Area Forecast Discussion
Issued by NWS Portland, OR

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716
FXUS66 KPQR 302117
AFDPQR

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

.SYNOPSIS...STRONG HIGH PRESSURE WILL BUILD OVER THE REGION FOR THE
REMAINDER OF THE WEEKEND. AS OFFSHORE FLOW DEVELOPS...TEMPERATURES
WILL WARM WELL ABOVE SEASONAL NORMALS ALONG COASTAL AND INLAND AREAS
SUNDAY...AND OVER INLAND AREAS MONDAY. AS THE HIGH PRESSURE MOVES
EASTWARD...FLOW BECOMES MORE SOUTHERLY/SOUTHWESTERLY LATE MONDAY.
THIS WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS MONDAY
AFTERNOON AND EVENING...PARTICULARLY NEAR THE CASCADES. AFTER
THAT...AN UPPER TROUGH SETTLES IN OVER THE EASTERN PACIFIC FOR A
SHOWERY AND COOLER WEEK AHEAD.
&&

.SHORT TERM...HIGH PRESSURE NOSES INTO BC/ALBERTA OVER THE NEXT 24
HOURS...BRINGING A WARM/DRY AIRMASS AND ELY/NELY FLOW TO THE AREA. BY
MONDAY...THIS UPPER HIGH MOVES TO EASTERN ALBERTA AS A PACIFIC TROUGH
APPROACHES THE WEST COAST. THE UPPER FLOW VEERS WITH TIME BECOMING
SLY/SWLY BY MIDDAY MONDAY. AT THE SAME TIME THERMAL TROUGH SHIFTS
INLAND...FOR COOLER TEMPS ALONG THE COAST AND ANOTHER WARM DAY
INLAND. WITH THE LOW TO MID LEVEL FLOW BECOMING SLY/SWLY...MOISTURE
INCREASES RAPIDLY SUCH THAT MIXED LAYER CAPE REACHES 500-1000 J/KG
AND PW APPROACHES 1 INCH BY TUESDAY 00Z. FCST SOUNDINGS SHOW VALLEY
LOCATIONS LIKELY TO REMAIN CAPPED MONDAY...BUT ELEVATED HEATING
ALONG CASCADE RANGE SHOULD BE SUFFICIENT TO INITIATE THUNDERSTORMS
MONDAY AFTERNOON/EVENING. AS THE UPPER TROUGH OVER THE EASTERN
PACIFIC MOVES CLOSER TO THE COAST TUESDAY...EXPECT THE CHANCE OF
SHOWERS TO BECOME MORE WIDESPREAD...WITH SUFFICIENT INSTABILITY TO
KEEP A FEW THUNDERSTORMS IN THE FORECAST ALONG AND NEAR THE
CASCADES. THE STRONGER ONSHORE FLOW TUESDAY WILL BRING COOLER
TEMPERATURES...ALTHOUGH STILL REMAINING 5-8 DEGREES ABOVE NORMAL
INLAND. BRIGHT

.LONG TERM...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...VFR CONDITIONS THROUGH THE OVERNIGHT HOURS WITH WINDS
INCREASING OUT OF THE NORTH TO NORTHWEST THIS AFTERNOON THROUGH
THIS EVENING.

KPDX AND APPROACHES...VFR THROUGH THE NEXT 24 HOURS. INCREASING
WINDS OUT OF THE N/NW THIS AFTERNOON AND EVENING WITH GUSTS AS
HIGH AS ABOUT 20 KT.
&&

.MARINE...A THERMAL TROUGH OVER THE SOUTH OREGON COAST WILL
CONTINUE TO STRENGTHEN...BRINGING INCREASING WINDS ACROSS THE
WATERS THROUGH THE AFTERNOON. THE STRONGEST WINDS ARE EXPECTED
SOUTH OF ABOUT CASCADE HEAD. WINDS NEAR SHORE SHOULD EASE LATER
THIS EVENING...BUT CONTINUE OVER THE OUTER MARINE ZONES INTO SUN
MORNING. THE THERMAL TROUGH EXPANDS NORTH SUNDAY THEN SHIFTS OVER
THE COASTAL WATERS SUN NIGHT AND CONTINUES TO THE WASHINGTON
COASTAL WATERS MON.

SEAS HAVE DROPPED SOME THIS AFTERNOON TO 6 TO 7 FT AS EXPECTED.
WILL LIKELY SEE SOME INCREASE THROUGH THE EVENING HOURS AS WINDS
PICK UP. DOMINANT WAVE PERIOD SHOULD REMAIN AROUND 11 SECONDS BUT
WILL
KEEP A CLOSE EYE ON SEAS IN CASE PERIODS DECREASE WITH INCREASING
WINDS TODAY TO CAUSE A RETURN OF SQUARE SEAS. BOWEN
&&

.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.
&&


$$


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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