Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 211702
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
902 AM PST FRI NOV 21 2014

.DISCUSSION...THE STRONG PACIFIC SYSTEM IS TAKING AIM RIGHT AT US
THIS MORNING AND PRECIPITATION HAS ALREADY REACHED THE COAST. SO
FAR IT`S BEEN LIGHT, BUT IT WILL INCREASE OVER TIME WITH MODERATE
TO HEAVY RAIN DEVELOPING ALONG THE COAST AND COASTAL RANGE THIS
AFTERNOON. ALSO WINDS ARE ALREADY RAMPING UP OVER THE MARINE
WATERS AND COAST. PREVIOUS FORECAST IS STILL ON TRACK. MADE SOME
ADJUSTMENTS TO THE POPS AND QPF TODAY. BASICALLY I ADJUSTED THEM
UP WEST OF THE CASCADES. THE MAIN FOCUS TODAY WILL BE TO TAKE A
CLOSER LOOK AT POPS, QPF, WINDS AND SNOW LEVELS FOR TONIGHT INTO
SATURDAY. SEE PREVIOUS DISCUSSION BELOW FOR DETAILS ON THE
INCOMING STORM. -PETRUCELLI


&&

.AVIATION...BASED ON THE 21/12Z TAF CYCLE...ABUNDANT LOW LEVEL
MOISTURE IS ALREADY HELPING TO CREATE LIFR CONDITIONS IN WEST SIDE
VALLEYS AROUND ROSEBURG AND MFR...AND THIS SHOULD CONTINUE THROUGH
THE MORNING. IN OTHER VALLEYS THERE IS A MIX OF IFR AND MVFR
EXPECTED THIS MORNING AS WELL AS AREAS OF IFR/MVFR CIGS ALONG THE
COAST.

A STRONG FRONT WILL APPROACH THE COAST TODAY WITH VERY STRONG WINDS
ABOVE THE SURFACE...LOW LEVEL WIND SHEAR CONDITIONS ARE EXPECTED
LATE THIS MORNING AND THIS AFTERNOON AT THE COAST AND IN THE UMPQUA
BASIN AROUND ROSEBURG. EVEN WITH STRONG WINDS ABOVE THE
SURFACE...SURFACE WINDS IN WEST SIDE VALLEYS SHOULD REMAIN
RELATIVELY LIGHT...AND CONDITIONS SHOULD STAY IFR OR MVFR THROUGH
THE DAY IN LOW CLOUDS. WIDESPREAD IFR IS EXPECTED FOR AREAS FROM THE
CASCADES WEST LATE THIS AFTERNOON THROUGH EARLY SATURDAY MORNING
WITH WIDESPREAD MOUNTAIN OBSCURATIONS.

EAST OF THE CASCADES...VERY STRONG SOUTHWEST WINDS ARE EXPECTED IN
THE AFTERNOON AND EVENING WITH CONDITIONS IMPROVING TO VFR THIS
AFTERNOON...THEN IFR AND MVFR REDEVELOPING THIS EVENING AND TONIGHT
AS PRECIPITATION INCREASE OVER THE AREA. /CC


&&

.MARINE...UPDATED 6 AM PST FRI NOV 21 2014...A STRONG FRONT MOVING
OVER THE WATERS THIS AFTERNOON AND EVENING WILL BE THE PRIMARY
CONCER. MODELS CONTINUE TO INDICATE STRONG SOUTH WINDS MAY BE
EXPECTED OVER THE COASTAL WATERS WITH WIND SPEEDS REACHING STORM
FORCE FOR WATERS WITHIN 25 NM OF THE COAST FROM GOLD BEACH NORTH
AND GALES LIKELY ELSEWHERE. VERY STEEP SEAS BUILDING TO 20 TO 24
FT ARE EXPECTED BY LATE THIS AFTERNOON INTO EARLY THIS EVENING IN
THE AREA WHERE STORM FORCE WINDS ARE EXPECTED WITH 16 TO 20 FT
SEAS DEVELOPING ELSEWHERE. THE STRONGEST WINDS AND HEAVIEST SEAS
WILL OCCUR AT LOW TIDE...SO ONLY LIMITED COASTAL FLOODING IS
EXPECTED. OF GREATEST CONCERN IS THE AREA NEAR PORT ORFORD.

THE COLD FRONT WILL MOVE ONSHORE LATE THIS EVENING AND TONIGHT AND
WINDS WILL SHIFT TO THE WEST AND DECREASE. MODERATE WESTERLY SWELL
WILL MOVE INTO THE WATERS SATURDAY...SO SEAS WILL REMAIN HAZARDOUS
FOR A WHILE LONGER. /CC


&&

.PREV DISCUSSION... /ISSUED 428 AM PST FRI NOV 21 2014/

DISCUSSION...
ONLY A FEW ALTERATIONS WERE MADE TO THE FORECAST OVERNIGHT FOR
TODAY AND TONIGHT`S INCOMING STRONG FRONTAL SYSTEM. THESE WERE
PRIMARILY TO ADD A WIND ADVISORY FOR THE SHASTA VALLEY AND TO
INCREASE PRECIPITATION AMOUNTS ALONG AND WEST OF THE CASCADE
MOUNTAINS IN THE 4 PM PST TODAY TO 4 AM PST SATURDAY MORNING TIME
PERIOD.

