Flood in Oregon, November 17 to 18, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
138 PM PST TUE NOV 17 2015

.SYNOPSIS...A MOIST FRONTAL BOUNDARY ACROSS THE CENTRAL WASHINGTON
COAST EARLY THIS AFTERNOON WILL CONTINUE TO SINK SOUTH LATE THIS
AFTERNOON AND TONIGHT. THERE WILL BE A BREAK IN THE ACTIVE WEATHER
PATTERN LATE TONIGHT AND WEDNESDAY...BUT THE NEXT MILD AND MOIST
SYSTEM IS EXPECTED TO BRING ANOTHER ROUND OF HEAVY RAINFALL TO
NORTHWEST OREGON WEDNESDAY NIGHT. WEAK HIGH PRESSURE ALOFT SETS UP
THURSDAY NIGHT AND FRIDAY. DRY CONDITIONS MAY HOLD THROUGH THE
WEEKEND.

&&

.SHORT TERM...FRONTAL BOUNDARY MOVING INTO SW WASHINGTON AS OF 21Z.
KLGX VELOCITY DEPICTION SHOWS NICE COLD FRONTAL SIGNATURE CLOSE TO
KHQM AT 21Z. RADAR ALSO INDICATES 55-60 KT WIND SPEEDS ABOUT 1200 FT
AGL OVER THE S WASHINGTON COASTAL WATERS. 12Z GFS HAS THE LEADING
EDGE OF THE 850 MB THERMAL GRADIENT AND 1000-700 MB THICKNESS PACKING
TO KAST AROUND 23Z...THEN TO KPDX AROUND 02Z WED AND TO THE CENTRAL
COAST AND LANE COUNTY AROUND 06Z WED. RAINFALL RATES OVER SW
WASHINGTON...ESPECIALLY THE WILLAPA HILLS...HAVE PICKED UP
DRAMATICALLY SINCE LATE MORNING. HUCKLEBERRY AND ABERNATHY RAWS SITES
HAVE GOTTEN ONE-HALF INCH FROM 20Z TO 21Z. NAM INDICATES 55-65 KT 850
MB WLY FLOW OVER SW WASHINGTON THROUGH 00Z WED. THUS...EXPECT RATES
OF 0.3 TO 0.5 INCHES PER HOUR TO CONTINUE THROUGH AT LEAST 00Z WED.
HAVE RE-WORKED THE 18Z-00Z WED AND 00Z-06Z QPF AND THE LATEST RIVER
FORECASTS SHOW THE GRAYS RIVER GETTING CLOSE TO MAJOR FLOOD STAGE. A
COUPLE OTHER NORTH OREGON COASTAL RIVERS GET CLOSE TO FLOOD STAGE AS
WELL. MODEL QPF FOR LATE THIS AFTERNOON AND EVENING SHOW VARYING
SOLUTIONS. GFS HAS A 1.5 TO 2.0 INCH 6-HR BULLSEYE OVER THE S WA
CASCADES IN THE 18Z-00Z PERIOD...FOLLOWED BY 1.5 TO 2.0 INCH 6-HR
CORE OVER THE N OREGON CASCADES AND FOOTHILLS 00Z-06Z WED.

THE SURFACE PRESSURE GRADIENT WILL CONTINUE TO TIGHTEN LATE THIS
AFTERNOON PRODUCING STRONG WIND THROUGH THIS EVENING. THE STRONGEST
GUSTS ARE EXPECTED FOR THE COAST...COAST RANGE AND THE CASCADES
THROUGH THE EARLY EVENING. THE HIGH WIND WARNING CONTINUES FOR THE S
WA AND N OREGON COAST...THE WILLAPA HILLS AND N OREGON COAST RANGE.
AT 21Z HAVE ALREADY HAD SOME GUSTS 60-65 MPH ALONG EXPOSED AREAS OF
THE S WASHINGTON COAST. CAPE DISAPPOINTMENT HAD A GUST TO 62 MPH AT
21Z. MAY ALSO GET A FEW GUSTS TO 60 MPH ON THE CENTRAL OREGON COASTAL
HEADLANDS LATE THIS AFTERNOON...BUT SHOULD NOT BE WIDESPREAD ENOUGH
TO WARRANT A WARNING. BESIDES STRONG GUSTY WINDS...BEACHES WILL HAVE
THE ADDITIONAL HAZARD OF DANGEROUS BREAKING WAVES. THOSE PLANNING ON
HEADING TO THE BEACH DURING BREAKS IN THE RAIN MAY WANT TO KEEP THEIR
DISTANCE FROM THE WATERS EDGE.

