Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 092120
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
219 PM PDT WED JUL  9 2014

.SYNOPSIS...GENERALLY STABLE WEST FLOW ALOFT WILL REMAIN OVER
SOUTHWEST WASHINGTON AND NORTHWEST OREGON THROUGH THURSDAY. MOIST AND
UNSTABLE SOUTH FLOW ALOFT SPREADS INTO THE AREA BEGINNING LATE
THURSDAY AND CONTINUING THROUGH FRIDAY NIGHT. THIS BRINGS THE THREAT
OF THUNDERSTORMS TO THE CASCADES AND POSSIBLY AS FAR WEST AS THE
COAST RANGE BY FRIDAY EVENING. AN UPPER LOW OFF THE NORTH CALIFORNIA
COAST SATURDAY IS EXPECTED TO MOVE NORTH TO NORTHEAST AND INLAND OVER
INTO EXTREME SW OREGON BY LATE SUNDAY FOR ANOTHER THREAT OF
THUNDERSTORMS. WELL-ABOVE NORMAL DAYTIME TEMPERATURES CAN BE EXPECTED
FRIDAY THROUGH AT LEAST EARLY NEXT WEEK.

&&

.SHORT TERM...TONIGHT THROUGH SATURDAY...THE FOCUS OF THIS FORECAST
WILL BE ON THE FRIDAY THROUGH FRIDAY NIGHT PERIOD. AFTERNOON WATER
VAPOR IMAGERY SHOWED A SHORT-WAVE DISTURBANCE MOVING ACROSS ERN
WASHINGTON. AN UPPER LEVEL TROUGH WAS LOCATED OVER BRITISH COLUMBIA
AND A BAGGY TROUGH WITH MULTIPLE CIRCULATIONS WAS NOTED OFF THE
CALIFORNIA COAST AROUND 130 TO 140W LONGITUDE. IT IS THIS TROUGH THAT
WILL BECOME A PLAYER AT THE END OF THE SHORT TERM PERIOD.

NO SIGN OF CONVECTION AS OF 20Z OVER THE CASCADES. SOME CUMULUS
DEVEOPING NEAR AND JUST EAST OF THE SOUTH OREGON CASCADE CREST BUT
SWLY STEERING FLOW WILL KEEP ANY DEVELOPMENT EAST OF THE FORECAST
AREA. THE MARINE LAYER HAS RETREATED TO JUST OFF THE COASTLINE...
EXCEPT FOR THE S WA AND FAR N OREGON COAST WHERE THE NW BOUNDARY
LAYER WIND EXISTS...INSTEAD OF A NORTH WIND DIRECTION FURTHER SOUTH.
THE BRITISH COLUMBIA UPPER TROUGH CONTINUES TO MOVE EAST TONIGHT AND
THURSDAY...MAINTAINING STABLE WLY FLOW OVER THE FORECAST AREA. ONE OF
THE BIGGEST CHANGES TODAY HAS BEEN THE DEW POINT READINGS. YESTERDAY
MANY AREAS HAD DEW POINTS IN THE 55-65F RANGE. 20Z READINGS WERE IN
THE UPPER 40S TO MID 50S...WHICH ARE PRETTY CLOSE TO NUMERICAL
GUIDANCE. 24-HR TEMPERATURE DIFFERENCES AT 20Z WERE GENERALLY 4-8
DEGREES COOLER.

