Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 010403
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
903 PM PDT SAT APR 30 2016

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL CONTINUE TO BUILD TONIGHT AND
SUNDAY OVER SOUTHWEST CANADA AND THE PACIFIC NORTHWEST WITH A LOW
OVER THE GREAT BASIN...LEADING TO A REX BLOCK FOR DRY AND MUCH
WARMER WEATHER IN SOUTHWEST WASHINGTON AND NORTHWEST OREGON UNDER
INCREASING OFFSHORE FLOW. A SOUTHERLY WIND REVERSAL WILL RESULT IN
COOLER TEMPS ALONG THE COAST MONDAY. THE APPROACH OF THE NEXT SYSTEM
OFF THE COAST WILL PULL UP SOME MOISTURE AND INSTABILITY NORTHWARD
INTO NORTHWEST OREGON AND SOUTHWEST WASHINGTON LATE MONDAY AND
ESPECIALLY MONDAY NIGHT AND TUESDAY FOR A CHANCE OF SOME SHOWERS OR
THUNDERSTORMS. THE SYSTEM APPROACHING FROM THE WEST WILL FINALLY
PUSH MARINE AIR MORE STRONGLY INLAND TUESDAY NIGHT AND WEDNESDAY
WITH SHOWERS CONTINUING...AND POSSIBLY A THUNDERSTORM OVER THE
CASCADES. UNSETTLED WEATHER WILL LIKELY CONTINUE THROUGH THE
REMAINDER OF THE COMING WORK WEEK...WITH SOME DRYING POSSIBLE NEXT
WEEKEND.
&&

.SHORT TERM...THE LAST REMAINING STRATOCUMULUS CLOUDS OVER THE HIGHER
TERRAIN ARE CLEARING THIS EVENING AS SUNSET HAS ARRIVED AND AN UPPER
RIDGE BUILDS IN NORTH OF OUR FORECAST AREA AND SETS UP OVER
SOUTHWEST CANADA AND THE PACIFIC NORTHWEST SUNDAY. THIS IN
COMBINATION WITH A LOW OVER THE GREAT BASIN WILL RESULT IN THE
FORMATION OF A REX BLOCK...WHICH WILL LEAD TO MUCH WARMER AND DRY
WEATHER FROM INCREASING OFFSHORE FLOW OVER SOUTHWEST WASHINGTON AND
NORTHWEST OREGON SUNDAY AND MONDAY. TEMPS WILL LIKELY STAY BELOW
RECORD VALUES...BUT WILL REACH THE LOWER TO MID 80S THE NEXT TWO
DAYS INLAND AND POSSIBLY AROUND 80 AT THE COAST SUNDAY.

A SYSTEM WILL BEGIN APPROACHING FROM THE WEST MONDAY WHICH WILL
INCREASE THE SOUTHERLY FLOW OVER OUR FORECAST AREA. THIS WILL RESULT
IN A SOUTHERLY WIND REVERSAL AND A STRATUS SURGE UP THE COAST MONDAY
WITH COOLER TEMPS SPREADING NORTHWARD WITH IT. INLAND AREAS WILL
STILL BE VERY WARM...BUT SOME MOISTURE AND INSTABILITY WILL BE DRAWN
NORTHWARD THAT WILL AFFECT THE OREGON CASCADES LATER MONDAY AND
POSSIBLY A GOOD PART OF SOUTHWEST WASHINGTON AND NORTHWEST OREGON
MONDAY NIGHT AND TUESDAY.

THE MARINE SURGE ALONG THE COAST LOOKS VERY SHALLOW...SO INLAND
PENETRATION MONDAY NIGHT AND TUESDAY MAY BE LIMITED. COOLING INLAND
ON TUESDAY INTO THE LOWER TO MID 70S OR SO MAY LARGELY BE DUE TO THE
CONVECTIVE CLOUDS AND ANY SHOWERS. BUT THIS COULD ALSO CONTINUE TO
KEEP THE DOOR OPEN TO A FEW THUNDERSTORMS TUESDAY AFTERNOON WEST OF
THE CASCADES SHOULD SUFFICIENT SUNBREAKS DEVELOP. LOOK FOR A STRONGER
PUSH OF MARINE AIR TUESDAY NIGHT AND WEDNESDAY AS CLOUDS AND SHOWERS
INCREASE MORE FROM THE OFFSHORE SYSTEM. TOLLESON

