Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202307
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
306 PM PST SAT DEC 20 2014

.SYNOPSIS...MILD AND VERY WET WEATHER IS EXPECTED TO CONTINUE OVER
SOUTHWEST WASHINGTON AND NORTHWEST OREGON THROUGH SUNDAY AS A STRONG
WESTERLY FLOW TRANSPORTS AN ATMOSPHERIC RIVER OR PLUME OF
ANOMALOUSLY HIGH MOISTURE INTO THE AREA. THE HEAVIEST RAIN WILL BE
OVER THE HIGHER TERRAIN. THE HEAVY RAIN SHOULD EASE LATE SUNDAY INTO
MONDAY. THERE IS THE STRONG POTENTIAL FOR RIVER FLOODING FROM
TONIGHT INTO EARLY NEXT WEEK. LONGER RANGE MODEL OUTPUT IS
SUGGESTING A COLDER AIR MASS WILL SETTLE OVER THE PACIFIC NORTHWEST
LATE NEXT WEEK WITH SNOW DOWN INTO AT LEAST THE CASCADE FOOTHILLS
AND COAST RANGE. &&

.SHORT TERM...TONIGHT THROUGH TUESDAY...WIDESPREAD HEAVY RAIN HAS
FALLEN ACROSS SW WASHINGTON AND NW OREGON TODAY AS A FRONTAL SYSTEM
WITH A CONNECTION TO A LONG FETCH SUB-TROPICAL MOISTURE SOURCE HAS
BEGUN TO MOVE ONSHORE. AMSU DERIVED SATELLITE IMAGERY IS SHOWING A
PLUME OF PRECIPITABLE WATER VALUES  THE HIGHEST PRECIPITATION TOTALS
SO FAR HAVE BEEN IN THE OREGON COAST RANGE WHERE MOST SITES HAVE SEEN
BETWEEN TWO AND FOUR INCHES OF RAIN SINCE LAST NIGHT. THE
COAST...WILLAPA HILLS...AND CASCADES HAVE SEEN AROUND ONE TO TWO
INCHES...WHILE THE INTERIOR LOWLANDS HAVE SEEN ONE HALF TO ONE INCH
SO FAR.

A WARM FRONTAL FEATURE APPROACHED THE COAST THIS MORNING AND HAS
SLOWLY MOVED ONSHORE THIS AFTERNOON. THERE HAVE BEEN SOME GUSTY
SOUTHWESTERLY WINDS ALONG THE COAST OUT AHEAD OF THE WARM
FRONT...WITH A FEW COASTAL LOCATIONS HAVING RECORDED GUSTS OF 45 TO
55 MPH. THE WINDS HAVE BEGUN TO SUBSIDE OVER THE OREGON COAST OVER
THE PAST COUPLE OF HOURS AS THE WARM FRONT PUSHES INLAND...AND THEY
ARE JUST NOW PEAKING ALONG THE S WA COAST. WINDS WILL STILL REMAIN
FAIRLY GUSTY OUT OF THE WEST/SOUTHWEST THROUGH TONIGHT AS WE SIT IN
THE WARM SECTOR OF THE FRONTAL SYSTEM.

IN ADDITION TO PRECIPITATION CONCERNS...THERE HAVE ALSO BEEN SOME
DANGEROUS SURF CONDITIONS ALONG THE BEACHES TODAY. WHILE THE OVERALL
SEAS CONTINUE TO DECREASE SLIGHTLY...WILL MAINTAIN THE HIGH SURF
ADVISORY AT THIS TIME AND ALLOW IT TO EXPIRE AT 7 PM. THE POTENTIAL
REMAINS FOR LARGE WAVES TO CREATE HAZARDOUS CONDITIONS IN THE SURF
ZONE WITH LARGE WAVES WITH THE ABILITY TO CRASH QUICKLY ON BEACHES
AND OVER JETTIES. BEACHGOERS AND STORM WATCHERS SHOULD REMAIN ALERT
AND EXERCISE EXTREME CAUTION NEAR THE COAST THROUGH THIS EVENING.