THURSDAY LOOKS SIMILAR TO TODAY WITH CONTINUED WLY FLOW ALOFT. GFS
AND ECMWF MODEL 850 MB TEMPS FOR PDX EXPECTED TO BE AROUND 17C TODAY
AND 18C THURSDAY. LATEST MAV/MET GUIDANCE SHOWS ABOUT 2-4 DEGREES
WARMING THURSDAY. HOWEVER...BY LATE THURSDAY SOUTH FLOW ALOFT
EXPECTED TO BE SPREADING INTO SWRN OREGON...WHICH IS A PRECURSOR
FOR THINGS TO COME. GFS AND ECMWF SHOW THE SLY FLOW MOVING NWD THU
NIGHT...AND BY 12Z FRI MODELS DEPICT A SHORT-WAVE NEAR KACV. MODELS
SHOW THIS DISTURBANCE LIFTING N FRI...SETTING THE STAGE FOR ANOTHER
POTENTIAL THUNDERSTORM THREAT. MADE SIGNIFICANT CHANGES TO THE FRI
AND FRI NIGHT FORECAST. LATEST SPC CONVECTIVE DISCUSSION SHOWS A
GENERAL THUNDERSTORM THREAT ALL THE WAY TO THE CENTRAL OREGON COAST
BY 12Z SAT. NAM CONVECTIVE PARAMETERS APPEAR TO BE MORE FAVORABLE
THAN THOSE FROM THE GFS. BASED ON THE NAM...THE DISTURBANCE OFF THE
FAR N CALIFORNIA COAST 00Z SAT MOVES SLOWLY NWD FRI NIGHT...BUT
ENCOUNTERS A SOMEWHAT DIFFLUENT FLOW ALOFT. NAM BRINGS A NICE
VORT-LOBE DUE N OVER THE CENTRAL AND N OREGON COAST RANGE FRI NIGHT.
THIS IS COUPLED WITH A NICE 700 MB THETA-E RIDGE THAT TRANSLATES NWD
AS WELL. HOWEVER...GFS MODEL SOUNDING FOR KEUG VALID 00Z SAT AND 06Z
SHOWS MINIMAL CONVECTIVE SUPPORT. ECMWF INDICATES AN QPF AREA S OF
MT. JEFFERSON AND WEST INTO THE CASCADE FOOTHILLS AND POSSIBLY FAR
EAST PORTION OF THE CENTRAL AND SOUTH WILLAMETTE VALLEY. AIR MASS
WILL BECOME QUITE MOIST WITH MODEL PRECIPITABLE WATER VALUES PUSHING
1.50 INCHES BY 12Z SAT. FOR NOW HAVE UPPED THUNDERSTORM PROBABILTIY
TO CHANCE CATEGORY FOR THE HIGHER CASCADES 00Z-06Z SAT AND INCLUDED
SLIGHT CHANCE FOR THE N AND CENTRAL CASCADE FOOTHILLS AND INTO THE
WILLAMETTE VALLEY. THIS PATTERN HAS THE POTENTIAL TO SPREAD ELEVATED
CONVECTION EVEN FURTHER W TO THE COAST RANGE. MAINTAINED THE
THUNDERSTORM THREAT FOR THE OREGON CASCADE ZONES 06Z-12Z SAT. THE
SHORT-WAVE DYNAMICS CONTINUE TO PUSH N LATE FRI NIGHT INTO SAT
MORNING...CROSSING THE COLUMBIA RIVER AROUND 12Z SAT.

SLIGHTLY MORE STABLE SWLY FLOW ALOFT WILL BE OVER THE AREA SAT...BUT
CANNOT RULE OUT AN AFTERNOON THUNDERSTORM OVER THE HIGHER CASCADES.
HOT AND HUMID CONDITIONS CAN BE EXPECTED SAT...WITH MODEL FORECAST
850 MB TEMPS FOR KPDX AROUND 20C...WHICH IS THE USUAL BENCHMARK FOR
90F OR HIGHER TEMPS. DEW POINTS WILL ALSO RETURN TO THE 55-65 DEG
RANGE. THIS WILL BE THE START OF A MULTI-DAY HOT SPELL. WEISHAAR

.LONG TERM...MAIN EVENT WILL BE THE CONTINUED HOT AND HUMID
CONDITIONS. BY SUN THE UPPER RIDGE AXIS SHIFTS TO WRN IDAHO AS AN
UPPER LOW OFF THE N CALIFORNIA COAST FINALLY WORKS ITS WAY NORTH AND
EAST. GFS AND ECMWF HAVE BEEN HANDLING THIS FEATURE DIFFERENLY THE
PAST COUPLE OF DAYS AND TODAY IS NO EXCEPTION. BY 00Z MON THE GFS
MAINTAINS A CLOSED LOW CIRCULATION OFF THE N CAL COAST WHILE THE
ECMWF HAS AN OPEN TROUGH. THE GFS APPEARS TO GENERATE MORE DYNAMICS
SUN NIGHT AS THE SHORT-WAVE LIFTS NORTHEAST. SHOULD THE ECMWF
VERIFY...THERE WOULD BE MUCH LESS OF A CONVECTIVE THREAT. SEVERAL
FACTORS TO CONSIDER REGARDING THUNDERSTORM POTENTIAL...INCLUDING
TIMING AND POSITIONING OF THE TROUGH. EITHER WAY...IT WILL REMAIN HOT
AND HUMID SUNDAY. 500 MB HEIGHTS REBOUND EARLY NEXT WEEK FOR
CONTINUED UNSEASONALLY HOT CONDITIONS. MUCH LARGER MODEL DIFFERENCES
CROP UP TUE AND BEYOND...WITH THE ECMWF HOLDING FIRM WITH THE MONSTER
RIDGE. WEISHAAR
&&

