Flood in Oregon, December 11 to 16, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
932 PM PST THU DEC 10 2015

.UPDATE...
UPDATES TO THE FORECAST THIS EVENING HAVE BEEN TO ISSUE A FLOOD
WARNING FOR THE COQUILLE RIVER AT COQUILLE, A FLOOD WATCH FOR THE
SOUTH FORK OF THE COQUILLE AT MYRTLE POINT, AND TO UPDATE SNOW
LEVELS DOWNWARD SOME FOR THIS EVENING THROUGH FRIDAY. BTL

&&

.DISCUSSION...
A POWERFUL LOW PRESSURE SYSTEM THAT DROPPED SIGNIFICANT RAIN AND
SNOW IN THE AREA IS STILL CAUSING THUNDERSTORMS ALONG THE CURRY
COAST THIS EVENING. SNOW LEVELS ACROSS THE AREA HAVE LOWER TO
BETWEEN 4KFT AND 3KFT THIS EVENING AND ARE EXPECTED TO LOWER A BIT
MORE TO 2500 TO 3500 FEET BY MORNING. PRECIPITATION RATES,
HOWEVER, WILL FALL OFF AS PREVIOUSLY EXPECTED, SO WINTER WEATHER
ADVISORIES FOR TONIGHT WILL BE ALLOWED TO EXPIRE.

FOR FRIDAY WE WILL LIKELY BE ISSUING NEW WINTER WEATHER
ADVISORIES FOCUSED FROM LATE MORNING THROUGH THE EVENING IN AND
NEAR THE CASCADES AND SISKIYOUS, WHERE NEW SNOW AMOUNTS ON THE
ORDER OF 5-10 INCHES CAN BE EXPECTED AS SNOW LEVELS RISE TO 3500
TO 4000 FEET DURING THE AFTERNOON.

THIS WEEKEND'S STORM LOOMS LARGE ON HORIZON, WITH FLOOD PRODUCTS
ALREADY BEING ISSUED TODAY FOR PORTIONS OF THE COQUILLE RIVER
BASIN. WE'LL BE CONSIDERING AREAL FLOOD WATCHES FOR THE WEST SIDE
FOR SATURDAY AND SUNDAY AS RAINFALL AMOUNTS/RATES WILL BE GREATER
FOR SOME AREAS THAN HAS BEEN OBSERVED, THUS FAR, FOR THIS STORM
SERIES. NUMERICAL MODELS CONTINUE TO SHOW A SURGE OF WARMER AIR IN
THE 850MB LAYER LATE SATURDAY AFTERNOON AND EVENING OVER THE
SISKIYOUS AND TOWARD THE OREGON CASCADES WHICH COULD CAUSE A RISE
IN SNOW LEVELS ACROSS THE SISKIYOUS, BUT COLDER AIR SURGES IN WHEN
PRECIPITATION RATES INCREASE TO MODERATE TO HEAVY OVERNIGHT INTO
SUNDAY MORNING. CURRENT FORECAST SNOWFALL AMOUNTS LOOK GOOD FOR
CRATER LAKE NATIONAL PARK, BUT MIGHT BE A BIT ON THE HIGH SIDE FOR
MOUNT ASHLAND PER THE LATEST MODEL RUNS. STILL 2+ INCHES OF WATER
EQUIVALENT LOOKS TO BE A GOOD BET AND THAT COULD EASILY TURN
UPWARD AGAIN ON THE NEXT ROUND OF MODEL RUNS. BTL

&&

.AVIATION...FOR THE 11/00Z TAF CYCLE...EXPECT WIDESPREAD MVFR
CIGS IN RAIN ACROSS OUR FORECAST AREA OVERNIGHT WITH MOUNTAINS
OBSCURED. RAIN WILL INCREASE IN INTENSITY OVERNIGHT AND THIS WILL
LEAD TO MORE IFR CIGS/VIS IN MODERATE RAIN SHOWERS AREA. AT THE
COAST THERE WILL BE A FEW MORE LIGHTNING STRIKES BUT THE ATMOSPHERE
IS EXPECTED TO BECOME MORE STABLE BY 9 PM TONIGHT. /FB

