633
FXUS66 KPQR 172320
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
320 PM PST SUN NOV 17 2024
SYNOPSIS
A PROLONGED PERIOD OF ACTIVE WEATHER HAS FINALLY
BEGUN ACROSS PACIFIC NORTHWEST. WE’LL START OFF WITH IMPACTS
FOCUSED ON HEAVY SNOW GENERALLY ABOVE 2,000 FT WHICH IS NOW IN
PROGRESSES ACROSS THE CASCADES PASSES AS WELL AS VALLEY RAIN
HEADED THROUGH THEY DAY TUESDAY. OUR ATTENTION THEN PIVOTS TO
AN ATMOSPHERIC RIVER EVENT LATE TUESDAY THROUGH FRIDAY/SATURDAY
TIME-FRAME WITH GUIDANCE CONTINUING TO NARROW IN ON THE OVERALL
SET-UP. RIVER FLOODING, URBAN FLOODING, AND LOCALLY STRONG WINDS
(COAST) ARE THE PRIMARY IMPACTS WE’RE MONITORING WITH THE
HIGHEST CONFIDENCE IN ONLY THE LATTER VARIABLE. AT LEAST FOR NOW
IT APPEARS THE HEAVIEST RAIN THROUGH WEDNESDAY NIGHT REMAINS IN
SOUTHERN OREGON AND NORTHERN CALIFORNIA BUT WE’LL NEED TO WATCH
CLOSELY LATER IN THE WEEK AS IT SWINGS NORTHWARD INTO NW OREGON
AND SW WASHINGTON. CONFIDENCE IN EXPECT PRECIPITATION AMOUNTS
ARE STILL ONLY LOW TO MODERATE AT THIS TIME.
DISCUSSION
TODAY THROUGH SATURDAY…CURRENTLY THE COLD FRONTAL
BOUNDARY HAS PASSES TO OUR EAST WITH A POST-FRONTAL SHOWER
REGIME DRIVEN BY BROAD LONG FETCH NORTHWESTERLY FLOW ALOFT IN
PLACE ACROSS THE REGION. SNOW-LEVEL HAVE BEEN QUICK TO RESPOND
AND AS OF THE MID-AFTERNOON HOURS HAVE CRASHED BELOW THE
MOUNTAIN PASSES AS INDICATED BY TRAFFIC CAMERAS. MODERATE TO
HEAVY SNOW IS EXPECTED TONIGHT INTO MONDAY OVER THE CASCADES AND
COAST RANGE ABOVE 2000 FEET, HEAVIEST ABOVE 2500 FEET, AS WAVES
OF FREQUENT SNOW SHOWERS CONTINUE TO PRODUCE PRECIPITATION
ACROSS THE AREA. LIGHTER SNOW COULD FALL DOWN TO 1500 FEET
OVERNIGHT, GENERALLY MIXED IN WITH HEAVIER RAIN SHOWERS BUT
ACCUMULATION WILL BE SLUSHY AND MAINLY ON GRASS/VEGETATION.
LOOKING AT THE LATEST GUIDANCE PROBABILITIES FOR 24-HR SNOW
AMOUNTS OVER ONE FOOT CONTINUE TO HOLD NEAR 95-100% ACROSS ALL
OF THE CASCADE PASSES WITH A 40-60% CHANCE FOR SNOW AMOUNTS OF
18 INCHES OR MORE THIS EVENING THROUGH 4PM MONDAY AT SANTIAM AND
WILLAMETTE PASS; CLOSE TO 35% US-26 NEAR GOVERNMENT CAMP. GIVEN
THE CURRENT STATE OF CONDITIONS OVER THE CASCADES THIS
AFTERNOON AND HIGH CONFIDENCE THEIR FURTHER DEGRADATION HEADED
INTO MONDAY MORNING, ANYONE PLANNING TO TRAVERSE ACROSS THE
PASSES NEEDS TO PREPARE FOR WINTER-LIKE TRAVEL CONDITIONS. A
WINTER STORM WARNING REMAINS IN EFFECT ABOVE 2000 FEET FOR THE
CASCADES. IT’S CERTAINLY WORTH HIGHLIGHTING AS WELL THE HIGHER
PORTIONS OF THE COAST RANGE WILL LIKELY SEE SNOW, ESPECIALLY IN
HEAVIER SHOWER BANDS WHERE IT MAY MIX DOWN TO 1,300-1,500 FT AT
TIMES. STILL, IMPACTS BEYOND SOME MINOR SLUSH-UPS FOR SECTIONS
OF HIGHWAY NEAR 1,500FT THE BEST AREAS FOR SNOWFALL STAY ABOVE
2000FT WHERE A WINTER WEATHER ADVISORY IN IN EFFECT. SNOW LEVELS
THEN BOTTOM OUT MONDAY NIGHT INTO TUESDAY MORNING WITH A MORE
PREDOMINATE EASTERLY FLOW FROM THE SURFACE TO 850MB NEAR THE
CASCADES ANY LEFTOVER SHOWER ACTIVITY MAY FALL AS WET SNOW IN
SPOTS LIKE THE HOOD RIVER VALLEY ABOVE 1000FT – LIMITED IMPACTS.
