Hazardous Seas Warning 61, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
827 PM PST MON DEC 17 2012

.UPDATE...TEMPERATURES HAVE COOLED TO NEAR OR BELOW FREEZING FOR
ALL LOCATIONS INLAND FROM THE COAST ALREADY THIS EVENING. A
DISTURBANCE IS MOVING ONTO THE COAST WHICH WILL BRING ANOTHER
ROUND OF CONVECTIVE SHOWERS TO THE WEST SIDE, WHICH WILL BE IN THE
FORM OF SNOW. THERE HAVE BEEN A FEW STRIKES WITHIN THE CELLS
OFFSHORE AND COOLING CLOUD TOPS SUGGEST THAT SNOW COULD COME DOWN
PRETTY GOOD WITHIN THE CORES. WOULD EXPECT LOW VISIBILITIES WITHIN
THE SHOWERS AND A QUICK ACCUMULATION OF AN INCH OR SO WHERE THESE
SHOWERS PASS, AND PERHAPS HIGHER AMOUNTS OVER THE MOUNTAINS.
CURRENT ROAD TEMPERATURES ARE STILL WARM ENOUGH OVER THE VALLEYS
THAT SIGNIFICANT ACCUMULATIONS ARE NOT EXPECTED ON THE ROADS, BUT
GRASSY AREAS WILL SEE ACCUMULATIONS. THE PASSES COULD GET A
LITTLE TRICKY TONIGHT THOUGH. THERE IS ANOTHER DISTURBANCE SLATED
FOR TOMORROW MORNING WHICH SHOULD BRING ANOTHER ROUND OF SNOW
SHOWERS, AND SINCE IT WILL BE COLDER, THEY WILL BE MORE LIKELY TO
STICK TO THE ROADS. A WINTER WEATHER ADVISORY REMAINS IN EFFECT
FOR THE WEST SIDE THROUGH TOMORROW AFTERNOON AND IT STILL LOOKS
GOOD. SKIES ARE CLEARING ON THE EAST SIDE AND WITH WIDESPREAD
FRESH SNOW COVER, TEMPERATURES ARE GOING TO GET VERY COLD. WE ARE
ALREADY APPROACHING OUR FORECAST LOWS IN SOME SPOTS, SO I WILL BE
UPDATING AT LEAST OUR LOW TEMP FORECAST FOR TONIGHT. -WRIGHT

&&

.AVIATION...A COLD AIR MASS WITH A SNOW LEVEL NEAR 1000 FT MSL
WILL PERSIST FOR THE REMAINDER OF THE EVENING WITH MAINLY VFR
SKIES BUT ALSO SCATTERED SNOW SHOWERS...LOCAL MVFR CEILINGS AND
AREAS OF MOUNTAIN OBSCURATIONS. LATER THIS EVENING...A WEAK LOW
PRESSURE TROUGH WILL ARRIVE AT THE COAST AND MOVE ACROSS THE AREA
THROUGH TUESDAY MORNING. THIS WILL SIGNIFICANTLY INCREASE THE
COVERAGE OF SHOWERS AND SNOW SHOWERS...ESPECIALLY WEST OF THE
CASCADES WITH THE SNOW LEVEL FALLING TO 500 FT MSL. THIS WILL
ALSO CREATE WIDESPREAD MVFR WITH OCCASIONAL IFR CONDITIONS. AFTER
18Z TUESDAY MORNING INTO TUESDAY EVENING...SHOWERS WILL DIMINISH
WITH CONDITIONS BECOMING MAINLY VFR BUT THE SNOW LEVEL WILL REMAIN
AROUND 1000 FT MSL AND THERE WILL BE LOCAL MVFR AND MOUNTAIN
OBSCURATIONS WITH THE LINGERING SHOWERS.

