705
FXUS66 KPQR 202322
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
322 PM PST THU FEB 20 2025
SYNOPSIS
HIGH PRESSURE DISSIPATES LATE FRIDAY AS A SERIES OF
FRONTAL SYSTEMS MOVE OVER THE PACIFIC NORTHWEST. THE FIRST WILL
ARRIVE ON SATURDAY NIGHT, WITH A SECOND ON SUNDAY. THESE SYSTEMS
WILL BE VERY WET AND BRING HEAVY RAINFALL. LOCALIZED FLOODING,
ESPECIALLY ALONG THE COAST, IS POSSIBLE. GUSTY WINDS WITH THIS
SYSTEM ARE EXPECTED. ANOTHER ACTIVE WEATHER DAY ON MONDAY THOUGH
CONFIDENCE IS LOW AT THIS TIME.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
HIGH PRESSURE TODAY HAS
LEAD TO PARTLY CLOUDY SKIES WITH SOME SUN BREAKS. LIGHT WINDS
AND ABOVE NORMAL TEMPERATURES HAVE DOMINATED THE FORECAST AREA
TODAY. OVERNIGHT, THERE WILL STILL BE CLOUD BREAKS WHICH COULD
PROMOTE THE DEVELOPMENT OF FOG. THIS IS COMMON WHEN WE SEE A
WEAK RIDGE TRAILING AFTER A FRONT LIKE WE HAD EARLIER THIS WEEK.
CONFIDENCE IS LOW AS IT WILL GREATLY DEPEND ON TOTAL CLOUD
COVER.
ON FRIDAY THE RIDGE WILL ERODE AS THE INITIAL STAGES OF THE MAIN
FRONTAL BANDS ADVANCES TOWARDS THE AREA. THIS FRONT IS WEAKER
THAN THOSE ARRIVING ON SATURDAY, BUT STEMS FROM THE SAME MAIN
LOW PRESSURE SYSTEM IN THE NORTHEAST PACIFIC. WILL SEE RAIN
BEGIN IN THE LATE AFTERNOON/EVENING WITH A FOCUS ON THE COAST.
INLAND AREAS, WITHIN THE WILLAMETTE VALLEY FOR EXAMPLE, WILL SEE
LESS RAIN INITIALLY BUT IT WILL SET THE STAGE FOR THE NEXT
WEATHER SHIFT. SOUTHERLY WINDS WILL INCREASE ALONG THE COAST
WITH THE ONSET OF THIS FRONT. THE BEACHES AND HEADLANDS COULD
SEE WIND GUSTS UPWARDS OF 40 MPH WHILE MORE INLAND SITES WILL BE
AROUND 25-30 MPH. IF THE SIDES ARE SLIGHTLY MORE SOUTHEASTERLY,
THESE WINDS WILL BE LESS. PRECIPITATION WILL RANGE FROM AROUND
0.05-0.20 IN THE VALLEY, NEAR 0.25-0.40 ALONG THE COAST AND
SIMILAR VALUES IN THE HIGHER TERRAIN OF THE COAST RANGE AND
CASCADES. ULTIMATELY THIS IS A FAIRLY "NORMAL" WEATHER PATTERN
FOR WINTER. -MUESSLE
LONG TERM...SATURDAY THROUGH WEDNESDAY
SATURDAY IS ACT ONE OF
THE WEATHER SYSTEMS. WHILE INDIVIDUAL WARM FRONTS, CUMULATIVELY
THEY WILL HAVE THE IMPACT OF AN ATMOSPHERIC RIVER. BASED ON
ENSEMBLE GUIDANCE, IT IS SHAPING UP TO BE WHAT IS CONSIDERED A
"MODERATE" ATMOSPHERIC RIVER THOUGH IT WILL BE OVER AN EXTENDED
PERIOD OF TIME (SATURDAY AND SUNDAY). THE TWO BIG WEATHER
FACTORS OVER BOTH DAYS TO LOOK AT ARE THE A) RAINFALL AMOUNTS,
AND B) WIND. LET'S START WITH RAIN.
