373  
FXUS66 KPQR 211700  
AFDPQR  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE PORTLAND OR  
1000 AM PDT SAT SEP 21 2019  
 
UPDATED AVIATION DISCUSSION  
   
SYNOPSIS
 
BRIEF HIGH PRESSURE WILL BRING CLEARING SKIES THIS  
AFTERNOON. HOWEVER, CLOUDS WILL BE ON THE INCREASE AGAIN TONIGHT  
AHEAD OF A COLD FRONT THAT WILL SPREAD MORE RAIN ACROSS THE FORECAST  
AREA SUNDAY. SUNDAY NIGHT MAY BE THE COOLEST NIGHT SO FAR THIS  
SEASON FOLLOWED BY DRY AND MILD WEATHER MONDAY. ADDITIONAL FRONTAL  
SYSTEMS MAY BRING MORE WET WEATHER TUESDAY AND AGAIN LATER IN THE  
WEEK WITH TEMPERATURES REMAINING A LITTLE COOLER THAN TYPICAL FOR  
LATE SEPTEMBER.  
 

 
   
SHORT TERM...TODAY THROUGH MONDAY
 
MADE A QUICK UPDATE THIS  
MORNING TO ADJUST CLOUD COVER TO BETTER REFLECT REALITY. ALSO ADDED  
DRIZZLE TO THE NORTH COASTAL AREAS WHERE LANGLEY HILL RADAR IS  
GETTING SUPPORT FROM KAST AND CAMERA OBS. REST OF THE PREVIOUS  
DISCUSSION FOLLOWS. /JBONK  
 
OTHERWISE, AREAS OF MORNING LOW CLOUDS AND FOG WILL GIVE WAY TO  
INCREASING SUNSHINE THROUGHOUT THE DAY, ALLOWING TEMPERATURES TO  
CLIMB CLOSE TO LATE-SEPTEMBER NORMALS WITH LOWER TO MID 70S FOR THE  
INLAND VALLEYS AND MID 60S TO LOWER 70S ALONG THE COAST.  
 
MODEL TIME-HEIGHTS AND 00Z HREF SUGGEST HIGH CLOUDS WILL INCREASE AND  
THICKEN THIS EVENING AS A FRONTAL SYSTEM NOW CROSSING 135W-140W  
APPROACHES THE REGION. RAIN WILL LIKELY MOVE ONSHORE BY DAWN SUNDAY,  
THEN SPREAD INLAND AND SOUTH ACROSS THE FORECAST AREA DURING THE DAY  
SUNDAY. JET FORCING CONTINUES TO LOOK WEAK AHEAD OF THIS SYSTEM, WITH  
WINDS GENERALLY 50 KT OR LESS ABOVE AT 500 MB AND ABOVE. THIS WILL  
KEEP WINDS MODEST AHEAD OF THE FRONT, AND SHOULD LIMIT THE POTENTIAL  
FOR OROGRAPHIC ENHANCEMENT RAINFALL AS THE FRONT MOVES THROUGH.  
THEREFORE WE ARE EXPECTING QPF TO BE MORE UNIFORM ACROSS THE AREA  
THAN THE PAST COUPLE FRONTS, AT LEAST BASED ON TERRAIN. MOST  
LOCATIONS IN OUR FORECAST AREA SHOULD RECEIVE AROUND 0.25" FROM THIS  
SYSTEM, PLUS OR MINUS 0.10" OR SO. MODEL SOUNDINGS SUGGEST SOME WEAK  
INSTABILITY/THIN CAPE ALONG AND JUST BEHIND THE FRONT, WHICH MAY  
INTRODUCE CONVECTIVE ELEMENTS WHICH COULD LOCALLY PUSH RAINFALL INTO  
THE 0.50 TO 1.00" RANGE. THERE WILL BE A BRIEF WINDOW FOR ISOLATED  
THUNDER SUNDAY AFTERNOON AND EVENING AS THE ASSOCIATED COLD POOL  
ALOFT SWINGS THROUGH. THE 06Z NAM CONTINUES TO SUGGEST A CAPPING  
INVERSION WILL QUICKLY DEVELOP AROUND 700 MB SUNDAY EVENING, WHICH  
SHOULD CAUSE SHOWERS TO TAPER OFF QUICKLY OVERNIGHT.  
 
