Flood in Oregon, December 18 to 19, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
920 PM PST THU DEC 17 2015

.SHORT TERM...A STRONG COLD FRONT IS MOVING INTO THE COAST THIS
EVENING AND TONIGHT AND WILL PUSH INLAND LATE TONIGHT THROUGH
FRIDAY. THIS FRONT IS FORECAST TO SLOW AS IT MOVES ACROSS THE
CASCADES AND THE EAST SIDE ON FRIDAY. SOUTH WINDS AHEAD OF THIS
FRONT HAVE STRENGTHENED WITH GUSTS OF AROUND 60 MPH AT THE
COAST...WHICH ARE EXPECTED TO PEAK LATE THIS EVENING INTO TONIGHT
WITH GUSTS OF 70 MPH. INLAND STRONG WINDS ARE EXPECTED OVER THE
MOUNTAINS, INTO THE SUMMER LAKE AREA AND IN THE SHASTA VALLEY. SEE
THE NPWMFR PRODUCT FOR DETAILS. HEAVY TO MODERATE PRECIPITATION IS
ALSO SPREADING INTO THE COAST THIS EVENING AND WILL SPREAD INLAND
TONIGHT AND FRIDAY MORNING. AROUND 0.75 TO 1.5 INCHES OF RAIN HAS
FALLEN ALONG THE COAST IN THE LAST 6 HOURS. MODELS INDICATE AN
ADDITIONAL 1 TO 3 INCHES WILL FALL LATE THIS EVENING THROUGH
FRIDAY MORNING. INLAND, MODERATE TO HEAVY PRECIPITATION IS
EXPECTED TO THE CASCADES WITH 0.5 TO 1.5 INCHES OF PRECIPITATION
THROUGH FRIDAY MORNING. EAST OF THE CASCADES, EXPECT LIGHTER
AMOUNTS RANGING FROM A TENTH OF AN INCH TO AROUND A HALF INCH
THROUGH FRIDAY AFTERNOON.

HEAVY PRECIPITATION WILL BRING  CONTINUED FLOODING ALONG MAINSTEM
RIVERS AND FOR AREA STREAMS ALONG THE COAST. ALSO EXPECT PONDING
OF WATER ON ROADWAYS. INLAND, SIGNIFICANT RISES ARE EXPECTED ON
RIVERS AND STREAMS. PLEASE SEE THE CURRENT FLSMFR...FLWMFR AND
ESFMFR FOR DETAILS.

BEHIND THE FRONTAL PASSAGE EXPECT A DECREASE IN THE RAINFALL
INTENTSITY LATE FRIDAY MORNING FOR AREAS WEST OF THE
CASCADES...WITH RAINFALL BECOMING LIGHTER AND SHOWERY. HOWEVER,
CONTINUING PRECIPITATION IS EXPECTED FROM THE CASCADES EAST AND
OVER MUCH OF NORTHERN CALIFORNIA AS THE FRONT SLOWLY SHIFTS
EASTWARD OVER THE AREA FRIDAY MORNING INTO FRIDAY AFTERNOON. THE
FRONT WILL SHIFT EAST OF THE AREA BY FRIDAY EVENING WITH
INCREASING SHOWERS SPREADING INLAND FRIDAY EVENING AND NIGHT AS
THE UPPER TROUGH MOVES INTO PLACE. SNOW LEVELS WILL REMAIN HIGH
TONIGHT AROUND 6000 FEET OR HIGHER FROM THE CASCADES WEST IN
OREGON AND AROUND 5000 TO 6000 FEET OVER THE EAST SIDE AND IN
CENTRAL AND EASTERN SISKIYOU COUNTY. SNOW LEVELS MAY BE SLIGHTLY
LOWER NEAR MOUNT SHASTA AROUND 4500 TO 5000 FEET THROUGH FRIDAY.
FROM THE CASCADES WEST, SNOW LEVELS LOWER FRIDAY TO AROUND 4000 TO
5500 FROM THE CASCADES WEST AND DOWN TO 4000 FT EAST OF THE
CASCADES FRIDAY EVENING AND NIGHT.