THE FIRST FRONTAL SYSTEM WILL ARRIVE SATURDAY AFTERNOON AND WILL
BE QUITE ROBUST AT FIRST. THERE IS SOME DISCONTINUITY WITH THE
TIMING OF THE FRONT WITH SOME MODELS, LIKE THE NAM, BEING MUCH
FASTER WITH THE ONSET WHILE THE GFS IS MORE DELAYED. RAINFALL
WITH THIS FIRST SYSTEM RANGES FROM 0.50-1.75 INCHES (10TH TO
90TH PERCENTILE). THE AREAS OF MOST FOCUS ARE ALONG THE COAST,
COAST RANGE AND THE CASCADES. WITHIN THE INLAND LOWER ELEVATIONS
THE PROBABILITY OF 1 INCH OF RAIN IN THE 24 HOURS ENDING AT 10
PM SATURDAY IS AROUND 25%. THIS IS LIKELY DUE TO A SLIGHT
SOUTHWESTERLY FLOW WHICH WOULD PROMOTE A WEAK RAIN SHADOW
EFFECT. THE SECOND COMPONENT IS WIND SPEEDS. ALONG THE COAST WE
WILL SEE OUR STRONGEST WINDS. THE BEACHES AND HEADLANDS WILL BE
THE MOST SUSCEPTIBLE WITH GUSTS UP TO 45 MPH. HOWEVER, THERE IS
AROUND A 40% CHANCE OF GUSTS GREATER THAN 50 MPH, AND AROUND A
10% CHANCE OF WIND GUSTS EXCEEDING 60 MPH ALONG THE BEACHES.
INLAND COASTAL LOCATIONS WILL NOT SEE QUITE AS STRONG OF WINDS,
BUT THEY WILL STILL BE ELEVATED.
ACT TWO WILL BE THE SECOND FRONT THAT ARRIVES ON SUNDAY. NOW
THIS SYSTEM APPEARS TO BE EVEN MORE ROBUST THAN THAT OF THE
SATURDAY SYSTEM IN THE FORM OF RAINFALL TOTALS THOUGH THE FRONT
IT SELF IS NOT AS STRONG. THE LOW PRESSURE SYSTEM THAT IS
FUELING THESE FRONTS WILL CONTINUE TO DROP SOUTH AND TIGHTEN THE
NORTH-SOUTH PRESSURE GRADIENT. WINDS WILL BE DUE SOUTH AND BUILD
UPON THE MIXING OF THE PREVIOUS DAYS WINDS. GUSTS ALONG THE
COAST ONCE AGAIN WILL BE STRONG, BUT THE DIFFERENCE WILL BE
INLAND. BASED ON THE NBM, MAXIMUM WIND GUSTS ON SUNDAY WILL
RANGE FROM 20-30 MPH. HOWEVER, CONFIDENCE IS LOW AS IT WILL
GREATLY DEPEND ON HOW THAT LOW ADVECTS. IF IT MOVES FURTHER
SOUTH (THE GFS SOLUTION), THEN WINDS WILL BE WEAKER THAN THE
ECMWF WHICH IS TAKING A MORE NORTHERLY TRACK. AT THIS POINT, THE
NORTHERLY TRACK IS CONSISTENT WITH THE OTHER GLOBAL MODELS SO
TRENDING ON THE STRONGER SIDE FOR WINDS. WINDS ON THE COAST WILL
BE SIMILAR TO THAT OF SATURDAY. AS FOR RAIN, AN ADDITIONAL 1.5-3
INCHES ARE POSSIBLE ALONG THE COAST, WITH 1-1.5 INCHES INLAND.
SNOW LEVELS WILL RISE TO 6000 FT OR MORE WHICH MEANS THAT
PRECIPITATION WILL FALL AS RAIN. THIS RAIN ON RECENT SNOWFALL
COULD BECOME PROBLEMATIC FOR LANDSLIDES IN AREAS, ESPECIALLY IN
AREAS WITH WEAKENED TREES.
