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272
FXUS66 KPQR 171756
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
954 AM PST WED DEC 17 2014

.SYNOPSIS...A CLOSED LOW JUST OFFSHORE WEST OF THE OR/CA BORDER WILL
SLOWLY WEAKEN AND EVENTUALLY MOVE ONSHORE ALONG THE N OR/S WA COAST
THIS AFTERNOON. THIS WILL MAINTAIN LIGHT SHOWER ACTIVITY...MAINLY
OVER THE HIGHER TERRAIN THIS MORNING. AN UPPER LEVEL SHORTWAVE WILL
PUSH ONSHORE LATER TODAY...LIKELY BRINGING A PERIOD OF STEADIER
RAINFALL THROUGH EARLY THU MORNING. EXPECT A FAIRLY QUIET PERIOD FOR
MUCH OF THE DAY THU...BUT THEN A MORE ORGANIZED FRONT WILL BRING
GUSTY WINDS AND LARGE SURF TO THE COAST AND RAIN SPREADING INLAND
THURSDAY NIGHT AND FRIDAY. RISING SNOW LEVELS WILL LIMIT SNOW TO THE
HIGHEST PEAKS...BUT COLDER AIR BEHIND THE FRONT MAY RESULT IN SOME
SNOW SHOWERS FOR THE CASCADES PASSES FRIDAY EVENING AND SATURDAY.
WARMER AND MOISTER WEATHER IS EXPECTED THIS WEEKEND. THERE IS THE
POTENTIAL FOR AN ATMOSPHERIC RIVER TYPE SET UP AND ASSOCIATED HEAVY
RAIN TO DEVELOP OVER THE WEEKEND INTO EARLY NEXT WEEK.

&&

.UPDATE...SUBTLE CHANGES FOR TODAY MAINLY BY INCREASING POPS FOR THE
AFTERNOON...AND LATE AFTERNOON PROBABLY IN REALITY. ALSO PLAN ON
RAMPING UP COAST RANGE AND CASCADE WINDS FOR THE NEXT FRONTAL SYSTEM
MAINLY LATE THURSDAY AFTERNOON AND THURSDAY NIGHT. NOT ANTICIPATING
ANY HIGHLIGHTS BUT PROBABLY A RUN OF THE MILL WINDY COASTAL STORM.

MAIN ATTENTION WILL BE PLACED ON THE ATMOSPHERIC RIVER EVENT SETTING
UP TO AFFECT THE REGION THIS WEEKEND WITH IMPACTS LASTING INTO NEXT
WEEK. RAW GFS MODEL RUN ACCUMULATED QPF AMOUNTS EXCEED 12 INCHES FOR
PORTIONS OF THE CASCADES AND 10 INCHES FOR THE COAST RANGE ENDING
MONDAY MORNING. MOST OF THAT OCCURS BEGINNING SATURDAY. THERE WOULD
BE DEEP WESTERLY FLOW FROM THE SURFACE UP TO THE JET LEVEL THUS
EXPECT THIS COULD BE AN IDEAL SITUATION TO EXTRACT A MAXIMUM AMOUNT
OF RAIN FROM WHATEVER COMES ASHORE. THERE IS GENERAL LARGE SCALE
SUPPORT FROM THE ECMWF ALBEIT WITH LESS QPF. PAST EXPERIENCE SHOWS
FOLLOWING THE HIGHER GFS QPF AMOUNTS IS STILL NOT ENOUGH AND THAT
REALITY BRINGS SIGNIFICANTLY MORE RAIN. ASSUMING THE CURRENT MODEL
RUNS STAY UNCHANGED IN THE FUTURE...WOULD EXPECT MULTIPLE MAINSTEM
RIVERS EXCEEDING FLOOD STAGE AS SOON AS SUNDAY MORNING.