.AVIATION...00Z TAF EXPECTATIONS...VFR TO CONTINUE TONIGHT WITH
HIGH END IFR TO LOW END MVFR STRATUS RETURNING TO THE COAST
SIMILAR TIMES TO LAST NIGHT...04Z AT KAST AND 08Z AT KONP. ALSO
SIMILAR TO LAST NIGHT EXPECT TO SEE MVFR STRATUS PUSH UP THE
LOWER COLUMBIA RIVER...POTENTIALLY REACHING KPDX AND KTTD LATE
OVERNIGHT. PERSISTENCE SEEMS LIKE A GOOD BURN OFF FORECAST FOR
TOMORROW WITH THE CENTRAL COAST CLEARING AROUND 17Z AND KAST
AROUND 21Z. WINDY...BUT A BIT LIGHTER...CONDITIONS ALSO CONTINUE
FOR KONP THURSDAY WITH GUSTS AROUND 25 KT. /JBONK

KPDX AND APPROACHES...VFR/SKC THROUGH MOST OF THE NIGHT. GIVING
ABOUT A 25 PERCENT CHANCE BROKEN MVFR STRATUS WILL WORK UP THE
COLUMBIA RIVER FROM THE COAST RIGHT AND ARRIVE AT THE FIELD AROUND
SUNRISE. FEEL MOST LIKELY A SCT DECK WILL PREVAIL. DECK SHOULD BE
AROUND 015 TO 020 AGL. /JBONK

&&

.MARINE...HIGH PRES WILL REMAIN OVER THE NW PAC THROUGH THE
WEEKEND...KEEPING WINDS FROM THE N TO NW. SMALL CRAFT ADVISORY WINDS
WILL CONTINUE THROUGH THU OVER THE OUTER WATERS WITH THE INNER
WATERS HAVING ENOUGH POCKETS REACHING CRITERIA TO WARRANT ADDING
THEM IN AS WELL. THE HIGHER SPEEDS WILL OCCUR ALONG THE IMMEDIATE
COAST AND CLOSER TO THE THE 45 TO 60 NM AREAS OFFSHORE. WILL SEE A
BIT OF A REPEAT THURSDAY ALTHOUGH THE INNER WATERS MAY STAY BELOW
CRITERIA. BY FRI...THE HIGH PRES WILL WEAKEN CAUSING WINDS TO
DROP AND STAY BELOW ADVISORY THRESHOLDS FOR THE WEEKEND.

MINIMAL SWELL ENTERS THE WATERS FROM OUTSIDE THE REGION OVER THE
NEXT FEW DAYS...LEAVING SEAS DOMINATED BY STEEP FRESH SWELL AND
LOCALLY DRIVEN WIND WAVES. AS A RESULT...THE WATERS WILL BE CHOPPY
AT TIMES THROUGH THURSDAY. SEAS DO BECOME SQUARE AT 8 FT 8 SEC AS
THE WINDS PEAK TODAY AND WILL CONTINUE THE SMALL CRAFT ADVISORY
FOR SEAS ISSUED EARLIER. /JBONK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 2 AM PDT THURSDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT
     THURSDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM MIDNIGHT
     TONIGHT TO 5 AM PDT THURSDAY.

&&

$$

MORE WEATHER INFORMATION ONLINE AT...
    HTTP://WEATHER.GOV/PORTLAND

INTERACT WITH US VIA SOCIAL MEDIA
    WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.PORTLAND.GOV
    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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