Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 192253
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
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 OREGONCASCADES
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


&&

.AVIATION...BASED ON THE 19/18Z TAF CYCLE...THE BULK OF THE SHOWERS
HAS PUSHED EAST AND VFR CIGS HAVE RETURNED. HOWEVER THERE IS A
CHANCE FOR BRIEF PERIODS OF MVFR CIGS IN SHOWERS THIS AFTERNOON WITH
PARTIAL MOUNTAIN OBSCURATIONS. WIND SPEED SHEAR WILL BE A CONCERN
TONIGHT FOR NORTH BEND...ROSEBURG AND MEDFORD TONIGHT AS A STRONG
WARM FRONT APPROACHES. CIGS WILL LOWER TO MVFR WITH REDUCED
VISIBILITIES AND MOUNTAIN OBSCURATIONS AS HEAVIER PRECIPITATION
ARRIVES OVERNIGHT TONIGHT AND IS LIKELY TO LAST THROUGH SATURDAY.
-PETRUCELLI


&&

.MARINE...UPDATED 830 AM PST FRI DEC 19 2014...HEAVY WEST SWELL WILL
BUILD TODAY...PEAKING AROUND 20 FEET AT 18 SECONDS THIS EVENING.
LONG PERIOD SWELL WILL REMAIN HEAVY THROUGH SATURDAY AS ANOTHER
ROUND OF GALE FORCE WINDS ARRIVES WITH A STRONG WARM FRONT. SUNDAY
INTO MONDAY...THE FRONT WILL LINGER ALONG THE COAST NORTH OF CAPE
BLANCO WHILE SEAS SUBSIDE AND WINDS GRADUALLY DIMINISH. THE NEXT
FRONT IS EXPECTED TO ARRIVE FROM THE NORTHWEST ON WEDNESDAY. EXPECT
MODERATE TO STRONG NORTH WINDS CHRISTMAS EVE INTO CHRISTMAS DAY.
-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 FROM 10 PM THIS EVENING TO 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.

$$

CC/BPN


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