Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 281626 RRA
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
926 AM PDT THU MAY 28 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BE OVER THE FORECAST AREA
THROUGH SATURDAY. A CLOSED UPPER LOW OVER THE NORTHERN ROCKIES WILL
CONTINUE TO DRIFT SOUTHEAST TODAY. EXPECT A LITTLE MORE WARMING
TODAY...AND THEN INLAND DAYTIME TEMPERATURE SHOULD PEAK FRIDAY. THE
UPPER RIDGE STARTS TO FLATTEN SATURDAY. THE HIGHER CASCADES WILL
CONTINUE TO HAVE A SLIM THREAT OF LATE-DAY THUNDERSTORMS THE NEXT
COUPLE OF DAYS. THE NEXT UPPER LOW SWINGS CLOSER TO THE OREGON COAST
SUNDAY...RESULTING IN A LITTLE MORE COOLING BUT A BETTER CHANCE OF
CASCADE THUNDERSTORMS. A MUCH DEEPER MARINE LAYER IS EXPECTED OVER
THE AREA EARLY NEXT WEEK.

&&

.MORNING UPDATE...
THE VISIBLE SATELLITE LOOP SHOWS PLENTY OF MARINE STRATUS AT THE
COAST THIS MORNING. A WEAK INLAND PUSH BROUGHT A THIN STRATUS LAYER
INTO THE COASTAL GAPS AND UP THE LOWER COLUMBIA. CLOUDS FILLED IN THE
I-5 CORRIDOR IN SW WASH AND REACHED THE PORTLAND/VANCOUVER METRO
AREA. THE REST OF THE WILLAMETTE VALLEY STAYED CLOUD FREE. EXPECT THE
INLAND STRATUS TO BURN OFF FAIRLY QUICKLY TODAY...LIKELY BY AROUND
18Z. THEN ANOTHER WARM DAY IS ON TAP FOR THE REGION. 850 MB TEMPS ARE
FCST TO REACH 14 TO 15 C WHICH SHOULD SUPPORT WIDESPREAD HIGHS INTO
THE LOW 80S FOR THE INTERIOR LOWLANDS. THE COAST WILL STAY MUCH
COOLER WITH CLOUDS HANGING ON FOR MUCH OF THE DAY AND A NW BREEZE OFF
OF THE OCEAN.

...PREVIOUS SHORT TERM DISCUSSION ISSUED 149 AM THU MAY 28...
.SHORT TERM...TODAY THROUGH SATURDAY...
WATER VAPOR LOOP SHOWS AN UPPER LOW OVER CENTRAL IDAHO...AND A SECOND
LOW NEAR 55N 131W. A 500 MB RIDGE AXIS EXTENDS BETWEEN 125W AND 130W.
WATER VAPOR ALSO SHOWS A DRY SLOT SLIDING SOUTH OVER VANCOUVER ISLAND
AND THE WA COAST. ON THE SMALLER SCALE...STRATUS HAS ALREADY REACHED
KKLS AT 08Z. THE 975 MB RH FORECAST FROM THE NAM VALID 09Z WAS A
LITTLE BEHIND...SHOWING THE 90 PCT OR GREATER VALUES A LITTLE FURTHER
WEST. MAIN FORECAST PROBLEM FOR TODAY AND FRIDAY WILL BE THE
POTENTIAL FOR THUNDERSTORMS FOR THE HIGHER CASCADES. THE UPPER LOW
THAT WAS CENTERED NEAR THE OREGON...WASHINGTON...IDAHO TRIPLE-POINT
00Z THU WILL CONTINUE TO SHIFT SOUTHEAST TODAY. THIS WILL ALLOW
NORTHWEST FLOW ALOFT OVER THE FORECAST AREA. HOWEVER...MODEL
SOUNDINGS FOR A POINT NEAR SANTIAM PASS...ESPECIALLY THE
NAM...MAINTAIN SOME DEGREE OF INSTABILITY FROM LATE-AFTERNOON THROUGH
THE EVENING TODAY AND FRI. BELIEVE THE MODELS MAY BE SLIGHTLY
OVER-DOING THE LOW-LEVEL DEW POINTS...THUS GENERATING
HIGHER CAPE VALUES. ACTUALLY THINK THE BEST CHANCE FOR CONVECTION...
ALBEIT SLIM...WILL BE OVER THE HIGHER S WA CASCADES.

