Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 191213
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
413 AM PST FRI DEC 19 2014

.DISCUSSION...A COLD FRONT IS PUSHING THROUGH THE FORECAST AREA THIS
MORNING...BRINGING WITH IT MODERATE TO OCCASIONALLY HEAVY
PRECIPITATION AND SOME MOUNTAIN AND EAST SIDE SNOWFALL AS SNOW
LEVELS DROP TO AROUND 4000 FEET THIS MORNING.

MODERATE SNOWFALL IS BEING OBSERVED ON WEBCAMS AT DIAMOND LAKE...AND
ALONG HIGHWAY 97 AT CHEMULT THIS MORNING. LATEST RADAR DATA SUGGESTS
THE SIGNIFICANT BAND OF SNOW OVER THE CASCADES AND HIGHWAY 97 SHOULD
DIMINISH SOME BEFORE SUNRISE. SNOW SHOWERS SHOULD CONTINUE OVER THE
CASCADES AT TIMES TODAY WITH A FEW MORE INCHES OF SNOW POSSIBLE.
ADDITIONALLY...THUNDERSTORMS ARE POSSIBLE OVER COOS AND WESTERN
DOUGLAS COUNTY THIS MORNING AS SOME STRIKES HAVE ALREADY BEEN
OBSERVED AT THE COAST THIS MORNING IN THE UNSTABLE AIR MASS BEHIND
THE FRONT.

ATTENTION TURNS TO AN ATMOSPHERIC RIVER EVENT THAT WILL BRING A
RELATIVELY LONG PERIOD OF MODERATE TO HEAVY PRECIPITATION TO THE
FORECAST AREA FROM SATURDAY THROUGH SUNDAY BEFORE THE PLUME OF
MOISTURE RETREATS TO THE NORTH. SNOW LEVELS WILL BE BETWEEN 4000
AND 5000 FEET WHEN PRECIPITATION BEGINS...SO MOUNTAIN PASSES
SHOULD GET A QUICK SHOT OF ACCUMULATING SNOWS LATE TONIGHT INTO
SATURDAY MORNING BEFORE SNOW LEVELS BUMP ABOVE 5000 FEET MID TO LATE
SATURDAY MORNING. THEREFORE...TRAVELERS WANTING TO AVOID SNOWFALL
OVER MOUNTAIN PASSES SHOULD WAIT UNTIL THE AFTERNOON TO TRAVEL.
HOWEVER...ALL TRAVELERS IN THE AREA WILL HAVE TO CONTEND WITH
MODERATE TO HEAVY RAIN ON SATURDAY AT LEAST. ADDITIONALLY...WINDS
WILL BE VERY GUSTY AT THE COAST AND EAST SIDE SATURDAY. 850 MB
WINDS ARE FROM THE SOUTHWEST...AND MODELS SUGGEST A 7-9 MB
PRESSURE GRADIENT FROM OTH- ACV...WHICH MAKES GUSTS TO 50 MPH SEEM
VERY REASONABLE. FUTURE SHIFTS MAY WANT TO BUMP THIS UP EVEN
FURTHER IF DATA SUPPORTS THIS. WE INCREASED WINDS NEAR SUMMER LAKE
FOR SATURDAY AFTERNOON AS 50-70KT 700MB WINDS TRAVERSE THAT AREA.
ADDITIONALLY...HAVE INCREASED SHASTA VALLEY WINDS SIMPLY DUE TO
THE STRONG SOUTH TO NORTH PRESSURE GRADIENT EVEN THOUGH THE 700MB
WINDS ARE FROM THE WEST.

THE HYDROLOGIC OUTLOOK COVERS THE HEAVY RAIN SITUATION WELL AT THIS
TIME. LATEST RIVER MODELS SUGGEST THE COQUILLE RIVER AT COQUILLE
REACHES ACTION STAGE...AND A FLOOD WATCH MAY BE NECESSARY IF FUTURE
RUNS INCREASE THIS FURTHER.  THE CURRENT FORECAST REFLECTS A BLEND
BETWEEN THE NAM AND GFS IN TERMS OF PRECIPITATION AMOUNTS...WHICH
BASICALLY IS 5 INCHES FOR THE OROGRAPHIC-FAVORED PORTIONS OF THE
COAST RANGE AND 5 INCHES FOR THE CASCADES FROM CRATER LAKE NORTH.
INTERESTINGLY...INTEGRATED VAPOR TRANSPORT...AN INDICATOR OF HOW
SIGNIFICANT A RAINMAKER THIS SYSTEM WILL BE...TRENDS HAVE DECREASED
SOMEWHAT OVER THE PAST FEW GFS ENSEMBLE RUNS...BUT STILL ARE
IMPRESSIVE WITH 5 STANDARD DEVIATIONS ABOVE NORMAL PER THE MOST
RECENT RUN.  SNOW LEVELS WILL PEAK AT 9000 FEET LATE SUNDAY...AND
MOST OF THE HEAVY PRECIPITATION WITH THE SYSTEM WILL FALL AS
RAIN...ENTERING THE RIVERS AND STREAMS.  THIS AGAIN SUGGESTS THAT
THERE WILL BE SOME HYDROLOGIC IMPACTS WITH THIS STORM.

