Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 190405
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
805 PM PST THU DEC 18 2014

.SYNOPSIS...A FRONTAL SYSTEM WILL PUSH ONSHORE LATER TONIGHT. A
COLDER UPPER TROUGH MOVES ACROSS THE AREA FRIDAY...WHICH WILL LOWER
SNOW LEVELS BELOW THE CASCADE PASSES. MILD AND VERY WET WEATHER IS
EXPECTED THIS WEEKEND WITH AN ATMOSPHERIC RIVER BRINGING HEAVY RAIN
TO THE REGION. THE EXACT LOCATION OF THE JET STREAM AND ASSOCIATED
MOISTURE PLUME IS STILL IN QUESTION...BUT THERE IS INCREASING
CONFIDENCE THAT IT WILL TAKE AIM AT SW WASHINGTON AND NW OREGON.
THERE IS THE POTENTIAL FOR SOME FLOODING LATE THIS WEEKEND INTO
EARLY NEXT WEEK.

&&

.SHORT TERM....FRONT HAVING PAST BUOY 46029 EARLY THIS EVENING
EXPECTED TO REACH THE SHORE AND BEGIN TO MOVE INLAND BY LATE
EVENING. FAIRLY SOLID BAND OF PRECIPITATION ACCOMPANIES THE FRONT ON
RADAR SO POPS WILL REMAIN HIGH EARLY TONIGHT UNTIL THE FRONT MOVES
THROUGH. POST FRONTAL SHOWERS EXPECTED TO PICK UP LATER IN THE
NIGHT AND EARLY FRI AS THE COLD UPPER TROUGH MOVES ACROSS.

REMAINDER OF SHORT TERM DISCUSSION UNCHANGED...SNOW LEVELS WILL
LOWER DOWN TO BELOW THE CASCADE PASSES BY EARLY FRIDAY MORNING AS
THE COLD UPPER TROUGH SLIDES OVER THE REGION. HOWEVER...THE BULK OF
THE PRECIPITATION WILL HAVE FINISHED BY THE TIME SNOW LEVELS COME
DOWN. OVERALL...A FEW INCHES OF SNOW AT THE PASSES ARE POSSIBLE WITH
A FEW ADDITIONAL INCHES OF SNOW AT THE HIGHER CASCADE ELEVATIONS.
ADDED A SLIGHT CHANCE OF THUNDERSTORMS TO THE FORECAST FOR THE COAST
RANGE AND POINTS WEST FOR EARLY TOMORROW MORNING. THE UPPER TROUGH
MOVES THROUGH THE AREA AND MODEL FORECAST SOUNDINGS INDICATE DECENT
INSTABILITY.

MODELS CONTINUE TO REMAIN IN GOOD AGREEMENT THAT A VERY MOIST
ATMOSPHERIC RIVER PATTERN WILL SET UP DIRECTING LARGE AMOUNTS OF
MOSITURE AT SW WASHINGTON AND NW OREGON THIS WEEKEND. HEAVY RAINFALL
LIKELY BEGINS BY EARLY SATURDAY MORNING AND CONTINUES THROUGH AT
LEAST SUNDAY. THE COAST RANGE...WILLAPA HILLS...CASCADES...AND
FOOTHILLS WILL LIKELY SEE ON THE ORDER OF 8 TO 12 INCHES OF RAINFALL.
LOCATIONS ON THE COAST MAY SEE 5 TO 7 INCHES OF RAIN...WHILE THE
INTERIOR VALLEY LOCATIONS CAN EXPECT 3 TO 4 INCHES. WHILE SOME
UNCERTAINTY IN THE PRECISE AREAS OF MAXIMUM RAINFALL
EXISTS...CONFIDENCE IS INCREASING THAT LARGE AMOUNTS OF PRECIPITATION
WILL OCCUR ACROSS THE FORECAST AREA WITH THIS SYSTEM. AS A
RESULT...THERE IS THE POTENTIAL FOR SHARP RISES ON AREA RIVERS AND
STREAMS THAT MAY RESULT IN FLOODING. SEE THE HYDROLOGY SECTION FOR
MORE DETAILS.