&&

.MARINE...UPDATED 145 PM PST THURSDAY 9 DEC 2015...WINDS HAVE
SUBSIDED BELOW GALE BUT WILL REMAIN SOLIDLY IN THE 25 TO 30 KNOT
RANGE TONIGHT. HOWEVER...GALE FORCE GUSTS MAY ACCOMPANY ANY
THUNDERSTORMS THROUGH THIS EVENING. WEST SWELL WILL PEAK THIS
EVENING AROUND 30 FEET...THEN SUBSIDE TO AROUND 25 FEET THROUGH
FRIDAY NIGHT. GALES ARE LIKELY TO RETURN WITH A FRONT ON SATURDAY. A
SERIES OF DISTURBANCES WILL CONTINUE INTO EARLY NEXT WEEK WITH SEAS
REMAINING HIGH AND VERY STEEP. /FB

&&

.PREV DISCUSSION... /ISSUED 253 PM PST THU DEC 10 2015/

SHORT TERM...THE ACTIVE WEATHER PATTERN WILL CONTINUE INTO
THE WEEKEND. THUNDERSTORMS THIS AFTERNOON AND EVENING...MOUNTAIN
SNOWS INTO FRIDAY...POTENTIAL RIVER FLOODING...AND DANGEROUS
WAVES/SEAS ARE SOME OF WHAT MOTHER NATURE HAS BROUGHT AND
CONTINUES TO BRING OUR WAY.

150 LIGHTNING STRIKES HAVE BEEN OBSERVED OVER CURRY COUNTY
TODAY...WITH 53 STRIKES OVER COOS COUNTY. A SEVERE THUNDERSTORM HAS
BEEN OBSERVED AT GOLD BEACH WITH 1 INCH HAIL. INSTABILITY AND
SHORTWAVE ENERGY CONTINUES INTO THIS EVENING FOR MUCH OF THE AREA
WEST OF THE CASCADES...THEN THUNDERSTORM CHANCES DIMINISH EARLY
FRIDAY MORNING.

SNOW SHOWERS WILL DIMINISH TONIGHT...AND A WINTER WEATHER ADVISORY
CONTINUES THROUGH THE EVENING AT WSW TO HIGHLIGHT SNOW MAINLY ABOVE
4000 FEET IN THE CASCADES...NORTHERN CALIFORNIA...AND THE EAST SIDE
MAINLY ALONG HIGHWAY 97 NEAR CHEMULT.  LESSER IMPACTS ARE EXPECTED
BELOW 4000 FEET WHERE A FEW INCHES OF SNOW WILL FALL ALL THE WAY TO
ABOUT 3500 FEET NEAR UNION CREEK WHERE CURRENT WEBCAM IMAGERY SHOWS
SNOW AFFECTING THE ROADWAYS.

A MODERATELY STRONG LOW PRESSURE SYSTEM WILL ARRIVE
FRIDAY...BRINGING WITH IT ANOTHER ROUND OF MOUNTAIN SNOWS AND
MODERATE TO BRIEFLY HEAVY RAIN TO THE COAST AND JUST INLAND. SNOW
LEVELS REMAIN ABOUT 3500 FEET. WE'LL BE CONSIDERING WINTER WEATHER
ADVISORIES FOR THIS DURING THE NEXT SHIFT.

THEN...MODELS HAVE BEEN PORTRAYING FOR SEVERAL DAYS NOW A VERY WET
FRONTAL SYSTEM ARRIVING SATURDAY AFTERNOON...WITH A WARM FRONT
BUMPING UP SNOW LEVELS INITIALLY TO 6000-7000 FEET. HEAVY RAIN RATES
WILL CAUSE RIVERS AND STREAMS TO RISE FURTHER...WITH FLOODING
POSSIBLE AT COASTAL RIVERS. A HYDROLOGIC OUTLOOK AND FLOOD WATCHES
FOR THE COQUILLE AT COQUILLE AND THE SOUTH FORK COQUILLE AT MYRTLE
POINT HAVE BEEN ISSUED TO HIGHLIGHT THE POTENTIAL FLOODING. MODELS
PEG AT LEAST TWO 6-HOUR PERIODS OF 1 INCH/6 HOUR RAIN RATES AT THE
COAST AND OVER TERRAIN ALONG AND WEST OF THE CASCADES. THIS
REPRESENTS HIGHER RAIN RATES THAN THE PAST FEW SYSTEMS...SO URBAN
AND SMALL STREAM FLOODING...AND WILDFIRE BURN SCAR FLOODING...COULD
BE A PROBLEM. WE'LL LIKELY BE ISSUING MORE HYDROLOGIC PRODUCTS
TOMORROW TO ADDRESS THESE CONCERNS.  SNOW WILL BE HEAVY WITH THIS
SYSTEM...BRINGING OUR TOTAL SNOW FORECAST FROM TODAY THROUGH SUNDAY
NIGHT TO 50 INCHES AT CRATER LAKE.  THIS REPRESENTS THE HIGHEST 3-
DAY SNOW TOTAL SINCE 2010 FOR THE HIGH CASCADES.  SIGNIFICANT
BENEFITS FOR RECREATION...AND POTENTIAL BENEFITS FOR WATER RESOURCES
SURROUND THIS HEFTY SNOW FORECAST...BUT THE SNOW WILL CERTAINLY HAVE
SIGNIFICANT TRAVEL IMPACTS IN THE CASCADES AND POTENTIALLY ON
INTERSTATE 5 AT SISKIYOU SUMMIT.

