Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 020943
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
243 AM PDT SUN AUG 2 2015

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE OVER THE PACIFIC NW WILL
BEGIN TO SHIFT E TODAY AND MON. AN UPPER LEVEL LOW OFF THE
CALIFORNIA COAST WILL STEER SOME MOISTURE N OVER WESTERN OREGON INTO
MONDAY BRINGING A THREAT OF THUNDERSTORMS. AN UPPER LEVEL TROUGH
WILL MOVE OVER THE AREA MONDAY THROUGH THURSDAY FOR GRADUAL COOLING.
&&

.SHORT TERM...RADAR AND SATELLITE SHOWED THUNDERSTORMS TENDING TO
REGENERATE OVER COASTAL PARTS OF SW OREGON AND UP OFF THE CENTRAL
OREGON COAST. THIS IS AN AREA AT THE HEAD OF A DRY SLOT SEEN IN
WATER VAPOR IMAGERY WHICH TENDS TO BE FAVORED FOR CONVECTION.
EVENING MVFR SOUNDING SUGGESTS CONVECTION IS FAIRLY HIGH
BASED...DRIVEN BY INSTABILITY ALOFT AND WEAK DIVERGENCE ALOFT. THE
UPPER RIDGE DOMINANT THE LAST FEW DAYS WAS BEGINNING TO SHIFT
E...ALLOWING THE LOW OFF THE CA COAST TO LIFT HIGH LEVEL MOISTURE
AND MARGINAL INSTABILITY N. WITH THE SOUTHERLY FLOW CONTINUING
THROUGH SUN NIGHT IT BECOMES DIFFICULT TO COMPLETELY RULE OUT
CONVECTION ANYWHERE...ALTHOUGH MODEL SOUNDINGS SUGGEST INSTABILITY
ALOFT IS MARGINAL AT BEST. FOR THE MORNING WILL STICK WITH CURRENT
TRENDS AND SUPPORTED BEST BY HRRR...AND EXPAND THE AREA FOR SHOWERS
AND THUNDERSTORMS N...ESP UP THE COAST. BY AFTERNOON MODELS RETURN
TO FAVORING CASCADES WITH BEST CONDITIONS FOR INSTABILITY...BUT
AGAIN WITH THE CONVECTIVE THREAT HIGH BASED WILL CARRY A THREAT W TO
THE COAST. MODELS TENDING TO INDICATE A WEAK SHORTWAVE LIFTING N
THROUGH WESTERN OREGON OVERNIGHT TONIGHT PROVIDING A POTENTIAL FOCUS
FOR THUNDERSTORM THREAT...SO WILL EXPAND CHANCES FOR THUNDER FURTHER
N AND W INTO THE COAST RANGE...BUT KEEP POPS LOW DUE TO MARGINAL
INSTABILITY. WEAKENING OF THE RIDGE ALOFT AND AN INCREASE IN ONSHORE
FLOW...ESP ACROSS THE CENTRAL OREGON COAST RANGE OVERNIGHT...WILL
CONTRIBUTE TO TEMPS BEGINNING TO MODERATE TODAY. H8 TEMPS STILL
SUPPORT INLAND HIGHS IN THE LOWER TO MID 90S TODAY SO WILL KEEP THE
HEAT ADVISORY IN EFFECT TODAY.

PROGRESSIVELY COOLER AIR PUSHED IN WITH A STRONGER NW ONSHORE FLOW
MON AND TUE...BRINGING TEMPS DOWN CLOSER TO NORMAL BY TUE. AS THE
UPPER FLOW TURN MORE SW MON...AND EVENTUALLY WESTERLY TUE TO
CONVECTIVE THREAT WILL BECOME LIMITED TO THE CASCADE CREST.

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...THE GENERAL
TREND IN THE EXTENDED PERIOD WILL BE TOWARDS COOLER WEATHER. MODELS
CONTINUE TO SHOW AN UPPER LEVEL TROUGH BRUSHING BY THE REGION LATE
TUESDAY...BUT KEEPS MOST OF THE ENERGY TO OUR NORTH. WILL KEEP A
SLIGHT CHANCE OF THUNDERSTORMS OVER THE LANE COUNTY CASCADES FOR LATE
TUESDAY DUE TO SOME LINGERING INSTABILITY. TEMPERATURES RETURN
TOWARDS SEASONAL NORMALS BY WEDNESDAY...BUT WILL INCREASE SLIGHTLY
FOR THE LATTER HALF OF THE WEEK AS A WEAK UPPER LEVEL RIDGE BUILDS
INTO THE PACIFIC NORTHWEST. MODELS DIVERGE SIGNIFICANTLY AS WE GO
INTO NEXT WEEKEND. AS SUCH...HAVE USED A BROAD BRUSH APPROACH FOR
NEXT WEEKEND AND INTRODUCED A SLIGHT CHANCE OF SHOWERS OVER THE SOUTH
WASHINGTON CASCADES AND A SLIGHT CHANCE OF THUNDERSTORMS FOR THE
OREGON CASCADES. /64

