Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 200423
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
823 PM PST FRI DEC 19 2014

.DISCUSSION...WON`T BE MAKING ANY UPDATES TO THE FORECAST THIS
EVENING AS IT CURRENTLY LOOKS ON TRACK. RECENT WATER VAPOR
IMAGERY INDICATES A LARGE AND LONG PLUME OF DEEP MOISTURE OFFSHORE
THAT WILL BE DIRECTED INTO THE PACNW OVER THE NEXT 36-48 HOURS.
THIS WILL RESULT IN A MODERATE TO HEAVY PRECIPITATION EVENT FOR
PORTIONS OF THE CWA...PARTICULARLY ALONG THE COAST, THE COASTAL
MOUNTAINS AND INTO THE CASCADES/CASCADE FOOTHILLS. LIQUID
PRECIPITATION AMOUNTS IN THESE AREAS WILL BE WIDELY IN THE 3 TO 6
INCH RANGE. EXPECT MANY AREA RIVERS/STREAMS TO RISE RAPIDLY
SATURDAY INTO SUNDAY, SO AREAL FLOOD WATCHES ARE OUT FOR THE COAST
AND PORTIONS OF DOUGLAS COUNTY WITH A MAIN STEM RIVER FLOOD WATCH
UP FOR THE COQUILLE AT COQUILLE. THESE CAN BE VIEWED AT
FFAMFR. STAY TUNED FOR POTENTIAL EXPANSION OF WATCHES OR UPGRADES
TO WARNINGS. RIGHT NOW, WE`RE EXPECTING RAIN AMOUNTS NEAR AN INCH
IN MEDFORD AND AROUND 0.50 OF AN INCH IN KLAMATH FALLS FOR THE
EVENT. LIGHTER RAINFALL WILL OCCUR FARTHER SOUTH AND EAST.

SNOW LEVELS RUNNING 4500 TO 5000 FEET TONIGHT INTO VERY EARLY
SATURDAY MORNING WILL RISE SIGNIFICANTLY ABOVE ALL BUT THE HIGHEST
PEAKS BY SATURDAY AFTERNOON. EXPECT A FEW TO SEVERAL INCHES OF
SNOW DOWN TO THE PASS NEAR LAKE OF THE WOODS (HIGHWAY 140) BEFORE
THE CHANGEOVER TO RAIN SATURDAY MORNING, WHILE AMOUNTS UP AT THE
RIM AT CRATER LAKE MAY EXCEED A FOOT PRIOR TO CHANGEOVER. THERE IS
A SPECIAL WEATHER STATEMENT (SPSMFR) UP FOR THE FOOTHILLS AND THE
CASCADES HIGHLIGHTING THE SNOW/RAIN.

GUSTY WINDS ARE ALSO LIKELY FOR THE SHASTA VALLEY AND PORTIONS OF
THE EAST SIDE SATURDAY. SEE NPWMFR FOR MORE SPECIFIC DETAILS. IT
SHOULD BE NOTED THAT GUSTY WINDS ARE ALSO LIKELY AT THE COAST, BUT
SHOULD REMAIN JUST BELOW WARNING LEVELS. SPILDE

&&

.AVIATION...FOR THE 20/00Z TAF CYCLE...ISOLATED SHOWERS MAY BRING
BRIEF REDUCTIONS TO CIG AND VIS TO THE REGION THIS EVENING, BUT
CONDITIONS ARE EXPECTED TO REMAIN VFR TO MVFR THROUGH EARLY TONIGHT.
A STRONG WARM FRONT WILL BRING WIDESPREAD RAIN AND MVFR CIGS AND VIS
TO THE WEST SIDE OVERNIGHT AND THEN SPREAD EAST OF THE CASCADES WITH
A MIX OF RAIN AND SNOW LATER TONIGHT. LOW LEVEL WIND SHEAR IS ALSO
EXPECTED TO DEVELOP AT WEST SIDE TERMINALS OVERNIGHT AS THE SURFACE
REMAINS STABLE BUT WINDS INCREASE ALOFT. WIDESPREAD RAIN WITH MVFR
CIGS/VIS AND BREEZY CONDITIONS ARE EXPECTED AT ALL TERMINALS ON
SATURDAY. -WRIGHT

&&

.MARINE...UPDATED 6 PM PST FRI DEC 19 2014...HEAVY WEST SWELL WILL
CONTINUE OVER ALL WATERS TONIGHT AND THEN SLOWLY DIMINISH SATURDAY.
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

