Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 021718 AAA
AFDPQR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1018 AM PDT SUN AUG 2 2015

UPDATED AVIATION MARINE AND W/W/A SECTIONS

.SYNOPSIS...AS A STRONG POSITIVELY TILTED UPPER LEVEL RIDGE SLOWLY
MOVES EAST TODAY...AN UPPER LEVEL LOW OFF THE CALIFORNIA COAST WILL
CONTINUE STEERING MORE MOISTURE AND INSTABILITY NORTHWARD OVER
WESTERN OREGON AND INTO SOUTHWEST WASHINGTON TODAY INTO MONDAY... FOR
A THREAT OF SOME SHOWERS OR THUNDERSTORMS. AN UPPER LEVEL TROUGH
ALONG THE B.C. COAST WILL BEGIN MOVING SOUTH TOWARD THE PACIFIC
NORTHWEST LATER TONIGHT AND MONDAY...AND HAVE AN INCREASING IMPACT
OVER SOUTHWEST WASHINGTON AND NORTHWEST OREGON DURING THE MID WEEK
PERIOD FOR COOLER TEMPS AND MORE NIGHT AND MORNING CLOUDS.
&&

.SHORT TERM...AS SUSPECTED SATURDAY...A CONSIDERABLE AMOUNT OF
CONVECTIVE CLOUDINESS AND DEBRIS HAVE ALREADY SPREAD OVER NORTHWEST
OREGON AND SOUTHWEST WASHINGTON OVERNIGHT AND THIS MORNING...AND EVEN
OVER THE COASTAL WATERS. LIGHTNING LATE SATURDAY WAS MAINLY NEAR
WILLAMETTE PASS...THEN SHIFTED TO OVER THE COASTAL WATERS OVERNIGHT
AND THIS MORNING.

THE AREA OF MOISTURE OVER THE COASTAL WATERS AND OVER THE NORTH
COASTAL MOUNTAINS INTO THE SOUTH WASHINGTON CASCADES WITH SOME
SHOWERS. HAVE NOT SEEN ANY LIGHTNING WITH THIS AREA IN A WHILE. THIS
AREA OF MOISTURE WILL MOVE NORTH INTO WEST CENTRAL AND NORTHWEST
WASHINGTON DURING THE MID DAY PERIOD AND SLOWLY OUT OF OUR FORECAST
AREA. THE MODELS THIS MORNING SHOWED A WEAK UPPER JET SEGMENT WITH
THIS MOISTURE THAT MOVES NORTH OUT OF OUR AREA LATER TODAY.

ANOTHER AREA OF MOISTURE IS MOVING NORTH FROM SOUTHWEST OREGON INTO
LANE COUNTY THIS MORNING...AND DID PRODUCE SOME LIGHTNING AN HOUR OR
TWO AGO AS IT WAS CROSSING INTO LANE COUNTY FROM DOUGLAS COUNTY. THIS
MOISTURE WILL CONTINUE MOVING NORTH THROUGH NORTHWEST OREGON AND
EVENTUALLY INTO SOUTHWEST WASHINGTON THROUGH THE AFTERNOON AND
TONIGHT. THE MODELS SHOW ANOTHER JET SEGMENT ASSOCIATED WITH A SHORT
WAVE PIVOTING THROUGH OUR FORECAST AREA FROM THE SOUTH TONIGHT INTO
MONDAY MORNING. THIS TAKES SOME OF THE MOISTURE BACK TO THE COAST AND
INTO THE COASTAL WATERS AGAIN. EXPECT A FEW SHOWERS TO MOVE ACROSS
THE AREA AS THIS MOISTURE CONTINUES TO FEED NORTH. CANNOT REALLY RULE
OUT THUNDER ANYWHERE AS WELL. THERE WILL BE SOME CHANCE OF THUNDER IN
THE SOUTH PART OF OUR AREA THIS MORNING SPREADING NORTH IN THE
AFTERNOON AND EVENING.

THE SHORT WAVE AND MOISTURE AREA WILL STILL BE OVER THE FORECAST AREA
EARLY MONDAY BEFORE MOVING EAST IN THE AFTERNOON.

BY MONDAY AN UPPER TROUGH ALONG THE B.C. COAST WILL BE SAGGING SOUTH
ALONG THE COAST TOWARD THE PACIFIC NORTHWEST. THIS WILL HELP TURN THE
UPPER FLOW MONDAY AFTERNOON TO MORE SOUTHWESTERLY...AND LIMIT THE
THUNDERSTORM POTENTIAL LATER MONDAY TO OUR SOUTHERN CASCADE AREAS AND
ESPECIALLY NEAR THE CREST. THE UPPER TROUGH WILL CONTINUE TO SAG
SOUTH WITH MORE ENERGY IN WASHINGTON BY TUESDAY...WITH MORE WESTERLY
FLOW ALOFT OVER SOUTHWEST WASHINGTON AND NORTHWEST OREGON.
AGAIN...THE MAIN THREAT OF THUNDER FOR OUR AREA WILL BE NEAR
WILLAMETTE PASS LATER TUESDAY.

