421  
FXUS66 KPQR 260401  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
900 PM PDT WED APR 25 2018  
 
AVIATION SECTION UPDATED.  
   
SYNOPSIS
 
HIGH PRESSURE OVER THE WILL SLOWLY SHIFT TOWARD THE  
ROCKIES TONIGHT AND THU. AT SAME TIME, UPPER LOW PRES WILL SLOWLY  
APPROACH FROM THE SOUTHWEST. SO, EXPECT A GRADUAL INCREASE OF ONSHORE  
FLOW ON THU, WITH MUCH COOLER AIR AND CLOUDS ACROSS THE REGION LATE  
THU AND THU NIGHT. AS THE UPPER LOW SHIFTS INTO THE REGION, WILL SEE  
SHOWER FROM TIME TO TIME, WITH PLENTY OF CLOUDS AND COOLER AIR FOR  
THE WEEKEND. DOES APPEAR THAT WILL HAVE RETURN TO DRIER AIR WITH MILD  
TEMPERATURES EARLY TO MIDDLE OF NEXT WEEK.  
 

 
   
SHORT TERM...TONIGHT THROUGH SATURDAY
 
NOT A LOT OF CHANGE IN  
OVERALL PATTERN TONIGHT. HIGH PRES SITTING OVER THE REGION WILL  
MAINTAIN DRY CONDITIONS INTO THU. THERMAL LOW PRES SITTING JUST  
INLAND FROM THE COAST. THIS SHOWS UP WELL WITH THE WIDESPREAD MARINE  
STRATUS ALONG THE COAST, WHERE TEMPERATURES ARE SOME 20 TO 30 DEG  
COOLER THIS AFTERNOON THAN AS SEEN ON TUE. THERMAL TROUGH WILL SLOWLY  
SHIFT TO THE INTERIOR TONIGHT, BUT MARINE LAYER REMAINS SHALLOW  
ENOUGH THAT WILL HAVE DIFFICULT TIME PUNCHING INLAND.  
 
UPPER LOW WILL SLOWLY APPROACH THE REGION FROM THE SOUTHWEST ON THU.  
BUT DUE TO ITS SLOWNESS, SEEMS THE THERMAL TROUGH WILL SIT OVER THE  
INTERIOR LOWLANDS INTO THU AFTERNOON. AS SUCH, WILL SEE WESTERLY  
ONSHORE BEGIN INCREASING TROUGH THE DRAINAGES IN THE COAST RANGE FROM  
LANE COUNTY IN THE MORNING, PROGRESSING NORTHWARD AS THE DAY  
PROGRESSES. THIS WILL KEEP SOME OFFSHORE FLOW AT PORTLAND/VANCOUVER  
METRO INTO THE AFTERNOON, THEN WILL SEE WINDS AT THAT AREA FLIP TO  
SOUTH OR SOUTHWEST TOWARDS LATE AFTERNOON. WITH THIS PATTERN, WOULD  
EXPECT TO SEE WIDE RANGE IN TEMPS, WITH UPPER 60S TO LOWER 70S AT  
CORVALLIS AND EUGENE, TO NEAR 80 AROUND PORTLAND/VANCOUVER METRO.  
 
THERMAL TROUGH WILL WORKS ITS WAY UP AND OVER THE CASCADES THU NIGHT,  
ALLOWING FOR DEEPENING MARINE LAYER ON THE WEST SIDE. THIS WILL  
RESULT IN MUCH MORE CLOUDS FOR THU NIGHT INT FRI AM.  
 
NOW, OTHER TWIST IN OUR FORECAST WILL BE THREAT OF SHOWERS AS THE  
UPPER LOW APPROACHES. AT MOMENT, NOT ALL THAT IMPRESSED WITH THE  
POTENTIAL, OWING TO FAIRLY DRY AIR MASS AND WEAK INSTABILITY  
INITIALLY. STILL, WITH PROXIMITY OF THERMAL TROUGH AND AFTERNOON  
SURFACE HEATING, PROBABLY BE ENOUGH TO POP AFTERNOON CUMULUS OVER THE  
CASCADES. WILL GO WITH 20 PCT POPS OVER THE CASCADES FROM SANTIAM  
PASS SOUTHWARD LATER THU AFTERNOON. UPPER FLOW APPEARS BIT MORE SOUTH  
TO SOUTHEASTERLY FOR THU NIGHT AND FRI. SO, AS SHOWERS POP UP OVER  
SOUTHERN OREGON AND THE CASCADES, WILL HAVE MOTION SUCH THAT SHOWERS  
WILL CONTINUE DRIFTING NORTHWESTWARD IN THE FLOW. DO NOT THINK WILL  
SEE THUNDERSTORM THREAT ON FRI, AS WILL HAVE FAIRLY DEEP MARINE LAYER  
BY THAT TIME. HOWEVER, WOULD NOT BE SURPRISED TO SEE A FEW  
THUNDERSTORMS OVER THE CASCADES ON FRI INTO FRI EVENING. HAVE NOT PUT  
IN FORECAST YET, AS WOULD LIKE TO SEE HOW THE NEXT FEW RUNS OF MODELS  
SHAKE OUT TO GET MORE CONFIDENCE.  
 