EXPECT A THINNER MARINE LAYER TODAY. THE 06Z NAM DOES NOT SHOW MARINE
STRATUS REACHING KPDX...ALTHOUGH THE HI-RES ARC DOES INDICATE STRATUS
GETTING TO NEAR MULTNOMAH FALLS BY 15Z. HI-RES MODEL ALSO SUGGESTING
THE BEACHES WILL REMAIN CLOUDY. MAY BE A SHORT PERIOD OF SCATTERED
SKY CONDITIONS LATE IN THE DAY FROM ABOUT KONP NORTHWARD. MODEL 850
MB TEMPS FORECAST TO BE AROUND 15C TODAY IN THE WILLAMETTE VALLEY...
UP ABOUT 1 DEG FROM WED. THIS SHOULD PUT THE INLAND VALLEYS IN THE
LOWER 80S. WARMEST DAY LOOKS TO BE FRI WITH A SLIGHTLY WARMER START.
THE UPPER RIDGE STARTS TO FLATTEN A BIT LATE FRI AS AN UPPER LOW OVER
NRN BRITISH COLUMBIA SLOWLY DRIFTS SOUTH.

LITTLE CHANGE SAT WITH 500 MB HIGH PRES REMAINING OVER THE AREA. A
SLIGHT AMPLIFICATION IN THE RIDGE SAT AFTERNOON DUE TO A DEVELOPING
LOW MODELS SHOW NEAR 34N 138W SAT AFTERNOON. THIS ALSO INDUCES
SLIGHTLY MORE UNSTABLE SWLY FLOW ALOFT INTO THE REGION. WILL LEAVE
THE SLIGHT THREAT OF THUNDERSTORMS FOR THE LANE COUNTY CASCADES SAT
AFTERNOON. WEISHAAR

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...WEAK SHORTWAVE
RIDGING MOVES THROUGH THE AREA EARLY SAT NIGHT WITH AN APPROACHING
UPPER LEVEL LOW PRESSURE SYSTEM NEARING 130W BY EARLY SUN. AS THIS
LOW PRESSURE TRACKS INLAND...INCREASING CLOUDS AND MUCH COOLER
TEMPERATURES MOVE INTO THE REGION. SHOWERS WILL BEGIN BY LATE SUN
AFTERNOON OR EVENING AS THE SURFACE BOUNDARY SLIDES ONSHORE AND
ACROSS THE REGION...WITH A CHANCE FOR THUNDERSTORMS IN THE CASCADES
SOUTH OF AROUND MT HOOD. AS THIS UPPER LOW CONTINUES TO TRACK ALONG
A GENERALLY SOUTHWEST TO EAST-NORTHEAST PATH ACROSS THE REGION AND
THEN EAST OF THE CASCADES...EXPECT CONTINUED RAIN CHANCES AND COOLER
WEATHER TO CONTINUE THROUGH AROUND MIDWEEK. WHILE SOME MODEST
DIFFERENCES IN PATTERN EVOLUTION BETWEEN MODEL SOLUTIONS SUGGEST A
BIT OF UNCERTAINTY IN LOCATION AND TIMING OF RAINFALL AMOUNTS...THE
MODEL GUIDANCE REMAINS IN REMARKABLY DECENT AGREEMENT WITH RESPECT
TO THE SHOWERY PATTERN ALONG WITH TEMPERATURES AT OR A FEW DEGREES
BELOW SEASONAL NORMALS.
&&

.AVIATION...MOSTLY VFR INLAND WITH IFR STRATUS ALONG THE COLUMBIA
RIVER. EXPECT THIS STRATUS TO THIN AND LIFT THROUGH 18Z. DRY
NORTHERLY FLOW ALOFT WILL KEEP CONDITIONS INLAND VFR...WITH A
SLIGHT CHANCE OF THUNDERSTORMS OVER THE CASCADES BETWEEN 20-04Z.
MARINE LAYER ALONG THE COAST WILL CONTINUE TO BRING A MIXTURE OF
IFR/MVFR CIGS TODAY AND TONIGHT.

KPDX AND APPROACHES...IFR STRATUS AROUND 600 FT WILL CONTINUE TO
BURN OFF THROUGH 17Z. VFR CONDITIONS CONTINUE THROUGH FRI. /64

&&

.MARINE...NOT MUCH CHANGE OVERALL. HIGH PRES REMAINS LOCKED OVER
THE NE PAC...WITH WEAK PRES GRADIENTS. SEAS CONTINUE AS A MIX OF W
AND SW SWELL TRAINS...BUT OVERALL SEAS CONTINUE AROUND 5 TO 6 FT
THROUGH THE COMING WEEKEND.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

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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