CONDITIONS DRY OUT MONDAY INTO TUESDAY BEFORE A COLD SYSTEM DROPS
DOWN FROM THE NORTHWEST AND EXHIBITS QUTIE DIFFERENT BEHAVIOR THAN
THE LAST SYSTEM...WITH SNOW LEVELS LOWERING SHARPLY AND THE
POTENTIAL FOR SNOW AS LOW AS 3000 FEET. THIS OF COURSE IS OF
IMPORTANCE TO ANYONE TRAVELING IN THE AREA OR HOPING FOR A WHITE
CHRISTMAS.


&&

.AVIATION...A FAST MOVING COLD FRONT IS TRACKING ACROSS THE AREA
THIS MORNING. IT IS PRODUCING MAINLY LIGHT TO MODERATE
PRECIPITATION WITH A MIX OF MVFR AND VFR CEILINGS AND
VISIBILITIES, AREAS OF MOUNTAIN OBSCURATION, AND GUSTY
SOUTHWESTERLY LOW LEVEL WINDS MAINLY AHEAD OF THE FRONT EAST OF
THE CASCADES. PRECIPITATION MAY BE HEAVY AT TIMES WITH IFR
CONDITIONS EARLY THIS MORNING WEST OF THE CASCADE CREST.
THUNDERSTORMS ARE POSSIBLE ALONG THE COAST AND JUST INLAND THIS
MORNING. ADDITIONALLY...FREEZING LEVELS SHOULD DROP BY ABOUT 2000
FEET THIS MORNING BEHIND THE COLD FRONT.

PRECIPITATION WILL TAPER TO DIMINISHING SHOWERS DURING THE DAY WITH
VFR CEILINGS OCCASIONALLY LOWERING TO MVFR UNDER SHOWERS. THE NEXT
FRONT WILL APPROACH THE COAST FRIDAY EVENING WITH LIGHT RAIN AND
MVFR CEILINGS DEVELOPING BEFORE CONDITIONS DETERIORATE WITH
HEAVIER PRECIPITATION SPREADING INLAND LATE FRIDAY NIGHT.

&&

.MARINE...UPDATED 1015 PM PST THU DEC 18 2014...A COLD FRONT HAS
MOVED INLAND THIS EVENING. SOUTHERLY WIND WAVES ARE DIMINISHING BUT
SEAS WILL REMAIN HIGH ON SATURDAY WITH THE WATERS DOMINATED IN THE
MORNING BY A WEST SWELL AT 13 SECONDS THAT WILL COMBINE WITH A
BUILDING LONG PERIOD WEST SWELL AT AROUND 20 SECONDS. THIS LONG
PERIOD WEST SWELL WILL BECOME DOMINANT FRIDAY AFTERNOON WITH SEAS
BUILDING TO A PEAK AROUND 20 FEET AT 18 SECONDS ON FRIDAY EVENING.
THE LONG PERIOD SWELL WILL REMAIN HEAVY THROUGH SATURDAY AS ANOTHER
ROUND OF GALE FORCE WINDS ARRIVES WITH A STRONG WARM FRONT. SUNDAY
INTO MONDAY THIS WARM FRONT WILL LINGER ALONG THE COAST NORTH OF
CAPE BLANCO AS SEAS SUBSIDE AND WINDS GRADUALLY DIMINISH WITH A
LINGERING LONG PERIOD WEST SWELL...BUT THE WEST SWELL AT 13 SECONDS
BECOMING DOMINANT.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH SURF ADVISORY FROM 11 AM THIS MORNING TO 10 PM PST SATURDAY
     FOR ORZ021-022-615-618.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 10 PM THIS EVENING TO 4 PM
     PST SATURDAY FOR PZZ350-356-376.
     HAZARDOUS SEAS WARNING FROM 10 AM THIS MORNING TO 10 PM PST
     SATURDAY FOR PZZ350-356-370-376.
     GALE WARNING FROM 4 AM TO 4 PM PST SATURDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 AM PST THIS
     MORNING FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS FROM 10 PM THIS EVENING TO 4 AM
     PST SATURDAY FOR PZZ370.

$$

NSK/NSK/BTL


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