THROUGH MONDAY NIGHT INTO EARLY TUESDAY MORNING THERE’LL ALSO
BE A CHANCE (15-35%) OF THUNDERSTORMS MAINLY LONG THE WHERE CAPE
VALUES OF 200-400 J/KG EXTENT UP IN THE -10 TO -20C MIXED
PHASED REGION OF THE ATMOSPHERE THAT CAN SUPPORT
ELECTRIFICATION. CAN'T COMPLETELY RULE OUT A FEW CELLS
STRENGTHENING ENOUGH INLAND TO PRODUCE A FEW LIGHTNING STRIKES
TOO BUT FOR THE MOST PART JUST EXPECTING PERIODS OF HEAVIER RAIN
SHOWERS. HEAVIER SHOWERS IN ADDITION TO THE PRIOR RAINFALL MAY
CAUSE MINOR URBAN FLOODING IN LOW-LYING AREAS WITH POOR DRAINAGE
BOTH ALONG THE COAST AND INLAND, ESPECIALLY IN LOCATIONS WITH
RECENTLY FALLEN LEAVES CLOGGING DRAINS.
FOR LATE TUESDAY INTO THE END OF THE WEEK, ENSEMBLE GUIDANCE
(GEFS, EURO, AND CMC) CONTINUES TO INDICATE THE WET PATTERN
PERSISTING WITH FAIRLY HIGH CONFIDENCE IN AN ATMOSPHERIC RIVER
EVENT IMPACTING THE WEST COAST. HOWEVER, THESE ENSEMBLE SYSTEM
HAVE TRENDED DOWNWARD IN REGARDS TO QPF FOR US LOCALLY DUE TO
THE MAIN AXIS OF MOISTURE GETTING AIMED PRIMARILY SOUTH OF THE
AREA INTO SOUTHWEST OREGON AND NORTHERN CALIFORNIA – A CHANGE
FOR YESTERDAY. AS FAR AS THE OVERALL PROGRESSION IS CONCERNED
DETERMINISTIC AND ENSEMBLE GUIDANCE ARE IN AGREEMENT SHOWING AN
IMPRESSIVE LOW PRESSURE DISTURBANCE UNDERGOING EXPLOSIVE
CYCLOGENESIS IN THE EASTERN PACIFIC WITH A CENTRAL PRESSURE
FALLING ROUGHLY 30-40MB IN 24 HRS LATE MONDAY THROUGH TUESDAY.
WHILE THE CENTER OF THIS LOW AND THE HIGHEST WINDS ARE SET TO
MOVE TOWARDS VANCOUVER ISLAND AND THEN STALL OVER THE PACIFIC,
IT WILL GUIDE AN INITIAL SURGE OF MOISTURE AND EXTREMELY STRONG
COASTAL JET TOWARDS THE AREA LATE TUESDAY. CONFIDENCE HAS GROWN
THIS FORECAST PRODUCT CYCLE FOR WIND GUSTS EXCEEDING 58 MPH
ALONG THE OREGON COAST TUESDAY EVENING, WITH A MAJORITY OF EPS
MEMBERS SHOWING GUSTS IN THE 50-60 MPH RANGE FOR SPOTS LIKE
NEWPORT. ALTHOUGH GIVEN THE ORIENTATION OF BOTH THE LOW LEVEL
JET AND SURFACE WINDS, NOT AS CONFIDENT IN GUSTS EXCEED 58MPH
NORTH OF ASTORIA. A HIGH WIND WATCH WAS ISSUED FOR THE CENTRAL
AND NORTHERN OREGON COAST PRIMARILY FOR THE BEACHES AND
HEADLANDS. SHOULD THE STRONG SURFACE LOW OFF THE COAST ADJUST A
TOUCH FURTHER EAST THIS HIGHLIGHT MAY NEED TO BE ADDED TO THE
SOUTH WASHINGTON COAST TOO.