DESPITE THE DIFFERENCES IN THESE TWO SYSTEMS, THE OVERALL
IMPACTS WILL BE COMBINED WITH THE THREAT OF LOCALIZED PONDING
AND URBAN FLOODING, AND RIVER FLOODING - ESPECIALLY ALONG THE
COAST). SEE THE HYDROLOGY SECTION BELOW FOR MORE DETAILS.
AS WE MOVE INTO LATER IN THE WEEK SOME MODELS ARE SHOWING A
DEEPENING LOW PRESSURE SYSTEM MOVING INTO THE NORTH PACIFIC FROM
THE SOUTH. THIS SYSTEM WOULD BRING EVEN MORE RAIN, BUT GUSTIER
WINDS. ENSEMBLE MODELS ARE STRUGGLING TO REALIZE THIS SYSTEM,
BUT BASED ON METEOGRAMS, THE MOST LIKELY RANGE (25-75TH
PERCENTILE) IS ANYWHERE FROM 30-45 MPH INLAND, AND UP TO 65 MPH
ALONG THE COAST. CONFIDENCE IS INCREDIBLY LOW AT THIS POINT AS
THE MAIN LOW PRESSURE CENTER IS SPLATTERED OVER THE NORTHEAST
PACIFIC. AS WE SEE HOW THESE WARM FRONTS SHAKE OUT, WE WILL HAVE
A BETTER IDEA FOR MONDAY. BUT, NOW IS THE TIME TO PREPARE FOR
THE POTENTIAL STRONG WINDS. -MUESSLE
AVIATION
HIGH PRESSURE TRANSITING THE REGION WILL YIELD LARGELY
VFR FLYING CONDITIONS WITH DIMINISHING LOW CLOUD COVERAGE AT 2-5
KFT AND UNRESTRICTED VIS. MVFR LOW STRATUS ALONG THE COAST WITH
AREAS OF DRIZZLE OR MIST MAY CONTINUE INTO THIS AFTERNOON, MOST
LIKELY AT ONP WHERE BRIEF IFR CONDITIONS ARE POSSIBLE. SOUTHERLY
TO SOUTHWESTERLY FLOW EARLY IN THE PERIOD WILL DEVELOP AN EASTERLY
COMPONENT AFTER 00-06Z FRIDAY AS HIGH PRESSURE SHIFTS INLAND,
RESULTING IN SOUTHEASTERLY TO EASTERLY FLOW ALONG THE COAST AND
NORTHEASTERLY TO EASTERLY AT INLAND TERMINALS. WINDS ACROSS THE
REGION LOOK TO REMAIN AT OR BELOW 5 KT, ASIDE FROM PDX/TTD WHERE
EASTERLY FLOW OUT OF THE GORGE WILL REACH 6-12 KT AFTER 12Z FRI.
LIGHT WINDS IN COMBINATION WITH CLEARING SKIES MAY RESULT IN FOG
OR MIST AT SLE/EUG AFTER 09Z FRI WITH MVFR/IFR VIS POSSIBLE.
PDX AND APPROACHES...HIGH PRESSURE WILL SEE VFR CONDITIONS
CONTINUE TO PREVAIL THROUGHOUT THE PERIOD. LOW-VFR CLOUD BASES AT
3-5 KFT WILL PERSIST WHILE COVERAGE DECREASES INTO THIS AFTERNOON.
LOW CHANCES, 10-20%, FOR IFR FOG/MIST AFTER 06-08Z FRI. -PICARD
MARINE
A BRIEF PERIOD OF BENIGN CONDITIONS ACROSS ALL WATERS IS
EXPECTED THROUGH TONIGHT AS HIGH PRESSURE LINGERS. HOWEVER, THIS
WILL BE SOMEWHAT SHORT LIVED AS A SERIES OF SYSTEMS WILL BRING
BACK ELEVATED WINDS AND SEAS FRIDAY AND SATURDAY. ON FRIDAY, A
FRONTAL SYSTEM WHICH IS ANCHORED TO A LOW PRESSURE SYSTEM MAKING
LANDFALL AROUND HAIDA GWAII, LOOKS TO BRING STRONG SMALL CRAFT OR
HAZARDOUS SEAS ACROSS ALL WATERS. EXPECT SOUTHERLY WINDS WITH
GUSTS UP TO 30 KT AND SEAS BUILDING TOWARDS 12 TO 15 FT AROUND 14
SECONDS. GIVEN THAT THERE IS SOME UNCERTAINTY AS IS SMALL CRAFT OR
HAZARDOUS SEA CONDITIONS WILL MANIFEST, HAVE ISSUED A HAZARDOUS
SEAS WATCH STARTING FRIDAY MORNING. THE SECOND, MUCH STRONGER
SYSTEM ON SATURDAY WILL LIKELY BRING SOUTHERLY GALE GUSTS UP TO 45
KT ACROSS ALL WATERS AS WELL AS MAINTAINING SEAS IN THE 12 TO 15
FT RANGE.
