130
FXUS66 KPQR 202337
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
337 PM PST FRI DEC 20 2024
SYNOPSIS
DRY WEATHER THROUGH THIS EVENING. NEXT FRONTAL
SYSTEM ARRIVES SATURDAY MORNING, RETURNING WIDESPREAD RAIN AND
SNOW ABOVE 6000 FEET. THE WEEKEND THROUGH LATE NEXT WEEK WILL BE
CHARACTERIZED BY A SERIES OF WEAK TO MODERATE ATMOSPHERIC
RIVERS. THE SHORT-DURATION OF THESE ATMOSPHERIC RIVERS WILL
HELP MINIMIZE IMPACTS, HOWEVER, THERE IS STILL A 20-40% CHANCE
FOR COASTAL RIVERS REACHING MINOR FLOOD STAGE OVER THE NEXT TEN
DAYS. SNOW LEVELS GENERALLY REMAIN HIGH AND WILL MINIMIZE
IMPACTS THROUGH THE CASCADE PASSES.
SHORT TERM...NOW THROUGH SUNDAY
SATELLITE AND RADAR IMAGERY
AS OF 2 PM FRIDAY SHOWS A WEAK FRONT MOVING EASTWARD ACROSS
NORTHWEST OREGON AND SOUTHWEST WASHINGTON, BRINGING HIGH CLOUDS
AND LIGHT RAIN AT TIMES. THE FRONT SHOULD EXIT THE AREA BY LATE
AFTERNOON, RETURNING A BRIEF PERIOD OF DRY WEATHER. SATELLITE
IMAGERY SHOWS CLEARING BEHIND THE FRONT, SO EXPECT TO SEE SOME
CLEARING SKIES THROUGH LATE TONIGHT UNTIL THE NEXT SYSTEM
ARRIVES EARLY SATURDAY MORNING. WINDS ARE CURRENTLY GUSTING UP
TO 30 MPH THROUGH THE COLUMBIA RIVER GORGE AND EAST PORTLAND
METRO, BUT THESE WINDS SHOULD BRIEFLY WEAKEN THIS AFTERNOON AS
KTTD-KDLS PRESSURE GRADIENTS LOOSEN BEFORE THE NEXT SYSTEM.
THE NEXT FRONTAL SYSTEM ARRIVES EARLY SATURDAY MORNING, RETURNING
WIDESPREAD RAIN TO THE REGION. HIGH RESOLUTION MODELS SUGGEST
RAIN BEGINNING ALONG THE COAST AND COAST RANGE AROUND 2-4 AM,
SPREADING INTO THE WILLAMETTE VALLEY AND CASCADES BY 4-6 AM. IT
WILL BE A QUICK-MOVING FRONT WITH GENERALLY NON-IMPACTFUL RAINFALL
AMOUNTS. FORECAST QPF AMOUNTS ARE AROUND 0.25-0.50 INCH ALONG
THE COAST AND INTERIOR LOWLAND VALLEYS, AND 0.50-1 INCH ACROSS
THE COAST RANGE, WILLAPA HILLS, AND CASCADES. WINDS WILL ALSO
STRENGTHEN THROUGH THE GORGE AND EAST PORTLAND METRO, WITH GUSTS
UP TO 30-40 MPH (POTENTIALLY HIGHER FOR MORE EXPOSED SPOTS IN
THE GORGE). NOT EXPECTING SNOW TO IMPACT THE CASCADE PASSES AS
SNOW LEVELS ARE FORECAST ABOVE 5000-6000 FEET; HOWEVER,
ELEVATIONS ABOVE 6000 FEET COULD RECEIVE AROUND 5-10 INCHES OF
SNOW. THE FRONT SHOULD EXIT THE AREA BY LATE SATURDAY MORNING OR
EARLY SATURDAY AFTERNOON, WITH STEADY RAIN TRANSITIONING TO
SHOWERS WITH MORE CLOUD BREAKS. WILL NOTE THAT THERE IS A 10-20%
CHANCE OF THUNDERSTORMS ALONG THE COAST ONCE THE FRONT MOVES
THROUGH AND THE ATMOSPHERE BECOMES MORE UNSTABLE (HREF ENSEMBLE
MEAN SHOWS SURFACE-BASED CAPE AROUND 200-400 J/KG ALONG THE
COAST).
