Area Forecast Discussion
Issued by NWS Portland, OR

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034
FXUS66 KPQR 300414
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
914 PM PDT FRI APR 29 2016

.SYNOPSIS...SHOWERS ON THE BACK SIDE OF A DEPARTING LOW WILL MOSTLY
END OVERNIGHT THOUGH CLOUDS AND SOME PATCHY FOG WILL PERSIST INTO
SATURDAY. AN UPPER RIDGE WILL BUILD INTO SOUTHWEST CANADA AS THE
DEPARTING SYSTEM SETS UP IN THE GREAT BASIN THIS WEEKEND...
FORMING AN REX BLOCK THAT WILL BRING DRY...CLEARING...AND WARMING
WEATHER TO SOUTHWEST WASHINGTON AND NORTHWEST OREGON THIS WEEKEND AND
INTO MONDAY. OFFSHORE FLOW WILL PICKUP THE SECOND HALF OF THE
WEEKEND. THE NEXT SYSTEM WILL APPROACH LATER MONDAY AND POSSIBLY
SPREAD SOME MOISTURE AND INSTABILITY FROM THE SOUTH NORTHWARD OVER
OUR FORECAST AREA FOR AN INCREASING CHANCE OF SHOWERS OR
THUNDERSTORMS MONDAY NIGHT AND TUESDAY...LIKELY PERSISTING FOR A GOOD
PART OF THE REMAINDER OF THE WEEK. AFTER MUCH ABOVE NORMAL TEMPS
SUNDAY AND MONDAY...TEMPS WILL FALL BACK NEAR NORMAL BY WEDNESDAY.
&&

.SHORT TERM....TONIGHT THROUGH MONDAY...THE LAST MAIN SHORT WAVE DOVE
SOUTH ACROSS SOUTHWEST WASHINGTON AND NORTHWEST OREGON THIS AFTERNOON
AND EVENING ON THE BACK SIDE OF A DEPARTING LOW PRESSURE SYSTEM.
THERE WAS ENOUGH INSTABILITY FOR A FEW THUNDERSTORMS TO DEVELOP.
WHILE LIFTED INDICES WERE MARGINAL...MODEL SOUNDINGS AND THE 00Z
SLE SOUNDING SHOWED A DECENT AMOUNT OF CAPE CAPPED JUST BELOW THE 500
MB LEVEL. THE MODELS ALL SAY THE SHOWERS WILL DECREASE AND MOSTLY END
OVERNIGHT AS THE SYSTEM MOVES SOUTHEAST.

THERE ARE STILL QUITE A BIT OF CLOUDS YET NEARBY...SO EXPECT A
DECENT AMOUNT OF CLOUDS OVERNIGHT INTO SATURDAY MORNING. THERE MAY BE
SOME GAPS IN THE CLOUDS...ESPECIALLY NEAR THE EAST SLOPES OF THE
COAST RANGE...AND IF SO...WE COULD SEE SOME PATCHY FOG AROUND AS WELL
LATER TONIGHT AND EARLY SATURDAY.

THE MODELS SHOW AN UPPER RIDGE BUILDING ONSHORE INTO SOUTHWEST CANADA
SATURDAY AND CONTINUING THE REMAINDER OF THIS WEEKEND AS THE
DEPARTING SYSTEM DEVELOPS INTO A LOW OVER THE GREAT BASIN...FORMING A
REX BLOCK. THIS WILL BRING DRY AND WARMER WEATHER TO OUR FORECAST
AREA...WITH TEMPS INTO THE LOWER 80S SUNDAY AND MONDAY. THE COAST MAY
ALSO GET AROUND 80 ON SUNDAY AS OFFSHORE FLOW DEVELOPS.

THE MODELS SHOW A SYSTEM APPROACHING LATER MONDAY THAT CAUSE SOME
ISOLATED THUNDERSTORMS TO DEVELOP LATER MONDAY OVER THE HIGHER
CASCADES AND POSSIBLY SPREAD NORTHWARD AND WESTWARD MONDAY NIGHT AND
TUESDAY. THIS MAY ALSO BE ENOUGH TO SPREAD SOME COOLER MARINE AIR AND
CLOUDS NORTHWARD ALONG THE COAST MONDAY AND MONDAY NIGHT. AS THESE
TRENDS BECOME MORE CERTAIN...EXPECT REFINEMENTS IN THE MONDAY NIGHT
AND TUESDAY FORECAST. TOLLESON