&&

.AVIATION...FOR THE 18/00Z TAF CYCLE...THE MAIN THREAT TO
AVIATION IN THE NEXT 6-9 HOURS IS POTENTIAL LOW LEVEL WIND SHEAR AT
KOTH AND KRBG. STRONG SOUTH WINDS OF 40-60 KT EXIST AT ABOUT 2000 FT
AGL WITH LIGHTER WINDS AT THE SURFACE. THIS THREAT WILL END AS A COLD
FRONT MOVES INLAND AFTER 09Z. THE FRONT WILL BRING MODERATE TO HEAVY
RAIN ALONG THE COAST WITH LIGHTER RAIN INLAND. MVFR CIGS WITH TERRAIN
OBSCURED WILL PREVAIL ALONG AND WEST OF THE CASCADES WITH VFR CIGS
FOR A TIME SOUTH OF THE UMPQUA DIVIDE (KMFR WILL HAVE A RAIN
SHADOW FOR A WHILE TONIGHT)...BUT RAIN SHOULD RETURN TOWARD MORNING.
EAST SIDE AREAS WILL HAVE MOSTLY VFR WITH PARTIAL TERRAIN OBSCURATION.
MVFR CIGS WILL DEVELOP OVERNIGHT WITH RAIN OR SNOW MOVING BACK IN
FRIDAY MORNING. PRECIPITATION WILL BECOME SHOWERY BEHIND THE FRONT
WEST OF THE CASCADES LATER SATURDAY MORNING OR AFTERNOON. SPILDE

&&

.MARINE...UPDATED 400 PM PST THURSDAY 17 DEC 2015...SOUTH WINDS WILL
BECOME VERY STRONG THIS EVENING AHEAD OF A COLD FRONT THAT WILL
MOVE ONSHORE LATE TONIGHT. WINDS WILL REACH STORM FORCE FROM GOLD
BEACH NORTHWARD OUT TO ABOUT 30 NM WITH GALES OVER THE REMAINDER OF
THE AREA. WINDS AND SEAS SUBSIDE LATE TONIGHT AND ON FRIDAY...BUT
A PERSISTENT MODERATE WEST TO NORTHWEST SWELL WILL CONTINUE INTO
EARLY NEXT WEEK. ANOTHER STRONG FRONT WILL MOVE INTO THE WATERS
SATURDAY NIGHT WITH THE POTENTIAL FOR GALES.  MORE FRONTS WILL
KEEP PERIODS OF STRONG WINDS IN THE FORECAST THROUGH THE EARLY TO
MIDDLE PART OF NEXT WEEK. SPILDE

&&

.PREV DISCUSSION... /ISSUED 413 PM PST THU DEC 17 2015/

SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...THE COLD FRONT THAT
WILL BE RESPONSIBLE FOR ANOTHER ROUND OF RAIN AND WIND THIS
EVENING AND TONIGHT LIES JUST OFF OUR COAST. THE WARM FRONT HAS
LIFTED TO THE NORTH, AND WITH IT, SNOW LEVELS HAVE RISEN AND MUCH
OF THE HEAVIER RAIN HAS COME TO AN END FOR MOST OF THE AREA.
HOWEVER, THE PRE-FRONTAL BAND OF RAIN AHEAD OF THE COLD FRONT HAS
ALREADY STARTED TO MOVE ONSHORE AT THE COAST, AND THIS WILL ONLY
BECOME HEAVIER THROUGH THE EVENING. WINDS WILL ALSO INCREASE AHEAD
OF THE FRONT, AND FORECAST PRESSURE GRADIENTS SUGGEST THAT WINDS
IN THE SHASTA VALLEY AND MUCH OF THE EAST SIDE WILL REACH WIND
ADVISORY CRITERIA, WHILE ALONG THE COAST AND THE MORE SUSCEPTIBLE
PORTIONS OF THE EAST SIDE WILL HAVE AT LEAST GUSTS THAT REACH HIGH
WIND WARNING PARAMETERS.