THE COLD FRONT FINALLY SHIFTS TO SOUTHERN OREGON OVERNIGHT. BY THE
TIME SNOW LEVELS DROP BACK DOWN TO CASCADE PASS LEVELS...THE BULK OF
THE PRECIP WILL HAVE ALREADY OCCURRED. THUS...NOT EXPECTING SNOW
ADVISORY CRITERIA TO BE MET. ANOTHER MOIST WARM FRONT WILL APPROACH
WEDNESDAY AFTERNOON FOR ADDITIONAL RAIN WEDNESDAY NIGHT AND THURSDAY.
THE SNOW LEVELS WILL BE SLOW TO RISE AHEAD OF THE FRONT AND EXPECT A
QUICK BURST OF SNOW FOR THE CASCADE PASSES AS THE MOISTURE FIRST
REACHES THE CASCADES WEDNESDAY NIGHT. THE SNOW LEVELS SHOULD RISE
ABOVE 6000 FEET EARLY THURSDAY MORNING...WITH A POSSIBLE DELAY FOR
THE WASHINGTON CASCADES.

THIS SYSTEM IS VERY MOIST AS SATELLITE DERIVED PRECIPITABLE WATER
VALUES NEAR THE ORIGIN POINT AT 20Z ARE AROUND 1.6 INCHES. THIS IS
DOWN FROM CLOSE TO 2.0 INCHES EARLIER THIS MORNING. THE PRECIPITABLE
WATER WILL DECREASE AS THE FRONT NEARS THE COAST...BUT THERE IS GREAT
POTENTIAL FOR ANOTHER ROUND OF HEAVY RAIN. EXPECT 1 TO 3 INCHES OF
RAIN FOR THE COAST...COAST RANGE AND THE CASCADES WEDNESDAY EVENING
THROUGH THURSDAY EVENING...AND 0.75 TO 1.25 INCH FOR THE INTERIOR LOW
LANDS. THE MAIN DIFFERENCE WITH THIS SYSTEM IS THAT THE MOISTURE CORE
IS AIMED MORE AT NORTHWEST OREGON INSTEAD OF WESTERN WASHINGTON.

MODELS FORECAST THAT THE BAROCLINIC ZONE WILL MOVE RATHER QUICKLY
ACROSS THE AREA...WITH RAIN ENDING THURSDAY EVENING. THIS WILL HELP
LIMIT THE RAINFALL TOTALS AND FLOODING POTENTIAL. IT ALSO LOOKS LIKE
THE AREA OF HEAVIEST RAIN WILL BE ACROSS NW OREGON RATHER THAN SW
WASHINGTON. THE RIVERS TO THE SOUTH HAVE TAKEN LESS OF A BEATING THE
PAST WEEK THAN WASHINGTON...IN REGARDS TO RAIN TOTALS...AND THIS MAY
ALSO HELP REDUCE FLOODING CONCERNS. 12Z MODELS SHOW PRECIP
DIMINISHING QUICKLY THU NIGHT...WITH A DISTINCT SEPARATION FROM THE
MOISTURE SOURCE. IN FACT...LIGHT LOW-LEVEL OFFSHORE FLOW DEVELOPS
EARLY FRI MORNING. HAVE REDUCED POPS THU NIGHT INTO FRI MORNING.
MODELS MAINTAIN THE OFFSHORE FLOW THROUGH FRI. LATEST GFS HAS A WEAK
SHORT-WAVE AIMED AT SW OREGON FRI...WITH THE POTENTIAL FOR SOME LIGHT
OVER-RUNNING PRECIP TO CLIP THE FAR SW ZONES FRI AFTERNOON. WEISHAAR

.LONG TERM...MODELS AGREE ON GENERAL TRENDS SAT AND SUN AS A NW FLOW
ALOFT FLATTENS OUT AND BECOMES MORE WESTERLY OVER THE WEEKEND. A
SHORTWAVE AND WEAK SURFACE LOW IN THE NW FLOW POTENTIALLY AFFECTS
THE REGION FRI NIGHT AND SAT...ALTHOUGH THE TRACK IS NOT WELL AGREED
UPON BY THE MODELS. AT THIS POINT TRENDS SUGGEST THIS SYSTEM CLIPS
MAINLY THE SOUTHERN PART OF THE FORECAST AREA...SO AT THIS POINT
WILL KEEP BEST CHANCES FOR RAIN IN THE SOUTH. AFTER RIDGING SUN AND
SUN NIGHT FOR A QUICK DRY SPELL...MODELS DIFFER CONSIDERABLY ON THE
PROSPECTS FOR THE NEXT TROUGH DIGGING DOWN OFF THE COAST MON AND
TUE. THERE IS CONSIERABLE SPREAD AMONGST ENSEMBLE MEMBERS...BUT 12Z
EC OPERATIONAL RUN APPEARS TO BEST FOLLOW EC ENSEMBLE MEAN. SUSPECT
THE SLOWER AND NOT AS DEEP EVOLUTION OF THE EC IS PREFERABLE...BUT
OVERALL THE TREND SUGGESTS COOLER AND WETTER AGAIN FOR THE EARLY
PART NEXT WEEK.
&&