IN ADDITION...THOSE PLANNING TO BE ALONG THE COAST AT AREAS BEACHES
SHOULD CLOSELY MONITOR THE CONDITIONS FOR THIS WEEKEND. RAPIDLY
BUILDING SEAS WILL BRING THE POTENTIAL FOR DANGEROUS HIGH SURF ALONG
THE AREA BEACHES ON FRIDAY. LONG PERIOD SWELLS MAY REACH SHORE AND
SURPRISE INDIVIDUALS WHO ARE UNAWARE. ANYONE ON THE BEACHES SHOULD
EXERCISE EXTREME CAUTION AND AVOID THE SURF ZONE AS LARGE WAVES MAY
WASH OVER BEACHES AND JETTIES WITH LITTLE WARNING. SOME POTENTIAL FOR
MINOR TIDAL OVERFLOW IS POSSIBLE FOR SATURDAY AND SUNDAY...ESPECIALLY
AROUND HIGH TIDES. THIS THREAT COULD BE ENHANCED BY HIGH FLOWS ON
RIVERS IN RESPONSE TO THE RAINFALL THIS WEEKEND.  CULLEN

&&

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. SUNDAY NIGHT
THROUGH THURSDAY...MODELS AGREE THE WEEKEND RAIN/FLOODING EVENT WILL
WIND DOWN SUNDAY NIGHT INTO MONDAY. A MUCH WEAKER FRONT MAY SLIDE
SOUTHWARD ACROSS NORTHWEST OREGON AND SOUTHWEST WASHINGTON MONDAY
NIGHT INTO TUESDAY. MODELS HAVE WAVERED A BIT ON THIS SYSTEM SO POPS
WERE GENERALLY KEPT IN THE HIGH END CHANCE TO LOW END LIKELY.
CONDITIONS SHOULD TEMPORARILY DRY OUT LATE TUESDAY BEFORE A COLDER
STORM SYSTEM BRINGS SHOWERS TO THE AREA ON WEDNESDAY...BUT
DISCREPANCIES CONTINUE AMONG THE MODELS. SNOW LEVELS WILL LIKELY
LOWER WELL BELOW PASS LEVEL SO HOLIDAY TRAVELERS HEADED OVER THE
CASCADE PASSES WILL CERTAINLY NEED TO MONITOR THE FORECAST. COLD
NORTHERLY WILL FOLLOW AND ALLOW TEMPERATURES TO COOL WELL BELOW
NORMAL AS CONDITIONS DRY OUT LATE WEEK. EASTERLY WINDS WILL LIKELY
RETURN. /NEUMAN

&&

.HYDROLOGY...SITUATION SETTING UP FOR A MEMORABLE HYDROLOGIC EVENT
MAINLY FOR LATER THIS WEEKEND AND HEADING INTO NEXT WEEK. STRONG AND
DEEP MOIST WESTERLY FLOW WILL BEGIN CROSSING THE PACNW COAST COME
SATURDAY MORNING. A VERY LONG FETCH OF MOISTURE IS STRETCHING ACROSS
THE PACIFIC WITH ORIGINS WEST TO THE SOUTH CHINA SEA. THIS MOIST AIR
MASS WILL BE PUSHED EAST BY A 150 TO 170 KT JET AND WESTERLY 25 TO
50 KT LOWER LEVEL WINDS. AS SUCH...THIS CONTINUES TO GIVE THE
APPEARANCE OF A CLASSIC HIGH PRECIPITATION ATMOSPHERIC RIVER EVENT
WHERE THE DEEP MOIST FLOW WILL SPEND A SIGNIFICANT AMOUNT OF TIME
ON A NEARLY PERPENDICULAR COURSE AGAINST THE COAST RANGE WITH THE
CASCADES TAKING A BIT HIGHER OF THE IMPACT. AS OF THE MORNING MODEL
RUNS AND RECENT NWRFC UPDATES...IT APPEARS MULTIPLE COAST RANGE
RIVERS HAVE A MODERATE POTENTIAL OF EXCEEDING FLOOD STAGE.
ADDITIONALLY...THIS EVENT HAS SUFFICIENT DEPTH TO BRING SIGNIFICANT
RAINS TO THE NORTH OREGON AND SOUTH WASHINGTON CASCADES WHERE RIVERS
WILL ALSO SEE POTENTIAL FOR NOTABLE FLOODING. WILL CONTINUE THE
HYDROLOGIC OUTLOOK (PDXESFPQR) PRODUCT HIGHLIGHTING CONCERNS. KEEP
IN MIND THAT DETAILS WILL ALWAYS BE IN FLUX UNDER THESE SCENARIOS AS
SUBTLE NORTH/SOUTH SHIFTS COLD MAKE DRAMATIC DIFFERENCES IN WHICH
BASINS RECEIVE EXTENDED PERIODS OF MODERATE TO HEAVY RAIN. PLEASE
CONTINUE TO FOLLOW THE LATEST FORECASTS AND IMPACTS AS CONDITIONS
WARRANT. RIVER FORECASTS ARE AVAILABLE ON OUR WEB PAGE AT:
HTTP://WATER.WEATHER.GOV/AHPS2/INDEX.PHP?WFO=PQR (ALL LOWER CASE)