&&

.PREV DISCUSSION... /ISSUED 340 PM PST MON DEC 17 2012/

DISCUSSION...A COLD AIR MASS ALOFT IS MOVING OVER THE FORECAST AREA
WITH PLENTY OF INSTABILITY SHOWERS MOVING IN FROM THE NORTHWEST. THE
MAIN CONCERN TONIGHT IS THE POTENTIAL FOR LOW ELEVATION SNOW.
CURRENT SATELLITE IMAGE SHOWS A DISTURBANCE NEAR 45N/127W AND
ANOTHER...BUT SLIGHTLY STRONGER ONE NEAR 48N/131W AND ARE HEADED IN
OUR DIRECTION. THE FIRST IS EXPECTED TO AFFECT WESTERN OREGON THIS
EVENING AND THE SECOND ONE LATE TONIGHT. SNOW LEVELS ARE EXPECTED TO
LOWER TO THE VALLEY FLOOR TONIGHT WITH THE POTENTIAL FOR AN INCH OR
SO IN MEDFORD BY DAYBREAK TUESDAY WITH 1 TO 2 INCHES OVER THE
SURROUNDING HILLS. SO ANYONE PLANING ON TRAVELING TONIGHT AND FOR
THE EARLY MORNING COMMUTE SHOULD ALLOW EXTRA TIME FOR TRAVEL AND BE
AWARE OF CHANGING CONDITIONS. THE MODEL HAVE BACKED OFF ON THE
AMOUNT OF QPF OVER THE AREA THIS EVENING. SO DO NOT THINK WE'LL GET
MUCH IF ANY ACCUMULATION. THE SECOND DISTURBANCE WILL BRING
INCREASING SHOWERS LATE TONIGHT INTO EARLY TUESDAY MORNING. IT'S
DURING THIS TIME WHERE THE CHANCE FOR ACCUMULATING SNOW IS HIGHER.

SNOW SHOWERS CONTINUE TUESDAY WITH A FEW THAT COULD BE MODERATE AT
TIMES. THE HIGHEST CHANCE FOR ACCUMULATING SNOW TUESDAY IS GOING TO
BE IN AREAS THAT GET CAUGHT UNDER HEAVIER SHOWERS. THE UPPER TROUGH
AXIS SHIFTS EAST OF THE AREA TUESDAY NIGHT WITH WEAK SHORTWAVE
RIDGING. THIS WILL GIVE US A RELATIVE BREAK IN THE WEATHER. HOWEVER
A COLD AIRMASS REMAINS IN PLACE SO WERE LIKELY TO SEE TEMPERATURES
DROP BELOW FREEZING IN MANY LOCATIONS.

ANOTHER STORM WILL TAKE SHAPE WEDNESDAY. A STRONG WARM FRONT WILL
MOVE INTO THE AREA WEDNESDAY MORNING. THE MODELS DIFFER SOMEWHAT
WITH THE TIMING AND AMOUNT OF PRECIPITATION. THIS IS IMPORTANT
BECAUSE IF PRECIPITATION ARRIVES EARLIER AND IS MORE
SIGNIFICANT...THEN WE COULD HAVE ANOTHER ROUND OF SNOW IN THE
VALLEYS DUE TO COLD AIR BEING TRAPPED AT THE SURFACE. IN ADDITION
MODERATE TO STRONG WINDS ARE EXPECTED AT THE COAST WEDNESDAY MORNING
AND LASTING THROUGH WEDNESDAY AFTERNOON.

A STRONG COLD FRONT ARRIVES WEDNESDAY AFTERNOON WITH MODERATE TO
HEAVY PRECIPITATION LIKELY FOR THE COAST RANGE AND CASCADES THROUGH
THURSDAY MORNING. SNOW LEVELS MAY COME UP TO AROUND 2500 FEET
WEDNESDAY AFTERNOON BEFORE COMING DOWN WEDNESDAY NIGHT....BUT NOT
CONFIDENT WE'LL SEE ANY RISE IN SNOW LEVELS DUE TO MODERATE TO HEAVY
PRECIPITATION DRAGGING SNOW COLD AIR ALOFT DOWN. MODERATE TO HEAVY
SNOW IS LIKELY OVER THE CASCADES AND SISKIYOUS.