RAINFALL AMOUNTS WILL BE SIGNIFICANT WITH THIS SYSTEM, AND THOUGH
THEY MIGHT NOT STACK UP TO SOME OF THE PREVIOUS SYSTEMS THIS
MONTH, THE SATURATED SOILS AND BANKFULL RIVERS AND STREAMS GIVE
CAUSE FOR CONCERN. WITH THE MAJORITY OF THIS NEW RAINFALL LIKELY
TO BECOME RUN- OFF, WATER LEVELS ARE LIKELY TO REACT QUICKLY. HAVE
THEREFORE UPGRADED THE AREAL FLOOD WATCH TO A WARNING, AS SOME
REPORTS OF HIGH STREAMS HAVE ALREADY ARRIVED, AND THE BULK OF THE
RAIN HAS YET TO DO SO ITSELF. SEVERAL MAIN STREAM RIVERS REMAIN IN
WATCH STATUS, ALTHOUGH FLOODING IS LIKELY, ESPECIALLY FOR THE
COQUILLE AND ITS TRIBUTARIES.

SNOW LEVELS HAVE RISEN TO ABOVE 7000 FEET FOR MOST AREAS,
ALTHOUGH SOME LOCATIONS OVER NORTHERN CALIFORNIA AND EAST OF THE
CASCADES COULD STILL SEE SOME SNOWFLAKES THIS AFTERNOON. BEHIND
THE FRONT, SNOW LEVELS WILL DROP QUICKLY TO AROUND 3000 FEET OR
LOWER, BUT THIS WOULD BE EXPECTED DURING THE PERIOD OF SHOWERS,
AND NOT DURING THE HEAVIEST PRECIPITATION. THEREFORE, THE HIGH
PEAKS WILL SEE HEAVY SNOW ONCE AGAIN, WHILE THE PASSES SHOULD ONLY
PICK UP A FEW INCHES.

THE FRONT SHOULD PASS COMPLETELY THROUGH THE AREA BY LATE FRIDAY
MORNING OR EARLY AFTERNOON, AND WINDS SHOULD DIMINISH AS PASSAGE
OCCURS. SHOWERS WILL CONTINUE INTO THE WEEKEND AS THE COLD POOL OF
AIR ALOFT PRODUCES WEAK INSTABILITY. THIS WILL BE QUICKLY FOLLOWED
BY THE NEXT, ALTHOUGH MUCH WEAKER, FRONTAL SYSTEM SUNDAY MORNING.
SNOW LEVELS WILL BEGIN AT AROUND 2000 FEET SUNDAY MORNING, BUT
RISE TO ABOVE 4000 FEET AS THE SYSTEM MOVES THROUGH. WINDS WILL BE
MUCH WEAKER, ALTHOUGH STILL BREEZY, AND RAINFALL AMOUNTS WILL NOT
BE AS EXTREME. SHOWERS WILL THEN CONTINUE THROUGH SUNDAY NIGHT.
-BPN

