Area Forecast Discussion
Issued by NWS Portland, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KPQR 301029
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
329 AM PDT SAT MAY 30 2015

.SYNOPSIS...A FLAT UPPER RIDGE OVER THE PACIFIC NORTHWEST WEAKENED A
BIT FRIDAY AND FRIDAY NIGHT AS VERY WEAK SHORT WAVE ENERGY MOVED
THROUGH AND LOWERED 500 MB HEIGHTS ABOUT 30 DM. THE RESULTING WEST
TO SOUTHWEST FLOW ALOFT REINFORCED DEEPENED THE MARINE LAYER THAT
WAS PUSHING INLAND THROUGH THE COASTAL GAPS AND WILL LIKELY SPREAD
INTO PARTS OF THE INLAND VALLEYS THIS MORNING. OCCASIONAL HIGHER
CLOUDS WILL MOVE THROUGH AS WELL. EXPECT A BIT OF COOLING TODAY. THE
UPPER FLOW WILL TURN MORE SOUTHERLY LATER TONIGHT AND SUNDAY AHEAD
OF THE NEXT LOW OFF THE COAST...SHARPENING THE UPPER RIDGE...
RESTRICTING THE MARINE LAYER MORE TO THE COAST AGAIN...AND ALLOWING
INLAND TEMPS TO WARM. AS THE LOW MOVES ONSHORE SUNDAY NIGHT AND
MONDAY...LOOK FOR MORE CLOUDS...AND CHANCE OF SHOWERS AND POSSIBLY A
FEW THUNDERSTORMS EVEN AT NIGHT...AS WELL AS SUBSTANTIAL COOLING.
THE COOLER UNSETTLED PATTERN WILL CONTINUE THROUGH MID WEEK OR
SO...THEN SOME DRYING AND A BIT OF WARMING IS POSSIBLE LATE NEXT
WEEK.
&&

.SHORT TERM...TONIGHT THROUGH MONDAY...A FLAT UPPER LEVEL WAS OVER
THE PACIFIC NORTHWEST...PINCHED BY AN UPPER LOW IN B.C. THAT WILL BE
MOVING EAST SUNDAY...AND AN UPPER LOW OFF THE NORTHERN CALIFORNIA
COAST BETWEEN 130W AND 140W. SOME WEAK UPPER LEVEL SHORT WAVE ENERGY
MOVING THROUGH OVERNIGHT HAS LOWERED 500 MB HEIGHTS ABOUT 30 DM OVER
THE REGION...AND THIS HAS REINFORCED AND DEEPENED THE MARINE LAYER
ALONG THE COAST. MID AND HIGH CLOUDS HAVE BEEN OBSCURING THE LOW
CLOUDS...BUT THEY HAVE BEEN PUSHING INLAND INTO THE COASTAL GAPS AND
EXPECT SOME AREAS OF LOW CLOUDS TO REACH THE WILLAMETTE VALLEY THIS
MORNING. ALL OF THIS SUGGESTS SOME MORE ADDITIONAL COOLING INLAND
TODAY...WITH INLAND TEMPS IN THE UPPER 70S TO AROUND 80. THIS WILL
KEEP BRISK WEST WINDS THROUGH THE GORGE CONTINUING. ANY CHANCE OF
THUNDER IN THE CASCADES WILL BE SLIM TODAY...MAINLY NEAR THE CASCADE
CREST IN LANE COUNTY.

THE LOW WEST OF CALIFORNIA WILL APPROACH FROM THE SOUTHWEST TONIGHT
AND SUNDAY...BACKING THE UPPER LEVEL FLOW TO MORE SOUTHERLY. THIS
WILL RESTRICT THE INLAND PENETRATION OF LOW CLOUDS SUNDAY MORNING...
AND AS A RESULT ALLOW TEMPS INLAND TO RISE AGAIN...INTO THE 80 TO 85
RANGE. THE ONLY RESTRICTING FACTOR TO THE WARMING WILL BE HIGHER
LEVEL CLOUDS AGAIN. AS THE LOW APPROACHES AND BEGINS TO MOVE ONSHORE
SUNDAY NIGHT...DIFFLUENT SOUTHERLY FLOW ALOFT DEVELOPS THAT WILL
LIKELY LEAD TO AN INCREASING THREAT OF SHOWERS AND THUNDERSTORMS.
SOME THUNDERSTORMS MAY DEVELOP OVER THE OREGON CASCADES LATE
SUNDAY...BUT THEN SOME NOCTURNAL THUNDERSTORMS ARE POSSIBLY IN THE
CASCADES AND FOOTHILLS AND POSSIBLY EVEN IN THE WILLAMETTE VALLEY.
WE WILL ALSO SEE A SOUTHWEST MARINE PUSH DEVELOP SUNDAY NIGHT AND
MONDAY MORNING THAT WILL BRING CLOUDY CONDITIONS AND SUBSTANTIALLY
COOLER TEMPS...POSSIBLY 2 TO 4 DEGREES BELOW NORMAL. THIS COULD
RESTRICT THE THREAT OF THUNDER TO EAST OF THE COAST RANGE...
DEPENDING ON ITS TIMING.