THE NOSE OF A STRONG PACIFIC JET STREAM THAT EXTENDS ALL THE WAY WEST
TO THE EAST ASIAN COAST WILL BE INCREASING OVER THE AREA TODAY.
BY SATURDAY MORNING 300MB WINDS WILL BE AROUND 150 KNOTS OVER THE
MIDDLE OF THE FORECAST AREA. IT IS VERY NOTABLE THAT STRONG WEST
WINDS IN EXCESS OF 50 KNOTS EXTEND DOWN TO BELOW THE 700MB LEVEL
ALONG THE CASCADE CREST BEGINNING THIS EVENING. IN FACT, THE NAM12
INDICATES WEST FLOW PEAKING AROUND 70 KNOTS OVER THE CASCADES AT
THE 10KFT LEVEL TONIGHT. THIS WILL RESULT IN VERY STRONG
OROGRAPHIC LIFT THAT IS LIKELY TO RESULT IN PRECIPITATION RATES OF
1 TO AS MUCH AS 2 INCHES IN A 6 HOUR TIME PERIOD THERE. MODEL MOS
GUIDANCE FOR ROSEBURG INDICATES 1 TO 2 INCHES OF RAIN IN THE 12
HOUR PERIOD FROM 4PM TODAY TO 4AM SATURDAY MORNING. ON THE LOW
END, FOR THE SAME PERIOD, MOS GUIDANCE FROM THE EUROPEAN, GFS, AND
NAM12 MODELS HAVE CONSISTENTLY INDICATED 0.75" TO 1.25" OF RAIN
EVEN FOR MEDFORD DURING THE LAST 3 DAYS. THE TREND IN THIS CLIMATOLOGY
BASED MOS GUIDANCE HAS BEEN UPWARD OVERNIGHT, AS WELL. SO
CONFIDENCE IS HIGH IN SIGNIFICANT WEST SIDE PRECIPITATION DURING
THIS 12 HOUR TIME PERIOD, WITH ENHANCED DOWNSLOPING EAST OF THE
CASCADES. UNFORTUNATELY, FOR SNOW PACK, SNOW LEVELS WILL REMAIN
ABOVE 7KFT FOR THE BULK OF THIS PRECIPITATION EVENT, ONLY COMING
DOWN ON SATURDAY MORNING AFTER THE PRIMARY PRECIPITATION BAND HAS
PASSED. SOME GUIDANCE DOES INDICATE A CHANGE OVER AT OR ABOVE
6-7KFT AT THE END OF THE FRONTAL BAND PRECIPITATION, THOUGH.

IT SHOULD BE NOTED THAT STRONG DYNAMICS IN TERMS OF WIND AND
OROGRAPHIC COMBINE WITH A CONVECTIVE ASPECT TO THE PRECIPITATION
AS IT COMES IN THIS EVENING AND OVERNIGHT. HAVE ADDED SOME SLIGHT
THUNDERSTORMS CHANCES TO ACCOUNT FOR THIS. TOTAL TOTALS EXCEED 52
AND LIFTED INDICES ARE BELOW ZERO AS THE BULK OF THE IMPRESSIVE
DYNAMICS MOVE THROUGH.

THE PRESSURE GRADIENT FROM REDDING TO MEDFORD PEAKS AT ABOUT 8MB
BETWEEN 06Z AND 09Z THIS EVENING. THIS IS USUALLY SUPPORTIVE OF AT
LEAST ADVISORY LEVEL WINDS IN THE SHASTA VALLEY. WHILE 700MB WIND
DIRECTION IS PRIMARY WEST TO SOUTHWEST, WHICH IS NOT IDEAL FOR
STRONG WINDS, THE LOWER LEVEL PRESSURE GRADIENT IS EXPECTED TO
DRIVE WINDS TO ADVISORY LEVELS. SUSPECT THAT THE HIGHER WINDS
ALOFT WILL SEND THE BULK OF THIS WIND EASTWARD AS IT APPROACHES
SISKIYOU SUMMIT SENDING IT TOWARD KLAMATH FALLS AND THE EAST
SIDE VERSUS THE ROGUE VALLEY. STILL EXPECT SOME GUSTINESS PRIOR
TO THIS EVENING IN THE SOUTHERN ROGUE VALLEY, BUT SUSPECT IT WILL
BE SUBSTANTIALLY LESS THAN THE 40MPH GUSTS OBSERVED THERE JUST A
COUPLE OF DAYS AGO.

SATURDAY INTO SUNDAY OROGRAPHICS AND SOME EMBEDDED SHORTWAVES IN
THE STRONG JET STREAM FLOW SHOULD RESULT IN APPRECIABLE SNOW
SHOWERS DOWN TO 4KFT ELEVATIONS, MOST NOTABLE IN THE CASCADES.
THIS IS NOT UNUSUAL FOR THIS TIME OF THE YEAR, BUT WILL BE FACTOR
FOR THOSE TRAVELING OVER THE PASSES. BTL


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING FROM 1 PM THIS AFTERNOON TO 1 AM PST SATURDAY
     FOR ORZ021-022-615-618.
     COASTAL FLOOD ADVISORY UNTIL 1 AM PST SATURDAY FOR
     ORZ021-615-619.
     HIGH SURF WARNING UNTIL 1 AM PST SATURDAY FOR
     ORZ021-022-615-618-619.
     HIGH WIND WARNING FROM 7 PM THIS EVENING TO 1 PM PST SATURDAY
     FOR ORZ030-031-624-625.

CA...HIGH WIND WARNING FROM 7 PM THIS EVENING TO 1 PM PST SATURDAY
     FOR CAZ085-285.
     FLASH FLOOD WATCH FROM 1 PM PST THIS AFTERNOON THROUGH LATE
     TONIGHT FOR CAZ080-081-280-281.
     WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 4 AM PST SATURDAY FOR
     CAZ081-281.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 AM PST THIS
     MORNING FOR PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 1 AM PST SATURDAY FOR
     PZZ350-356-370-376.
     STORM WARNING UNTIL 1 AM PST SATURDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 1 AM PST SATURDAY FOR PZZ356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 AM PST THIS
     MORNING FOR PZZ350-356-370-376.

$$


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