LONG TERM...MONDAY THROUGH THURSDAY...THE FOCUS OF THE LONG TERM
FORECAST IS ON ITS FIRST 48 HOURS. THE 12Z GFS AND 12Z ECMWF ARE
IN EXCELLENT THOUGH NOT PERFECT AGREEMENT ON A STORMY FORECAST
FOR MONDAY AND MONDAY NIGHT AND QUITE CLOSE TO THE FORECAST
INDICATED BY THEIR PREVIOUS RUN. THE FORECAST LEANS TOWARD THE
WETTER GFS WITH A BLEND TO THE SLIGHTLY FASTER ARRIVAL OF THE
ECMWF. A STRONG...VERY WET WARM FRONT IS FORECAST TO BRING HEAVY
RAIN TO THE COAST BY MID TO LATE MONDAY MORNING WITH MODERATE TO
HEAVY PRECIPITATION SPREADING INLAND DURING THE AFTERNOON THROUGH
MONDAY NIGHT. THE HEAVIEST AMOUNTS IN THE 24 HOUR PERIOD ARE
EXPECTED WEST OF THE CASCADES...ESPECIALLY ALONG THE COAST AND
NEAR THE COASTAL RANGE WITH 3 TO 6 INCHES OF RAIN. THIS HAS THE
POTENTIAL TO CREATE OR EXACERBATE FLOODING WEST OF THE
CASCADES...ESPECIALLY NEAR THE COAST. THE MOST UNCERTAINTY...BASED
UPON THE TIMING OF THE FRONT...IS REGARDING HOW QUICKLY SNOW
LEVELS WILL RISE ON MONDAY. SNOW LEVELS ARE FORECAST TO RISE FROM
AROUND 4000 FT MSL ON MONDAY MORNING TO AROUND 6500 FT MSL LATE
MONDAY NIGHT. THUS...A HEAVY SNOWFALL IS LIKELY IN THE HIGH
COUNTRY BUT THE IMPACT ON THE MAJOR HIGHWAY PASSES WILL LIKELY NOT
BE AS SIGNIFICANT AS PRECIPITATION WILL BE RAIN OR SNOW RELATIVELY
QUICKLY CHANGING TO RAIN.

THE FORECAST LEANS TOWARD THE STRONGER GFS SOLUTION REGARDING THE
TRAILING COLD FRONT ON TUESDAY INTO TUESDAY NIGHT. SNOW LEVELS ARE
FORECAST TO FALL BELOW 5000 FEET DOWN TO AROUND 3000 FEET MSL
ON TUESDAY NIGHT. THE ECMWF MERELY GENERATES AROUND ANOTHER HALF
AN INCH TO AN INCH AND A HALF OF RAINFALL AT THE COAST DURING
TUESDAY AND TUESDAY NIGHT WHILE THE GFS SOLUTION IS A MUCH MORE
SIGNIFICANT TWO TO THREE INCHES.

MODEL AGREEMENT DIMINISHES BEYOND TUESDAY NIGHT. THERE IS GENERAL
AGREEMENT THAT THE PATTERN WILL REMAIN ACTIVE WITH A WET WESTERLY
FLOW AND VERY BRIEF BREAKS BETWEEN SYSTEMS INTO CHRISTMAS.
HOWEVER...THERE IS LOW CONFIDENCE IN THE TIMING...TRACK AND
STRENGTH OF ADDITIONAL FRONTS. THESE FRONTS ARE LIKELY TO BE
LESS INTENSE BUT COLDER THAN THE MONDAY/TUESDAY SYSTEM WITH SNOW
LEVELS BELOW THE MAJOR PASSES. /DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING UNTIL 4 AM PST FRIDAY FOR ORZ021-022.
     FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR ORZ021>024.
     HIGH WIND WARNING UNTIL 10 AM PST FRIDAY FOR ORZ030-031.

CA...HIGH WIND WARNING UNTIL 10 AM PST FRIDAY FOR CAZ085.
     WIND ADVISORY UNTIL 10 AM PST FRIDAY FOR CAZ081.

PACIFIC COASTAL WATERS...HIGH WIND WARNING UNTIL 4 AM PST FRIDAY FOR PZZ356.
     STORM WARNING UNTIL 1 AM PST FRIDAY FOR PZZ350-356-370-376.
     GALE WARNING UNTIL 1 AM PST FRIDAY FOR PZZ350-356-370-376.

CC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
1235 AM PST FRI DEC 18 2015

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

1200 AM     HEAVY RAIN       1 ENE BROOKINGS         42.06N 124.28W
12/18/2015  M4.44 INCH       CURRY              OR   TRAINED SPOTTER

            OBSERVER LOCATION IN TOWN NEAR SCHOOL
            COMPLEX.

&&

CS