AT THIS POINT...THERE WILL BE VERY LITTLE CHANGE IN THE OVERALL
SYNOPTIC PATTERN THROUGH TONIGHT INTO SUN MORNING. BEHIND THE WARM
FRONTAL PASSAGE...WE WILL SIT IN WARM SECTOR OF THE SYSTEM. STRONG
W/SW FLOW AT LOW AND MID LEVELS WILL DRIVE SIGNIFICANT OROGRAPHIC
LIFT ALONG THE COAST RANGE AND CASCADES. WITH THE ENHANCED
SUBTROPICAL MOISTURE ALSO REMAINING IN PLACE...WE WILL SEE A
PROLONGED PERIOD OF HEAVY RAIN IN THE HIGHER TERRAIN. SINCE WE ARE
LOSING A LOT OF THE FORCING ASSOCIATED WITH ISENTROPIC LIFT ALONG THE
WARM FRONT...THE MAIN FORCING FOR PRECIPITATION WILL NOW BE THE
OROGRAPHIC LIFT. THUS...PRECIPITATION WILL BE SIGNIFICANTLY LESS FOR
THE LOWER ELEVATIONS GOING FORWARD. THIS IS PARTICULARLY TRUE FOR THE
WESTERN SIDE OF THE WILLAMETTE VALLEY...WHERE THERE WILL LIKELY
BE SIGNIFICANT RAIN SHADOWING.

AS WE GET INTO LATER SUNDAY...THE COLD FRONT THAT IS CURRENTLY
SITTING WELL TO OUR NORTH OFF THE BRITISH COLUMBIA AND NORTHERN
WASHINGTON COAST WILL SLOWLY BEGIN TO WORK IT/S WAY SOUTHWARD INTO
OUR CWA. BEHIND THE COLD FRONT...THE STRONG OROGRAPHIC FLOW WILL
WEAKEN AND PRECIPITATION TAPER OFF CONSIDERABLY. THE CURRENT FCST
MODEL TIMING HAS THE PRECIP OVER S WASHINGTON TAPERING OFF SUN
AFTERNOON...AND THE N OREGON CASCADES AND COAST RANGE DROPPING OFF
SUN EVENING. THE HEAVIER PRECIPITATION BECOMES INCREASINGLY CONFINED
TO THE CENTRAL OR CASCADES AND COAST RANGE TOMORROW. EVENTUALLY THE
COLD FRONTS ALL THE WAY THROUGH THE FCST AREA SUN NIGHT INTO EARLY
MON MORNING. SNOW LEVELS WILL FALL BEHIND THE COLD FRONT...WHICH MAY
ALLOW FOR A FEW INCHES OF SNOWFALL ACCUMULATION DOWN TO NEAR THE
CASCADE PASSES LATE SUNDAY OR EARLY MON BEFORE THE PRECIPITATION
COMPLETELY ENDS.

CONDITIONS LOOK DRIER FOR MON AS UPPER LEVEL RIDGING BUILDS OVER THE
PAC NW. THE 12Z ECMWF IS INDICATING THAT THE BAROCLINIC ZONE TO OUR
SOUTH MAY TRY TO LIFT NORTHWARD AGAIN AS A WARM FRONT ON MON...SO DID
NOT COMPLETELY REMOVE POPS. BUT THE NAM AND GFS ARE COMPLETELY
DRY...SO STAYED WITH LOW CHANCE POPS FOR NOW.

MAINLY DRY CONDITIONS WILL LIKELY CONTINUE ON FOR MUCH OF TUE.
HOWEVER...FCST CONFIDENCE IS A LITTLE BETTER THAT WE WILL SEE SOME
LIGHT RAIN ON TUE NIGHT OR WED AS A WEAK FRONTAL SYSTEM TO THE NORTH
MOVES THROUGH THE WEAKENING UPPER LEVEL RIDGE. PYLE