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...
TUESDAY NIGHT THROUGH SATURDAY. BROAD UPPER TROUGH REMAINS OVER THE
EASTERN PACIFIC JUST OFF THE CALIFORNIA COAST...PROVIDING FOR SOUTH
TO SOUTHWEST FLOW ALOFT OVER THE REGION. THIS WILL KEEP SHOWER
CHANCES IN PLACE THROUGH THURSDAY. THUNDER CHANCES TUESDAY NIGHT AND
WEDNESDAY AFTERNOON/EVENING WILL BE GREATEST IN THE CASCADES AND
FOOTHILLS...BUT LATEST MODELS SUGGEST ENOUGH INSTABILITY TO KEEP A
SLIGHT CHANCE MENTION FOR THE WILLAMETTE VALLEY. MAY NOT BE ENOUGH OF
A TRIGGER TO TAP INTO THIS...BUT GIVEN THE POTENTIAL IN THE MODEL
SOUNDINGS FEEL A SLIGHT CHANCE REMAINS WARRANTED. EXPECT SOME WARMING
ON FRIDAY AND SATURDAY...WITH PERHAPS SOME DRY CONDITIONS... AS THE
UPPER LOW MIGRATES EASTWARD INTO THE GREAT BASIN AND HIGH PRESSURE
BUILDING INTO THE GULF OF ALASKA AS REX BLOCK DEVELOPS OVER THE
REGION. HOWEVER...MAINTAINED THE FORECAST ALONG THE LINES SUGGESTED
BY A BLEND OF MODELS AS THE ECMWF CONTINUES TO REMAIN WITH A MORE WET
SOLUTION AND SOME SPREAD IN THE GFS ENSEMBLE MEMBERS.
&&

.AVIATION...INCREASING OFFSHORE FLOW SHOULD BRING PREDOMINANTLY VFR
CONDITIONS TO ALL TAF SITES THROUGH 06Z MONDAY. 5SM VISIBILITY AT
KAST SEEMS SUSPICIOUS BASED ON WEB CAMERAS SO KEPT THEM VFR EVEN
THOUGH THE OBSERVATIONS SUGGEST OTHERWISE.

KPDX AND APPROACHES...INCREASING OFFSHORE FLOW WILL BRING VFR
CONDITIONS THROUGH 06Z MONDAY. WINDS SHOULD SWITCH FROM WEST TO EAST
AROUND 19Z SUNDAY. /NEUMAN
&&

.MARINE...A THERMAL TROUGH OVER THE SOUTH OREGON COAST WILL CONTINUE
TO STRENGTHEN AND BUILD NORTHWARD TONIGHT. THIS IS CURRENTLY
PRODUCING GUSTY 25 TO 30 KT WINDS TO THE WATERS OFF THE CENTRAL
OREGON COAST. DUE TO THE INCREASE IN WINDS...DOMINANT PERIODS HAVE
LOWERED AND BECOME WIND DOMINATED SO ISSUED A SMALL CRAFT ADVISORY
FOR STEEP AND HAZARDOUS SEAS THROUGH 3 AM. FARTHER NORTH...WINDS ARE
LIGHTER...BUT STILL LIKELY GUSTING TO 25 KT OFF THE NORTH OREGON
COAST. AS THE FLOW TURNS MORE OFFSHORE OVERNIGHT...WINDS SHOULD RELAX
ACROSS THE INNER WATERS. CURRENT SMALL CRAFT ADVISORIES FOR WINDS
COVER THIS WELL.

A SOUTHERLY WIND REVERSAL WILL PUSH UP THE COAST SUNDAY NIGHT INTO
MONDAY AND COULD BRIEFLY BRING A PERIOD OF 20 TO 25 KT WIND GUSTS.
NOT SURE A SMALL CRAFT ADVISORY WILL BE NEEDED THOUGH. OTHERWISE...AN
UPPER LEVEL TROUGH SPLITTING AND HEADING SOUTH OF THE REGION SHOULD
BRING A RETURN TO A NORTHERLY WIND PATTERN TOWARDS THE MIDDLE OF NEXT
WEEK WITH SMALL CRAFT ADVISORY LEVEL WIND GUSTS OF 25 TO 30 KT
POSSIBLE. HIGH PRESSURE THEN MAY SHIFT MORE SQUARELY OVER THE
NORTHEAST PACIFIC LATE IN THE WEEK AND FOCUS NORTHERLY WINDS ACROSS
THE CENTRAL OREGON WATERS. EVEN THOUGH SEAS LOOK TO REMAIN UNDER 10
FT INDEFINITELY...SEAS WILL LIKELY BECOME FRESH SWELL/WIND DOMINATED
DURING THE MIDDLE TO LATTER HALF OF THE WORK WEEK SO IT STILL LOOKS A
BIT CHOPPY AND ROUGH FOR SMALLER BOATS. /NEUMAN
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 9 AM PDT SUNDAY FOR WATERS
     FROM CAPE SHOALWATER WA TO FLORENCE OR FROM 10 TO 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL MIDNIGHT PDT TONIGHT FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT
     10 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 3 AM PDT SUNDAY
     FOR COASTAL WATERS FROM CASCADE HEAD OR 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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