734
FXUS66 KPQR 211801 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1000 AM PST SUN DEC 21 2025
..UPDATED AVIATION DISCUSSION
SYNOPSIS
WE REMAIN UNDER THE INFLUENCE OF A FAIRLY TYPICAL
COOL AND UNSETTLED WEATHER PATTERN INTO EARLY NEXT WEEK. WITH
SNOW LEVELS HOLDING NEAR THE PASSES, WINTER-LIKE TRAVEL
CONDITIONS PERSIST. FORECAST UNCERTAINTY INCREASES SUBSTANTIALLY
ON WEDNESDAY AS A POTENTIAL SCENARIO INVOLVING WIDESPREAD
STRONG SOUTH WINDS GAINS ADDITIONAL TRACTION AMONG A SUBSET OF
MODELS (20-30% EPS) - WE'LL WATCH THIS POTENTIAL OUTCOME WITH
GREAT INTEREST. OTHERWISE, BY NEXT WEEKEND THE OVERALL TREND IS
SHIFTING TOWARDS A RIDGE OF HIGH PRESSURE ATTEMPTING TO BUILD
OVERHEAD AND THUS DRIER WEATHER, ALBEIT ONLY TEMPORARILY.
DISCUSSION...NOW THROUGH SATURDAY
EARLY THIS MORNING A WARM-
FRONTAL BOUNDARY IS SLOWLY WORKING NORTHWARD INTO LANE COUNTY
WHILE THE REGION SITS UNDER BROAD SOUTHWEST FLOW. THIS IS ALL
THANKS TO AN APPROACHING PACIFIC SHORTWAVE TROUGH EVENTUALLY
USHERING IN AN INCREASE IN SHOWER COVERAGE AS THE DAY
PROGRESSES. BEYOND THE AFOREMENTIONED WARM-FRONT WHICH IS
EXPECTED TO PIVOT EASTWARD BY THIS AFTERNOON, MORE ORGANIZED
PRECIPITATION IS EXPECTED THIS EVENING INTO TONIGHT AS THE
SHORTWAVE TROUGH AND AN ACCOMPANYING COLD FRONTAL BOUNDARY MOVE
INLAND. WHILE THIS SYSTEM IS NOT EXPECTED TO PRODUCE WIDESPREAD
LOWLAND IMPACTS, RENEWED SNOWFALL ACROSS THE CASCADE PASSES IS
LIKELY TO CREATE ADDITIONAL TRAVEL CHALLENGES. WITH THE LATEST
GUIDANCE INDICATING DECENT SNOW ACCUMULATION POSSIBLE AT PASS
ELEVATIONS (50-70% CHANCE FOR MORE THAN 6 INCHES OF SNOW OVER 24
HOURS, HIGHEST SANTIAM PASS SOUTHWARD), THE WINTER WEATHER
ADVISORY HAS BEEN MAINTAINED THROUGH 4 AM MONDAY.
THE ACTIVE AND PROGRESSIVE PATTERN CONTINUES AS BROAD UPPER
LEVEL TROUGHING REMAINS ANCHORED OVER THE NORTHEASTERN PACIFIC.
EMBEDDED SHORTWAVE DISTURBANCES WILL MOVE THROUGH THE REGION IN
SUCCESSION WITH BRIEF BREAKS BETWEEN EACH, MAINTAINING PERIODIC
CHANCES FOR SHOWERS ACROSS NORTHWEST OREGON AND SOUTHWEST
WASHINGTON. BEYOND THE ONE SLATED TO PASS THROUGH THE PACIFIC
NORTHWEST LATE TODAY INTO TONIGHT, ANOTHER UPPER-LEVEL SHORTWAVE
DISTURBANCE IS EXPECTED TO ARRIVE THE LATTER HALF OF MONDAY,
ACCOMPANIED BY INCREASING SOUTH WINDS AND LOCALLY BREEZY
CONDITIONS. ENSEMBLE GUIDANCE SUGGESTS COASTAL AREAS WILL BE
MOST SUSCEPTIBLE TO STRONGER WIND GUSTS WITH THIS SYSTEM (15-30%
CHANCE OF GUSTS ABOVE 50 MPH), WHILE INLAND LOCATIONS SHOULD
GENERALLY SEE MORE MODEST WINDS (20-40% CHANCE OF GUSTS ABOVE 35
MPH). GIVEN HIGHLY SATURATED SOILS, EVEN WIND GUSTS IN THE
30-40 MPH RANGE MAY BE ENOUGH TO RESULT IN ISOLATED TREE DAMAGE.
