Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 281055
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
255 AM PST WED JAN 28 2015

.SYNOPSIS...A WEAK STATIONARY FRONT OVER SW WA AND NW OREGON THIS
MORNING WILL CONTINUE TO WEAKEN TODAY AND LIFT BACK TO THE N.
ANOTHER UPPER LEVEL RIDGE IS EXPECTED TO DEVELOP OVER THE PACIFIC
NORTHWEST LATER IN THE WEEK AND CONTINUE INTO THE WEEKEND FOR MORE
DRY WEATHER. THE NEXT CHANCE FOR RAIN IS PROBABLY NOT UNTIL LATER
SUNDAY AND MONDAY.

&&

.SHORT TERM...WEAK BAROCLINIC ZONE FROM SW WA CASCADES ACROSS THE NW
CORNER OF OREGON EARLY THIS MORNING IS BEST EVIDENCED BY THE LIGHT
RAINFALL SEEN IN SURFACE OBSERVATIONS OVER THE REGION. 00Z MODELS
CONTINUED TO INDICATE THE FRONT LINGERING THIS MORNING BEFORE SLOWLY
LIFTING N LATER TODAY AND TONIGHT. A WEAK SURFACE LOW OFFSHORE IS
EXPECTED TO HELP LIFT THE BOUNDARY N TODAY...AND ALSO PROVIDES A BIT
OF LOW LEVEL MOISTURE OVERRUNNING THE FRONT TODAY...SO WILL KEEP
POPS IN CHANCE CATEGORY THROUGH THE AFTERNOON AND INTO THE EVENING.

LOW LEVEL FLOW TRANSITIONS TO OFFSHORE TONIGHT AS A WEAK SURFACE
RIDGE OF HIGH PRES IS EXPECTED TO BUILD DOWN E OF THE CASCADES. THIS
WILL GRADUALLY BRING SOME DRYING TO LOWER LEVELS TONIGHT AND
THU...FINALLY BRINGING AN END TO THE CHANCES FOR SHOWERS. A WEAK
UPPER LEVEL LOW CAUGHT IN THE RIDGE WILL SLOWLY WANDER ACROSS
TONIGHT AND WED...KEEPING SOME MID AND HIGH CLOUDS OVER THE REGION.
THE CLOUDS MAY HINDER FOG DEVELOPMENT TONIGHT AND THU MORNING...BUT
IT IS NOT LIKELY TO PRECLUDE SOME VALLEY FOG AS A LOW LEVEL
SUBSIDENCE INVERSION DEVELOPS.

BETTER RADIATIVE CONDITIONS ARE EXPECTED THU NIGHT AND FRI MORNING
UNDER A STRONGER SUBSIDENCE INVERSION. THIS APPEARS MORE FAVORABLE
FOR WIDESPREAD FOG IN THE INLAND VALLEYS...AND WITH THE STRONG
INVERSION IS MORE LIKELY TO LINGER WELL INTO THE AFTERNOON AND
KEEPING TEMPS COOLER IN THE VALLEYS.

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. FRIDAY NIGHT
THROUGH TUESDAY...THE UPPER RIDGE CONTINUES THROUGH SATURDAY OFF THE
PACNW COAST AS A HIGH AMPLITUDE PATTERN IN THE NORTH PACIFIC
CONTINUES. THIS WILL MEAN DRY WEATHER WITH FOG IN THE INTERIOR
VALLEYS WHILE THE MOUNTAINS WILL BE MILD NEARLY CLOUD FREE.  MODELS
ARE CONTINUE TO SHOW THE RIDGE SHIFTING INLAND AS A MORE
CONSOLIDATED JETSTREAM APPROACHES THE WEST COAST. ECMWF...GFS AND
GFS ENSEMBLE MEAN ARE IN GOOD AGREEMENT IN BRINGING A WARM FRONT
THROUGH THE AREA LATE SUNDAY INTO MONDAY. THE ECMWF FLATTENS THE
RIDGE MORE SO SNOW LEVELS WILL BE LOWER BUT STILL ABOVE MOST CASCADE
PASSES. WITH THE WEAKER RIDGE AND STRONGER JET STREAM POINTED INTO
THE REGION WE CAN EXPECT MORE CLOUDS AND HIGHER CHANCES FOR RAIN FOR
THE REMAINDER OF THE LONG TERM.  OVERALL HAVE INCREASED POPS SUN
NIGHT THROUGH TUE WITH EMPHASIS ON SUN NIGHT AND MONDAY.  THERE MAY
BE ANOTHER FRONT TUE BUT MODEL SOLUTIONS DIVERGE REGARDING THIS
FEATURE. /26
&&

.AVIATION...A STALLED FRONTAL BOUNDARY CONTINUES TO PRODUCE
WIDESPREAD DRIZZLE AND IFR CONDITIONS ACROSS THE NORTHERN
WILLAMETTE VALLEY. SOUTH OF THIS BOUNDARY...WEAK SOUTHERLY FLOW
HAS HELPED MAINTAIN VFR CONDITIONS. AS A WEAK LOW PRESSURE
OFFSHORE SHIFTS NORTHWARD THIS MORNING...THE AFOREMENTIONED FRONT
WILL SHIFT NORTHWARD WITH IT. THIS SHOULD ALLOW THE VFR CONDITIONS
CURRENTLY FOUND AT KONP...KEUG AND KSLE TO SPREAD NORTHWARD THIS
AFTERNOON. HOWEVER...THIS IMPROVEMENT MAY BE SHORT LIVED AS
ADDITIONAL LIFR AND IFR CONDITIONS WILL THEN LIKELY REDEVELOP
AFTER 03Z THURSDAY AT MANY TAF SITES. INCREASING EASTERLY WINDS
NEAR THE COLUMBIA RIVER GORGE MAY KEEP CONDITIONS FROM DETERIORATING
AT KTTD AND KPDX THOUGH.

KPDX AND APPROACHES...PERIODS OF DRIZZLE AND IFR CONDITIONS WILL
CONTINUE THIS MORNING...BEFORE CONDITIONS LIKELY IMPROVE TO MVFR
AND THEN FINALLY VFR THIS AFTERNOON. STRENGTHENING EASTERLY WINDS
TONIGHT MAY ALLOW VFR CONDITIONS TO PERSIST THROUGH 12Z
THURSDAY...BUT THERE IS A CHANCE CONDITIONS COULD DETERIORATE
INTO MVFR OR IFR TOWARDS THAT PERIOD IF THE WINDS DO NOT
MATERIALIZE. /NEUMAN

&&

.MARINE...A WEAK LOW PRESSURE WILL PUSH NORTHEASTWARD TODAY ALONG
A FRONT CURRENTLY STALLED OVER THE WATERS...BUT EXPECT FEW IMPACTS
TO MARINE INTERESTS. HIGH PRESSURE WILL THEN STRENGTHEN OVER THE
NORTHEAST PACIFIC AS THERMAL LOW PRESSURE STRENGTHENS OVER
NORTHERN CALIFORNIA. THIS SHOULD SET THE STAGE FOR A MORE SUMMER
LIKE PATTERN OF NORTHERLY WINDS ACROSS THE WATERS THURSDAY THROUGH
SATURDAY. A WEAKENING FRONTAL STORM SYSTEM WILL THEN LIKELY IMPACT
THE WATERS ON SUNDAY. A MORE ACTIVE STORM PATTERN CERTAINLY
APPEARS POSSIBLE NEXT WEEK...BUT UNCERTAINTY IN DETAILS REMAINS
HIGH. /NEUMAN

&&

.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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