HIGH PRESSURE BUILDS INTO THE REGION SUNDAY NIGHT AND EARLY MONDAY,  
WHICH MAY LEAD TO RAPID CLEARING FOR THE VALLEYS. GIVEN THE COOL AIR  
MASS LEFT BEHIND (WITH 850 MB TEMPS AROUND +5 DEG C) AND IMPROVING  
CONDITIONS FOR RADIATIONAL COOLING, THE STAGE MAY BE SET FOR THE  
COOLEST NIGHT SO FAR THIS SEASON FOR MANY LOCATIONS WITHIN THE  
FORECAST AREA. MOST LOCATIONS WILL LIKELY DIP WELL INTO THE 40S  
SUNDAY NIGHT, WITH SOME HIGHER ELEVATION VALLEYS POSSIBLY GETTING  
INTO THE UPPER 30S. IS THIS ENOUGH FOR RECORDS MONDAY? NOT EVEN  
CLOSE. THE RECORD LOW FOR MONDAY IS A FROSTY 31 DEGREES AT HILLSBORO  
AND EUGENE, WHILE THE RECORD IS 40 FOR PDX. OUR FORECAST LOWS FOR  
MONDAY ARE A GOOD 10 OR MORE DEGREES WARMER THAN THESE TEMPERATURES.  
STILL, IT WILL BE A NOTICEABLE TOUCH OF AUTUMN AFTER A SUMMER WHERE  
MILD TO WARM NIGHTS HAVE BEEN THE NORM.  
 
AFTER A COOL START WITH AREAS OF VALLEY FOG MONDAY MORNING, HIGH  
PRESSURE SHOULD RESULT IN INCREASING SUNSHINE MONDAY AFTERNOON WITH  
TEMPERATURES REBOUNDING TO THE MID TO UPPER 60S FOR THE LOWLANDS. ONE  
TRICKY ASPECT ABOUT MONDAY MAY BE HOW SLOW MORNING FOG/LOW CLOUDS ARE  
TO CLEAR; WITH LITTLE LOW-LEVEL FLOW TO SPEAK OF WEST OF THE  
CASCADES, MIXING MAY BE SLOWER THAN USUAL TO OCCUR. WITH MONDAY BEING  
THE FIRST DAY OF ASTRONOMICAL AUTUMN, THE SUN ISN'T AS STRONG AS IT  
WAS A FEW WEEKS AGO BUT SHOULD STILL BE ENOUGH TO POKE SOME DECENT  
SUNBREAKS INTO THE STRATUS DECK MONDAY AFTERNOON. WEAGLE  
   
LONG TERM...MONDAY NIGHT THROUGH FRIDAY
 
STRONG BUT FLAT UPPER  
LEVEL RIDGING DEVELOPS ACROSS THE NE PACIFIC MONDAY AND TUESDAY,  
RESULTING IN FAIRLY STRONG ZONAL FLOW INTO THE BC/WA THROUGH MIDWEEK.  
THIS MAY CLIP OUR PRIMARILY OUR NORTHERN ZONES WITH SOME LIGHT RAIN  
AT TIMES, MAINLY LATE MONDAY NIGHT/EARLY TUE AND AGAIN WED NIGHT.  
AREAS PORTLAND-TILLAMOOK NORTHWARD WILL LIKELY REMAIN CLOUDIER  
THROUGH MIDWEEK THAN AREAS TO THE SOUTH, DUE TO THEIR PROXIMITY TO  
THE ABOVE-MENTIONED ZONAL JET. THEREFORE AREAS SALEM SOUTHWARD HAVE A  
BETTER CHANCE OF REACHING THE 70S TUESDAY AND POTENTIALLY WEDNESDAY,  
THOUGH OUR FORECAST FOR WED IS A LITTLE COOLER DUE TO THE POTENTIAL  
FOR INCREASING HIGH CLOUDS. ZONAL FLOW BEGINS TO BUCKLE WEDNESDAY  
NIGHT AS A DEEP UPPER TROUGH BEGINS TO DEVELOP OVER WESTERN CANADA,  
PUSHING INTO THE PAC NW THURSDAY AND FRIDAY. THE 00Z ECMWF REMAINS  
MORE AMPLIFIED/LESS PROGRESSIVE WITH THE LATE-WEEK UPPER TROUGH,  
KEEPING THE TROUGH AXIS OFFSHORE THROUGH SATURDAY WHILE THE 00Z GFS  
PUSHES THE TROUGH AXIS ONSHORE BY FRIDAY. EITHER SOLUTION WOULD BE  
CHILLY FOR OUR FORECAST AREA, BUT THE PLACEMENT IS IMPORTANT IN  
DETERMINING WHETHER THE BULK OF ASSOCIATED SHOWER ACTIVITY REMAINS  
OVER OUR FORECAST AREA OR EAST OF THE CASCADES, AND WHETHER OR NOT  
SNOW LEVELS WILL DIP LOW ENOUGH TO BRING THE FIRST SNOW OF THE SEASON  
TO MANY OF OUR SKI RESORTS AND CASCADE PASSES.WEAGLE  
 