&&

.PREV DISCUSSION... /ISSUED 253 PM PST FRI DEC 19 2014/

SHORT TERM...SCATTERED SHOWERS WILL CONTINUE BEHIND A FRONT THIS
AFTERNOON INTO EVENING. MEANWHILE A WARM FRONT WILL MOVE INTO THE
COAST AND BRING RAIN. PRECIPITATION IS EXPECTED TO INCREASE ALONG
THE COAST AND SPREAD INLAND OVERNIGHT AS THE WARM FRONT MOVES
INLAND TO THE NORTH AND A MOIST AIRMASS WITH ONSHORE FLOW MOVES
OVER THE AREA. MODELS CONTINUE TO SHOW THAT HEAVY TO MODERATE
PRECIPITATION WILL DEVELOP OVER MUCH OF THE AREA SATURDAY AND
CONTINUE INTO SUNDAY AS A DEEP MOIST FRONTAL SYSTEM IMPACTS THE
REGION. MODEL STORM TOTAL PRECIPITATION CONTINUES TO INDICATE 2 TO
4 INCHES IN THE COASTAL MOUNTAINS AND INTO THE SOUTHERN OREGON
CASCADES SATURDAY AND SUNDAY WITH ISOLATED AMOUNTS UP TO 6
INCHES. GIVEN THE SUSTAINED DEEP WESTERLY MOISTURE TRANSPORT INTO
SOUTHERN OREGON SATURDAY AND SUNDAY, THE HAVE GONE TOWARDS THE
UPPER END OF THE MODEL HEAVY RAINFALL WILL BRING THE POTENTIAL FOR
SMALL STREAM AND URBAN FLOODING, ESPECIALLY ALONG COASTAL AREAS
AND INTO DOUGLAS COUNTY. ALSO HEAVY RAIN MAY CAUSE MUDSLIDES AND
DEBRIS FLOWS ON AREAS ROADWAYS ESPECIALLY NEAR THE COAST AND INTO
THE SOUTH CENTRAL OREGON CASCADES, NORTH OF HIGHWAY 140.

INITIALLY, SNOW LEVELS ARE EXPECTED AROUND 4500 TO 5000 FT
TONIGHT INTO EARLY SATURDAY MORNING...RISING TO 7000 TO 8000 FT
WEST OF THE CASCADES BY SATURDAY AFTERNOON AND TO 5500 FT ACROSS
THE EAST SIDE. THEN SATURDAY EVENING, EXPECT SNOW LEVELS OF 7000
TO 9000 FT OVER THE AREA WITH HIGH SNOW LEVELS PERSISTING THROUGH
SUNDAY NIGHT. THE LOWER SNOW LEVELS WITH LINGERING COLD AIR OVER
THE AREA TONIGHT INTO EARLY SATURDAY MORNING EXPECT SOME SNOW
ACCUMULATIONS FOR HIGHER PASSES IN THE CASCADES AND FOR MOUNTAIN
PASSES EAST OF THE CASCADES. CURRENT FORECASTS SHOW 2 TO 5 INCHES
OF SNOW IN THE SOUTHERN OREGON CASCADES TONIGHT INTO SATURDAY
MORNING WITH ISOLATED AMOUNTS OF 6 TO 8 INCHES NEAR CRATER LAKE.
WILL NEED TO MONITOR SNOW LEVELS AND SNOW IMPACTS TONIGHT INTO
SATURDAY MORNING. THEN SNOW IS EXPECTED TO CHANGE OVER TO
MODERATE TO HEAVY RAINFALL.

RAINFALL WILL BRING SIGNIFICANT RIVER RISES TO THE AREA RIVERS
WITH A POTENTIAL FOR SMALL STREAM AND URBAN FLOODING NEAR THE
COAST AND INTO DOUGLAS COUNTY WHERE HIGHER RAINFALL AMOUNTS OF 2
TO 4 INCHES ARE EXPECTED. HEAVY RAINFALL OF 2 TO 5 INCHES IS ALSO
EXPECTED IN THE SOUTH CENTRAL CASCADES AND INTO THE FOOTHILLS OF
DOUGLAS COUNTY. HEAVY RAIN MAY CAUSE TRAVEL IMPACTS INCLUDING
WATER ON ROADWAYS, LIMITED VISIBILITIES, AND THE POTENTIAL FOR
MUDSLIDES AND DEBRIS FLOW.

