561
FXUS66 KPQR 200551
AFDPQR
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE PORTLAND OR
951 PM PST THU DEC 19 2024
SYNOPSIS
RELATIVELY QUIET WEATHER THROUGH FRIDAY EVENING.
WEAK FRONTS THIS AFTERNOON AND MID-DAY FRIDAY WILL BRING LIGHT
RAIN TO THE COAST AND COAST RANGE. WIDESPREAD RAIN RETURNS THIS
WEEKEND INTO NEXT WEEK AS A SERIES OF WEATHER SYSTEMS TAKE AIM
AT THE PACIFIC NORTHWEST. THESE BACK-TO-BACK SYSTEMS COULD
POTENTIALLY BRING STRONG WINDS AND/OR COASTAL RIVER FLOODING.
SHORT TERM...TODAY THROUGH SATURDAY NIGHT
RADAR AND SATELLITE
IMAGERY AS OF 230 PM SATURDAY DEPICT A WEAK COLD FRONT PUSHING
THROUGH NORTHWEST OREGON AND SOUTHWEST WASHINGTON. THIS WEAK
FRONT IS BRINGING A BAND OF LIGHT RAIN AND HIGH CLOUDS TO THE
AREA. INLAND LOCATIONS EAST OF THE COAST RANGE ARE FORECAST TO
REMAIN MOSTLY DRY (QPF AMOUNTS GENERALLY LESS THAN 0.05 THROUGH
TONIGHT), WHILE HIGHER AMOUNTS AROUND 0.10-0.25 ARE FORECAST
ALONG THE COAST AND COAST RANGE. MODELS SUGGEST THAT THE FRONT
WILL WEAKEN AND MOVE EASTWARD THROUGH THIS EVENING, WITH RAIN
GRADUALLY DIMINISHING BY EARLY FRIDAY MORNING. BREEZY WINDS
THROUGH THE COLUMBIA RIVER GORGE AND FAR EASTERN PORTLAND METRO
CONTINUE THIS AFTERNOON DUE TO -6 TO -7 MB KTTD-KDLS PRESSURE
GRADIENTS, BUT SHOULD BEGIN TO GRADUALLY WEAKEN THIS EVENING AS
GRADIENTS LOOSEN.
TOMORROW (FRIDAY) LOOKS SIMILAR TO TODAY (THURSDAY) WITH MOSTLY
DRY CONDITIONS FOR INLAND VALLEY LOCATIONS, MAINLY IN THE
MORNING. BY LATE MORNING OR EARLY AFTERNOON, ANOTHER WEAK
FRONTAL SYSTEM SWINGS INTO WESTERN OREGON AND WASHINGTON
BRINGING LIGHT PRECIPITATION TO THE COAST AND COAST RANGE AGAIN.
THE TOTAL RAINFALL ASSOCIATED WITH THIS NEXT DISTURBANCE SHOULD
ONLY AMOUNT TO 0.05-0.20 INCH FOR THE COAST/COAST RANGE AND
LESS ELSEWHERE.
THIS FAIRLY BENIGN PATTERN DOES COME TO AN END EARLY SATURDAY
MORNING AS AN ELONGATED, NEGATIVELY TILTED UPPER-LEVEL TROUGH
AND ACCOMPANYING COLD FRONT SWINGS INTO THE PACIFIC NORTHWEST,
RETURNING WIDESPREAD PRECIPITATION. THE CURRENT TIMING BRINGS
RAIN TO THE COAST BY EARLY SATURDAY MORNING (4-7 AM) FOLLOWED
BY THE INTERIOR VALLEYS AND CASCADES BY 7-10 AM. 24 HOUR QPF
TOTALS ENDING 4 AM SUNDAY ARE FORECAST BETWEEN 0.20-0.40 INCH
ALONG THE COAST AND INTERIOR LOWLAND VALLEYS, AND 0.50-0.75 INCH
IN THE COAST RANGE AND CASCADES. AS THE SYSTEM MOVES THROUGH,
SNOW LEVELS WILL REMAIN ABOVE 5000-6000 FEET, SO WE'RE NOT
EXPECTING IMPACTFUL SNOWFALL THROUGH THE CASCADE PASSES. MODEL
GUIDANCE STILL SUGGESTS THE AXIS OF HEAVIEST PRECIPITATION IS
AIMED TOWARD SOUTHERN OREGON AND NORTHERN CALIFORNIA, HOWEVER,
IF THIS AXIS SHIFTS NORTHWARD, QPF AMOUNTS COULD BE HIGHER. THE
CURRENT PROBABILITY OF 24 HR QPF EXCEEDING 1 INCH ON SATURDAY
IS GENERALLY 40-60% IN THE COAST RANGE AND CASCADES, AND LESS
THAN 5% EVERYWHERE ELSE.