WILL BEGIN TO ISSUE SOME OUTLOOK PRODUCTS TODAY WITH THE CAVEAT THAT
MODELS HAVE RELATIVELY RECENTLY SHIFTED THE FOCUS FROM NORTHERN
WASHINGTON/BRITISH COLUMBIA SOUTH TO OUR AREA. ADDITIONAL SHIFTING
IS EXPECTED AS WELL AS TIMING DIFFERENCES. STAY TUNED AS THIS
SITUATION EVOLVES OVER TIME. /JBONK

&&

.PREV DISC... /ISSUED 259 AM PST WED DEC 17 2014/

SHORT TERM...TODAY THROUGH SATURDAY...VERY LIGHT RAIN CONTINUES TO
IMPACT SW WASHINGTON THIS MORNING BUT HAS OTHERWISE STARTED TO
DISSIPATE OVER THE SOUTHERN PORTION OF THE FORECAST AREA. WATER
VAPOR IMAGERY SHOWS A CLOSED LOW WEAKENING AS IT HAS PUSHED ONSHORE
NEAR THE OREGON/CALIFORNIA BORDER...WHILE AN UPPER LEVEL SHORTWAVE
IS ELONGATING AS IT APPROACHES THE PACIFIC NORTHWEST COASTLINE. NOT
MUCH CHANGE IN THE KTTD-KDLS GRADIENT...WHICH REMAINS AROUND -5
EARLY THIS MORNING. EAST WINDS CONTINUE TO GUST NEAR 25 MPH THROUGH
THE GORGE...BUT EXPECT THE EASTERLY GRADIENT TO WEAKEN BY LATE
TONIGHT.

AFTER A PERIOD OF LIGHT RAIN THIS MORNING...MODELS REMAIN CONSISTENT
IN SHOWING AN UPTICK IN PRECIP BY THIS AFTERNOON ASSOCIATED WITH THE
VORT MAX JUST OFFSHORE AROUND 45N 134W. THE LOWER LEVEL MOISTURE
ASSOCIATED WITH THE SURFACE LOW COMBINED WITH THE UPPER LEVEL FORCING
FROM THE SHORTWAVE SHOULD DRIVE A PERIOD OF STEADIER PRECIP THIS
EVENING AND THROUGH TONIGHT. THE VORT MAX PUSHES EAST OF THE CASCADES
BY 12Z THU...AFTER WHICH SHOWER ACTIVITY SHOULD DROP OFF
SIGNIFICANTLY.

WITH CLEARING SKIES AND LIGHT WINDS...SHOULD SEE SOME SHALLOW FOG TO
DEVELOP IN INTERIOR VALLEYS TONIGHT THROUGH EARLY THU MORNING. MODELS
MAINTAIN A THREAT FOR LIGHT PRECIP OVER THE HIGHER TERRAIN MUCH OF
THU...BUT OTHERWISE EXPECT DRY CONDITIONS TO PERSIST TO LOWER
ELEVATIONS. THE NEXT SIGNIFICANT FRONTAL SYSTEM ARRIVES LATE
THU...SPREADING RAIN AND BRINGING GUSTY COASTAL WINDS TO THE REGION
THROUGH FRI. PRECIPITABLE WATER IS EXPECTED TO BE NEAR AN INCH AND AN
APPROACHING JET STREAK SHOULD PROVIDE GOOD LIFT AND EXPECT THE
HIGHEST RAINFALL TOTALS OF 0.75 TO 1 INCH ACROSS THE COAST AND COAST
RANGE THROUGH MIDDAY FRI. OTHER LOCATIONS WILL SEE ON AVERAGE 0.5
INCHES OF RAIN. SNOW LEVELS SHOULD REMAIN ABOVE 5000 FEET DURING THE
PEAK RAIN PERIOD...BUT LOWER TO NEAR OR BELOW THE CASCADE PASSES
BEHIND THE FRONT FRIDAY AFTERNOON.

STRONG LOW PRESSURE OVER THE GULF OF ALASKA WILL PUSH INLAND LATE FRI
INTO EARLY SAT MORNING...SIMULTANEOUSLY FLATTENING A BROAD AREA OF
HIGH PRESSURE OVER THE EASTERN PACIFIC. THERE IS INCREASING
CONFIDENCE AN ATMOSPHERIC RIVER SCENARIO WILL SET UP...WITH ABUNDANT
MOISTURE AIMED DIRECTLY AT THE PACIFIC NORTHWEST SAT.