LONG TERM...MONDAY THROUGH THURSDAY NIGHT...THE LONG TERM OPENS
WITH THE DEPARTING TROUGH OVER THE ROCKIES, WITH LARGE AMPLITUDE
RIDGING OVER THE EASTERN PACIFIC. THIS PLACES THE FORECAST AREA
UNDER SWIFT NORTHERLY FLOW, ON THE COLD SIDE OF THE BOUNDARY BETWEEN
AIR MASSES. MODELS HAVE SHOWN A POSSIBLE SHORTWAVE WITHIN THIS FLOW
MOVING SOUTH OVER OUR AREA MONDAY MORNING, WHICH WOULD LIKELY RESULT
IN SHOWER ACTIVITY THROUGH MUCH OF THE DAY. WITH SNOW LEVELS DOWN TO
ABOUT 1600 FEET, ALL BUT THE COAST AND THE WEST SIDE VALLEY FLOORS
HAVE A DECENT CHANCE OF PICKING UP SOME LIGHT SNOW ACCUMULATIONS.
EVEN THE ROGUE VALLEY NEAR MEDFORD HAS A SMALL CHANCE, BUT
CONFIDENCE IS TOO LOW TO ADD TO THE FORECAST AT THIS TIME.

BEYOND MONDAY, MODEL FORECASTS DIVERGE, BUT SOME GENERAL TRENDS ARE
EVIDENT. THE RIDGE JUST OFFSHORE OF THE PACIFIC NORTHWEST WILL COME
UNDER  PRESSURE FROM SEVERAL WAVES EMINATING FROM A LARGE BERING
STRAIGHT TROUGH. THE ECMWF IS MORE PRONOUNCED WITH ONE SUCH FEATURE
TUESDAY, HAVING IT PASS JUST TO OUR NORTH. THIS WOULD GIVE US AN
INCREASED CHANCE FOR PRECIPITATION, BUT THE GFS IS SLOWER AND MUCH
WEAKER, KEEPING THE BULK OF THE ACTION WELL TO OUR NORTH. HAVE KEPT
A CHANCE OF SHOWER IN THE FORECAST THROUGH WEDNESDAY MORNING TO
ACCOUNT FOR THIS.

BOTH THE GFS AND ECMWF SHOVE THE BERING TROUGH TO THE SOUTHEAST
TOWARDS THE WEST COAST LATE WEDNESDAY INTO THURSDAY. THIS SYSTEM HAS
ALL THE HALLMARKS OF BEING A WET AND WINDY STORM, BUT AT THIS TIME
RANGE, THEM MODELS ARE NOT RESOLVING THE DETAILS, AND CONFIDENCE
REMAINS LOW. FOR NOW, HAVE ONLY INCREASED THE CHANCE OF
PRECIPITATION AND WINDS UNTIL CONFIDENCE INCREASES. IT DOES APPEAR
THE THE WET PATTERN WILL CONTINUE, ALTHOUGH TONED DOWN QUITE A
BIT FROM THE PREVIOUS WEEKS. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING ABOVE 4500
     FEET FOR FOR ORZ029>031.
     HIGH SURF WARNING UNTIL 2 AM PST SATURDAY FOR ORZ021-022.
     WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING ABOVE 4500
     FEET FOR FOR ORZ025-027-028.

CA...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING ABOVE 4000
     FEET FOR FOR CAZ080>083.

PACIFIC COASTAL WATERS...
- HAZARDOUS SEAS WARNING UNTIL 7 AM PST SATURDAY FOR
  PZZ350-356-370-376.

BTL/NSK/FJB