000  
FXUS66 KPQR 291059  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
359 AM PDT MON MAY 29 2017  
   
SYNOPSIS
 
COOLER FOR MONDAY, WITH A LOT MORE IN WAY OF LOW CLOUDS  
IN THE MORNING INTO EARLY AFTERNOON. APPROACHING LOW PRESSURE FROM  
THE WEST WILL BRING INCREASING SOUTHERLY FLOW ALOFT. THIS WILL  
RESULT IN THREAT OF LATE AFTERNOON/EARLY EVENING THUNDERSTORMS OVER  
THE CENTRAL OREGON CASCADES TODAY. THE THUNDER THREAT SPREADS  
FURTHER NORTH TUESDAY. OTHERWISE, BACK TO TYPICAL LATE MAY/EARLY  
JUNE WEATHER, WITH PARTLY TO MOSTLY CLOUDY SKIES AND NEAR SEASONABLE  
TEMPERATURES.  

 
   
SHORT TERM
 
(TODAY THROUGH WEDNESDAY NIGHT) LOW CLOUDS CONTINUE TO  
STREAM INLAND THROUGH THE COAST RANGE GAPS. THEY WILL CONTINUE TO  
LARGELY FILL THE I-5 CORRIDOR THIS MORNING AND WILL RESULT IN  
ANOTHER 3-5 DEGREE DROP TO TEMPERATURES TODAY INLAND. TRICKY AREA  
WILL BE THE COLUMBIA RIVER GORGE AND JUST HOW FAR EAST THE COOLER  
MARINE AIR WILL INFLUENCE CONDITIONS TODAY. FEEL THE SURFACE THERMAL  
TROUGH WILL STILL HAVE SOME INFLUENCE FOR THE CENTRAL GORGE WITH THE  
HOOD RIVER AREA STILL MAKING IT INTO THE UPPER 80S TODAY BUT THEN  
RAPIDLY COOLING THIS EVENING AS A WESTERLY MARINE PUSH DOMINATES.  
 
ON THE LARGER SCALE, THE APPROACHING TROUGH WILL STAY OFFSHORE TODAY  
BUT THERE IS A SOUTHERN PIECE OFF THE NORTHERN CALIFORNIA COAST  
WHICH HAS UNDERGONE CYCLOGENESIS SPINNING UP INTO A NEARLY MESOSCALE  
CLOSED LOW. THAT APPEARS TO HAVE TAKEN ENOUGH ENERGY TO NOW CONFINE  
THE THUNDERSTORM THREAT CLOSER TO WILLAMETTE PASS. MOST OF THE  
COOLER AIR ALOFT WILL REMAIN OVER THE OCEAN AND THIS LEAVE A  
GENERALLY MORE STABLE AIR MASS OVER THE AREA. ADDITIONALLY, THE  
COOLER INLAND TEMPERATURES WILL MAKE IT HARDER FOR SURFACE PARCELS  
TO OVERCOME A MIDLEVEL CAP SITTING AROUND 750 MB. LATER THIS EVENING  
AND OVERNIGHT, MODELS CONTINUE TO SHOW SOME FORM OF LIGHT SHOWER  
ACTIVITY ACROSS THE REGION. CONFIDENCE IS VERY LOW FOR PRECISE  
LOCATION THUS HAVE BROADBRUSHED THE THREAT. AMOUNTS SHOULD REMAIN  
RATHER LIGHT, HOWEVER.  
 
FOR TUESDAY, MODELS ARE IN MUCH BETTER AGREEMENT REGARDING THE SHAPE  
AND STRENGTH OF THE SHORT-WAVE TROUGH APPROACHING THE AREA. THE  
TROUGH AXIS PASSES OVERHEAD TUESDAY AFTERNOON WITH THE COLDER AIR  
ALOFT HOLDING OFF UNTIL AFTER DARK. THIS WILL GREATLY REDUCE THE  
POTENTIAL FOR THUNDERSTORMS ACROSS THE AREA AND HAVE REDUCED THE  
THREAT TO THE CASCADES. EVEN THEN, DO NOT HAVE STRONG FEELINGS THEY  
WILL DEVELOP WEST OF THE CASCADE CREST. BEST CHANCE WILL BE TUESDAY  
AFTERNOON BUT FEEL MOST ACTIVITY WILL DEVELOP OVER THE EAST SLOPES  
LATE TUESDAY AFTERNOON AND EVENING LEAVING JUST MODEST SHOWER  
ACTIVITY ON THE WEST SIDE.  
 
