494
FXUS66 KPQR 210002
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
402 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 SHIFTING EASTWARD OUT OF THE REGION
WILL YIELD CONTINUED LARGELY VFR FLYING CONDITIONS WITH FEW-SCT
LOW CLOUDS AT 2-5 KFT AND UNRESTRICTED VIS. MVFR LOW STRATUS AT
AST LOOKS TO CONTINUE THROUGH THIS EVENING, WHILE LOW-LEVEL
CLEARING WITH INCREASING COVERAGE OF HIGH CIRRUS ELSEWHERE
OVERNIGHT. GENERALLY LIGHT AND VARIABLE WINDS EXPECTED AT ALL
TERMINALS THROUGH TONIGHT, ASIDE FROM EASTERLY GORGE WINDS OF
5-10 KT AT PDX/TTD.
TONIGHT, CLEARING AND CALM TO LIGHT WINDS MAY ALLOW FOR AREAS OF
FOG WITHIN THE WILLAMETTE VALLEY, MOST LIKELY AFTER 08-09Z FRI
AT EUG/SLE AND ALSO POSSIBLY UAO/HIO. MVFR/IFR VIS ARE POSSIBLE
WITHIN FOG, WITH IFR FAVORED AT EUG/SLE WHERE FOG CHANCES ARE
ELEVATED. IF HIGH CIRRUS COVERAGE MOVES IN MORE QUICKLY, CHANCES
FOR FOG WILL BE LESSENED AS RADIATIVE COOLING IS STYMIED.
OTHERWISE, SOUTHERLY TO SOUTHEASTERLY FLOW INCREASES AS RAIN
SHOWERS APPROACH FROM THE NORTHWEST LATE IN THE PERIOD, WITH
FLYING CONDITIONS MOST LIKELY IMPACTED BY MVFR VIS AT AST AFTER
21Z FRI.
PDX AND APPROACHES...VFR FLYING CONDITIONS EXPECTED TO PERSIST
INTO TONIGHT WITH FEW-SCT LOW CLOUD COVERAGE AT 2-4 KFT AND
UNRESTRICTED VIS. LOW CLOUDS COVERAGE WILL TREND DOWNWARD WHILE
HIGH CLOUDS AT 10-20 KFT INCREASE FROM THE NORTHWEST THROUGH
TONIGHT, WHILE EASTERLY FLOW OUT OF THE GORGE CONTINUES AT 5-10
KT. HIGH CLOUDS WILL MITIGATE THE RISK FOR ANY PATCHY FOG
DEVELOPMENT OVERNIGHT, BUT THERE REMAINS A LOW CHANCE, 10-20%,
FOR IFR FOG/MIST TO DEVELOP AFTER 06-08Z THROUGH 13-15Z FRI.
-PICARD
MARINE
A BRIEF PERIOD OF BENIGN CONDITIONS ACROSS ALL WATERS
CONTINUES THROUGH TONIGHT AS HIGH PRESSURE SHIFTS INLAND, WITH A
SERIES OF SYSTEMS EXPECTED TO BRING REPEATED BOUTS OF ELEVATED
AND POTENTIALLY HAZARDOUS WINDS AND SEAS TOMORROW INTO EARLY
NEXT WEEK. A FIRST FRONTAL SYSTEM WILL MOVE INTO THE REGION
FRIDAY, YIELDING SOUTHERLY WINDS WITH GUSTS UP TO 30 KT AND SEAS
BUILDING TO 12 TO 16 FT AT AROUND 14 SECONDS. HAZARDOUS SEAS
WARNINGS ARE IN EFFECT FOR ALL WATERS INCLUDING THE COLUMBIA
RIVER BAR FROM 7 AM FRIDAY THROUGH 7 AM SATURDAY.
WHILE WINDS BRIEFLY SLACKEN FRIDAY NIGHT, ANOTHER MORE POTENT
FRONTAL SYSTEM WILL LIKELY BRING GALE CONDITIONS SATURDAY
THROUGH SATURDAY NIGHT, WITH SOUTHERLY WIND GUSTS OF 40 TO 45
KT AND SEAS OF 13 TO 17 FT EXPECTED. A GALE WATCH HAS BEEN
HOISTED FROM 7 AM SATURDAY THROUGH 1 AM SUNDAY, HOWEVER THERE
REMAINS A 25 TO 35 PERCENT CHANCE FOR STORM-FORCE WINDS WITH
THIS SYSTEM. FOLLOWING ANOTHER BRIEF LULL SUNDAY, YET ANOTHER
POTENT SYSTEM MAY BRING ADDITIONAL GALE OR STORM CHANCES ON
MONDAY. -PICARD
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. -MUESSLE
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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