COME TUESDAY HIS SHORTWAVE DISTURBANCE PULLS AWAY TO OUR
NORTHEAST AND 500MB HEIGHTS BEGIN TO BUILD IN RESPONSE TO SOME
WEAK RIDGING MOVING OVERHEAD. WHILE THIS WON'T BE ENOUGH TO
COMPLETELY END PRECIPITATION REGION-WIDE, IT WILL HELP TO
CONSOLIDATE LINGERING SHOWERS TO TERRAIN FEATURES LIKE THE COAST
RANGE/CASCADES WHILE PROVING MORE DRY-TIME ACROSS THE INLAND
VALLEYS DURING TUESDAY AFTERNOON. HIGH CONFIDENCE IN LIGHTER
WINDS RETURNING ON TUESDAY AS WELL.
FORECAST UNCERTAINTY INCREASES SUBSTANTIALLY DURING THE MIDDLE
OF THE WEEK AS ENSEMBLE GUIDANCE DIVERGES ON THE EVOLUTION OF A
CLOSED LOW TO OUR SOUTH AND THE PLACEMENT ATTENDANT SHORTWAVE
DISTURBANCES. MOST ENSEMBLE SOLUTIONS KEEP THE STRONGEST WINDS
AND HEAVIEST PRECIPITATION DISPLACED WELL TO THE SOUTH AND EAST.
HOWEVER, A GROWING SUBSET OF ENSEMBLE MEMBERS (25-30% OF THE
EPS), AND THE 00Z DETERMINISTIC ECMWF, DEPICT A RAPIDLY
STRENGTHENING COMPACT SURFACE LOW SLING-SHOTTING NORTHWARD
THROUGH WESTERN OREGON ON WEDNESDAY; A SET-UP FAVORABLE FOR
UNUSUALLY STRONG WINDS. IN THIS CASE, A ROBUST SURFACE PRESSURE
GRADIENT OF ~8-15MB WOULD ALIGN ACROSS THE WILLAMETTE VALLEY AND
COAST SUPPORTED BY 60-80 KNOT 850MB WINDS JUST ABOVE THE
SURFACE. GIVEN THE DYNAMIC AND KINEMATIC PROFILE, THIS COULD BE
CHARACTERIZED AS A "STING JET" SET-UP ALTHOUGH NOT FROM OUR
MORE TYPICAL W TO E OF SW TO NE PROGRESSION. IN ANY CASE IT
WOULD LEAD TO A ROUGHLY 6 HOUR PERIOD OF STRONG SOUTH WIND GUSTS
AROUND 45 TO 65+MPH. WINDS OF THIS MAGNITUDE WOULD PRODUCE
SIGNIFICANT IMPACTS LIKE WIDESPREAD POWER OUTAGES, TREE DAMAGE,
ETC. SO WHILE THIS SCENARIO IS NOT FAVORED AT THIS TIME NOR
REFLECTED IN THE FORECAST, (~70-75% CHANCE IT DOESEN'T OCCUR)
IT WARRANTS WATCHING WITH GREAT CARE AS THE NUMBER OF EPS
ENSEMBLE MEMBERS FAVORING THIS SCENARIO HAS BEEN STEADILY
GROWING RUN TO RUN SETTING OFF THIS FORECASTER'S PROVERBIAL
"ALARM BELL". IT'LL BE INTERESTING TO SEE IF THIS TREND
CONTINUES IN FUTURE MODEL RUNS.
BEYOND THIS POINT CONFIDENCE IN SPECIFIC IMPACTS THURSDAY INTO
FRIDAY ARE LOW DUE TO LARGE DISCREPANCIES IN THE BROADER TROUGH
FEATURE EITHER HOLD OFF THE COAST FOR ANOTHER DAY OR TWO, OR
MOVING INLAND. IN AN CASE WE'LL MORE THAN LIKELY HOLD ONTO
SHOWER ACTIVITY THROUGH FRIDAY - WHETHER IT'S STREAM OVERHEAD
FROM THE SOUTH OR THE WEST REMAINS TO BE SEEN. HOWEVER, THERE
IS ENSEMBLE AND DETERMINISTIC MODEL CONVERGENCE (70-80%
CONFIDENCE) SURROUNDING SOME DEGREE OF AN UPPER-LEVEL RIDGE
FEATURE WORKING INTO THE PACIFIC NORTHWEST AROUND FRIDAY NIGHT
INTO NEXT EARLY WEEKEND SUGGESTING A PERIOD OF DRIER AND CALMER
WEATHER ON THE FAR HORIZON. -99/12
AVIATION
RADAR IMAGERY AS OF LATE SUNDAY MORNING DEPICTS
SHOWERS ALONG THE COAST AND RAIN OVER THE SOUTHEASTERN PORTION OF
NORTHWEST OREGON AS A WARM FRONT CLIPS THE REGION. CURRENTLY HAVE
A MIX OF VFR AND MVFR CIGS ACROSS THE AREA. LATER THIS AFTERNOON
AFTER 21-23Z SUN, THERE IS INCREASING CONFIDENCE (50-70% CHANCE)
FOR MVFR CONDITIONS AS ANOTHER WEAK FRONT MOVES INTO THE AREA AND
BRINGS INCREASED SHOWERS AND LOWER CIGS/VIS. CHANCES FOR IFR CIGS
OR LOWER AT ANY GIVEN TERMINAL TODAY ARE AROUND 5-15%. MVFR CIGS
WILL PERSIST THROUGH EARLY MONDAY MORNING. AFTER 12Z MON, CIGS
BEGIN TO TREND HIGHER TOWARD LOW-END VFR, BUT THERE REMAINS A
30-40% CHANCE FOR MVFR CIGS LASTING THROUGH THE END OF THE TAF
PERIOD FOR ANY GIVEN TERMINAL. WINDS GENERALLY SOUTHERLY TO
SOUTHWESTERLY UNDER 10 KT, EXCEPT FOR EASTERLY WINDS THROUGH THE
COLUMBIA RIVER GORGE.
