Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 201715
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
915 AM PST SAT DEC 20 2014

.SHORT TERM...THE FORECAST IS ON TRACK WITH A DEEP MOIST AIRMASS
BRINGING HEAVY RAINFALL TO THE AREA TODAY THROUGH SUNDAY.
SATELLITE IMAGERY SHOWS A LARGE AREA OF DEEP MOISTURE MOVING INTO
THE SOUTHERN OREGON COAST WITH PRECIPITABLE WATER VALUES OF 1.5
TO 1.75 INCHES. THIS AREA OF DEEP MOISTURE EXTENDS WEST-NORTHWEST
OFF MUCH OF NORTHEAST PACIFIC. STRONG WESTERLY FLOW WILL ALLOW
HEAVY PRECIPITATION ESPECIALLY ALONG THE COAST, COAST MOUNTAINS
AND INTO THE SOUTHERN OREGON CASCADES TODAY AND SUNDAY. VALLEY
LOCATIONS WEST OF THE CASCADES IN SOUTHERN OREGON ARE EXPECTED TO
SEE MODERATE RAINFALL FOR MUCH OF THIS PERIOD. FURTHER SOUTH IN
NORTHERN CALIFORNIA AND EAST OF THE CASCADES EXPECT LIGHT TO
MODERATE PRECIPITATION. SNOW LEVELS ARE RISING THIS MORNING WITH
SNOW LEVELS AROUND 6000 FEET OR HIGHER FROM THE CASCADES WEST AND
AROUND 5000 TO 5500 FT EAST OF THE CASCADES. THESE SNOW LEVELS
WILL RISE FURTHER TO 8000 TO 9000 FT BY LATE AFTERNOON FOR MOST
AREAS.

HEAVY RAINFALL WITH BRING FLOODING POTENTIAL, ESPECIALLY TO THE
COAST, JUST INLAND TO PORTIONS OF JOSEPHINE COUNTY, DOUGLAS COUNTY
AND INTO THE SOUTH CENTRAL OREGON CASCADES. THE MAIN FLOOD IMPACTS
FOR THESE AREAS ARE SMALL STREAM AND URBAN FLOODING, PONDING ON
ROADWAYS, AS WELL AS THE POTENTIAL FOR MUDSLIDES OR DEBRIS FLOWS. STORM
TOTAL RAINFALL OF 3 TO 5 INCHES IS EXPECTED ALONG THE COAST AND
COAST MOUNTAINS AS WELL AS INTO THE SOUTH CENTRAL OREGON CASCADES
AND DOUGLAS FOOTHILLS WITH ISOLATED HIGHER AMOUNTS UP TO 6 INCHES
POSSIBLE. AREAS INLAND WEST OF THE CASCADES IN OREGON ARE
FORECAST TO RECEIVE AROUND 1 TO 2.5 INCHES OF RAIN THROUGH SUNDAY.

IN ADDITION, GUSTY WINDS ARE EXPECTED WITH THIS STORM TODAY INTO
SUNDAY WITH BREEZY AND GUSTY WINDS ALONG THE COAST, IN THE
MOUNTAINS, FOR AREAS EAST OF THE CASCADES AND INTO THE SHASTA
VALLEY. SOUTH TO SOUTHWEST WINDS ARE INCREASING IN MANY OF THESE
AREAS THIS MORNING AND GUSTS OF 35 TO 40 MPH ARE EXPECT FOR MOST
COAST AREAS. IN THE MOUNTAINS MUCH HIGHER GUSTS ARE POSSIBLE WITH
GUSTS TO AROUND 50 MPH. WIND ADVISORIES CONTINUE TO FOR WINDS
GUSTS TO AROUND 50 MPH IN THE SHASTA VALLEY. EAST OF THE CASCADES
ALSO EXPECT VERY GUSTY WINDS IN THE HIGHER TERRAIN AND SUMMER LAKE
AREA. BASED ON THE CURRENT TRENDS AND MODEL FORECASTS, MAY NEED TO
INCREASE WIND GUSTS TO 60 MPH OR MORE IN THE SUMMER LAKE AREA LATE
THIS AFTERNOON AND TONIGHT WHEN WINDS ALOFT ARE FORECAST TO
INCREASE AND MOVE INTO THAT ARE. WILL EVALUATE THIS AND UPDATE AS
NEEDED.