THE MARINE LAYER IS AGAIN SHALLOW AND NEAR THE COAST THIS MORNING.
WILL CONTINUE THE HEAT ADVISORY FOR THE INLAND VALLEYS TODAY...
THOUGH THE CLOUDS MAY AFFECT HOW WARM WE GET TODAY. HUMIDITIES WILL
BE SLOWLY RISING TODAY AS WELL. THE MARINE LAYER WILL BEGIN PUSHING
INTO THE COASTAL GAPS TONIGHT AND MONDAY MORNING...BUT INLAND
COVERAGE WILL BE SPOTTY. INLAND TEMPS WILL BE LOWER MONDAY DUE TO THE
GRADUAL COOLING OF THE AIR MASS ALOFT. EXPECT BETTER INLAND COVERAGE
OF LOW CLOUDS TUESDAY MORNING...ESPECIALLY NORTH. TEMPS TUESDAY WILL
BE CLOSER TO NORMAL ESPECIALLY NORTH. TOLLESON

.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...BROAD AREA OF INSTABILITY MOVING ACROSS THE REGION
FROM SOUTH TO NORTH. MOSTLY MID LEVEL SHOWERS AT THIS POINT
ALTHOUGH THERE IS THUNDERSTORM ACTION FROM ABOUT KRBG TO THE SOUTH
AT THIS HOUR. EXPECT THE GENERAL THREAT FOR THUNDER TO MOVE NORTH
TODAY THROUGH THIS EVENING AND POTENTIALLY OVERNIGHT AS A SHORT
WAVE MOVING NORTH ACTS AS A LIFTING TRIGGER. IN GENERAL...AM
EXPECTING ISOLATED COVERAGE WITH LITTLE CONFIDENCE IN WHERE THOSE
SINGLE STORMS WILL SPECIFICALLY DEVELOP AND THUS LOW CONFIDENCE FOR
TAF INCLUSION AT THIS TIME. WILL CONTINUE TO MONITOR AND AMEND AS
CONDITIONS EVOLVE. REGARDLESS...COULD GET SOME OUTFLOW GUSTS
AROUND 25 KTS WITH AN OUTSIDE CHANCE OF 35 KTS FROM THE STORMS
THAT DO FORM. DO NOT EXPECT MUCH LOW CLOUD FROM THESE SHOWERS OR
STORMS AND NOT ANY VSBY REDUCTIONS EITHER.

WILL CONTINUE TO SEE STRATUS IMPACTS AT THE COAST TODAY AND A BIT
LONGER THAN THE PAST COUPLE DAYS. STILL SEEMS LIKE IT WILL BURN
BACK OFFSHORE THIS AFTERNOON BUT WILL HAVE A HARD TIME FOLLOWING
VIA SATELLITE AS THE ADVANCING MID LEVEL CLOUDS ARE OBSCURING.
THUS WILL HAVE LESS CONFIDENCE IN THE ACTUAL EXTENT TODAY. HAVE NO
REASON TO DOUBT LOW CLOUDS WILL RETURN TONIGHT. /JBONK

KPDX AND APPROACHES...VFR CONDITIONS. HOWEVER...PLENTY OF MID
LEVEL CLOUDS WITH THE POTENTIAL FOR A THUNDERSTORM. BEST TIMING
WILL BE FROM 23Z THROUGH ABOUT 04Z. /JBONK

&&

.MARINE...MAIN CHANGE FOR TODAY IS THE INTRODUCTION OF SHOWERS AND
A THREAT FOR THUNDERSTORMS. DONT FEEL LIKE THERE WILL BE A
SIGNIFICANT AMOUNT OF THUNDER COVERAGE BUT COULD SEE SOME OUTFLOW
GUSTS 25 TO 30 KT UNDER THE STRONGEST STORMS.

OTHERWISE...LITTLE CHANGE TO THE OVERALL PATTERN FOR SUNDAY WITH
N WINDS OVER THE WATERS. SPEEDS HAVE DRAMATICALLY DROPPED OFF THIS
MORNING AS EXPECTED. EXPECT ANOTHER ROUND OF WIND GUSTS IN THE 20
TO 25 KT RANGE THIS AFTERNOON AND EVENING PER MODELS BUT AM HAVING
SOME DOUBTS AS THEY APPEAR TO BE MORE THERMALLY DRIVEN FROM
HEATING OVER NORTHERN CALIFORNIA. CURRENT CLOUD COVER OVER SW
OREGON AND NRN CALIFORNIA MAY INHIBIT THE STRENGTH OF THE HEATING.
WILL CONTINUE WITH THE MODEL GUIDANCE FOR NOW AND KEEP THE
AFTERNOON AND EVENING ADVISORY FOR WINDS IN PLACE.

MEANWHILE...THE PERSISTENT NORTHERLY WINDS ARE GENERATING A STEEP
FRESH SWELL 5 TO 6 FEET AT 7 TO 9 SECONDS. AM SEEING OCCASIONAL
SQUARE SEAS OUT AT BUOY 89 WHEN COMBINED WITH THE LONG PERIOD SW
SWELL. IT APPEARS TO BE ISOLATED AND SPORADIC WITH FOCUS TOWARD
THE WESTERN BOUNDARY OF OUR BORDERS SINCE THERE HAS NOT BEEN ANY
INDICATION OF SQUARE SEAS SINCE LATE LAST EVENING. AS
SUCH...DROPPED THE ADVISORY FOR SEAS. STILL FAIRLY STEEP
NONETHELESS. /JBONK

&&

.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 FROM 3 PM THIS AFTERNOON TO
     MIDNIGHT PDT TONIGHT 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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