&&

.AVIATION...VFR INLAND THIS MORNING BUT WITH SOME MID/HIGH CLOUDS
FROM CONVECTION OVER SW OREGON WILL DRIFT OVER THE REGION. SLIGHT
CHANCE OF SEEING RAIN/THUNDER OVER THE SOUTHERN HALF OF THE
FORECAST AREA 10Z-17Z BUT CHANCE APPEARS SMALL ENOUGH TO PRECLUDE
MENTION IN ANY PARTICULAR TAF. AT THE COAST...SHALLOW IFR STRATUS
WILL CONTINUE ALONG THE CENTRAL COAST AND LIKELY DEVELOPS ALONG
THE NORTH COAST BY 11Z. THIS STRATUS WILL RETREAT OFFSHORE AROUND
18Z FOR VFR CONDITIONS ALONG THE COAST. EXPECT DEVELOPING CUMULUS
SUN AFTERNOON/EVENING WITH THE POSSIBILITY OF THUNDERSTORMS
EXPANDING OVER MUCH OF THE AREA EAST OF THE COAST RANGE 03Z-10Z
TUE...BUT AGAIN INSUFFICIENT CONFIDENCE TO INCLUDE IN ANY
PARTICULAR TAF AT THIS TIME.

KPDX AND APPROACHES...VFR CONDITIONS TONIGHT AND SUNDAY. SOME
RESIDUAL MID/HIGH CLOUDS FROM CONVECTION OVER SW OREGON WILL DRIFT
OVERHEAD THIS MORNING. LIKELY SEE CUMULUS DEVELOPMENT THIS
AFTERNOON WITH THE POTENTIAL FOR A THUNDERSTORM. CHANCES BEST S
AND E OF TERMINAL AND IN CASCADES...BUT CANNOT RULE OUT ONE
IMPACTING THE TERMINAL DURING 04Z-10Z.   CULLEN

&&

.MARINE...A FEW THUNDERSTORMS OFFSHORE ARE DRIFTING FROM S TO N
INTO THE OUTER CENTRAL OREGON COASTAL WATERS EARLY THIS MORNING.
POTENTIAL THREATS ARE LIGHTNING AND GUSTY OUTFLOW WINDS...WITH THE
THREAT AREA EXPANDING TO COVER MUCH OF THE COASTAL WATERS THIS
MORNING AND AGAIN IN THE EVENING HOURS.

OTHERWISE...LITTLE CHANGE TO THE OVERALL PATTERN FOR SUNDAY WITH
N WINDS OVER THE WATERS. AN OVERNIGHT ASCAT PASS REVEALED WINDS
STILL AROUND 20 KT OVER THE OUTER WATERS...SO WILL ALLOW THE
ADVISORY FOR WINDS TO CONTINUE THROUGH 10 AM AS AREAS OF
MARGINALLY ADVISORY STRENGTH WINDS MAY STILL EXIST. ANOTHER SCA
FOR WINDS IN EFFECT FOR THIS AFTERNOON/EVENING AS MORE WIDESPREAD
GUSTS TO 25 KT EXPECTED TO REDEVELOP.

MEANWHILE...THE PERSISTENT NORTHERLY WINDS ARE MAINTAINING STEEP
SEAS OVER THE WATERS OF 6 TO 7 FEET AT 6 TO 8 SECONDS.
THEREFORE...WITH CONDITIONS FLUCTUATING ABOVE OR VERY NEAR OUR
CRITERIA FOR HAZARDOUS SEAS...THE ADVISORY FOR HAZARDOUS SEAS
LOOKS ON TRACK FOR TODAY. CULLEN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HEAT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR CENTRAL COLUMBIA
     RIVER GORGE-CENTRAL WILLAMETTE VALLEY-GREATER PORTLAND
     METRO AREA-LOWER COLUMBIA-SOUTH WILLAMETTE VALLEY-UPPER
     HOOD RIVER VALLEY-WESTERN COLUMBIA RIVER GORGE.

WA...HEAT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR CENTRAL COLUMBIA
     RIVER GORGE-GREATER VANCOUVER AREA-I-5 CORRIDOR IN COWLITZ
     COUNTY-WESTERN COLUMBIA RIVER GORGE.

PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 AM PDT THIS MORNING FOR
     WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR FROM 10
     TO 60 NM-WATERS FROM CASCADE HEAD TO FLORENCE OR FROM 10 TO
     60 NM.

     SMALL CRAFT ADVISORY FOR WINDS FROM 3 PM THIS AFTERNOON TO
     MIDNIGHT PDT TONIGHT FOR COASTAL WATERS FROM CAPE SHOALWATER
     WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM PDT THIS
     AFTERNOON FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

&&

$$

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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