THE LONGER WAVE UPPER TROUGH WILL SPLIT APART WEDNESDAY WITH ANOTHER  
SEGMENT OF ENERGY CROSSING SOUTH OF THE REGION AND INTO NORTHERN  
CALIFORNIA WITH THE PRIMARY LOW STAYING WELL NORTHWEST. THIS COULD  
LEAVE WEDNESDAY LARGELY DRY AS WE SIT IN BETWEEN THESE TWO SEGMENTS.  
THERE MAY BE ENOUGH LEFT OF A TRAILING COLD (COOL?) FRONT TO BRING  
LIGHT RAIN WEDNESDAY NIGHT, BUT IT IS ALREADY SHOWING SIGNS OF  
SPLITTING APART ON MODELS WHICH USUALLY LEADS TO LITTLE OR NO PRECIP  
IN REALITY. /JBONK  
   
LONG TERM
 
(THURSDAY THROUGH SUNDAY) NO CHANGES. BULK OF  
THE PREVIOUS DISCUSSION FOLLOWS. ADDITIONAL SHORTWAVES WILL MOVE  
THROUGH THE AREA THURSDAY AND FRIDAY WHICH WILL INCREASE SHOWER  
CHANCES. THE FORECAST BECOMES A LOT MORE UNCERTAIN TOWARDS NEXT  
WEEKEND AS THE ECMWF TRIES TO CUT OFF AN UPPER LOW OVERHEAD WHILE  
THE GFS STRENGTHENS A RIDGE INTO THE AREA. WENT WITH A CONSENSUS  
BLEND TODAY AND WILL WORK TO ADD MORE DETAILS THIS WEEK AS THINGS  
BECOME MORE CLEAR. /BENTLEY  
 

 
   
AVIATION
 
HIGH IFR CIGS AROUND 900 FT WILL FILL MOST OF THE  
INTERIOR TONIGHT AND EARLY MONDAY STARTING IN THE SOUTH AND  
WORKING NORTHWARD AS WELL AS SPREADING UP THE COLUMBIA RIVER TO  
KPDX. CLOUDS WILL DISSIPATE OVER THE INTERIOR THROUGH MIDDAY MON  
WHILE COASTAL AREAS ARE LIKELY TO REMAIN CLOUDY.  
 
KPDX AND APPROACHES...CIGS AT 800 TO 900 FT THROUGH MUCH OF  
MONDAY MORNING, DISSIPATING BY AROUND 18Z FOR SKC THE REST OF  
THE DAY. BOWEN  
 

 
   
MARINE
 
QUIET CONDITIONS CONTINUE WITH WINDS BELOW 20 KT  
THROUGH AT LEAST THE MIDDLE OF THIS WEEK AND LIKELY LONGER. WINDS  
TURN LATE TUESDAY FROM OUT OF THE NORTHWEST TO OUT OF THE  
SOUTHWEST THEN SOUTH. SEAS AROUND 4 FT AND WILL CONTINUE THROUGH  
AT LEAST THE MIDDLE OF THE WEEK.  
 
NEXT CHANCE FOR WINDS ABOVE 20 KT WILL BE NEXT WEEKEND AS A  
BROAD UPPER-LEVEL RIDGE BUILDS OVER THE NE PACIFIC, SETTING UP A  
SUMMER-LIKE GUSTY NORTHERLY WIND PATTERN OVER OUR WATERS.  
BOWEN/MCCOY  
 

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  
PZ...NONE.  

 
 

 
 
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. THE AREA IS  
COMMONLY REFERRED TO AS THE FORECAST AREA.  
 
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