Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 280850 RRA
AFDPQR

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

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BE OVER THE FORECAST AREA
THROUGH SATURDAY. THE CLOSED UPPER LOW OVER CENTRAL IDAHO TONIGHT
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.

&&

.SHORT TERM...TODAY THROUGH SATURDAY...WATER VAPOR LOOP SHOWS ONE
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 ARW 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...VFR TODAY OVER MUCH OF THE REGION...WITH DRIER STABLE
N TO NW FLOW ALOFT. SHALLOW MARINE LAYER OVER THE PAC WILL KEEP
IFR STRATUS ON THE COAST JAMMED AGAINST THE COAST RANGE. TOPS
LIKELY IN 1000 TO 1200 FT RANGE. DO HAVE POCKETS OF STRATUS
EXTENDING INTO THE COAST RANGE AND UP THE COLUMBIA RIVER THIS
AM. STRATUS AT KKLS WILL CONTINUE PUSHING UPSTREAM...REACHING KPDX
AND KTTD ARUOND 12Z...THEN STRATUS WILL PUSH BIT MORE TO THE SOUTH
AGAINST THE CASCADES FOOTHILLS. BUT THOSE INLAND CLOUDS WILL BURN
OFF BETWEEN 16Z AND 18Z.

KPDX AND APPROACHES...VFR TODAY WITH DRY STABLE AIR MASS ALOFT.
LIKE WED AM...LOW STRATUS WITH CIGS NEAR 800 FT WILL ARRIVE FROM
THE N AROUND 12Z...BUT WILL BURN OUT BETWEEN 16Z AND 17Z. ROCKEY.
&&

.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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