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...
MONDAY NIGHT THROUGH FRIDAY. BROAD UPPER TROUGH OVER THE EASTERN
PACIFIC WILL SPLIT WITH AN UPPER LOW CLOSING OFF AND TAKING UP
RESIDENCE OFF OF THE NORTHERN CALIFORNIA COAST EARLY NEXT WEEK. THIS
FEATURE WILL KEEP THE REGION IN SOUTH TO SOUTHWEST FLOW ALOFT...
WHICH WILL SERVE TO SEND MID-LEVEL MOISTURE INTO THE REGION. MONDAY
NIGHT LIKELY REMAINS DRY...BUT BY TUESDAY SOME PRECIPITATION DEVELOPS
INTO THE FORECAST AREA. WHILE SOME MODEL DIFFERENCES DO REMAIN AND
THERE IS SOME QUESTION OVER JUST HOW MUCH INSTABILITY WILL BE
PRESENT...ENOUGH SUPPORT FROM THE FORECAST MODELS TO EXTEND
THUNDERSTORM CHANCES OVER THE EASTERN PORTION OF THE FORECAST AREA
FOR TUESDAY AND WEDNESDAY.  THIS UPPER LOW REMAINS IN PLACE THROUGH
MIDWEEK...BEFORE SHIFTING ONSHORE AND INTO THE GREAT BASIN BY LATE IN
THE WEEK. TEMPERATURES WILL REMAIN WARMER THAN SEASONAL NORMALS NEXT
WEEK BUT GRADUALLY COOL DURING THE LAST FEW DAYS OF NEXT WEEK.
&&

.AVIATION...SHOWERS WERE SLOWLY DIMINISHING THIS EVENING...WITH MOST
OF THE ACTIVITY SHIFTING TOWARDS THE CASCADES AND CASCADE FOOTHILLS.
WITH A LIGHT ONSHORE FLOW CONTINUING OVERNIGHT CLOUDS WERE BECOMING
MORE TIED TO UPWIND SIDE OF TERRAIN...OVER THE CASCADES AND FOOTHILLS
AS WELL AS THE W SLOPES OF THE COAST RANGE. CONDITIONS THIS EVENING
HAVE BEEN GENERALLY VFR...WITH A FEW AREAS OF MVFR CIGS ON THE COAST.
AS AIR MASS SETTLES OUT LATER TONIGHT EXPECT TO SEE MVFR CIGS
REDEVELOP BOTH ALONG THE COAST BY AROUND 09Z...AND INLAND VALLEYS
MOST LIKELY BETWEEN 08Z AND 12Z. EXPECT THE MVFR CIGS THEN TO
CONTINUE THROUGH MOST OF THE MORNING...BEFORE BREAKING UP INTO VFR
CONDITIONS WITH SCATTERED CLOUDS AFTER 19Z TO 21Z.

KPDX AND APPROACHES...VFR CONDITIONS THIS EVENING LIKELY TO GIVE WAY
TO MVFR CIGS LATE TONIGHT AFTER 08Z AS LOW CLOUDS ARE EXPECTED TO
FILL BACK IN. THESE CLOUDS THAN ARE LIKELY TO REMAIN THROUGH THE
MORNING BEFORE BREAKING UP MIDDAY...18Z-21Z...FOR A RETURN TO VFR
CONDITIONS.
&&

.MARINE...NNW SMALL CRAFT WINDS...GUSTING TO AROUND 25 KT THIS
EVENING OVER THE COASTAL WATERS...ARE EXPECTED TO SLOWLY DIMINISH
LATE TONIGHT AS THE SURFACE HIGH SLOWLY MOVES OVER. SEAS HAVE BEEN
GENERALLY RUNNING JUST UNDER 10 FT...BUT WITH DOMINANT PERIODS
RANGING FROM 8 TO 12 SECONDS. WILL CONTINUE WITH THE SAME ADVISORIES
OVERNIGHT AS HAVE BEEN PREVIOUSLY ISSUED...WITH THE HAZARDOUS SEAS
MAINLY FOCUSED ON STEEP SEAS WITH COMBINES WAVE HEIGHTS AT TIMES
EXCEEDED BY THE SHORT PERIODS.

WINDS WILL EASE FOR A TIME SATURDAY BUT THERMAL TROUGH/LOW PRESSURE
OVER NORTHERN CALIFORNIA AND FAR SOUTHERN OREGON WILL INDUCE MORE OF
A SUMMERTIME NORTHERLY WIND PATTERN BY SATURDAY EVENING AND CONTINUE
THROUGH MUCH OF SUNDAY AS WELL. STRONGEST WINDS WILL LIKELY BE LATE
AFTERNOON THROUGH THE EVENING.

AS THE WINDS PICK UP LATE SAT...SO WILL THE CHOPPY WIND DRIVEN
SEAS...REACHING ABOUT 8 TO 10 FT S OF NEWPORT AT TIMES IN THE
AFTERNOON/EVENINGS. WILL LIKELY NEED SMALL CRAFT ADVISORIES FOR GUSTY
WINDS AND/OR SEAS THIS WEEKEND...BUT WILL NOT ISSUE UNTIL THE CURRENT
SERIES OF ADVISORIES EXPIRE IN ORDER TO AVOID CONFUSION.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 6 AM PDT SATURDAY FOR
     WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR FROM 10 TO
     60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM PDT SATURDAY
     FOR WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR FROM 10
     TO 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 3 AM PDT SATURDAY 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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