SHOWERS WILL CONTINUE SATURDAY NIGHT THROUGH EARLY SUNDAY
MORNING, BUT THE NEXT SYSTEM IN THE SERIES OF FRONTS ARRIVES
LATE MORNING TO EARLY AFTERNOON SUNDAY. IT LOOKS LIKE A WETTER
DAY, WITH QPF AMOUNTS FORECAST AROUND 0.50-0.75 INCH ALONG THE
COAST AND INTERIOR LOWLAND VALLEYS, AND 0.75-1.25 INCH ACROSS
THE COAST RANGE, WILLAPA HILLS, AND CASCADES. SOME LOCALIZED
SPOTS IN HIGHER TERRAIN COULD RECEIVE UP TO 1.50 INCH OF
PRECIPITATION. MINIMAL CONCERNS FOR THE CASCADE PASSES AS SNOW
LEVELS ARE FORECAST ABOVE 7000 FEET WITH THIS FRONT. WHILE THESE
SYSTEMS OVER THE WEEKEND ARE NOT EXPECTED TO CAUSE CONCERNS FOR
RIVER FLOODING, NOW IS A GOOD TIME TO CLEAR ANY ADDITIONAL
LEAVES OR DEBRIS FROM YOUR GUTTERS AND/OR STORM DRAINS AS NEXT
WEEK CONTINUES TO LOOK VERY WET. -ALVIZ
LONG TERM...SUNDAY NIGHT TO FRIDAY
THE LONG TERM FORECAST IS
CHARACTERIZED BY A SERIES OF WEAK TO MODERATE ATMOSPHERIC
RIVERS MOVING INTO THE PACIFIC NORTHWEST. HOWEVER, THE SHORT-
DURATION OF EACH ONE WITH BREAKS IN BETWEEN WILL HELP MINIMIZE
CONCERNS FOR WIDESPREAD, LARGE-SCALE IMPACTS.
A TRANSIENT RIDGE ON MONDAY WILL BRING A BRIEF BREAK IN THE RAIN
BEFORE THE NEXT SYSTEM ARRIVES MONDAY NIGHT INTO TUESDAY. GEFS
AND ECMWF ENSEMBLE MEAN SHOW IVT VALUES BETWEEN 500-750 KG/MS
WITH THIS SYSTEM, WHICH WOULD CLASSIFY THIS AS A MODERATE
ATMOSPHERIC RIVER. HOWEVER, 20-30% OF ENSEMBLE MEMBERS
(DOMINATED BY THE ECMWF) DO SUGGEST IVT VALUES COULD REACH AS
HIGH AS 750-1100 KG/MS, WHICH WOULD CLASSIFY THIS SYSTEM AS A
STRONG OR EXTREME ATMOSPHERIC RIVER. WHILE THIS SCENARIO IS NOT
AS LIKELY, IF THIS WERE TO PAN OUT, THE SHORT-LASTING NATURE
(LESS THAN 24 HOURS) OF THIS SYSTEM WILL HELP MINIMIZE FLOODING
IMPACTS.
ANOTHER ATMOSPHERIC RIVER LOOKS TO ARRIVE SOMETIME WEDNESDAY TO
THURSDAY, HOWEVER, THERE IS STILL UNCERTAINTY WITH THE EXACT
TRACK OF THE LOW PRESSURE SYSTEM, AS WELL AS TIMING. RIVER
FLOODING IS HIGHLY DEPENDENT ON OUR RAINFALL FORECAST, AND THE
QPF FORECAST IS DEPENDENT ON THE LOW TRACK. BY THIS TIME, WE
WOULD HAVE EXPERIENCED BACK-TO-BACK SYSTEMS, SO ANY TREND
TOWARD A STRONGER SYSTEM LATE IN THE WEEK COULD LEAD TO MORE
SIGNIFICANT FLOODING IMPACTS. SAME GOES WITH DETERMINING
POTENTIAL FOR STRONG WINDS. AT THIS TIME, CONFIDENCE STILL
REMAINS LOW TO MODERATE FOR THESE FLOOD AND WIND IMPACTS. THE
LATEST HEFS GUIDANCE SUGGESTS A 20-40% CHANCE THAT RIVERS ALONG
THE COAST/COAST RANGE REACH MINOR FLOOD STAGE LATE NEXT WEEK.
SNOW LEVELS WILL RAIN MAINLY NEAR OR ABOVE THE PASSES, RUNNING
4000 TO 7000 FEET, THE HIGHEST SNOW LEVELS WILL OCCUR AHEAD OF
FRONTAL PASSAGES. -ALVIZ
AVIATION
CONDITIONS ARE GENERALLY VFR ACROSS THE REGION
THIS AFTERNOON AND WILL CONTINUE INTO THE OVERNIGHT HOURS. A
DECAYING FRONTAL BOUNDARY HAS BROUGHT INCREASING CLOUD COVER TO
THE REGION AND LITTLE TO NO PRECIPITATION. WINDS LIKELY STAY
BELOW 10-15 KNOTS AT ALL SITES EXCEPT FOR GUSTY EASTERLY WINDS
AT TTD AND SOUTHERLY WINDS ALONG THE COAST.
