848
FXUS66 KPQR 242201
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
300 PM PDT THU SEP 24 2020
SYNOPSIS
A WARM FRONT WILL BRUSH THE NORTH COASTAL AREAS LATE
TONIGHT, THEN A COLD FRONT WILL MOVE EAST ACROSS THE REGION FRIDAY
BRINGING ANOTHER ROUND OF RAIN. A COOL UNSTABLE AIR MASS KEEPS A
CHANCE OF SHOWERS GOING THROUGH SATURDAY. THERE WILL BE A CHANGE TO
A DRIER AND WARMER WEATHER PATTERN SUNDAY INTO NEXT WEEK AS A LIGHT
OFFSHORE FLOW DEVELOPS.
SHORT TERM...TONIGHT THROUGH SUNDAY
SHOWERS, SOME WITH BRIEF
HEAVY RAIN, CONTINUED THURSDAY AFTERNOON ACROSS MUCH OF THE FORECAST
AREA. EXPECT SHOWERS TO DECREASE THIS EVENING AS AIR MASS SLOWLY
STABILIZES, BUT THERE MAY NOT BE MUCH OF A BREAK BETWEEN SYSTEMS AS
THE NEXT FRONTAL SYSTEM APPROACHES THE COAST LATE TONIGHT FROM THE
WEST. A WARM FRONT FROM THIS SYSTEM IS EXPECTED TO BRUSH MAINLY THE
NORTH COASTAL AREAS AREAS WITH INCREASING CHANCES FOR RAIN LATE
TONIGHT AND EARLY FRIDAY MORNING, THEN A COLD FRONT QUICKLY FOLLOWS
FRIDAY MOVING SOUTHEAST ACROSS THE FORECAST AREA. AS WITH THE
PREVIOUS SYSTEM WEDNESDAY, MODELS SHOW THIS SYSTEM TAPPING INTO
SUBTROPICAL MOISTURE FROM ACROSS THE PACIFIC, WITH PRECIPITABLE
WATER VALUES IN THE GFS 12Z RUN PEAKING BETWEEN 1.2 AND 1.4 INCHES
ALONG THE COAST FRIDAY MORNING. COUPLED WITH SOUTHWEST 850 MB WINDS
INTO THE COAST RANGE LIKELY PEAKING BETWEEN 45 AND 55 KT POTENTIALLY
BRINGS A PERIOD OF FAIRLY HEAVY RAIN AHEAD OF THE FRONT FRIDAY, BUT
PERHAPS A LITTLE WEAKER THAN THE WATER VAPOR TRANSPORT VALUES SEEN
WEDNESDAY. AS THE FRONT REMAINS PROGRESSIVE, EXPECT TO SEE THE
STEADIER RAIN EARLY IN THE DAY TURNING TO SHOWERS IN THE AFTERNOON.
SOUTH WINDS WILL INCREASE ALONG THE COAST AHEAD OF THE FRONT LATE
TONIGHT, WITH SOUTH GUSTS LIKELY PEAKING AROUND 45 MPH ALONG THE
NORTHERN BEACHES AND HEADLANDS BRIEFLY FRIDAY MORNING. AN ENHANCED
SNEAKER WAVE THREAT CONTINUES ALONG THE COAST THROUGH FRIDAY AS
INCOMING WAVES WILL BE DOMINATED BY A LONG PERIOD WESTERLY SWELL.
MODEL SOUNDINGS SHOW A MOIST AND UNSTABLE LOW LEVEL AIR MASS
PERSISTING FRIDAY NIGHT THROUGH SATURDAY NIGHT UNDER A WESTERLY FLOW
ALOFT. THIS WILL KEEP A THREAT OF SHOWERS GOING THROUGH SATURDAY
NIGHT BEFORE AIR MASS BEGINS TO STABILIZE AGAIN SUNDAY WITH
SUBSIDENCE CAUSED BY UPPER LEVEL RIDGING. LOW LEVEL FLOW TURNS
NORTHERLY SUNDAY AS WELL, HELPING TO DRY THE AIR MASS AND START
WARMING DAYTIME TEMPERATURES BACK TO NORMAL.