&&

.AVIATION...FOR THE 20/12Z TAF CYCLE...EXPECT WIDESPREAD MVFR
CIGS/VIS ACROSS THE AREA TODAY AND TONIGHT WITH TERRAIN OBSCURED.
LOCAL IFR IS ALSO POSSIBLE. EXPECT MAINLY MODERATE TO LIGHT
PRECIPITATION...EXCEPT AT THE COAST AND IN THE MOUNTAINS WHERE IT
WILL BE HEAVY AT TIMES. FREEZING LEVELS AROUND 5000 FEET WILL RISE
TO AROUND 9000 FEET SATURDAY AND REMAIN THERE THROUGH MOST OF
SUNDAY. LOW- LEVEL WIND SHEAR WILL BE ENDING AT THE COAST AS WINDS
BEGIN TO SURFACE, BUT MAY CONTINUE AT KRBG THROUGH 15Z. /CC

&&

.MARINE...UPDATED 8 AM PST SAT DEC 20 2014...HEAVY WEST SWELL
WILL GRADUALLY LOWER TODAY. HOWEVER, A STRONG WARM FRONT WILL
BRING SOUTH GALES TO THE WATERS WHICH WILL KEEP VERY STEEP
COMBINED SEAS GOING EVEN AS SWELL DIMINISHES. WINDS WILL DIMINISH
SUNDAY AND THEN REMAIN RELATIVELY LIGHT THROUGH EARLY NEXT WEEK,
BUT MODERATE SWELL IS LIKELY TO CONTINUE THROUGH MUCH OF NEXT
WEEK. A STRONG COLD FRONT MAY BRING MODERATE NORTH WINDS TO THE
WATERS CHRISTMAS EVE AND CHRISTMAS DAY WITH A CORRESPONDING
INCREASE IN WIND WAVES. -WRIGHT/CC




&&

.PREV DISCUSSION... /ISSUED 341 AM PST SAT DEC 20 2014/

DISCUSSION...A MAJOR PRECIPITATION EVENT IS UNDERWAY FOR PORTIONS
OF THE FORECAST AREA. AN EXTREMELY IMPRESSIVE FETCH OF DEEP
MOISTURE EXTENDS FROM THE COAST TO NEARLY 3000 MILES
OFFSHORE...POINTED AT THE OREGON COAST. THIS WILL MAINTAIN
MODERATE TO HEAVY RAINFALL OVER THE COAST...COAST RANGE...CASCADE
FOOTHILLS AND CASCADES THROUGH SUNDAY. SNOW LEVELS ARE CURRENTLY
ABOUT 5500 FEET AND ARE RISING...SO THIS WILL BE PRIMARILY A HEAVY
RAIN EVENT AND FLOODING WILL BE THE MAIN IMPACT. ADDITIONAL
IMPACTS WILL INCLUDE DANGEROUS SEAS...HIGH SURF AT THE COAST...AND
GUSTY TO STRONG WINDS AT THE COAST...SHASTA VALLEY...AND EAST
SIDE.

MODELS CONTINUE TO PAINT A FAIRLY CONSISTENT PICTURE...OVER THE PAST
4 RUNS AT LEAST...OF 48 HOUR PRECIPITATION TOTALS OF 5-7 INCHES OVER
THE CASCADES AND 4-5 INCHES AT THE COAST. WE HAVE ENSURED THAT THE
FORECAST REFLECTS THIS...WITH SOME ENHANCED RAINFALL IN THE MOST
OROGRAPHICALLY FAVORED LOCATIONS SUCH AS THE CURRY COUNTY COAST AND
THE HIGH CASCADES FROM CRATER LAKE NORTH.