/JBONK

&&

.AVIATION...MOSTLY LOW TO MID RANGE VFR ACROSS REGION...BUT DO
HAVE AREAS OF MVFR CIGS WITH RAIN OVER COAST RANGE AND ALONG
COAST THIS EVENING. THIS WILL PUSH INLAND THROUGH 08Z. FRONT NOW
JUST ONSHORE...AND WILL PUSH THE CASCADES BY 08Z. CONDITIONS
SLOWLY IMPROVE TO VFR WITH TRANSITION TO SHOWERS BEHIND THE FRONT.
WILL KEEP SLIGHT CHANCE OF TS ALONG THE COAST FOR LATER TONIGHT
AND INTO FRI AM. OTHERWISE...MOSTLY VFR ON FRI WITH POCKETS OF
MVFR CONDITIONS UNDER SHOWERS.

PDX AND APPROACHES...VFR THIS EVENING AND FRI. BUT WILL HAVE
PERIOD OF MVFR CIGS DOWN TO 2500 FT AS FRONT MOVES ACROSS REGION.
BEST TIMING SEEMS TO BE 07Z TO 12Z FOR SUCH CONDITIONS. OTHERWISE
NO SIGNIFICANT IMPACTS EXPECTED FOR OPS AREA.         ROCKEY.
&&

.MARINE...WITH FRONT JUST ONSHORE...WINDS HAVE NOW EASED.
GENERALLY GUSTING TO NEAR 25 KT. SO WILL REPLACE GALE WARNING WITH
SMALL CRAFT ADVISORIES FOR BOTH WINDS AND SEAS. BOTH ADVISORIES
WILL EXTEND THROUGH FRI NIGHT.

SEAS HOLDING AT 12 TO 14 FT TONIGHT BUT WILL DROP BACK A FEW FEET
FOR FRI. BUT WITH INCREASING WINDS LATER FRI NIGHT...SO SEAS WILL
BUILD. STILL LOOK LIKE BUILDING UP TO NEAR 20 FT BY LATE FRI
AFTERNOON...AND LIKELY AROUND 25 FT FRI NIGHT. WINDS AND SEAS WILL
EASE BACK LATER SAT NIGHT AND SUN.                    ROCKEY.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH SURF ADVISORY FROM 10 AM FRIDAY TO 4 AM PST SATURDAY FOR
     CENTRAL OREGON COAST-NORTH OREGON COAST.

WA...HIGH SURF ADVISORY FROM 10 AM FRIDAY TO 4 AM PST SATURDAY FOR
     SOUTH WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR BOTH WINDS AND HAZARDOUS SEAS FOR
         TONIGHT THROUGH FRI NIGHT.
     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR CONDITIONS
         THROUGH FRI NIGHT.

&&


$$

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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