEN 500-700 KG/MS WITH
THE LOW END FORECASTS BETWEEN 300-500 KG/MS, WHICH IS STILL
QUITE A BIT OF MOISTURE. THE PRECISE TIMING AND LATITUDE OF
THESE PLUMES REMAIN UNCERTAIN, BUT CONFIDENCE CONTINUES TO
INCREASE THAT THE REGION WILL EXPERIENCE A PROLONGED PERIOD OF
MODERATE TO HEAVY RAINFALL. WINDS EARLY NEXT WEEK MAY ALSO TREND
BREEZY, BUT ENSEMBLE SPREAD REMAINS WIDE. EVEN MODERATE GUSTS
IN A 30-40 MPH RANGE COULD BE SUFFICIENT TO BRING DOWN ISOLATED
TREES DUE TO INCREASINGLY SATURATED SOILS FROM OVER 5 DAYS OF
MODERATE RAIN. THIS REMAINS A DETAIL TO REFINE AS THE EVENT
DRAWS CLOSER. ONE THING TO NOTE IS THESE ARE WARM WEATHER
SYSTEMS, MEANING SNOW LEVELS ARE VERY LIKELY TO REMAIN ABOVE
6000 FEET WITH LITTLE TO NO SNOW EXPECTED OVER THE CASCADES.
OVERALL, THE MONDAY THROUGH WEDNESDAY TIME PERIOD REMAINS THE
PRIMARY FOCUS FOR POTENTIAL HIGH-IMPACT HYDROLOGIC (SEE
HYDROLOGY SECTION BELOW FOR MORE DETAILS) AND WIND CONCERNS.
CONFIDENCE IN A MULTI-DAY ATMOSPHERIC RIVER IS RISING, BUT EXACT
RAINFALL TOTALS AND TIMING DETAILS STILL REQUIRE SEVERAL MORE
FORECAST CYCLES TO RESOLVE. WHILE RAIN IS LOOKING TO CONTINUE
THROUGH AT LEAST THURSDAY, RAIN AMOUNTS LOOK MUCH LESS THURSDAY
AND ONWARD.-12/03
AVIATION
SHOWERS HAVE BACKED OFF TODAY AS THE MAIN FRONTAL BAND
HAS DISSIPATED AND SHIFTED TO THE EAST. BEHIND THIS FRONT
CONDITIONS HAVE BEEN A BIT MORE COMPLICATED AS WESTERLY WINDS HAVE
EASED TO SOME EXTENT AND SKIES BEGIN TO CLEAR TO VFR. SOME
SCATTERED MVFR LAYERS PERSIST WHICH OVERNIGHT MAY FILL IN TO MVFR.
THERE IS AROUND A 30% CHANCE OF THOSE CONDITIONS REDEVELOPING IN
THE NORTH AND AROUND A 60-70% CHANCE IN THE SOUTHERN WILLAMETTE
VALLEY. OVERALL, EXPECT BOUNCY CONDITIONS OVER THE NEXT 24 HOURS
WITH SCATTERED LIGHT SHOWERS. A WEAK DISTURBANCE WILL PASS OVER
THE AREA LATE IN THE FORECAST PERIOD BRINGING ANOTHER ROUND OF
RAIN AND BREEZY SOUTHWESTERLY TO WESTERLY WINDS.
KPDX AND APPROACHES...A MIXTURE OF LOW END VFR AND HIGH END MVFR
THROUGH THE NEXT 24 HOURS. IN A BREAK PERIOD FOR THE NEXT 6 HOURS
OR SO AS THE POST FRONTAL ENVIRONMENT TAKES OVER. WILL SEE PARTIAL
CLEARING AT TIMES UNTIL AROUND 10Z SAT. SHOWERS PERSIST THROUGH
THE FORECAST BUT WILL BE NON-IMPACTFUL. 20-30% CHANCE OF MVFR
CIGS AFTER 20Z SAT. WILL NOTE THAT AT AROUND 700 FT MSL, WINDS ARE
SSW AROUND 30 KT. NOT NEARLY ENOUGH TO ADD LLWS TO THE TAF, BUT
FOR EAST APPROACHES CANNOT RULE OUT THE POTENTIAL FOR ISOLATED
PERIODS OF GUSTY CROSSWINDS. -27
MARINE
BREEZY WEST-SOUTHWESTERLY WINDS WITH GUSTS UP TO 25 KT
CONTINUE ACROSS THE WATERS AS A FRONTAL SYSTEM PROGRESSES THROUGH
THE AREA. SMALL CRAFT ADVISORIES REMAIN IN EFFECT ACROSS ALL WATERS
INCLUDING THE COLUMBIA RIVER BAR THROUGH LATE SATURDAY EVENING. SEAS
OF 7-9 FT AT 10-11 SECONDS BUILD TO 11-14 FT AT 13 SEC SATURDAY
MORNING AS A NORTHWESTERLY SWELL MOVES IN. WILL NOTE THAT A VERY
STRONG EBB MAY LEAD TO SEAS OF 12-13 FT IN THE MAIN CHANNEL OF THE
COLUMBIA RIVER BAR AROUND 530 PM SATURDAY. THERE IS ALSO A 60-80%
CHANCE THAT SEAS BUILD ABOVE 13 FT, WITH THE HIGHEST CHANCES NORTH
OF CAPE LOOKOUT AND BEYOND 10 NM. THERE IS ALSO 30-50% CHANCE SEAS
PEAK AS HIGH AS 15 FT.