THE FRONT WILL MOVE INTO NORTHERN CALIFORNIA BY THURSDAY EVENING
WITH PRECIPITATION GRADUALLY DECREASE FROM NORTHWEST TO SOUTHEAST.
-PETRUCELLI

LONG TERM...THURSDAY NIGHT THROUGH SUNDAY...AN ACTIVE PATTERN WILL
CONTINUE OVER THE AREA THURSDAY NIGHT INTO THE WEEKEND AS A LARGE
TROUGH OFF THE PACNW COAST SENDS MODERATE TO STRONG DISTURBANCES
INTO THE AREA. BEGINNING SUNDAY OR MONDAY THE UPPER TROUGH IS
EXPECTED TO SHIFT INLAND BRINGING SHOWERS FOLLOWED BY A BRIEF PERIOD
OF DRY CONDITIONS WITH A WEAK UPPER LEVEL RIDGE BUILDING OVER THE
AREA. THIS RIDGE MAY NOT LAST VERY LONG AS MODELS ARE SHOWING
ANOTHER FRONTAL SYSTEM APPROACHING ON TUESDAY.

FOR THURSDAY NIGHT AND FRIDAY...MODELS ARE IN AGREEMENT SHOWING
CONTINUED MODERATE TO LIGHT RAIN AND SNOW AS A STRONG COLD FRONT
EXITS THE AREA AND ANOTHER FRONT AND SHORTWAVE MOVING INTO THE AREA.
SNOW LEVELS ARE EXPECTED IN THE 2000 TO 3000 FT LEVEL DURING THIS
PERIOD.

THEN ON SATURDAY...EXPECT ADDITIONAL RAIN AND SNOW TO MOVE INTO THE
AREA AS STRONG SHORTWAVE MOVES INTO NORTHERN CALIFORNIA. THIS MAY
ALLOW MODERATE TO HEAVY PRECIPITATION TO MOVE INTO NORTHERN
CALIFORNIA. PRECIPITATION FURTHER NORTH IS MAINLY LIGHT TO
MODERATE. SNOW LEVELS EXPECTED TO RISE TO AROUND 3000 TO 3500 FT
SATURDAY.

ADDITIONALLY...PERIODS OF BREEZY AND GUSTY WINDS ARE POSSIBLE LATE
THURSDAY THROUGH SATURDAY WITH THESE FRONTS...ESPECIALLY OVER HIGHER
TERRAIN AND INTO THE SHASTA OR SUMMER LAKE VALLEYS.

SUNDAY INTO MONDAY...MODELS SHOW THE UPPER TROUGH GRADUALLY SHIFTING
INLAND. THE ECMWF CONTINUES TO BRING THIS TROUGH INLAND
FASTER...MOVING IT OVER THE AREA SUNDAY FOLLOWED BY A WEAK HIGH
PRESSURE RIDGE BUILDING INTO THE AREA MONDAY. THE GFS IS SLOWER WITH
THE TROUGH MOVEMENT INLAND AND DOES NOT BRING RIDGING INTO THE AREA
UNTIL MONDAY NIGHT INTO TUESDAY. THE UPPER TROUGH IS EXPECTED TO
BRING A VERY COLD  AIRMASS INTO THE AREA SUNDAY INTO MONDAY WITH
LIGHT SHOWERS POSSIBLE. BEHIND THE TROUGH ANY HIGH PRESSURE RIDGING
IS EXPECTED TO BE WEAK AND THE GFS AND ECMWF BOTH SHOW ANOTHER
FRONTAL SYSTEM APPROACHING TUESDAY INTO WEDNESDAY. OF CONCERN WILL
BE HOW FAST THIS NEXT FRONT MOVES INLAND...WITH A WARM FRONT
BRINGING THE POTENTIAL FOR LIGHT TO MODERATE RAIN AND SNOW AS EARLY
AS CHRISTMAS DAY. /CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR ORZ030.
     WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR ORZ029.
     WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR ORZ024.
     HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING
     FOR ORZ021-022.
     WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR ORZ025.
     WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY ABOVE 1000 FEET
     FOR FOR ORZ021>023.
     WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR ORZ026.

CA...NONE.

PACIFIC COASTAL WATERS...GALE WATCH FROM LATE TUESDAY NIGHT THROUGH LATE
     WEDNESDAY NIGHT FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL NOON PST TUESDAY FOR
     PZZ370.
     HAZARDOUS SEAS WATCH FROM LATE TUESDAY NIGHT THROUGH LATE
     WEDNESDAY NIGHT FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS FROM 4 AM TO NOON PST TUESDAY FOR
     PZZ376.