&&

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...MODELS REMAIN
CONSISTENT IN FLATTENING AN UPPER LEVEL RIDGE LATE TUESDAY INTO
WEDNESDAY. THERE ARE SOME MODEL DISCREPANCIES CONCERNING HOW FAR
SOUTH THE NEXT SHORTWAVE WILL MOVE INTO THE PACIFIC NORTHWEST...BUT
OVERALL AN UPPER LEVEL TROUGH WILL SAG SOUTH AND MOVE INLAND EARLY
WEDNESDAY. THIS WILL USHER IN ANOTHER BATCH OF COOL AND RAINY
CONDITIONS...WITH SNOW LEVELS DROPPING TO NEAR 2000 FT SO EXPECT
SNOW SHOWERS OVER CASCADE PASSES RIGHT IN TIME FOR HOLIDAY TRAVEL.
AGAIN...HOLIDAY TRAVELERS HEADED OVER THE CASCADE PASSES WILL
CERTAINLY NEED TO MONITOR THE FORECAST. LINGERING MOISTURE CONTINUES
INTO CHRISTMAS DAY...BUT WILL LIKELY BE OCCASIONAL SHOWERS WITH
PARTLY CLOUDY SKIES FOR THE MOST PART. COLDER NORTHERLY FLOW
PERSISTS INTO EARLY NEXT WEEKEND...WITH DRIER CONDITIONS EXPECTED
FOR FRIDAY. A NEW DEVELOPMENT IN THE 12Z MODEL RUNS HAS BEEN ANOTHER
SHORTWAVE DISTURBANCE DROPPING SOUTH OVER THE FORECAST AREA LATE
FRIDAY...BRINGING A THREAT FOR RAIN AND SNOW ON THE MOUNTAINS.
/27
MONDAY NIGHT THROUGH FRIDAY...AN UPPER LEVEL RIDGE WILL AMPLIFY OVER
THE REGION LATE MONDAY INTO TUESDAY. EXTENDED MODELS AGREE ON A WEAK
SHORTWAVE ATTEMPTING TO FLATTEN THE RIDGE TUESDAY MORNING AS AN UPPER
LEVEL TROUGH BEGINS TO DEEPEN IN THE GULF OF ALASKA. CLOUDY AND RAINY
CONDITIONS WILL LINGER INTO THE MIDDLE OF NEXT WEEK AS THIS DIRTY
RIDGE REMAINS OVER THE AREA. THE NEXT MORE SIGNIFICANT SYSTEM ARRIVES
LATE WEDNESDAY AFTERNOON AS THE UPPER LEVEL TROUGH AXIS BECOMES MORE
NEGATIVELY TILTED AND STARTS TO SHIFT INLAND. THIS MARKS THE NEXT
BEST SHOT FOR THE CASCADES TO FINALLY SEE SOME SNOW
ACCUMULATIONS...AS SNOW LEVELS DROP TO 2000 TO 2500 FT THROUGH
CHRISTMAS DAY. HOLIDAY TRAVELERS HEADED OVER THE CASCADE PASSES WILL
CERTAINLY NEED TO MONITOR THE FORECAST. COLDER NORTH FLOW WILL FOLLOW
AND ALLOW TEMPERATURES TO COOL WELL BELOW NORMAL AS CONDITIONS DRY
OUT NEXT FRIDAY. /27
&&

.HYDROLOGY...A WEST TO EAST ORIENTED BAND OF MOISTURE ORIGINATING
FROM THE TROPICS...CONTINUES TO TAKE AIM AT NORTHWEST OREGON AND
SOUTHWESTERN WASHINGTON. OROGRAPHIC ENHANCEMENT RESULTED IN HEAVY
RAIN AT TIMES ALONG THE COAST THIS MORNING. PRECIPITATION TOTALS
HAVE MATCHED FORECASTED VALUES REASONABLY WELL TO THIS POINT. AS A
RESULT...OPTED TO ISSUE FLOOD WARNINGS FOR SEVEN COASTAL RIVERS
INCLUDING THE GRAYS...NEHALEM AT FOSS...THE
WILSON...TRASK...SILETZ...ALSEA AND SIUSLAW AS MOST...IF NOT ALL OF
THESE RIVERS SHOULD REACH FLOOD STAGE LATER TONIGHT OR ON SUNDAY
BASED ON OBSERVED AND FORECASTED RAINFALL. ONE GENERAL REGION THAT
HAS EXCEEDED EXPECTATIONS IS IN THE CENTRAL/NORTH OREGON COAST RANGE
WHERE 3 TO 4.5 INCHES OF RAIN HAVE FALLEN SO FAR...RATHER THAN THE
EXPECTED 2 TO 3 INCHES TO THIS POINT. BECAUSE THIS REGION HAS
EXCEEDED EXPECTATIONS...AND RAINFALL RATES HAVE HOVERED IN THE
QUARTER TO HALF INCH PER HOUR...SEVERAL OF THESE
RIVERS...PARTICULARLY THE WILSON AND SILETZ RIVERS...MAY REACH FLOOD
STAGE SEVERAL HOURS SOONER THAN THE CURRENT FLOOD WARNINGS INDICATE.
WILL REEVALUATE THIS PORTION OF THE RIVER FORECAST THIS AFTERNOON.