LONG TERM
SUNDAY NIGHT THROUGH THURSDAY..MODELS IN GENERAL
AGREEMENT DEPICTING A SHARPENING UPPER RIDGE OVER THE PACIFIC
NORTHWEST EARLY NEXT WEEK, AND THEN HANGING ON TO THE RIDGE INTO THE
LATTER HALF OF THE WEEK. A MILD, DRY, AND FOR THE MOST PART LIGHT
OFFSHORE FLOW APPEARS LIKELY TO PERSIST IN THE LOW LEVELS FOR MUCH
OF THE WEEK, RESULTING IN WARMER THAN NORMAL DAYTIME TEMPERATURES
AND SEASONABLY COOL NIGHTTIME LOWS. THE EASTERLY OFFSHORE FLOW WILL
LIKELY BRING WHATEVER WILDFIRE SMOKE IS AVAILABLE FROM OVER THE
CASCADES AND JUST EAST OF THE CASCADES WESTWARD INTO THE REGION,
ASSUMING THE FIRES ARE STILL GENERATING SMOKE.
AVIATION
ONSHORE FLOW IN THE POST FRONTAL ENVIRONMENT IS
ALLOWING SHOWERS TO PERSIST THIS AFTERNOON. RADAR SHOWS SOME MORE
INTENSE SHOWERS POPPING UP AT TIMES BUT MOST ARE QUICKLY
PASSING. SATELLITE DEPICTS MOSTLY PATCHY SKIES INLAND WITH
CLEARING OVER THE MARINE AREAS. ALTHOUGH MAINLY VFR THROUGH MOST
LOCATIONS, PERIODS OF MVFR CIGS ARE LIKELY WITH PASSING SHOWERS.
SOME LOCALIZED MIST AND HAZE IS PRESENT THROUGH KONP AND HAS BEEN
STUBBORN TO CLEAR. LIKELY WILL REMAIN WITH MVFR VISIBILITY
THROUGH THE NEXT SEVERAL HOURS. WINDS ARE SOUTH-SOUTHWESTERLY
THIS AFTERNOON AND THOSE WINDS WILL CONTINUE THROUGH THE NEXT
24-HOURS BECOMING GUSTY AT TIMES DURING THE AFTERNOON.
LATER TONIGHT, A VERY WEAK WARM FRONT WILL ADVANCE TOWARDS THE
AREA CAUSING WINDS TO BEGIN TO INTENSIFY ALONG COASTAL AIRPORTS.
AS THIS FRONT SHIFTS INLAND, EXPECT THOSE SOUTHERLY WINDS TO PICK
UP THROUGH THE VALLEY AND ALONG THE CASCADES. AS THE WARM FRONT
MOVES EASTWARD, THERE IS A CHANCE THAT THERE COULD BE SOME LLWS
THROUGH THE MORNING AFTER 12Z FRI, ESPECIALLY THROUGH THE
WILLAMETTE VALLEY. OPTED OUT OF INCLUDING IN TAFS DUE TO THE
MINIMAL SPEED/DIRECTIONAL SHEAR. NOTE HOWEVER, WINDS ALOFT AROUND
1500-2000 FT COULD BE AROUND 30-45 KTS. MODERATE RAIN WILL
LIKELY ACCOMPANY THIS FRONT WHICH WILL LAST THROUGH THE REMAINDER
OF THE PERIOD.