SURFACE PRESSURE GRADIENTS ACROSS THE CASCADES WILL ALSO TIGHTEN
BACK UP AGAIN WITH THIS SYSTEM, RETURNING BREEZY/GUSTY EAST
WINDS THROUGH THE COLUMBIA RIVER GORGE PEAKING LATE FRIDAY NIGHT
INTO EARLY SATURDAY MORNING. THE GFS, NAM, AND SREF ARE
SUGGESTING GRADIENT OF -5 TO -7 MB AGAIN BETWEEN KTTD AND KDLS.
COULD DEFINITELY SEE WIND GUSTS AROUND 30-40 MPH NEAR TROUTDALE
AND 40-50 MPH FOR HIGHER TERRAIN NEAR THE GORGE LIKE CORBETT AND
THREE CORNER ROCK. -ALVIZ/SCHULDT
LONG TERM...SUNDAY THROUGH THURSDAY
BOTH ENSEMBLE AND
DETERMINISTIC GUIDANCE IS IN FAIRLY GOOD AGREEMENT PORTRAYING AN
ACTIVE AND PROGRESSIVE WEATHER PATTERN MOVING FORWARD WITH
BROAD SOUTHWEST TO WEST-SOUTHWEST FLOW ALOFT STEERING A SERIES
WEATHER SYSTEMS INTO THE PACIFIC NORTHWEST. CONFIDENCE REMAINS
HIGH IN THE ARRIVAL OF ANOTHER ROBUST FRONTAL SYSTEM ON SUNDAY
INTO SUNDAY NIGHT.
AFTER A TRANSIENT RIDGE ON MONDAY ANOTHER SYSTEM LIKELY MOVES
OVERHEAD COME TUESDAY. AFTERWARDS, IT'S A RINSE AND REPEAT OF
THIS PATTERN WITH A TROUGH FEATURE MOVING WSW TO ENE INTO
WESTERN CONUS EVERY 24-48 HOURS THROUGH THE END OF THE WEEK.
WPC CLUSTERS STILL SHOW LITTLE VARIATION BETWEEN ENSEMBLE
MEMBERS RESOLVING THE LARGE SCALE PATTERN EVEN OUT PAST DAYS
SEVEN AND EIGHT. FINER DETAILS LIKE THE SURFACE LOW PRESSURE
PLACEMENT ASSOCIATED WITH A STRONG SYSTEM SLATED FOR THE
WEDNESDAY/THURSDAY TIME PERIOD WILL DETERMINE OUR IMPACTS
LOCALLY. FOR EXAMPLE, RIVER FLOODING DEPENDS ON OUR QPF
FORECAST, AND THE QPF FORECAST IS DEPENDENT ON THE LOW TRACK.
SAME GOES WITH DETERMINING POTENTIAL FOR STRONG WINDS.
CONFIDENCE STILL REMAINS LOW TO MODERATE FOR THESE IMPACTS. THE
LATEST HEFS GUIDANCE SUGGESTS A 15-35% CHANCE THAT RIVERS ALONG
THE COAST/COAST RANGE REACH AT LEAST MINOR FLOOD STAGE IN THE
NEXT 10 DAYS. WILL ALSO NOTE THAT THESE SYSTEMS LOOK RELATIVELY
WARM - WHILE SNOW LEVELS WILL FLUCTUATE BETWEEN 3500 TO 7000
FEET THROUGH NEXT WEEK, THE HIGHEST SNOW LEVELS WILL OCCUR
DURING FRONTAL PASSAGES.-ALVIZ/SCHULDT
AVIATION
INLAND TAFS ARE CURRENTLY ALL SEEING VFR CONDITIONS,
WHILE COASTAL TAFS ALTERNATE BETWEEN IFR/MVFR CIGS AS THE NEXT
FRONT BEGINS TO APPROACH. A VERY WEAK BAND OF MOISTURE IS
EXPECTED TO PUSH THROUGH AROUND 9-12Z FRI, BUT LITTLE TO NO
PRECIPITATION IS EXPECTED. COASTAL TAF SITES SHOULD IMPROVE BACK
TO VFR, WITH 80-90% CONFIDENCE IN VFR CIGS FOR THE REST OF THE TAF
PERIOD. AFTER THIS MOISTURE PASSES THROUGH THOUGH, SLIGHT
CLEARING OF CLOUD COVER COULD LEAD TO THE FORMATION OF SOME FOG IN
THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY. LIFR CONDITIONS WILL
BE POSSIBLE AT KSLE AND KEUG FROM AROUND 10Z ONWARDS, POTENTIALLY
LASTING THROUGH AROUND 18-20Z FRI. NORTHERN VALLEY TAF SITES
SHOULD SEE ENOUGH EAST WIND OUT OF THE COLUMBIA RIVER GORGE TO
KEEP FOG FROM FORMING.