WINDS WILL ALSO INCREASE WITH THIS FRONTAL SYSTEM ON SATURDAY WITH
GUSTY SOUTHWEST WINDS DEVELOPING ALONG THE COAST, IN THE MOUNTAINS
AND INTO THE SHASTA VALLEY AND AREAS EAST OF THE CASCADES. WINDS
GUSTING TO AROUND 45 TO 50 MPH ARE EXPECTED IN THE SOUTHERN SHASTA
VALLEY AND FOR AREAS EAST OF THE CASCADES WHERE WIND ADVISORIES
HAVE BEEN ISSUED.

MOISTURE TRANSPORT DECREASES SUNDAY NIGHT INTO MONDAY AS A RIDGE
BUILD NORTH INTO THE REGION. THIS WILL ALLOW PRECIPITATION TO
DIMINISH FROM SOUTH TO NORTH OVER THE AREA SUNDAY EVENING INTO
MONDAY. BY MONDAY, MODELS INDICATE ONLY LINGERING LIGHT SHOWERS,
MAINLY IN SOUTHWEST OREGON, AS FLOW BECOMES DRIER AND MORE
NORTHWESTERLY OVER THE AREA.

LONG TERM...TUESDAY THROUGH FRIDAY NIGHT...A LARGE UPPER LEVEL
RIDGE WILL BE IN PLACE OVER THE AREA TUESDAY, AND WHILE THIS WILL
PUSH TEMPERATURES UP ABOVE NORMAL AND  KEEP MUCH OF THE FORECAST
AREA DRY, SEVERAL SMALL SCALE WAVES WITHIN THE SWIFT BELT OF
WESTERLIES JUST TO OUR NORTH WILL CONTINUE TO PUSH MOISTURE ONSHORE.
HAVE KEPT A CHANCE OF PRECIPITATION IN THE FORECAST FOR THE COAST,
THE UMPQUA BASIN, AND THE CASCADES NORTH OF CRATER LAKE. ALL OTHER
AREAS SHOULD REMAIN DRY, ASIDE FROM A STRAY SHOWER OR TWO.

THIS RELATIVELY DRY PERIOD WILL NOT LAST LONG, AS A DEEP TROUGH
OVER THE EASTERN PACIFIC WILL PUSH THE RIDGE ASIDE AND MOVE
INLAND WEDNESDAY AND WEDNESDAY NIGHT. THIS WILL BE A COLD SYSTEM,
AND WILL DROP SNOW LEVELS OF 8000 TO 9000 FEET ON TUESDAY TO BELOW
4000 FEET BY EVENING ON CHRISTMAS EVE, MEANING ALL BUT THE HIGHEST
PEAKS WILL SEE PRECIPITATION BEGIN AS RAIN, BEFORE GRADUALLY
CHANGING OVER TO SNOW AS THE COLD FRONT PASSES CHRISTMAS EVE
NIGHT. WINDS WILL ALSO PICK UP AS THE FRONT PASSES, MAINLY OVER
THE USUAL PROBLEM AREAS OF THE COAST, HIGHER TERRAIN, AND THE EAST
SIDE. THE FRONT WILL PASS QUICKLY, MOVING OUT OF THE AREA BEFORE
CHRISTMAS MORNING, LEAVING ONLY SHOWERS IN ITS WAKE AS ONSHORE
FLOW CONTINUES THROUGH THE DAY ON CHRISTMAS.

RIDGING IS THEN EXPECTED TO REBUILD INTO THE REGION THURSDAY
NIGHT INTO FRIDAY, ALTHOUGH WITH THE RECENT TRENDS IN THE MODELS,
CONFIDENCE IS LOW THAT THERE WILL BE ANY SIGNIFICANT DRY PERIOD.
HAVE KEPT PRECIPITATION CHANCES BELOW SLIGHT, ALTHOUGH FURTHER
MODEL RUNS MAY SUGGEST A BETTER CHANCE FOR SHOWERS WITH SHORTWAVES
AND/OR ONSHORE FLOW. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH SUNDAY EVENING FOR
     ORZ021-022-615-618.
     HIGH SURF ADVISORY UNTIL 10 PM PST SATURDAY FOR
     ORZ021-022-615-618.
     FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH SUNDAY EVENING FOR
     ORZ023-616-617-619-620.
     WIND ADVISORY FROM 10 AM SATURDAY TO 9 PM PST SUNDAY FOR
     ORZ030-031-624-625.

CA...WIND ADVISORY FROM 10 AM SATURDAY TO 9 PM PST SUNDAY FOR
     CAZ085-285.
     WIND ADVISORY FROM 7 AM SATURDAY TO 1 AM PST SUNDAY FOR
     CAZ081-281.

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

$$

MAS/CC/TRW/BPN


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