.AVIATION...MAIN PUSH OF RAIN MOVING THROUGH THE REGION THIS
AFTERNOON. INLAND...SOUTH WINDS 15-25 KT WITH GUSTS NEAR 30-35 KT
AND MODERATE RAIN WILL MAINTAIN VFR/MVFR CONDITIONS THROUGH AT
LEAST 01Z-02Z WED. EXPECT MOSTLY MVFR/IFR CONDITIONS ALONG THE
COAST WITH STRONGER WIND GUSTS UP TO 40-45 KT. RAIN TAPERS OFF
TONIGHT AND EARLY TUESDAY AM...WITH OVERALL CONDITIONS IMPROVING
TO MOSTLY VFR. THEN A STRONG TRAILING COLD FRONT MOVES THROUGH
LATER TUE AFTERNOON AND EVENING. HEAVY RAIN...DECREASING CIGS AND
VSBYS...AND VERY GUSTY SW WINDS TO ACCOMPANY THE COLD FRONT.

KPDX AND APPROACHES...MOSTLY MVFR CIGS AROUND 1500-3500 FT IN
RAIN AND BREEZY SW WINDS WITH GUSTS 25-30 KT THROUGH 02Z WED THIS
AFTERNOON AS A WARM FRONT LIFTS NORTH. VFR CONDITIONS RETURN
TONIGHT THEN NEXT STRONG COLD FRONT ARRIVES TUE AFTERNOON AND
EVENING...BRINGING HEAVIER RAIN...GUSTY S WINDS AND MVFR
CONDITIONS. FRONT IS EXPECTED TO MOVE THROUGH THE TERMINAL BY
AROUND 03Z WED...WITH WINDS SWITCHING TO W-NW BEHIND THE FRONT.
/27

&&

.MARINE...GALE FORCE SOUTH-SOUTHWEST WINDS 20-30 KT WITH GUSTS
40-45 KT CONTINUE THROUGH THIS EVENING. COULD SEE A FEW
LOCAL GUSTS NEAR 50 KT POSSIBLE THROUGH 5 PM WITH THE STRONGEST
PUSH OF WINDS. EXPECT A RAPID SHIFT FROM SOUTH-SOUTHWESTERLY TO
NORTHWESTERLY BEHIND THE FRONT EARLY TONIGHT. NORTHWEST SMALL
CRAFT ADVISORY WINDS LINGER OVER THE WATERS THROUGH AT LEAST 12Z
WED...BEFORE WINDS DROP BELOW 20 KT ALTOGETHER WEDNESDAY AND
WEDNESDAY AFTERNOON.

ANOTHER FRONTAL SYSTEM IS EXPECTED FOR WED NIGHT INTO THURSDAY AND
LOOKS TO HAVE A SURFACE LOW HEADED STRAIGHT FOR NW OREGON...WHICH
WOULD BRING YET ANOTHER ROUND OF GUSTY WINDS TO THE WATERS...
PARTICULARLY OVER THE CENTRAL OREGON WATERS. SOUTHWEST WINDS WITH
GUSTS UP TO 35 KT LOOK POSSIBLE FOR THIS SYSTEM. MODELS THEN
AGREE ON HIGHER PRESSURE BUILDING OVER THE NE PAC FOR THE END OF
THE WEEK AND THE WEEKEND...BRINGING QUIET MARINE CONDITIONS TO THE
WATERS.

EXPECT SEAS TO PEAK AROUND 20-21 FT OVER THE NORTHERN WATERS THIS
EVENING...AND PEAK AROUND 18 FT OVER THE CENTRAL WATERS. HIGH
SURF CONDITIONS TO AFFECT TO THE SW WASHINGTON AND NW OREGON COAST
THROUGH TONIGHT. SEAS DROP TO 15-17 FT TONIGHT...REMAINING AROUND
12-14 FT THROUGH WEDNESDAY. MODELS SHOW SEAS DROPPING BELOW 10 FT
BY THURSDAY. /27

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING UNTIL 7 PM PST THIS EVENING FOR COAST RANGE OF
     NORTHWEST OREGON-NORTH OREGON COAST.

     HIGH SURF ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR NORTH OREGON
     COAST.

     FLOOD WATCH THROUGH WEDNESDAY AFTERNOON FOR COAST RANGE OF
     NORTHWEST OREGON-NORTH OREGON COAST.

WA...HIGH WIND WARNING UNTIL 7 PM PST THIS EVENING FOR SOUTH
     WASHINGTON COAST-WILLAPA HILLS.

     HIGH SURF ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR SOUTH
     WASHINGTON COAST.

PZ...GALE WARNING 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 11
     AM PST WEDNESDAY.

&&

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.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PORTLAND OR
143 PM PST TUE NOV 17 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1200 PM     HIGH SUST WINDS  CLATSOP SPIT            46.22N 124.00W
11/17/2015  M41.00 MPH       CLATSOP            OR   OFFICIAL NWS OBS

            41 MPH SUSTAINED. WIND GUSTS 46 MPH.

1245 PM     NON-TSTM WND GST CAPE DISAPPOINTMENT     46.27N 124.08W
11/17/2015  M63.00 MPH       PACIFIC            WA   OFFICIAL NWS OBS

&&

TW