Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 020954
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
254 AM PDT WED SEP  2 2015

.SYNOPSIS...MULTIPLE FRONTAL BOUNDARIES WILL MOVE EASTWARD THROUGH
SOUTHWEST WASHINGTON AND NORTHWEST OREGON TODAY WITH SHOWERS AT TIMES
OVER MUCH OF THE AREA. THE PARENT UPPER TROUGH WILL BE SLOWLY SAGGING
SOUTH AND THE COOLING ALOFT WILL GIVE A CHANCE OF THUNDER OVER THE
NORTHERN COASTAL WATERS TODAY AND OVER THE NORTH INTERIOR THIS
AFTERNOON AND EVENING. SCATTERED SHOWERS WILL CONTINUE TONIGHT AND
THURSDAY OVER THE AREA...ESPECIALLY NORTH...AS A COUPLE PIECES OF
ENERGY ROTATE AROUND THE LOW AND ONSHORE. TEMPS COOL ALOFT A BIT MORE
ON THURSDAY FOR ANOTHER CHANCE OF THUNDER ESPECIALLY NORTH. THE LOW
WILL DROP SOUTH THURSDAY NIGHT AND FRIDAY AS ANOTHER BATCH OF ENERGY
DROPS SOUTH ON THE BACK SIDE OF THE LOW...MOVING ONSHORE TO OUR
SOUTH. HOWEVER...WITH THE COOL UPPER TROUGH OVERHEAD AND SOME
SUNSHINE EXPECTED TO BREAK THROUGH THE CLOUDS AT TIMES ON FRIDAY...
THIS WILL GIVE A CHANCE OF SHOWERS OR POSSIBLY A CHANCE OF THUNDER
ESPECIALLY OVER THE HIGHER TERRAIN. THE LOW WILL MOVE OFF TO THE EAST
THIS WEEKEND FOR IMPROVING WEATHER...THOUGH ANOTHER SYSTEM IS
POSSIBLE EARLY NEXT WEEK.
&&

.SHORT TERM...AN UPPER LOW REMAINS CENTERED ALONG THE B.C COAST EARLY
THIS MORNING WITH A SERIES OF FRONTAL BOUNDARIES AROUND THE AREA. THE
FIRST MOVED ONSHORE OVERNIGHT AND BROUGHT SOME DECENT RAINS TO THE
NORTHERN INTERIOR SECTIONS. INFRARED SATELLITE IMAGERY SHOWS ANOTHER
DIFFUSE BOUNDARY BETWEEN HOQUIAM AND ASTORIA BENEATH WEST TO EAST
ORIENTED SHEAR VORTICITY AND THE UPPER JET. THIS BOUNDARY WILL BE
MOVING ONSHORE EARLY THIS MORNING INTO SOUTHWEST WASHINGTON AND
NORTHWEST OREGON AND MOVE THROUGH THE NORTHERN PART OF OUR FORECAST
AREA THIS MORNING...DROPPING SOUTH THROUGH THE CASCADES THROUGH THE
AFTERNOON. HAVE DECIDED TO BUMP UP POPS WITH THIS FEATURE MORE INTO
THE LIKELY CATEGORY WITH SOME LOCAL EMBEDDED CATEGORICAL AREAS.
DESPITE THE SHALLOW NATURE OF THESE BOUNDARIES...THEY HAVE BEEN
PRODUCING MORE QPF THAN THE MODELS HAVE BEEN INDICATING...AND THIS
COULD CONTINUE TODAY.

THE MODELS SHOW THAT SOME COOLER AIR ALOFT WILL ACCOMPANY THIS SECOND
BOUNDARY TODAY AS THE UPPER LOW SLOWLY SAGS A BIT SOUTH. THIS SHOULD
GIVE A CHANCE OF THUNDER TO AT LEAST THE NORTHERN PART OF OUR COASTAL
WATERS...AND FROM THE PORTLAND AREA NORTHWARD IN THE INTERIOR.

THE MODELS SHOW ANOTHER SHORT WAVE SWINGING ONSHORE THIS EVENING THAT
SHOULD KEEP AT LEAST SOME SCATTERED SHOWERS GOING ACROSS THE NORTH
PART OF OUR FORECAST AREA TONIGHT. THERE IS ANOTHER SHORT WAVE THAT
ROTATES ONSHORE THURSDAY AS WELL. AS THE LOW DRIFTS SOUTH THE AIR
ALOFT WILL CONTINUE TO COOL...AND MODEL LIFTED INDICES AND CAPE
FORECASTS SUGGEST THAT WE HAVE ANOTHER CHANCE OF THUNDER THURSDAY
ESPECIALLY ACROSS THE NORTH.

