Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 290425
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
925 PM PDT MON JUL 28 2014

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL BE CENTERED INLAND OVER THE
PACIFIC NORTHWEST THROUGH THIS WEEK WITH AN UPPER LOW CENTERED OFF
THE B.C. COAST. THE RESULTING LIGHT SOUTHWEST FLOW ALOFT WILL PRODUCE
VERY WARM AND DRY WEATHER TO SOUTHWEST WASHINGTON AND NORTHWEST
OREGON...EXCEPT FOR AN INCREASING CHANCE FOR THUNDERSTORMS IN THE
CASCADES AND ESPECIALLY IN OREGON IN THE AFTERNOONS AND EVENINGS.
THE MARINE LAYER WILL BE SHALLOW BUT IS MORE SOLID...WITH A LITTLE
SEEPAGE THROUGH THE COASTAL GAPS EXPECTED AS THE WEEK PROGRESSES.
&&

.UPDATE...HAD ONE GOOD THUNDERSTORM DEVELOP OVER FAR SOUTHEASTERN
LANE COUNTY AND LASTED FOR THE BETTER PART OF A COUPLE HOURS. PRECIP
ESTIMATES FROM THE MEDFORD RADAR PUT UPWARDS OF AN INCH OF RAIN ON
THE TUMBLEBUG COMPLEX BURN SCAR FROM 2009. GROUND TRUTH OF 0.54
INCHES AT A NEARBY RAWS AT LEAST GIVES CREDENCE TO THOSE ESTIMATES.
ISSUED A COUPLE NOWCASTS AND HIGHLIGHTED CONCERN FOR SOME LOCALIZED
DEBRIS FLOW COMING OUT OF TUMBLEBUG CREEK AND ECHO CREEK. IF ANY
FLOWS DID OCCUR...THEY ULTIMATELY COULD DRAIN INTO THE UPPER REACHES
OF THE WILLAMETTE MIDDLE FORK. IN OTHER AREAS...THE COASTAL STRATUS
HAS PUSHED A LITTLE FURTHER INLAND BRINGING VERY PATCHY FOG WITH
NEWPORT AIRPORT MAINLY REPORTING IN THE 1/2 MILE TO 1 MILE RANGE,
BUT BRIEFLY FALLING BELOW 1/4 MILE A COUPLE HOURS AGO. AS THE SEAS
BREEZE EASES UP THIS EVENING...EXPECT THERE TO BE ADDITIONAL PATCHY
FOG WITH MORE WIDESPREAD COVERAGE EXPECTED OVERNIGHT. HAVE DOUBTS
THE STRATUS WILL PUSH VERY FAR INLAND PER SHORT TERM MODEL DATA BUT
WILL GIVE THE PREVIOUS SHIFT THE BENEFIT OF THE DOUBT IN BRINGING
THE CLOUDS IN TO AROUND KELSO. /JBONK

.PREV DISC... /ISSUED 204 PM PDT MON JUL 28 2014/

SHORT TERM...AN UPPER LOW OFF THE B.C. COAST AND AN UPPER LEVEL
RIDGE ANCHORED INLAND OVER THE WESTERN U.S. WILL BE THE FEATURES
THAT PRODUCE THE WEATHER PATTERN THAT WILL AFFECT THE PACIFIC
NORTHWEST AND SOUTHWEST WASHINGTON AND NORTHWEST OREGON THROUGH THIS
WEEK. THIS WILL PRODUCE LIGHT MOSTLY SOUTHWEST FLOW ALOFT WITH HIGH
500 MB HEIGHTS. A MARINE LAYER HAS FORMED ALONG THE COAST...BUT THE
ASSOCIATED SUBSIDENCE WILL KEEP THE MARINE LAYER RATHER SHALLOW
THROUGH THE WEEK. WE WILL SEE SOME SEEPAGE INLAND THROUGH COASTAL
GAPS AS THE WEEK PROGRESSES.

SKIES HAVE MOSTLY CLEARED ALONG THE COAST BUT THE FOG AND LOW CLOUDS
ARE STILL FAIRLY CLOSE TO THE COAST...AND MAY NOT CLEAR BACK OFFSHORE
TOO MUCH MORE. THERE ARE SOME CUMULUS BEGINNING TO DEVELOP IN SOUTH
CENTRAL OREGON IN KLAMATH AND SOUTHERN DESCHUTES COUNTY...INCLUDING
JUST EAST OF WILLAMETTE PASS. WILL KEEP THE SLIGHT CHANCE OF THUNDER
IN FAR EASTERN LANE COUNTY BUT NOT SURE WE WILL ACTUALLY SEE ANY
LIGHTNING ON THE WEST SIDE OF THE CASCADE CREST THIS AFTERNOON AND
EVENING.

