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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