DRY WEATHER IS EXPECTED OVERNIGHT WITH VFR CONDITIONS PERSISTING
INTO THE OVERNIGHT. THE NEXT WEATHER SYSTEM IS EXPECTED TO REACH
THE COAST LATE TONIGHT AROUND 12-15Z AND INLAND BY 18Z. LIGHT
TO MODERATE RAIN IS EXPECTED WITH A MIX OF VFR AND MVFR
CONDITIONS EXPECTED AND POSSIBLY SOME IFR ALONG THE COAST.
CONDITIONS DRY OUT LATE SATURDAY AFTERNOON.
PDX AND APPROACHES...VFR CIGS/VIS CONTINUES THROUGH THE TAF
PERIOD WITH PERSISTENT EASTERLY WINDS COMING FROM THE COLUMBIA
RIVER GORGE. THE NEXT IMPACTFUL SYSTEM ENTERS THE AREA LATE
TONIGHT, BRINGING LIGHT TO MODERATE RAIN AND A MIX OF MVFR AND
VFR CONDITIONS. -BATZ
MARINE
ACTIVE CONDITIONS CONTINUE THE NEXT WEEK AND BEYOND AS
A BROAD LOW PRESSURE REMAINS OVER THE NE PACIFIC STEERING A
PARADE OF FRONTAL BOUNDARIES INTO THE COAST WATERS EVERY
24-36HRS. HAZARDOUS SEAS AND SMALL CRAFT CONDITIONS PERSIST
THROUGH EARLY TONIGHT BEFORE THE NEXT FRONTAL BOUNDARY ENTERS
THE AREA, INCREASING WINDS BACK INTO GALE CRITERIA GENERALLY
AFTER 4 AM. EXPECT GUSTS BETWEEN 35-45 KNOTS WITH SEAS
INCREASING INTO THE LOW TEENS BY SATURDAY MORNING AND UPPER
TEENS TO AROUND 20 FEET IN THE AFTERNOON. SEAS MAY DECREASE A
FEW FEET INTO THE MID TEENS SATURDAY NIGHT BUT WILL JUMP BACK UP
INTO THE UPPER TEENS WITH THE NEXT FRONTAL SYSTEM ON SUNDAY.
EXPECT THE ASSOCIATED WITH WAVE PERIODS IN THE UPPER TEENS TO
NEAR 20 SECONDS THROUGH EARLY NEXT WEEK AS WELL. MARINERS SHOULD
BE PREPARED FOR CONTINUED HAZARDOUS CONDITIONS THROUGH THE
MIDDLE TO END END OF NEXT WEEK. -BATZ
BEACH HAZARDS
A LARGE, ENERGETIC WESTERLY SWELL WILL BUILD
OVER THE COASTAL WATERS AND BEGIN IMPACTING THE COASTLINE THIS
WEEKEND INTO EARLY NEXT WEEK. SEAS IN EXCESS OF 15 TO 20 FEET
WITH A PERIOD OF AROUND 20 SECONDS COULD RESULT AS BREAKING
WAVES APPROACHING 25 TO 30 FEET IN THE SURF ZONE. THUS A HIGH
SURF ADVISORY HAS BEEN ISSUED FOR SATURDAY MORNING THROUGH
MONDAY EVENING - LARGEST BREAKERS ON THE LATTER DAY. FORECASTS
STILL SHOW WAVE HEIGHT AND PERIOD JUST UNDER WARNING THRESHOLD
BUT SLIGHT INCREASES IN EITHER PARAMETER WOULD PUSH ENERGY
VALUES TO WARNING CRITERIA. CONTINUE TO MONITOR FUTURE FORECASTS
FOR CHANGING CONDITIONS. BEACHGOERS SHOULD BE PREPARED FOR
DANGEROUS SURF CONDITIONS AND LARGE WAVES RUNNING FAR UP ONTO
THE BEACH BEGINNING LATE SUNDAY AND CONTINUING THROUGH EARLY
NEXT WEEK. -BATZ
PQR WATCHES/WARNINGS/ADVISORIES
OR...HIGH SURF ADVISORY FROM 7 AM SATURDAY TO 10 PM PST MONDAY FOR
ORZ101>103.
WA...HIGH SURF ADVISORY FROM 7 AM SATURDAY TO 10 PM PST MONDAY FOR
WAZ201.
PZ...SMALL CRAFT ADVISORY UNTIL 4 AM PST SATURDAY FOR PZZ210-251>253.
GALE WARNING FROM 4 AM TO 1 PM PST SATURDAY FOR PZZ210-251>253-
271>273.
HAZARDOUS SEAS WARNING UNTIL 4 AM PST SATURDAY FOR PZZ271>273.
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