THE CONTROLLING WEATHER PATTERN IS THE SAME ON TUESDAY...THOUGH THERE
ARE SOME SUBTLE DIFFERENCES. IT WILL STILL BE WARM INLAND WITH TEMPS
CLOSE TO 90. EXPECT THE MARINE LAYER TO CONTINUE NEAR THE COAST WITH
FOG AND LOW CLOUDS BACK ONTO THE COAST FAIRLY EARLY THIS EVENING BUT
REMAINING QUITE LOW AND SHALLOW...WITH SOME LOW CLOUDS LOCALLY
INLAND ALONG THE COLUMBIA RIVER AND POSSIBLY CLOSE TO KELSO EARLY
TUESDAY. ALSO...THE MODELS ARE SHOWING A BIT MORE MOISTURE SPREADING
UP FROM THE SOUTH ON TUESDAY AS PRECIPITABLE WATER VALUES RISE TO
NEAR 1 INCH. THUS EXPECT A BETTER CHANCE OF THUNDERSTORMS IN THE
AFTERNOON AND EVENING IN THE OREGON CASCADES...PROBABLY STAYING
SOUTH OF MOUNT JEFFERSON. WHILE THESE THUNDERSTORMS MAY STILL TEND
TO BE A BIT DRY...A FEW MAY EVENTUALLY PRODUCE SOME RAINFALL...AND
THE GFS MODEL EVEN DEVELOPS A QPF BULLSEYE...POSSIBLY DUE TO
CONVECTIVE FEEDBACK.

THE PATTERN WEDNESDAY LOOKS VERY SIMILAR TO TUESDAY...WITH A CHANCE
OF THUNDERSTORMS AGAIN OVER THE CASCADES IN THE AFTERNOON AND
EVENING. PWS REMAIN AROUND 1 INCH. THE LIGHT SOUTHWEST FLOW WILL
PROBABLY KEEP THUNDERSTORMS MAINLY SOUTH OF THE COLUMBIA RIVER AGAIN.
THE MODELS IMPLY THE MARINE LAYER MAY BECOME MORE SOLID ALONG THE
COAST WEDNESDAY...AND MAY TRY TO EXTEND INLAND TO NEAR PORTLAND BUT
ANYTHING WILL BE VERY BRIEF AND NOT HAVE MUCH IMPACT. TEMPS INLAND
WILL CONTINUE TO BE VERY WARM WEDNESDAY...IN THE UPPER 80S TO AROUND
90. NOT SEEING MUCH CHANGE FROM WEDNESDAY TO THURSDAY AND THE
FORECAST GRIDS ARE NOT MUCH DIFFERENT. TOLLESON

LONG TERM...THURSDAY NIGHT THROUGH MONDAY. THE RIDGE IN PLACE OVER
THE WESTERN U.S. WILL REMAIN IN PLACE THROUGH THE END OF THE WEEK. A
SERIES OF SHORTWAVES ARE FORECAST TO TRAVEL UP THE WEST SIDE OF THE
RIDGE...POSSIBLY IMPACTING OUR AREA. THESE IMPULSES BRING CHANCES
FOR THUNDERSTORMS...MAINLY IN THE CASCADES...THROUGH THE WEEKEND.
MODEL UNCERTAINTY EXISTS ON THE TIMING AND STRENGTH OF THESE
SHORTWAVES AS MODEL RESOLUTION ACCURACY DECLINES RAPIDLY FURTHER IN
THE FORECAST PERIOD...ESPECIALLY FOR THESE SMALLER FEATURES. HAVE
DECREASED POPS FURTHER NORTH ON FRIDAY AS THE MODELS HAVE CONVERGED
ON A MORE SOUTHERLY TRACK FOR STORM CHANCES...AND DECREASED
CONFIDENCE OF THUNDER CHANCE OVER THE WEEKEND DUE TO GREAT MODEL
UNCERTAINTY ON TIMING AND LOCATION. -MCCOY

&&

.AVIATION...LIFR/VLIFR STRATUS AND FOG PUSHED ONTO THE CENTRAL OR
COAST THIS AFTERNOON AND WILL LIKELY REMAIN IN PLACE THROUGH TONIGHT
AND INTO TOMORROW MORNING. IFR/LIFR STRATUS SHOULD ALSO PUSH INTO
THE N OR AND S WA COAST...INCLUDING KAST...BETWEEN 06Z AND 09Z.
COASTAL STRATUS SHOULD BURN BACK OFFSHORE BY EARLY TOMORROW
AFTERNOON. INLAND SITES TO REMAIN VFR THROUGH THE NEXT 24 HRS AS
HIGH PRES RESIDES OVER THE REGION...WITH DRY SWLY FLOW ALOFT.

KPDX AND APPROACHES...VFR IN CONTROL FOR THE NEXT 24 HRS. PYLE

&&

.MARINE...N/NW FLOW REMAINS IN CONTROL THIS WEEK WITH HIGH PRES OVER
THE NE PAC AND A THERMALLY INDUCED SURFACE TROF OVER NW CALIF AND
FAR SW OREGON. PRES GRADIENTS WILL FLEX FROM TIME TO TIME...BUT
TIGHTEST GRADIENT WILL REMAIN OVER THE NEAR SHORE WATERS. DECIDED TO
END THE SMALL CRAFT ADVISORY FOR TONIGHT AS THE PRES GRADIENT HAS
BEGUN TO WEAKEN...BUT ISSUED ANOTHER FOR TOMORROW AFTERNOON AND
EVENING OVER THE INNER WATERS.

SEAS GENERALLY RUNNING 4 TO 6 FT OVER THE NEXT SEVERAL DAYS.
CONDITIONS MAY BECOME A BIT CHOPPY AT TIMES DURING THE AFTERNOON AND
EVENING HOURS IN RESPONSE TO THE STRONGER WINDS. PYLE

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 2 PM TO 11 PM PDT TUESDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD
     OR OUT 10 NM-COASTAL WATERS FROM CASCADE HEAD TO FLORENCE
     OR OUT 10 NM.

&&

$$

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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