THE PARADE OF FRONTS CONTINUE THROUGH THE WEEKEND AND INTO EARLY
NEXT WEEK. CHANCES FOR WIDESPREAD AND FREQUENT GALE FORCE WIND GUSTS
OF 34 KT OR GREATER REMAIN UNDER 15% THROUGH THIS WEEKEND; HOWEVER,
CHANCES INCREASE TO 30-40% ON MONDAY FOR THE INNER WATER ZONES OUT
10 NM AND COLUMBIA RIVER BAR DUE TO A POTENTIAL COASTAL JET WITH THE
NEXT SYSTEM. SEAS ARE FORECAST TO HOVER CLOSE TO 15 FT FROM LATE
MONDAY THROUGH LATE WEDNESDAY, WITH A 10% CHANCE SEAS PEAK AROUND 17-
18 FT. -10/23
BEACH HAZARDS
COASTAL FLOOD ADVISORIES REMAIN IN EFFECT FROM
FOR MINOR TIDAL OVERFLOW DURING HIGH TIDE FROM 9 AM TO 3 PM SATURDAY
FOR THE SOUTH WASHINGTON COAST AND CLATSOP COUNTY COAST IN OREGON.
MINOR FLOODING UP TO 1 FOOT ABOVE GROUND LEVEL IS POSSIBLE DURING
HIGH TIDE IN LOW LYING AREAS NEAR BAYS, SLOUGHS, AND THE LOW REACHES
OF THE COASTAL RIVERS. COASTAL RESIDENTS IN THE WARNED AREA SHOULD
REMAIN ALERT FOR RISING WATER AND TAKE APPROPRIATE ACTION TO PROTECT
LIFE AND PROPERTY. -10
HYDROLOGY
A SERIES OF FRONTAL SYSTEMS WILL KEEP CONDITIONS
WET THROUGH THE WEEKEND AND MUCH OF NEXT WEEK. THE MOST NOTABLE
PERIOD WILL BE LATE MONDAY THROUGH LATE WEDNESDAY, WHERE A
PROLONGED ATMOSPHERIC RIVER MAY BRING SIGNIFICANT RAINFALL AND
RISING RIVERS ACROSS SOUTHWEST WASHINGTON AND NORTHWEST OREGON.
HOWEVER, RIVER FLOODING FOR SOME LOCATIONS COULD CONTINUE INTO
THURSDAY AND BEYOND AS SOME RIVERS TAKE LONGER TO RESPOND TO
HEAVIER RAINFALL. RIVERS DRAINING THE COAST RANGE AND WILLAPA
HILLS HAVE A 30-60% CHANCE OF REACHING MODERATE FLOOD STAGE AND
A 10-30% CHANCE OF REACHING MAJOR FLOOD STAGE. ADDITIONALLY,
MANY WILLAMETTE RIVER TRIBUTARIES THAT DRAIN FROM THE COAST
RANGE AND CASCADES HAVE ANYWHERE FROM A 10-55% CHANCE OF
REACHING MINOR FLOOD STAGE AND A 10-25% CHANCE OF REACHING
MODERATE FLOOD STAGE. FLOODING OF THE WILLAMETTE MAINSTEM RIVERS
IS UNLIKELY TO OCCUR (LESS THAN 10%). PROBABILITIES FOR
SPECIFIC RIVER POINTS CAN BE FOUND AT THE NATIONAL WATER
PREDICTION SERVICE WEBSITE.
THERE IS ALSO INCREASING CONFIDENCE IN THE POTENTIAL FOR
FLOODING ALONG SMALL CREEKS AND STREAMS AS WELL AS URBAN
FLOODING, INCLUDING ROADWAY FLOODING, FOR LOCATIONS IN THE
CENTRAL WILLAMETTE VALLEY NORTH INTO THE SOUTHWEST WASHINGTON
LOWLANDS, INCLUDING THE PORTLAND METRO AREA. PERIODS OF HEAVY
RAIN WILL ALSO INCREASE THE RISK FOR LANDSLIDES IN AREAS OF
STEEP TERRAIN AND DEBRIS FLOWS OVER RECENTLY BURNED AREAS.
PQR WATCHES/WARNINGS/ADVISORIES
OR...COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SATURDAY FOR
ORZ101.
WA...COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SATURDAY FOR
WAZ201.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST SATURDAY FOR PZZ210-
251>253-271>273.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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