STILL COOL AND SHOWERY ON SATURDAY AS THE UPPER LOW SHIFTS INTO  
NORTHERN CALIFORNIA AND SOUTHERN OREGON./ROCKEY.  
   
LONG TERM...SAT NIGHT THROUGH TUESDAY
 
MODELS CONSISTENT IN  
SHOWING THE UPPER LOW PROGRESSING SLOWLY ACROSS THE PAC NW, AUGMENTED  
BY ANOTHER SHORTWAVE ATTACHING TO THE LOW SAT NIGHT AND SUN. THIS  
WILL KEEP A DECENT CHANCE OF SHOWERS OVER THE REGION INTO SUN, WHICH  
COMBINED WITH THE LOW LEVEL ONSHORE FLOW KEEPS TEMPS A LITTLE BELOW  
SEASONAL NORMALS. SUN NIGHT INTO MON MODELS IN PRETTY GOOD AGREEMENT  
THAT THE UPPER TROUGH SHIFTS EAST AS A RIDGE OF HIGH PRES PRESSES IN  
FROM THE WEST. THIS WILL ALLOW TEMPS TO MODERATE SOME DURING THE  
EARLY NEXT WEEK, WHILE CHANCES FOR SHOWERS DIMINISH.  
 

 
   
AVIATION
 
MARINE CLOUDS WILL CONTINUE TO PRODUCE AREAS OF IFR  
CONDITIONS ALONG THE COAST THIS EVENING FROM AROUND KTMK  
SOUTHWARD. CONFIDENCE IS LOWER NORTH OF KTMK, BUT EXPECT THAT  
LIGHT OFFSHORE FLOW MAY KEEP LOW STRATUS OFFSHORE FOR THE  
SOUTHERN WASHINGTON AND FAR NORTHERN OREGON COASTAL AREAS.  
TO THE SOUTH, INCLUDING AT KONP, EXPECT IFR CONDITIONS TO  
GRADUALLY IMPROVE INTO MVFR AS THE MARINE LAYER DEEPENS TONIGHT  
AND THURSDAY. THERE IS A CHANCE VERY HIGH END IFR TO MVFR STRATUS  
COULD WORK ITS WAY INTO KEUG TOWARDS 12-15Z THURSDAY, BUT  
CONFIDENCE IS LOW. ELSEWHERE, EXPECT MARINE CLOUDS TO SPREAD  
ACROSS THE REST OF THE FORECAST AREA AFTER 00Z FRIDAY.  
 
KPDX AND APPROACHES...OFFSHORE FLOW WILL RESULT IN VFR CONDITIONS  
THROUGH 00Z FRIDAY. MARINE CLOUDS WILL LIKELY SPREAD OVER THE  
TERMINAL AFTER 00Z FRIDAY, PERHAPS NOT UNTIL AROUND 03Z. CULLEN  
 

 
   
MARINE
 
WEAK WESTERLY WINDS THIS AFTERNOON SHOULD RETURN TO A  
MORE SOUTHERLY DIRECTION OVERNIGHT, BUT SHOULD REMAIN WELL LESS  
THAN 25 KT. WEAK PRESSURE GRADIENTS OVER THE WATERS SHOULD KEEP  
WINDS GENERALLY BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH THE  
FIRST HALF OF THE WEEKEND. A WEAK FRONT DROPPING SOUTHEASTWARD  
ACROSS THE WATERS ON SUNDAY MAY RESULT IN SMALL CRAFT ADVISORY  
LEVEL WIND GUSTS OF 25 KT ACROSS THE WATERS SUNDAY AND EARLY  
MONDAY. THESE WINDS SHOULD RESULT IN SEAS CLIMBING INTO THE 9-12  
FT RANGE DURING THIS TIME. HIGH PRESSURE RETURNING TO THE  
NORTHEAST PACIFIC SHOULD RESULT IN WINDS AND SEAS RELAXING EARLY  
NEXT WEEK. /NEUMAN  
 

 
   
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. THIS AREA IS  
COMMONLY REFERRED TO AS THE CWA OR FORECAST AREA.  
 
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