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000
FXUS66 KPQR 190353
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
838 PM PDT TUE JUN 18 2013

.SYNOPSIS...AN UPPER LEVEL LOW JUST OFF THE PACIFIC NORTHWEST COAST
IS CAUSING SHOWERS AND EVEN A FEW THUNDERSTORMS THIS EVENING.
THESE WILL SLOWLY DIMINISH OVERNIGHT. WEDNESDAY WILL BE COOL AND
CLOUDY WITH OCCASIONAL RAIN...WITH THE THUNDERSTORM THREAT LIKELY
LIMITED TO THE CASCADE CREST EASTWARD. SHOWERS WILL ONLY GRADUALLY
TAPER OFF THURSDAY AND FRIDAY AS THE UPPER LOW LINGERS OVER EASTERN
WASHINGTON. THE WEEKEND WARMUP IS LOOKING LESS LIKELY WITH RECENT
MODEL RUNS...IN FACT SOME MODELS ARE BRINGING IN A PACIFIC FRONTAL
SYSTEM FOR MORE
RAIN.

&&

.SHORT TERM...A BROAD AREA OF SHOWERS EXTENDS OVER THE SOUTH
WASHINGTON...NORTH OREGON AND LANE COUNTY CASCADE FOOTHILLS AND
WESTERN COLUMBIA GORGE AT 830PM. THESE SHOWERS WILL CONTINUE TO MOVE
EAST. THERE ARE ALSO A FEW SHOWERS POPPING UP ELESEWHERE SUCH AS
ONES OVER VANCOUVER WASHINGTON.  THE ATMOSPHERE WILL STABILIZE SOME
IN THE LOWER LEVELS OVERNIGHT...BUT WILL STILL REMAIN UNSTABLE
ENOUGH UNDER THE INFLUENCE OF THE UPPER LOW AND INCREASING COOLING
ALOFT...FOR ISOLATED SHOWERS SUCH AS THESE OVERNIGHT. THERE WILL
CONTINUE TO BE A SLIGHT CHANCE OF THUNDERSTORMS IN THE NORTH OREGON
AND SOUTH WASHINGTON FOOTHILLS AND CASCADES UNTIL AFTER MIDNIGHT BUT
WITHOUT A STRONG LIFTING MECHANISM SUCH AS A SHORTWAVE...THE MODELS
INDICATE THAT THE THREAT OF THUNDERSTORMS IS MINIMAL ELSEWHERE
OVERNIGHT. SCHNEIDER

UNSEASONABLY COOL...CLOUDY AND DAMP WEATHER IS LIKELY FOR WEDNESDAY
AS THE UPPER LOW DRIFTS EAST ACROSS THE STATE OF OREGON. CONFIDENCE
IS GROWING THAT PRECIPITATION WILL BE MORE STEADY AND STRATIFORM
ACROSS MOST OF THE FORECAST AREA...WITH CONVECTION LIMITED TO THE
CASCADE CREST EASTWARD. NAM CROSS SECTIONS SHOW BROAD LOW-MID LEVEL
LIFT WITHIN A VERY MOIST LAYER...ALSO INDICATIVE OF MORE STRATIFORM
PRECIP. ANY SUN BREAKS COULD PROVIDE MORE OF A CONVECTIVE NATURE TO
THE PRECIP...BUT AT THIS POINT IT APPEARS SUNBREAKS WILL BE VERY FEW
AND FAR BETWEEN IF ANY WEDNESDAY.

BY THURSDAY MODELS START TO DIVERGE ON WHAT THE UPPER LOW DOES. THE
TREND HAS BEEN FOR SLOWER MOVEMENT OF THE SYSTEM...WITH IT LINGERING
SOMEWHERE OVER THE MID-COLUMBIA BASIN THURSDAY AND POSSIBLY FRIDAY.
WITH THIS PROXIMITY THERE WILL BE THE CONTINUED THREAT OF WRAPAROUND
MOISTURE AND SHOWERS...MOST PROLIFIC ON THE 12Z GFS AND CANADIAN
MODELS. ADJUSTED POPS UPWARD FOR THESE DAYS AS MODELS SEEM TO BE
HANGING ON TO THE SHOWER THREAT LONGER THAN EARLIER RUNS.  WEAGLE

.LONG TERM...FRIDAY NIGHT THROUGH MONDAY...GIVEN THE LAST COUPLE OF
MODEL RUNS WE ARE STARTING TO LOSE CONFIDENCE IN OUR WEEKEND RIDGING
AND WARMUP. THE UPPER LOW FESTERING OVER THE MID-COLUMBIA BASIN NOW
APPEARS TO LINGER INTO FRIDAY...NOT REALLY ALLOWING THE UPPER RIDGE
TO BUILD IN FULL FORCE BEFORE THE NEXT PACIFIC FRONTAL SYSTEM
APPROACHES FOR THE WEEKEND. THERE ARE A COUPLE FACTORS TO CONSIDER
HERE. THERE IS A HISTORICALLY STRONG UPPER LEVEL RIDGE OVER ALASKA...
WITH OUR UPPER LOW STUCK BELOW IT IN A REX BLOCK PATTERN. THE
TENDENCY WILL BE FOR THE PACIFIC JET TO TRY TO UNDERCUT THE ALASKAN
RIDGE THIS WEEKEND AND THIS IS WHAT THE MODELS ARE BEGINNING TO SHOW.
ADDITIONALLY THE MADDEN-JULIAN OSCILLATION SEEMS TO BE ENTERING ITS
MOST ACTIVE PHASE SINCE FEBRUARY...WHICH IS IMPRESSIVE FOR JUNE. ALL
THIS POINTS TO A WET WEEK NEXT WEEK...SO WE SIGNIFICANTLY TRENDED
POPS UPWARD AND COOLED OFF TEMPERATURES BEGINNING SUNDAY.  WEAGLE

&&

.AVIATION...PREDOMINATELY VFR ACROSS THE REGION...WITH LOTS OF
SHOWERS AROUND. NOT MUCH CHANGE THROUGH THE EVENING...BUT WILL
SEE CLOUDS INCREASING ACROSS THE REGION TONIGHT AS ONSHORE FLOW
BEGINS INCREASING. CLOUDS NOT SOLID OFFSHORE...BUT STILL LOOKS
LIKE MVFR WITH POCKETS OF IFR ON COAST LATER TONIGHT...WITH
INCREASING LOW VFR AND HIGH END MVFR CLOUDS INLAND. ISOLATED
TSTORMS OVER THE CASCADE FOOTHILLS ENDING BY 05Z.

KPDX AND APPROACHES...WILL REMAIN VFR THIS EVENING...BUT LATER
WILL HAVE AREAS OF MVFR CIGS FORMING AS MARINE AIR FILLS
WILLAMETTE VALLEY. ISOLATED TSTORMS AROUND KPDX OPS AREA THROUGH
05Z.

&&

.MARINE...LITTLE CHANGE AS A BROAD AREA OF LOW PRES OFFSHORE WILL
CONTINUE TO SLOWLY TRACK TOWARD THE COAST THROUGH WED. WINDS
GENERALLY 15 TO 20 KT THIS EVENING...THEN EASING OVERNIGHT.
SEAS WILL REMAIN WELL BELOW 10 FEET THROUGH THE WEEK.

&&

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

$$

MORE WEATHER INFORMATION ONLINE AT...
HTTP://WEATHER.GOV/PORTLAND

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.