WILL MORE THAN LIKELY BE ISSUING ADDITIONAL FLOOD WARNINGS LATER
THIS AFTERNOON AND/OR EVENING AS CONFIDENCE GROWS THAT ADDITIONAL
RIVERS IN THE AREA WILL REACH FLOOD STAGE. AT THIS POINT...NEARLY 20
RIVERS STAND A DECENT SHOT OF REACHING FLOOD STAGE. DEPENDING ON
WHERE THE HEAVIEST RAIN AXIS SETS UP...A COUPLE CERTAINLY STAND A
CHANCE OF REACHING MAJOR FLOOD STAGE...BUT CONFIDENCE IS STILL NOT
TERRIBLY HIGH WHERE THIS WILL BE. CURRENT MODELS AND FORECASTS
SUGGEST THE CLACKAMAS RIVER NEAR ESTACADA AND THE MARYS RIVER NEAR
PHILOMATH STAND THE BEST CHANCE...BUT THESE ARE CERTAINLY SUBJECT TO
CHANGE...AND NO FLOOD WARNINGS HAVE BEEN ISSUED FOR THESE RIVERS AS
OF SATURDAY MID AFTERNOON. WOULD NOT BE SUPRISED IF ONE OR TWO
RIVERS ALONG THE COAST REACH MAJOR FLOOD STAGE...BUT WHICH ONE OR
TWO REMAINS UNCERTAIN. BASED ON TRENDS TODAY...THE WILSON AND SILETZ
HAVE OUR ATTENTION. PLEASE MONITOR
WATER.WEATHER.GOV/AHPS2/INDEX.PHP?WFO=PQR FOR THE LATEST RIVER
OBSERVATIONS AND FORECAST INFORMATION.

IN ADDITION TO RIVER FLOODING CONCERNS...WE HAVE ALSO BEEN DEALING
WITH SOME FLOODING ISSUES FROM TIDAL OVERFLOW. DESPITE LOWER FLOWS ON
COASTAL RIVERS THIS MORNING...SOME MINORTIDAL OVERFLOW WAS OBSERVED
ALONG THE COAST. THE HIGH TIDE DURING LATE MORNING ON SUNDAY WILL BE
OF ABOUT THE SAME MAGNITUDE...AND WITH MUCH HIGHER FLOWS EXPECTED DUE
TO THE ABUNDANT RAINFALL OVER THE COASTAL RIVER BASINS...CONFIDENCE
IS FAIRLY HIGH THAT AT LEAST SOME MINOR TIDAL OVERFLOW IMPACTS WILL
BE OBSERVED ON SUNDAY WITH TOTAL TIDES PUSHING NEAR 11 FT WITH
COASTAL RIVERS APPROACHING OR EXCEEDING BANKFULL. LOW LYING AREAS
NEAR WILLAPA BAY...TILLAMOOK BAY...DEPOE BAY...WALDPORT...AND
FLORENCE...ALONG WITH STRETCHES OF HIGHWAY 101 ALONG THE COAST...MAY
EXPERIENCE MINOR TIDAL OVERFLOW DURING THE HIGH TIDE AROUND 11 AM
SUNDAY. PEAK IMPACTS ARE LIKELY BETWEEN ABOUT 9 AM AND 3 PM. WITH
RIVERS CONTINUING TO RUN AT OR NEAR FLOOD STAGE...THE MIDDAY HIGH
TIDE ON MONDAY MAY AGAIN CAUSE SOME MINOR ISSUES.

THERE HAVE ALREADY BEEN SEVERAL REPORTS OF ROCKS AND MUDSLIDES
IMPACTING TRAVEL ALONG THE OREGON AND WASHINGTON COASTS...COAST
RANGE AND IN THE COLUMBIA RIVER GORGE. EXPECT ADDITIONAL INCIDENTS
THROUGH THE WEEKEND IN AREAS OF STEEPER TERRAIN. BURN SCARS FROM THE
36 PIT FIRE IN THE CLACKAMAS RIVER BASIN NEAR ESTACADA AND THE
DECEPTION COMPLEX NEAR OAKRIDGE...WILL BE PARTICULARLY VULNERABLE.
/NEUMAN

&&

.AVIATION...GENERALLY LOWER MVFR CONDITIONS ACROSS THE INTERIOR
THIS AFTERNOON WITH CIGS STEADY AROUND 1500 FT AND VIS REMAINING
IN THE 3-5 SM RANGE. MEANWHILE...THE COASTAL AREAS REPORT MOSTLY
IFR CIGS AND VSBYS. EXPECT LITTLE CHANGE THROUGH THIS EVENING AS
FRONTAL BAND WILL SLIDE SOUTH INTO THE REGION AND RAIN CONTINUES.
GUSTY S WINDS TO 35 KT CAN BE EXPECT FOR THE COASTAL AREAS...IN
ADDITION TO SOME PORTIONS OF THE INTERIOR INCLUDING KSLE. SOME
LOCAL POCKETS OF LOWER FLIGHT CONDITIONS...IFR FOR THE INTERIOR
AND LIFR FOR THE COAST...MAY DEVELOP THROUGH TONIGHT. EXPECT WINDS
TO BECOME MORE W BY AROUND 12Z SUN AS SURFACE FRONT MOVES ACROSS
REGION.