AFTER THE LOW MOVES THROUGH LATE MONDAY AND MONDAY EVENING...THE
MODELS SHOW A TRAILING WESTERLY FLOW WITH SEVERAL SHORT WAVES MOVING
THROUGH THAT WILL MAINTAIN THE STRONG ONSHORE FLOW WITH OCCASIONAL
SHOWERS INTO THE MIDDLE OF NEXT WEEK. TOLLESON

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...
MONDAY NIGHT THROUGH FRIDAY...BY MONDAY NIGHT THE BASE OF A
NEGATIVELY TILTED UPPER LEVEL TROUGH WILL BE PASSING OVER THE REGION.
THE COLD CORE OF THE UPPER LOW WILL MOVE FROM WEST-SOUTHWEST TO
NORTH-NORTHEAST ACROSS THE FORECAST AREA BY EARLY TUESDAY AND BRING
CONTINUED SHOWERS AND A SLIGHT CHANCE OF THUNDER IN THE CASCADES. A
SHORTWAVE TROUGH MAY PROVIDE FOR ADDITIONAL SHOWERS ON WEDNESDAY SO
MAINTAINED A SLIGHT CHANCE OF SHOWERS ACROSS MUCH OF THE AREA.
CONFIDENCE IS SOMEWHAT LOWER FOR SECOND HALF OF THE WEEK. EXPECT
THURSDAY TO GENERALLY BE DRY FOR MOST LOCATIONS BUT MODELS SUGGEST
THE NEXT UPPER TROUGH WILL STRENGTHEN INTO A CLOSED LOW. WHILE THE
GFS MAINTAINS THIS LOW CENTERED OVER WASHINGTON AND OREGON FOR THE
END OF THE WEEK...THE ECMWF CENTERS THE LOW OVER CALIFORNIA AND INTO
THE SOUTHERN GREAT BASIN...WHICH WOULD ENABLE SOME RIDGING TO BUILD
OVER THE PACIFIC NORTHWEST. THEREFORE GIVEN THIS LOWER CONFIDENCE
FORECAST...ELECTED TO MAINTAIN THE CURRENT FORECAST OF TEMPERATURES
RETURNING TO NEAR SEASONAL NORMS AND AREAS OF SLIGHT CHANCE POPS.
&&

.AVIATION...SOLID MVFR STRATUS ALONG THE COAST AND INTO MAJOR COASTAL
RIVER DRAINAGES. STRATUS ALREADY AT KKLS AS OF 08Z. COASTAL AREAS TO
REMAIN MVFR...WITH LOCALIZED IFR THROUGH THE MORNING HOURS. AREAS
SOUTH OF KONP MAY SEE CIGS BECOME BKN MID TO LATE AFTERNOON. IF THIS
DOES OCCUR...EXPECT A RETURN TO OVC LOW-END MVFR OR HIGH END IFR
DURING THE EVENING. ELSEWHERE...SWLY MARINE PUSH OCCURRING IN THE
CENTRAL AND SOUTH INTERIOR VALLEYS TONIGHT. GOOD CHANCE MVFR CIGS
WILL DEVELOP IN THE SOUTH WILLAMETTE VALLEY AROUND 12-14Z.
ALSO...EXPECT LOW-END MVFR CIGS TO DEVELOP IN THE SW WA INTERIOR
LOWLANDS AND FAR N WILLAMETTE VALLEY AS WELL. NEARLY ALL INLAND AREAS
WILL BE VFR BY 18Z SAT.

KPDX AND APPROACHES...VFR THROUGH 12Z SUN. HOWEVER...EXPECT LOW-END
MVFR CIGS TO DEVELOP AT THE TERMINAL AND VICINITY BETWEEN 12Z AND
14Z. RETURN TO VFR BY 17Z. WEISHAAR
&&

.MARINE...RATHER BENIGN MARINE CONDITIONS FOR THE NEXT SEVERAL DAYS.
WIND SPEEDS GENERALLY 15 KT OR LESS...WITH AFTERNOON AND EVENING
GUSTS UP TO 20 KT AT TIMES.

SEAS PRIMARILY 5 FT OR LESS THROUGH NEXT WEEK. SPECTRAL ANALYSIS
SUGGESTS SEVERAL 2 OR 3 FT SWELL SETS THROUGH EARLY NEXT WEEK...ANY
OF WHICH COULD BE THE DOMINANT FEATURE. EXPECT MAINLY WIND-WAVE
DOMINATED CONDITIONS THROUGH THE WEEKEND...WITH A SECONDARY
LONGER-PERIOD SW SWELL. WEISHAAR
&&

.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.



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.