ONCE WE GET INTO WEDNESDAY AND THURSDAY THE GEFS/EPS GUIDANCE
KEEPS BULKS OF THE ATMOSPHERIC RIVER TO OUR SOUTH WITH IVT
VALUES NOW ONLY AROUND 200-300 KG/MS STAYING OVERHEAD. IT’LL BE
A LITTLE SOGGY FOR SPOTS LIKE THE COAST RANGE AND PORTIONS OF
THE CASCADES/CASCADE FOOTHILLS WHERE SW TO NE UPSLOPE FLOW CAN
TAKE ADVANTAGE OF THIS MOISTURE. STILL IT LOOKS LIKE WE’RE IN A
MUCH BETTER SPOT THAN YESTERDAY AS FAR AS RAINFALL TOTALS ARE
CONCERNED. THE LATEST NBM MEAN FORECAST WOULD STILL LIKELY STILL
LEAD TO SOME IMPACTS, ESPECIALLY WITH THE RECENT SNOWFALL DOWN
TO 2000FT, PROJECTING 3.5-7 INCHES IN THE MOUNTAINS, 4-6 INCHES
AT THE COAST, AND 1.5-2.5 INCHES FOR THE INTERIOR LOWLANDS OVER
A 72 HR PERIOD ENDING 4AM FRIDAY MORNING. HOWEVER IT’LL BE THE
END OF THIS PERIOD INTO THE WEEKEND WE’LL STILL HAVE TO KEEP A
VERY CLOSE EYE ON AS MODELS DO SHOW THE AXIS OF THE MOISTURE
TEMPORARILY SHIFTING NORTHWARD OVERHEAD IN RESPONSE TO A
SECONDARY LOW PRESSURE SLING-SHOTING AROUND THE SOUTHEASTERN
PERIPHERY OF THE BROADER LOW PRESSURE FEATURE OVER THE PACIFIC.
REGARDLESS OF THE EXACT STRENGTH/DURATION OF THE ATMOSPHERIC
RIVER AND EXACT RAIN AMOUNTS, FLOODING IS A POSSIBILITY IN LOW-
LYING URBAN AREAS AS WELL AS FOR OUR “FLASHIER” RIVERS IN AND
ALONG THE COAST/COAST RANGE LATE WEEK INTO THE WEEKEND. THE
LATEST HEFS GUIDANCE IS SHOWING COASTAL RIVERS HAVING A 5-25%
CHANCE OF REACHING MINOR FLOOD STAGE WITHIN THE NEXT TEN DAYS,
HIGHEST AT THE WILSON RIVER NEAR TILLAMOOK AND SILETZ RIVER AT
SILETZ – A DOWNTREND FROM THE LAST FEW DAYS INDICATIVE OF THE
RECENT CHANGE TO A SOUTHERLY MOISTURE TRACK.
AVIATION
THE FRONT CONTINUES TO MOVE THROUGH THE AREA, WITH
RAIN SLOWLY TRANSITIONING TO SHOWERS OVER THE COURSE OF SUNDAY
AFTERNOON. CURRENTLY THE AREA IS MOSTLY SEEING VFR, THOUGH BRIEF
OCCASIONAL DROPS TO MVFR ARE OCCURRING WITH STRONGER PASSING
SHOWERS. SOUTHERLY WINDS UP TO 20KT INLAND (25KT AT THE COAST)
WILL SLOWLY DECREASE THROUGHOUT THE AFTERNOON AND EVENING, DOWN
TO AROUND 7-10 KT BY 10Z MON. A SECOND WAVE OF MOISTURE PUSHES
THROUGH AROUND THAT TIME AS WELL (10Z MON), AND HIGH RES MODELS
SUGGEST AROUND A 40-50% CHANCE OF MVFR AT THAT TIME.
PDX APPROACHES...GENERALLY VFR EXPECTED FOR THE REST OF DAYTIME
HOURS, THOUGH BRIEF DROPS TO MVFR WILL BE POSSIBLE IF A HEAVIER
SHOWER PASSES OVERHEAD. WINDS CURRENTLY GUSTING UP TO ABOUT 20 KT,
AND THESE WILL DECREASE VERY SLOWLY, BOTTOMING OUT AROUND 11Z MON
AT 5-7 KT. SLIGHT (40%) CHANCE OF MVFR CONDITIONS RE- DEVELOPING
AROUND 07Z MON, BUT THIS RETURN TO VFR AROUND SUNRISE ON MONDAY.
