371  
FXUS66 KPQR 182208  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
305 PM PDT SAT AUG 18 2018  
   
SYNOPSIS
 
ONSHORE FLOW WILL KEEP MARINE AIR AND SOME CLOUDS ON THE  
COAST TONIGHT, WHILE THE INLAND AREAS SEE MOSTLY CLEAR SKIES. A WEAK  
UPPER LEVEL LOW PRESSURE SYSTEM WILL APPROACH OREGON SUNDAY, THEN  
LINGER OVER THE REGION THROUGH AT LEAST WEDNESDAY. THE UPPER LOW  
WILL BRING A SLIGHT CHANCE FOR THUNDERSTORMS WITH IT, MAINLY TO THE  
HIGH CASCADES. SLOWLY WARMING TEMPERATURES CAN BE EXPECTED THROUGH  
TUESDAY AS ONSHORE FLOW IS WEAKENED, THEN COOLER TEMPERATURES ARE  
EXPECTED TO RETURN LATE IN THE WEEK AS A BROAD TROUGH OF LOW  
PRESSURE ALOFT REPLACES THE WEAK CUTOFF LOW.  
 

 
   
SHORT TERM...TONIGHT THROUGH TUESDAY
 
SATELLITE PICTURES SHOWED  
CLOUDS HAD RECEDED TO JUST OFF THE COAST EARLY THIS AFTERNOON,  
LEAVING SKIES MOSTLY CLEAR. A CLOSED LOW SEEN IN WATER VAPOR  
PICTURES OFF THE COAST NEAR 46N 135W IS EXPECTED TO TRACK EAST  
TONIGHT AND SUN, REACHING THE COAST SUN AFTERNOON. SATELLITE  
PICTURES SHOWED A DEARTH OF ANY CLOUDS OF DEPTH ASSOCIATED WITH THE  
LOW, SUPPORTING THE RELATIVELY DRY MODEL TIME HEIGHT PROFILES FOR  
THE NEXT FEW DAYS. WHILE THE LOW MAY OFFER SOME DIVERGENCE ALOFT AS  
A SOURCE OF LIFT, THE LACK OF MOISTURE HINDERS APPEARS TO PROHIBIT  
MUCH IN THE WAY OF INSTABILITY AS THE LOW MOVES INLAND.  
ADDITIONALLY, MODELS REMAIN UNCERTAIN AS TO HOW THE LOW MOVES AND  
DEVELOPS MON AND TUE. MAKING IT DIFFICULT TO PIN DOWN THE MOST  
LIKELY LOCATIONS FOR ANY CONVECTIVE ACTIVITY. AS SUCH, WILL CUT BACK  
ON THE THREAT OF THUNDER OVER THE NEXT FEW DAYS, AND LIMIT SLIGHT  
CHANCES TO THE MORE CLIMATOLOGICALLY FAVORED CASCADES LATE SUN  
THROUGH TUE.  
 
LOW LEVEL FLOW TAKES ON MORE OF A NORTH TO NE FLOW IN  
THE COMING DAYS, AS MODELS SUGGEST A WEAK THERMAL INDUCED TROUGH  
SHIFTING WEST TO THE OREGON COAST BY TUE. THIS FLOW IS LIKELY TO  
BRING ADDITIONAL LOW LEVEL HAZE AND SMOKE FROM BRITISH COLUMBIA AND  
EASTERN WA BACK INTO THE AREA AS EARLY AS SUNDAY NIGHT, THEN  
LINGERING IN THE REGION THROUGH TUE. ADDITIONALLY SOME UPPER LEVEL  
SMOKE/HAZE WILL LIKELY SPREAD IN AS WELL MON AND TUE WHEN THE UPPER  
FLOW SWITCHES TO THE NE. MODELS CONTINUE TO SUGGEST WARMING TEMPS IN  
LOWER LEVELS DESPITE THE LINGERING UPPER LOW OVER THE NEXT THREE  
DAYS, WITH 850 MB TEMPS REACHING 20C OR A LITTLE BETTER BY MON AND  
TUE. WHILE THIS SUGGESTS TEMPS CLIMBING BACK INTO THE LOWER 90S, ANY  
SORT OF SMOKE LAYER MAY TEND TO HOLD HIGH TEMPS DOWN A FEW DEGREES  
FROM WHAT THE 850 MB TEMPS WOULD OTHERWISE SUGGEST.  
   
LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
 
UPPER-LEVEL TROUGH  
SWINGS THROUGH TUESDAY NIGHT INTO WEDNESDAY. THERE'S UNCERTAINTY IN  
THE LOCATION OF THIS UPPER-LEVEL TROUGH, WHICH MAKES PREDICTING THE  
CHANCE OF SHOWERS AND THUNDERSTORMS DIFFICULT. FOR NOW, WITH THE  
CURRENT PREDICTED LOCATION OF THE TROUGH, HAVE KEPT A SLIGHT CHANCE  
OF THUNDERSTORMS OVER OUR CASCADES TUESDAY NIGHT AND WEDNESDAY  
AFTERNOON AND EVENING. THIS COULD VERY WELL NOT HAPPEN, HOWEVER, AS  
THE ECMWF KEEPS THE TROUGH FARTHER EAST. THIS WOULD KEEP THE  
THUNDERSTORM THREAT EAST OF THE CASCADES.  
 
ONSHORE FLOW PICKS UP DURING THE DAY ON WEDNESDAY, WITH A FAIRLY  
STRONG MARINE PUSH STARTING TO BRING DOWN TEMPERATURES. THURSDAY  
MORNING EXPECT MARINE CLOUDS TO PUSH INTO AT LEAST THE NORTH  
WILLAMETTE VALLEY. STRONGER ONSHORE FLOW WILL KEEP TEMPERATURES ON  
THURSDAY BACK DOWN INTO THE UPPER 70S TO MID 80S. FRIDAY LOOKS LIKE  
ANOTHER FINE DAY, WITH ONSHORE WINDS KEEPING TEMPERATURES DOWN  
CLOSER TO NORMAL. NORTHWESTERLY FLOW PATTERN SETS UP GOING INTO NEXT  
WEEKEND, WHICH SHOULD KEEP TEMPERATURES FAIRLY MILD AND WEATHER  
FAIRLY SEASONABLE. -MCCOY  
 

 
 
   
AVIATION
 
EXPECT HIGH END IFR TO LOW END MVFR STRATUS TO  
RETURN TO THE COAST BETWEEN 00-03Z SUNDAY AND LINGER THROUGH  
~18Z SUNDAY. GIVEN THE LOW LEVEL NORTHWESTERLY FLOW PATTERN,  
THERE IS A CHANCE SOME OF THESE CIGS COULD MAKE IT AS FAR INLAND  
AS THE PORTLAND METRO FOR A COUPLE HOURS SHORTLY AFTER DAYBREAK  
ON SUNDAY.  
 
KPDX AND APPROACHES...A TYPICAL SUMMERTIME LOW LEVEL NORTHWESTERLY  
FLOW PATTERN WILL PRODUCE PREDOMINANTLY VFR CONDITIONS THROUGH  
18Z SUNDAY. THERE IS A CHANCE OF MVFR CIGS BETWEEN 13-17Z SUNDAY  
AS MARINE STRATUS ATTEMPTS TO MOVE UP THE COLUMBIA RIVER. /NEUMAN  
 

 
   
MARINE
 
HIGH PRESSURE OVER THE NORTHEAST PACIFIC AND THERMALLY  
INDUCED LOW PRESSURE OVER NORTHERN CALIFORNIA AND THE GREAT BASIN  
WILL MORE OR LESS CONTINUE FOR MUCH OF THE UPCOMING WEEK RESULTING  
IN LITTLE DAY TO DAY CHANGE IN THE WINDS AND SEAS. GUSTS OVER THE  
CENTRAL OREGON OUTER WATERS LOOK TO ONCE AGAIN FLIRT WITH ADVISORY  
CRITERIA OF 25 KT THIS EVENING, PARTICULARLY FOR OUR FAR SOUTHERN  
WATERS OFF OF FLORENCE, OREGON. EXPECT SEAS GENERALLY TO REMAIN  
IN THE 4 TO 6 FT RANGE FOR MUCH OF THE NEXT WEEK, BUT WITH DOMINANT  
WAVE PERIODS GENERALLY IN THE 7 TO 8 SECOND RANGE SEAS WILL BE  
RELATIVELY CHOPPY. /NEUMAN  
 

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 1 AM PDT SUNDAY FOR WATERS  
FROM CASCADE HEAD TO FLORENCE OR FROM 10 TO 60 NM.  
 

 
 

 
 
INTERACT WITH US VIA SOCIAL MEDIA:  
WWW.FACEBOOK.COM/NWSPORTLAND  
WWW.TWITTER.COM/NWSPORTLAND  
 
THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON  
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THIS AREA IS  
COMMONLY REFERRED TO AS THE CWA OR FORECAST AREA.  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab OR Page
The Nexlab WA Page Main Text Page