AS THE START OF THE UPCOMING WEEK APPROACHES, WINDS WILL SUBSIDE,
BUT SEAS WILL CONTINUE TO BE ELEVATED. HOWEVER, MODELS ARE SHOWING
A 980MB LOW MOVING TOWARDS VANCOUVER ISLAND HAS THE POTENTIAL TO
BRING AT A MINIMUM OF GALES INTO OUR WATERS WITH AROUND A 35%
PROBABILITY OF STORM FORCE CONDITIONS. SEAS ARE ALSO EXPECTED TO
BUILD TOWARDS 17 TO 19 FT WITH A 25% PROBABILITY FOR 20 FT SEAS.
WILL CONTINUE TO MONITOR THE SITUATION AS THE TRACK OF THE MONDAY
LOW WILL DICTATE WHERE THE STRONGEST CONDITIONS MANIFEST. /42
HYDROLOGY
AN SERIES OF FRONTAL SYSTEMS WILL BRING HEAVY
RAINFALL TO NORTHWEST OREGON AND SOUTHWEST WASHINGTON THIS
WEEKEND. RAIN WILL BEGIN SATURDAY AFTERNOON, AND INTENSIFY
OVERNIGHT THROUGH SUNDAY. THIS WILL LEAD TO RISES ON RIVERS AND
CREEKS, ESPECIALLY ALONG THE COAST ON FEBRUARY 22ND THROUGH THE
23RD. MAIN STEM RIVERS MAY BE DELAYED TO RESPOND, AND FLOODING
MAY OCCUR BEYOND THIS TIME FRAME.
THERE IS AROUND A 25% CHANCE OF THE WILSON RIVER, THE GRAYS RIVER,
AND OTHER LOCALIZED QUICK RESPONDING COASTAL RIVERS OF REACHING
MINOR FLOOD STAGE ON SUNDAY. CONFIDENCE IN FLOODING IS LOW AS THE
LOCATION OF HEAVIEST PRECIPITATION WILL GREATLY DEPEND ON WHERE THE
WARM FRONT SETS UP. IN THE CASE THAT THIS SYSTEM OVER PERFORMS, MORE
WIDESPREAD FLOODING IS POSSIBLE.
ALONG THE CASCADES HEAVY RAINFALL IS EXPECTED. HEAVY RAIN COMBINED
WITH RECENT SNOW WILL ELEVATE THE LANDSLIDE RISK.
HEAVY RAINFALL MAY ALSO LEAD TO PONDING OF WATER, GENERAL LOWLAND
FLOODING, AND LOCALIZED URBAN FLOODING, ESPECIALLY IN LOW-LYING
AREAS OR OTHER POOR-DRAINAGE AREAS. HEAVY RAINFALL WILL ALSO
INCREASE THE POTENTIAL FOR LANDSLIDES IN AREAS OF STEEP TERRAIN AND
DEBRIS FLOWS OVER AREAS THAT HAVE BEEN BURNED BY WILDFIRES OVER THE
PAST FEW YEARS.
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...HAZARDOUS SEAS WARNING FROM 7 AM FRIDAY TO 7 AM PST SATURDAY
FOR PZZ210-251>253-271>273.
GALE WATCH FROM SATURDAY MORNING THROUGH LATE SATURDAY NIGHT
FOR PZZ210-251>253-271>273.
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