SOME CONFIDENCE TOOLS CONTINUE TO SHOW IMPRESSIVE NUMBERS THIS
MORNING...WITH IVT VALUES OF 500 KG/M/S FOR 24 HOURS STRAIGHT ALONG
AND NORTH OF CAPE BLANCO. THESE IVT...OR INTEGRATED VAPOR
TRANSPORT...VALUES WHICH SUGGESTS HOW SIGNIFICANT THE MOISTURE IS
OVER THE REGION...ARE PEAKING AT VALUES THAT ONLY OCCUR ONCE EVERY 5-
10 YEARS OVER THE CASCADES...AND ONCE EVERY 2-5 YEARS AT THE COAST.
HOWEVER...THE SHEAR DURATION OF THESE HIGH VALUES MEANS THIS EVENT
COULD EVEN BE MORE SIGNIFICANT.

SO...WITH ALL THAT SAID...HAVE ADDED SOME AREAL FLOOD WATCHES TO
BOTH EASTERN CURRY AND JOSEPHINE COUNTIES...AS WELL AS THE CASCADE
FOOTHILLS AND CASCADES FROM CRATER LAKE NORTHWARD. THESE ARE IN
ADDITION TO AREAL FLOOD WATCHES THAT COVER THE COAST AND JUST INLAND
AT FFAMFR. THE CONCERNS HERE ARE NOT ONLY FOR
MUDSLIDES...ROCKSLIDES...AND LANDSLIDES...BUT ALSO FOR STREAMS
FLOODING AND URBAN FLOODING WITH PONDING OF WATER ON ROADWAYS
EXPECTED AT LEAST. TRAVELING TODAY INTO TOMORROW WILL BE DIFFICULT
WITH THE HEAVY RAIN...WHICH WILL REDUCE VISIBILITY. THE MAIN STEM
RIVER THAT IS FORECAST TO OVERFLOW ITS BANKS IS THE COQUILLE AT
COQUILLE...WHICH IS FORECAST TO REACH MINOR FLOOD STAGE BY SUNDAY
AFTERNOON. MORE RIVERS CERTAINLY WILL NEAR FLOOD STAGE WITH THIS
SIGNIFICANT EVENT.

VERY GUSTY WINDS WILL IMPACT THE COAST THIS MORNING...SHASTA
VALLEY...WITH A LONG-DURATION GUSTY WIND EVENT EAST OF THE CASCADES
DUE TO CONTINUAL 50KT+ H7 FLOW THROUGH SUNDAY EVENING.

THINGS DRY OUT MONDAY INTO TUESDAY AS RIDGING BUILDS SOME...LIKELY
BRINGING MORNING VALLEY FOG BACK TO THE REGION.  THE NEXT SYSTEM TO
MOVE IN WILL BE A COLD ONE FROM THE NORTHWEST...BRINGING SNOW LEVELS
DOWN TO 3000 FEET ON CHRISTMAS EVE...WITH AMOUNTS TO BE DETERMINED
GIVEN MODEL DIFFERENCES BETWEEN THE GFS AND ECMWF AT THIS TIME. WILL
NO DOUBT SHIFT FOCUS TO THAT ONCE HEAVY RAINS AND WIND BEGINS TO
DIMINISH ON SUNDAY.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY UNTIL 9 PM PST SUNDAY FOR ORZ030-031-624-625.
     FLOOD WATCH FROM 4 PM PST THIS AFTERNOON THROUGH SUNDAY EVENING
     FOR ORZ025-027-617-623-624.
     FLOOD WATCH THROUGH SUNDAY EVENING FOR ORZ024-618-621.
     HIGH SURF ADVISORY UNTIL 10 PM PST THIS EVENING FOR
     ORZ021-022-615-618.
     FLOOD WATCH THROUGH SUNDAY EVENING FOR ORZ616-619-620.
     FLOOD WATCH THROUGH SUNDAY EVENING FOR ORZ021-022-615.
     FLOOD WATCH FROM 4 PM PST THIS AFTERNOON THROUGH SUNDAY EVENING
     FOR ORZ023.

CA...WIND ADVISORY UNTIL 9 PM PST SUNDAY FOR CAZ085-285.
     WIND ADVISORY UNTIL 1 AM PST SUNDAY FOR CAZ081-281.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 4 PM PST THIS AFTERNOON FOR
     PZZ356.
     GALE WARNING UNTIL 4 PM PST THIS AFTERNOON FOR
     PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 10 PM PST THIS EVENING FOR
     PZZ350-356-370-376.

$$

CC



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