KPDX AND APPROACHES...LOWER MVFR CIGS PREVAIL THIS
EVENING...AROUND 1500 FT. MAY SEE SOME OCCASIONAL LOWERING TO NEAR
1000 FT ALONG WITH SOME RESTRICTION IN VIS...INTO THE 3-4 SM
RANGE WITH CONTINUING RAIN. LIGHT RAIN AND MVFR FLIGHT CONDITIONS
LIKELY CONTINUE THROUGH THE TAF PERIOD. S WINDS WILL BECOME MORE
SW OR WSW AFT 14Z SUN AS FRONTAL BOUNDARY MOVES THROUGH. CULLEN

&&

.MARINE...WINDS HAVE EASED A LITTLE FROM THEIR PEAK EARLIER
TODAY...BUT GUSTS REMAIN AROUND 35 KT THIS AFTERNOON. ADDITIONALLY
SHORT TERM MODELS SUGGEST ANOTHER BURST OF STRONGER GUSTS ARE
POSSIBLE THROUGH THIS EVENING. THEREFORE...WILL CONTINUE THE GALE
WARNING AT THIS TIME. WINDS WILL EASE GRADUALLY THIS
EVENING...WITH WINDS DECREASING TO SMALL CRAFT ADVISORY RANGE OVER
ALL WATERS BY MIDNIGHT. WINDS CONTINUE TO EASE THROUGH DAY
SUN...WITH WINDS GENERALLY 15 KT OR LESS AND BECOMING MORE W AND
THEN NW. WINDS MAY INCREASE AGAIN AROUND MIDWEEK INTO SMALL CRAFT
ADVISORY RANGE AS A FRONTAL SYSTEM APPROACHES.

SEAS REMAIN AROUND 18 TO 20 FT RANGE THROUGH THIS EVENING...BEFORE
SUBSIDING TO NEAR 15 FT SUNDAY MORNING. HOWEVER...SEAS LIKELY
REMAIN IN THE LOW TO MID TEENS THROUGH AT LEAST THE FIRST HALF OF
THE WEEK AND POSSIBLY UNTIL FRIDAY. CULLEN


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...FLOOD WATCH THROUGH MONDAY AFTERNOON FOR CASCADE FOOTHILLS IN
     LANE COUNTY-CASCADES IN LANE COUNTY-CENTRAL COAST RANGE OF
     WESTERN OREGON-CENTRAL COLUMBIA RIVER GORGE-CENTRAL OREGON
     COAST-CENTRAL WILLAMETTE VALLEY-COAST RANGE OF NORTHWEST
     OREGON-GREATER PORTLAND METRO AREA-LOWER COLUMBIA-NORTH
     OREGON COAST-NORTHERN OREGON CASCADE FOOTHILLS-NORTHERN
     OREGON CASCADES-SOUTH WILLAMETTE VALLEY-UPPER HOOD RIVER
     VALLEY-WESTERN COLUMBIA RIVER GORGE.

     HIGH SURF ADVISORY UNTIL 7 PM PST THIS EVENING FOR CENTRAL
     OREGON COAST-NORTH OREGON COAST.

     COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SUNDAY FOR CENTRAL
     OREGON COAST-NORTH OREGON COAST.

WA...FLOOD WATCH THROUGH MONDAY AFTERNOON FOR CENTRAL COLUMBIA RIVER
     GORGE-GREATER VANCOUVER AREA-I-5 CORRIDOR IN COWLITZ COUNTY-
     SOUTH WASHINGTON CASCADE FOOTHILLS-SOUTH WASHINGTON
     CASCADES-SOUTH WASHINGTON COAST-WESTERN COLUMBIA RIVER
     GORGE-WILLAPA HILLS.

     HIGH SURF ADVISORY UNTIL 7 PM PST THIS EVENING FOR SOUTH
     WASHINGTON COAST.

     COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SUNDAY FOR SOUTH
     WASHINGTON COAST.

PZ...GALE WARNING UNTIL MIDNIGHT PST TONIGHT FOR COASTAL WATERS FROM
     CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 6 PM PST
SUNDAY.

&&

$$

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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