/JLIU
MARINE
A STRONG WNW SWELL CONTINUES THE REST OF TODAY INTO
MONDAY, RAMPING UP WAVE HEIGHTS TO THE UPPER TEENS BY AROUND
MIDNIGHT SUNDAY NIGHT. HAZARDOUS SEAS REMAIN ON TRACK, WITH
CURRENT WAVE HEIGHTS AROUND 12 FT AT 10 SECONDS (STILL
INCREASING). THESE CONDITIONS CONTINUE UNTIL MONDAY EVENING, WHEN
SEAS SLIGHTLY COME DOWN TO THE LOW TEENS THROUGH TUESDAY MORNING.
ANOTHER STORM APPROACHES THE WATERS TUESDAY, BRINGING POSSIBLE
STORM FORCE WINDS, WITH CURRENT GUIDANCE SHOWING AROUND A 80%
CHANCE OF SOUTHERLY WINDS 54 KT OR HIGHER BEGINNING TUESDAY
AFTERNOON. STORM WATCH REMAINS ON TRACK. OF NOTE, THE MOST RECENT
GUIDANCE SHOWS AROUND A 20% CHANCE OF HURRICANE FORCE WINDS (64
KTS OR HIGHER). STILL VERY LOW PROBABILITY FOR NOW, AND WILL KEEP
TABS ON IT AS WE GET CLOSER. WITH STRONG WIND WAVES AND SWELL
REMAINING ELEVATED, SEAS WILL BE QUITE HIGH, WITH CURRENT
FORECASTED PEAK WAVES AT 24-27 FT AT 13 SECONDS TUESDAY EVENING.
WIND GUSTS UP TO 55-60 KT DURING THAT TIME. /JLIU
BEACH HAZARDS
HIGH SNEAKER WAVE THREAT REMAINS IN PLACE
THROUGH TONIGHT DUE TO AN INCREASING WESTERLY SWELL WITH A
DOMINANT WAVE PERIOD AROUND 10-14 SECONDS. WITH THE PERIGEAN
SPRING TIDES UNDERWAY (COMMONLY REFERRED TO AS "KING TIDES"), IT
IS A GOOD IDEA TO TAKE EXTRA PRECAUTION ON BEACHES. WAVES CAN RUN
UP SIGNIFICANTLY FARTHER ON A BEACH THAN NORMAL, INCLUDING OVER
ROCKS AND JETTIES. SNEAKER WAVES CAN SUDDENLY KNOCK PEOPLE OFF OF
THEIR FEET AND QUICKLY PULL THEM INTO THE FRIGID OCEAN WHICH MAY
LEAD TO SERIOUS INJURY OR DROWNING. THE SNEAKER WAVE THREAT LOOKS
TO REMAIN HIGH THROUGH EARLY NEXT WEEK.
MINOR TIDAL OVERFLOW REMAINS POSSIBLE AROUND HIGH TIDE MONDAY AS
THE PERIGEAN SPRING TIDES CONTINUE, BUT MONDAY LOOK TO REMAIN JUST
BELOW COASTAL FLOOD ADVISORY CRITERIA. NO ADVISORY HAS BEEN
ISSUED AS A RESULT, BUT SOME MINOR ISOLATED TIDAL OVERFLOW COULD
OCCUR. IMPACTS INCLUDE FLOODING UP TO A FEW INCHES ABOVE GROUND
LEVEL, IMPACTING PORTIONS OF HIGHWAY 101 NEAR RAYMOND AND LOW
LYING AREAS NEAR BAYS, SLOUGHS AND LOWER REACHES OF THE COASTAL
RIVERS. ANY FLOODING WOULD BE VERY MINOR AND SHORT- LIVED (AROUND
ONE HOUR OR LESS). FROM TUESDAY ONWARDS, TIDES DROP, AND NO MORE
COASTAL FLOODING IS EXPECTED.
PQR WATCHES/WARNINGS/ADVISORIES
OR...COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR ORZ101-
102.
WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM PST
MONDAY FOR ORZ106.
WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 10 PM PST
MONDAY FOR ORZ124-125.
WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR ORZ126>128.
WA...COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR WAZ201.
WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR WAZ211.
PZ...HAZARDOUS SEAS WARNING UNTIL 7 PM PST MONDAY FOR PZZ210-251>253-
271>273.
STORM WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY MORNING FOR
PZZ251>253-271>273.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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