THE MODELS CONTINUE TO SHOW ENERGY DROPPING SOUTH OFF THE COAST ALONG
THE WEST OR BACK SIDE OF THE LOW THURSDAY NIGHT AND FRIDAY AND MOVING
ONSHORE TO OUR SOUTH. THUS...THERE SHOULD BE A MINIMUM OF SHOWERS
THURSDAY NIGHT INTO FRIDAY MORNING. HOWEVER...THIS DRAGS THE UPPER
LOW ACROSS OUR FORECAST AREA ALONG WITH ITS COLD POOL ALOFT... WHICH
WILL BE OVER THE AREA FRIDAY AFTERNOON AND EVENING. THIS TOGETHER
WITH MORE AREAS OF SUNSHINE DUE TO MORE BREAKS IN THE CLOUDS...WILL
LIKELY LEAD TO SOME SHOWERS AGAIN AND POSSIBLY A THUNDERSTORMS IN THE
AFTERNOON AND EVENING...ESPECIALLY OVER THE HIGHER TERRAIN.

WITH UPPER TROUGH MOVING THROUGH...TEMPERATURES WILL BE A BIT COOLER
THE NEXT FEW DAYS AND REMAIN BELOW NORMAL THROUGH AT LEAST THE END OF
THE WORK WEEK WITH HIGH TEMPERATURES AROUND 70 DEGREES INLAND AND 60
TO 65 ALONG THE COAST. INLAND LOW TEMPERATURES WILL ALSO BE
SIGNIFICANTLY MORE COMFORTABLE WITH LOWS WELL BELOW 60 DEGREES.
TOLLESON

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY. THE MODELS SAY THE UPPER
LOW FROM FRIDAY WILL BE MOVING EAST ON SATURDAY...THOUGH WE MAY GET
CLIPPED BY A LITTLE ENERGY ON THE BACK SIDE OF THE LOW NEAR THE
CASCADE CREST. OTHERWISE LOOK FOR DRIER AND WARMER WEATHER SATURDAY.
THE MODELS DO SHOW A VERY WEAK SYSTEM DROPPING THROUGH ON SUNDAY
POSSIBLY LINGERING INTO MONDAY IN NORTHWEST FLOW ALOFT THAT MIGHT
GIVE A SLIGHT CHANCE OF SHOWERS TO AREAS MAINLY NORTH AND WEST OF
PORTLAND. THEN IT LOOKS DRIER AND WARMER AGAIN DURING THE MIDDLE PART
OF NEXT WEEK. TOLLESON
&&

.AVIATION...ALL TAF LOCATIONS CURRENTLY VFR BUT WITH SATURATED LOWER
LEVELS...NOT TAKING MUCH TO SEE LOWER CIGS AND VSBY AS LIGHT TO
MODERATE SHOWERS PASS BY. COASTAL AREAS HAVE DROPPED TO IFR AT TIMES
OVERNIGHT WHILE INLAND TAF TERMINALS GENERALLY STAYED NO LOWER THAN
MVFR WITH CIGS AT 015. EXPECT LITTLE CHANGE IN OVERALL CONDITIONS
WITH SHOWERS CONTINUING ACROSS THE AREA...ALTHOUGH AREAS NORTH OF A
KONP-KPDX LINE WILL SEE A THUNDER THREAT ADDED IN. MAIN THREAT SHOULD
OCCUR 18Z-03Z.

KPDX AND APPROACHES...GENERALLY VFR BUT WITH INCREASING CHANCES OF
MVFR CIGS AROUND 025-030 AS SHOWERS DEVELOP MAINLY AFTER 18Z. THERE
ALSO WILL BE A THREAT FOR THUNDERSTORMS MAINLY NORTH AND WEST OF THE
TERMINAL AREA MAINLY 18-03Z. /JBONK
&&

.MARINE...UPPER LOW PRESSURE WILL LINGER OVER THE AREA BRINGING
INCREASING CONVECTIVE SHOWER AND POSSIBLY THUNDERSTORM THREATS. THE
ASSOCIATED SURFACE LOW WILL SLIDE DOWN THE BC COAST BEFORE MOVING
INLAND ACROSS PUGET SOUND THIS EVENING. MAIN IMPACT IS THE GENERATION
OF A FRESH SWELL AND PROBABLE 10 FT SEAS JUST BARELY REACHING THE
OUTER WATERS TODAY THROUGH EARLY THIS EVENING. CURRENT GUIDANCE
APPEARS TO MATCH FAIRLY WELL AND HAVE ISSUED A SMALL CRAFT ADVISORY
FOR SEAS AS A RESULT.

SURFACE PATTERN HAS HIGH PRESSURE RETURNING TO THE WATERS AS A
SURFACE THERMAL LOW DEVELOPS ALONG THE NRN CALIFORNIA COAST. MODELS
HAVE EASED UP ON THE STRENGTH OF THE PRESSURE GRADIENT BUT COULD
STILL SEE SOME MARGINAL SCA GUSTS FOR THE CENTRAL OREGON WATERS
FRIDAY NIGHT. /JBONK
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 7 AM THIS MORNING
     TO 9 PM PDT THIS EVENING FOR WATERS FROM CAPE SHOALWATER WA
     TO CASCADE HEAD OR FROM 10 TO 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 AM TO
     10 AM PDT THIS MORNING.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 PM TO
     10 PM PDT THIS EVENING.

&&

$$

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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