AT AROUND 20Z FRI, A SLIGHTLY STRONGER FRONT PASSES THROUGH,
THOUGH IT SHOULD MOSTLY FALL APART BEFORE IT HITS THE INLAND
VALLEY. THAT SAID, RAIN CAN BE EXPECTED AT MOST TAF SITES, THOUGH
ALL TERMINALS SHOULD JUST REMAIN VFR. THIS SHOULD WIPE OUT ANY FOG
THAT FORMED IN THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY. WINDS
REMAIN FAIRLY MILD WHILE THIS PASSES THROUGH EVERYWHERE BUT KTTD,
WHICH CONTINUES TO SEE BREEZY EASTERLY FLOW THROUGH THE GORGE.
PDX AND APPROACHES...VFR THROUGHOUT THE PERIOD, WITH GRADUALLY
WEAKENING EASTERLY WINDS COMING FROM THE COLUMBIA RIVER GORGE.
LIGHT RAIN AT TIMES AFTER 20Z AS A WEAK FRONT PASSES THROUGH,
THOUGH CIGS REMAIN VFR THROUGHOUT. /JLIU
MARINE
GALE FORCE GUSTS ARE BEGINNING TO DISSIPATE ACROSS THE
COASTAL WATERS THIS AFTERNOON AS A WEAK COLD FRONT CLEARS THE
AREA. WINDS WILL BACK SOUTHEASTERLY THIS EVENING AND WEAKEN TO
10-20 OVERNIGHT IN THE WAKE OF THE FRONT, BUT A 8-10 FT WESTERLY
SWELL WILL MAINTAIN SMALL CRAFT ADVISORY LEVEL SEAS THROUGH THE
NIGHT. ANOTHER FRONT WILL ARRIVE FRIDAY MORNING, BRINGING ANOTHER
ROUND OF GALES TO THE OUTER ZONES THROUGH FRIDAY AFTERNOON. THE
PATTERN REMAINS VERY ACTIVE THIS WEEKEND AND THROUGH THE END OF
NEXT WEEK AS LOW PRESSURE REMAINS OVER THE NE PACIFIC, SENDING A
PARADE OF FRONTS THROUGH THE WATERS EVERY 24 HRS OR SO. PERIODS OF
GALES ARE LIKELY BOTH SATURDAY AND SUNDAY, WITH MODEL GUIDANCE
DEPICTING AROUND A 40% CHANCE FOR STORM FORCE GUSTS IN THE OUTER
WATERS ON SUNDAY. AS NUMEROUS FRONTAL SYSTEMS CONTINUE TO
TRAVERSE THE WATERS EARLY NEXT WEEK, A LARGE AND ENERGETIC
WESTERLY SWELL WILL CONTRIBUTE TO LARGE AND CHAOTIC SEAS GOING
FORWARD. EXPECT SEAS TO REMAIN IN THE MID TO UPPER TEENS FROM
SATURDAY THROUGH MUCH OF THE NEXT WEEK, WITH SEAS POTENTIALLY
BUILDING INTO THE 20-24 FT RANGE BY MONDAY. MARINERS SHOULD BE
PREPARED FOR CONTINUED HAZARDOUS CONDITIONS THROUGH THE END OF
NEXT WEEK. /CB
BEACH HAZARDS
A LARGE, ENERGETIC WESTERLY SWELL WILL BUILD
OVER THE COASTAL WATERS AND BEGIN IMPACTING THE COASTLINE LATE
THIS WEEKEND INTO EARLY NEXT WEEK. SEAS IN EXCESS OF 20 FEET WITH
A PERIOD OF 20 SECONDS COULD RESULT AS BREAKING WAVES APPROACHING
30 FEET IN THE SURF ZONE. BEACHGOERS SHOULD BE PREPARED FOR
DANGEROUS SURF CONDITIONS AND LARGE WAVES RUNNING FAR UP ONTO THE
BEACH BEGINNING LATE SUNDAY AND CONTINUING THROUGH TUESDAY OF
NEXT WEEK. /CB
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 6 AM PST SATURDAY FOR PZZ251>253.
SMALL CRAFT ADVISORY UNTIL 6 AM PST FRIDAY FOR PZZ271>273.
GALE WARNING FROM 6 AM TO 3 PM PST FRIDAY FOR PZZ271>273.
WWW.WEATHER.GOV/PORTLAND
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