 
   
AVIATION
 
EXPECT A MIX OF CONDITIONS TO CONTINUE THROUGH MIDDAY  
WITH WIDESPREAD MVFR CIGS AND LOCAL IFR STRATUS IN THE INTERIOR  
LOWLANDS. CONDITIONS THEN BECOME VFR BETWEEN 18-21Z, WITH SOME  
SUNBREAKS EXPECTED THIS AFTERNOON AND EVENING DUE TO VARIABLE MID  
AND HIGH CLOUDS MOVING ACROSS THE REGION AHEAD OF AN APPROACHING  
FRONT. THIS FRONT WILL BRING THE RETURN OF LIGHT RAIN AND IFR  
CONDITIONS TO THE COAST TONIGHT, WITH RAIN AND REDUCED FLIGHT  
CONDITIONS SPREADING INLAND DURING THE OVERNIGHT HOURS.  
 
KPDX AND APPROACHES...MVFR CIGS WILL CONTINUE THROUGH MIDDAY. VFR  
CONDITIONS IS THEN EXPECTED THROUGH TONIGHT WITH VARIABLE MID AND  
HIGH CLOUDS. MVFR CIGS UNDER LIGHT RAIN LIKELY AFTER 10Z TONIGHT.  
/64  
 

 
   
MARINE
 
A TRANSIENT SURFACE RIDGE OVER THE WATERS WILL SHIFT  
INLAND THIS EVENING. A FRONT WILL MOVE ACROSS THE WATERS TONIGHT  
AND ASHORE SUNDAY MORNING WITH HIGH PRESSURE BUILDING OVER THE  
WATERS SUNDAY AFTERNOON. EXPECT SMALL CRAFT ADVISORY CONDITIONS  
OVER THE NORTHERN MARINE ZONES AHEAD OF THE FRONT. THE NORTHERN  
OUTER ZONES SHOULD HAVE NORTHWEST WIND GUSTING 25 KT INTO SUNDAY  
EVENING AS HIGH PRESSURE BUILD BEHIND THE FRONT. RIGHT NOW, NOT  
EXPECTING SMALL CRAFT ADVISORY CONDITIONS FOR THE CENTRAL OREGON  
MARINE ZONES BUT FUTURE MODEL RUNS MAY INCREASE WINDS INTO THE  
ADVISORY CATEGORY. THE NEXT FRONT FOR LATER MONDAY LOOKS TO BE A  
LITTLE WEAKER THAN THE SUNDAY FRONT.  
 
SEAS WILL REMAIN IN THE RANGE OF 4 TO 6 FT THROUGH SATURDAY EVENING.  
THE COLD FRONT SUNDAY WILL BOOST SEAS INTO THE 8 TO 10 FT RANGE  
THROUGH SUNDAY NIGHT. A WEST TO NORTHWEST FETCH DEVELOPING IN THE  
NORTHEAST PACIFIC WILL BRING BUILDING SEAS TO ABOVE 10 FT AROUND MID  
WEEK.  
 

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  
PZ...SMALL CRAFT ADVISORY FROM 3 AM TO 11 PM PDT SUNDAY FOR WATERS  
FROM CAPE SHOALWATER WA TO CASCADE HEAD OR FROM 10 TO 60  
NM.  
 
SMALL CRAFT ADVISORY FROM 3 AM TO 1 PM PDT SUNDAY FOR COASTAL  
WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 10  
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 FORECAST AREA.  
 
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