REFER TO HTTP://WEATHER.GOV/ZSE FOR DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
KPDX AND APPROACHES...THE MAIN CONCERN FOR THE NEXT 24-HRS IS
INCREASING SOUTHERLY WINDS. WITH CLEARING DURING THE DAY, WINDS
HAVE REMAINED GUSTY AND SHOWERS CONTINUE TO PUSH THROUGH THE
AREA. SHOWERS WILL TAPER OFF SLIGHTLY BEFORE MORE STRATIFORM RAIN
MOVES IN LATE TONIGHT. WINDS WILL BEGIN TO INTENSIFY OVERNIGHT
THROUGH FRI MORNING AFTER 14Z WITH THE FRONTAL PASSAGE. THIS IS A
VERY WET SYSTEM SO EXPECT RAIN BECOMING HEAVY AT TIMES. A CONCERN
PREVIOUSLY MENTIONED IS THE POTENTIAL FOR SOME LLWS. WITH WINDS
ALOFT AROUND 45-50 KT, THERE IS A CHANCE IT COULD MIX DOWN JUST
SLIGHTLY. HOWEVER, THERE IS LITTLE SPEED SHEAR GIVEN THAT WINDS
AT THE SURFACE LIKELY WILL BE GUSTING TO 20+ KT. DECIDED TO LEAVE
IT OUT OF THE TAF. -MUESSLE
MARINE
A HIGH ENERGY PATTERN CONTINUES TODAY WITH HIGH SEAS
AND GUSTY WINDS. SEAS AROUND 15 FT HAVE BEEN THE NORM TODAY AND
WILL CONTINUE TO BE THROUGH THE NEXT SEVERAL HOURS. A SECOND
SYSTEM WILL INTENSIFY BOTH WINDS AND WAVES TONIGHT. THIS FRONT,
WHICH IS STEMMING FROM THE GULF OF ALASKA, WILL PUSH OVER THE
WATERS LATE TONIGHT. WINDS WILL BEGIN TO INCREASE IN THE NORTHERN
ZONES THIS EVENING, SPREADING SOUTH THROUGH THE EARLY MORNING.
WHILE WINDS REMAIN BELOW SCA LEVELS, THEY WILL EASILY INCREASE TO
MEET WIND CRITERIA FOR THE ADVISORY.
BY MIDNIGHT TONIGHT ALL WATERS WILL BE EXPERIENCING WINDS OF AT
LEAST 15-20 KT WITH GUSTS UP TO 30 KT. THE INCREASE IN WINDS WILL
ENHANCE THE WIND WAVES AND THUS BUILD THE WAVE HEIGHTS. EXPECT
SEAS TO BUILD TO NEAR 18 FT EARLY FRIDAY MORNING. WINDS WILL
INCREASE EVEN FURTHER WITH GUSTS REACHING NEAR GALE WARNING
CRITERIA WITH GUSTS UP TO 40 KT POSSIBLE. A GALE WATCH IS
CURRENTLY IN EFFECT FOR FRIDAY. EXPECT SEAS AROUND 18 FT AND
GUSTS AROUND 35-40 KT THROUGH FRIDAY AFTERNOON. SEAS WILL SLOWLY
EASE TO NEAR 15 FT BY FRIDAY AFTERNOON WITH WINDS FOLLOWING SUIT.
MORE SETTLED WEATHER RETURNS ON SATURDAY AS THE LOW PRESSURE
SHIFTS NORTH AND OUT OF THE AREA. HIGH PRESSURE IS GOING TO BEGIN
TO BUILD IN ACROSS THE WATERS ON SATURDAY WHICH WILL ALLOW WINDS
TO CALM AND SEAS TO FALL BELOW 10 FT. CONDITIONS WILL REMAIN
STEADY THROUGH EARLY NEXT WEEK AS THE HIGH PRESSURE ONLY BUILDS
FURTHER NORTH. THERE IS A CHANCE FOR SOME STRONGER NORTHERLY
WINDS ON TUESDAY AS THERMALLY INDUCED LOW PRESSURE DEVELOPS NEAR
THE CALIFORNIA-OREGON BORDER, BUT AT THIS TIME, THOSE EFFECTS
ARE GOING TO BE VERY TIMING DEPENDENT. -MUESSLE
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...GALE WATCH FROM MIDNIGHT PDT TONIGHT THROUGH FRIDAY MORNING FOR
COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
OUT 60 NM.
SMALL CRAFT ADVISORY UNTIL MIDNIGHT PDT TONIGHT FOR COASTAL
WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60
NM.
GALE WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON FOR
COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60
NM.
SMALL CRAFT ADVISORY UNTIL 5 AM PDT FRIDAY FOR COASTAL WATERS
FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.
SMALL CRAFT ADVISORY UNTIL 11 AM PDT SATURDAY FOR COLUMBIA
RIVER BAR.
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND
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