LONG TERM...SATURDAY NIGHT THROUGH TUESDAY...AS THIS TROUGH MOVES ON
SHORE SATURDAY...THE ASSOCIATED COLD FRONT MOVES ONSHORE AND STALLS
EAST-TO-WEST ACROSS NORTHWEST OREGON AND SOUTHWEST WASHINGTON. THIS
PUTS OUR AREA IN THE PATH OF RAIN STARTING SATURDAY THROUGH MONDAY.
SOME UNCERTAINTY EXISTS IN WHERE THIS BOUNDARY WILL SET UP...WHICH
WILL DETERMINE HOW MUCH RAINFALL WE WILL GET. ON TUESDAY...GEFS
ENSEMBLE SPAGHETTI PLOTS GET MESSY AND SIGNIFICANT DIFFERENCES START
TO SHOW UP BETWEEN THE GFS AND ECMWF...DECREASING CONFIDENCE ON HOW
THE REST OF THE WEEK WILL SHAPE UP.  AS OF NOW...THE MOST COMMON
SOLUTION IS THAT HIGH PRESSURE RIDGING WILL START TO BUILD BACK OVER
THE WESTERN U.S. WHICH SUGGESTS DRIER WEATHER STARTING TUESDAY...
THOUGH UNCERTAINTY IS VERY HIGH. -MCCOY

&&

.AVIATION...VFR CONDITIONS TO PERSIST AT MOST TAF SITES THROUGH
THIS AFTERNOON. AS SHOWERS MOVE IN...THERE MAY BE PERIODS OF
MVFR...ESPECIALLY AT SOUTH WILLAMETTE VALLEY SITES. CLEARING IS
POSSIBLE THIS EVENING...ALLOWING FOG TO DEVELOP IFR CIGS AND
VIS...BUT UNCERTAINTY IS HIGH BECAUSE THE MODELS ARE HINTING AT A
WEAK LOW PRESSURE SYSTEM OFF THE SOUTH OREGON COAST MOVING INLAND
THIS EVENING. THIS COULD BRING ADDITIONAL SHOWERS AND WINDS WHICH
WOULD KEEP CIGS VFR/MVFR. IF ANY CLEARING DOES OCCUR...EXPECT CIGS
AND VIS TO DROP TO IFR WITH THE DEVELOPMENT OF FOG/LOW STRATUS.

KPDX AND APPROACHES...VFR CONDITIONS TO PERSIST WEDNESDAY.
RAIN MAY BRING PERIODS OF MVFR CIGS AND VIS. CIGS COULD DROP TO
IFR TONIGHT WITH THE DEVELOPMENT OF FOG/LOW STRATUS AFTER 09Z
THURSDAY. -MCCOY

&&

.MARINE...WEST SWELL AROUND 10 FT BRINGING SEAS UP TO SMALL CRAFT
CRITERIA TODAY. SEAS DROP BELOW 10 FT LATER THIS EVENING. THE
SYSTEM OF INTEREST WILL BE TOMORROW WHICH WILL LIKELY BRING
SOUTHERLY GALES THROUGH EARLY FRIDAY. THERE IS STILL SOME
UNCERTAINTY ON TIMING...BUT MODELS ARE COMING INTO AGREEMENT THAT
WINDS WILL START TO INCREASE EARLY THURSDAY MORNING...REACHING
GALE FORCE BY EARLY AFTERNOON. SEAS BUILD INTO THE TEENS THURSDAY
AFTERNOON. SEAS DROP BACK DOWN TO 10 TO 12 FT ON FRIDAY AHEAD OF
THE NEXT SYSTEM WHICH WILL BRING SEAS UP EVEN HIGHER ON SATURDAY.

THERE IS STILL UNCERTAINTY ON THE TIMING OF THE SATURDAY SYSTEM...BUT
AS OF NOW MODELS ARE SUGGESTING THAT WINDS COULD AGAIN REACH GALE
FORCE EARLY SATURDAY...WHICH COULD BUILD SEAS INTO THE LOW 20S.
SEAS START TO FALL EARLY SUNDAY...DROPPING BACK INTO THE LOW
TEENS BY LATE SUNDAY OR EARLY MONDAY. AN ACTIVE WEATHER PATTERN
WILL CONTINUE THROUGH THIS WEEKEND...KEEPING SEAS ELEVATED
THROUGH EARLY NEXT WEEK WITH PERIODS OF GALES POSSIBLE. -MCCOY


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...GALE WATCH FROM THURSDAY MORNING THROUGH THURSDAY EVENING FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 9 PM PST THIS
     EVENING FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 4 PM PST THIS AFTERNOON.

&&

$$

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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