KPDX AND APPROACHES...VFR CONDITIONS UNTIL 21-22Z SUN. AFTER 22Z
SUN-00Z MON, HIGH CONFIDENCE FOR MVFR CIGS AS A FRONT MOVES
THROUGH AND RETURNS SHOWERS. THIS TREND CONTINUES THROUGH EARLY
MONDAY MORNING, WITH CIGS LIFTING TO LOW-END MVFR AND HIGH-END VFR
AFTER 12-15Z MON. OFFSHORE PRESSURE GRADIENTS MAINTAIN EASTERLY
WINDS THROUGH THE GORGE UNTIL 00-03Z MON. AFTERWARDS, WINDS TURN
MORE SOUTH-SOUTHWESTERLY, REMAINING UNDER 10 KT. -10
MARINE
A WEAK FRONT WILL MAINTAIN BREEZY CONDITIONS TODAY,
BUT WINDS SHOULD STAY LIGHTER ACROSS OUR SOUTHERN WATERS AS THE
BULK OF THE ENERGY STAYS A TOUCH FURTHER NORTH. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT FOR ZONES PZZ271, PZZ251, PZZ272,
PZZ152 AND THE COLUMBIA RIVER BAR THROUGH 1 PM TODAY. SEAS
SUBSIDE HOLD AROUND 7-9 FT AT 10 SEC BEFORE OUR NEXT ROBUST
FRONTAL SYSTEM ARRIVES ON MONDAY, RETURNING BREEZY SOUTHWESTERLY
WINDS AND BUILDING SEAS. A GALE WATCH IN EFFECT FOR ALL WATERS
INCLUDING THE COLUMBIA RIVER BAR BETWEEN 7 AM TO 7 PM MONDAY FOR
SOUTHWESTERLY WIND GUSTS UP 40 KT. GUIDANCE CURRENTLY SHOWS A
50-65% CHANCE FOR GALE FORCE WIND GUSTS ON MONDAY, WITH THE
HIGHEST CHANCES ACROSS THE INNER WATERS OUT 10 NM. SEAS ALSO
BUILD TO 12-15 FT AT 10-11 SEC ON MONDAY AS A WESTERLY SWELL
MOVES IN. GUIDANCE SUGGESTS A 20-45% CHANCE THAT SEAS RISE
ABOVE 15 FT. MARINE CONDITIONS BRIEFLY SETTLE DOWN TUESDAY TO
WEDNESDAY BEFORE MORE ACTIVE WEATHER RETURNS AT THE END OF THE
WEEK IN ADDITION TO A FAIRLY PRONOUNCED SOUTHERLY SWELL. -99/42
HYDROLOGY
WHILE THE HEAVIEST RAIN HAS ENDED OVER THE AREA
AND SHOWERS CONTINUE, MINOR RIVER FLOODING PERSIST FOR THE PUDDING
RIVER AT AURORA. EXPECT THE PUDDING RIVER AT AURORA TO FALL
BELOW FLOOD STAGE TUESDAY MORNING. THE LATEST RIVER FORECASTS
ACROSS THE REGION CAN BE FOUND AT: WWW.WATER.NOAA.GOV/WFO/PQR.
BE SURE TO NEVER DRIVE THROUGH A FLOODED ROAD AND HEED ANY
REMAINING ROAD CLOSURES.
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR ORZ126>128.
WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 6 PM PST THIS EVENING FOR PZZ210.
GALE WATCH FROM MONDAY MORNING THROUGH MONDAY EVENING FOR
PZZ210-251>253-271>273.
SMALL CRAFT ADVISORY UNTIL 1 PM PST THIS AFTERNOON FOR PZZ251-
252-271-272.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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