Heavy Snow in California, December 6, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
344 AM PST FRI DEC 6 2013

.SHORT TERM...A LOW PRESSURE CENTER IS LOCATED APPROXIMATELY 100
MILES OFF THE COAST OF NORTHERN AND CENTRAL OREGON. AS THIS LOW
MOVES INLAND IT WILL BRING SIGNIFICANT SNOW TO THE AREA. MODEL
FORECASTS REMAIN ON TRACK SHOWING THIS LOW MOVING INTO THE
SOUTHERN OREGON COAST DURING THE MID TO LATE MORNING...THEN THE
LOW IS FORECAST TO TRACK INLAND INTO SOUTHWEST OREGON DURING THE
AFTERNOON BEFORE MOVING INTO EXTREME SOUTHEAST OREGON AND MODOC
COUNTY DURING THE EVENING. THE VERY COLD CONDITIONS AHEAD OF THIS
LOW WILL ALLOW THE MAJORITY OF THE PRECIPITATION TO FALL AS SNOW.

EARLY THIS MORNING LIGHT SNOW HAS BEGUN IN MUCH OF COOS COUNTY
AND DOUGLAS COUNTY. THIS IS SLIGHTLY EARLIER THAN THE 00Z MODEL
RUNS INDICATED. AS THIS LOW CONTINUES TO MOVE INTO THE COAST THIS
MORNING EXPECT MODERATE TO LOCALLY HEAVY SNOW TO DEVELOP ALONG THE
COAST AND IN DOUGLAS COUNTY.

LIGHT SNOW IS EXPECTED TO BEGIN IN OTHER AREAS FROM THE CASCADES
WEST LATER THIS MORNING, INCLUDING JOSEPHINE, JACKSON AND WESTERN
SISKIYOU COUNTIES. SNOW WILL INCREASE DURING THE LATE MORNING INTO
THE AFTERNOON FOR INLAND AREAS FROM CASCADES WEST WITH MODERATE TO
HEAVY SNOW EXPECTED ACROSS THESE AREAS. CURRENT MODEL FORECASTS
CONTINUE TO SHOW THAT SNOW PERSISTS INTO THE EVENING FROM THE
CASCADES WEST...DECREASING FROM NORTHWEST TO SOUTHEAST AS THE LOW
TRACKS EAST OF THE CASCADES. BY FRIDAY NIGHT, EXPECT ACTIVITY TO
DECREASE TO LIGHT SHOWERS WITH ACCUMULATING SNOW MOST LIKELY ALONG
THE CASCADES AND SISKIYOUS AND IN THE FOOTHILLS. ALONG THE COAST
TODAY, EXPECT MOST THE SNOW TO OCCUR DURING THE MORNING BELOW 500
FEET. THEN EXPECT RAIN TO MIX WITH SNOW IN THE AFTERNOON OVER THE
LOWER ELEVATIONS WITH CONTINUED SNOW ACCUMULATIONS, ESPECIALLY
ABOVE 1000 FEET ELEVATION. HAVE MADE ONLY FINE ADJUSTMENTS TO THE
SNOWFALL FORECAST. TODAY THROUGH TONIGHT, STILL EXPECT 3 TO 6
INCHES OF SNOW IN MOST WEST SIDE VALLEYS AND EVEN ALONG THE COAST
WITH 6 TO 12 INCHES IN THE CASCADES, SISKIYOUS AND MOUNTAINS WEST
OF THE CASCADES.

EAST OF THE CASCADES, LIGHT SNOW IS EXPECTED TO DEVELOP IN
NORTHERN KLAMATH COUNTY THIS MORNING. THEN MODERATE TO LOCALLY
HEAVY SNOW WILL DEVELOP IN THE AFTERNOON INTO THE EARLY EVENING.
SNOW WILL PERSIST OVERNIGHT BUT DECREASE TO LIGHT TO MODERATE
SHOWERS. SOUTH WINDS COMBINED WITH THE DRY SNOW MAY PRODUCE
LIMITED VISIBILITIES AT TIMES, ESPECIALLY IN THE AFTERNOON AND
INTO THE EVENING WHEN WINDS ARE BREEZY AT 10 TO 20 MPH OVER THE
MOUNTAINS AND EAST OF THE CASCADES.

BY SATURDAY MORNING...THE LOW WILL HAVE SHIFTED WELL EAST OF THE
AREA INTO NORTHEAST NEVADA BUT A VERY COLD UPPER LEVEL TROUGH WILL
REMAIN OVER THE AREA AND WRAP AROUND MOISTURE WILL BRING SHOWERS.
THE 00Z MODEL RUNS SHOW ONLY LIGHT AND ISOLATED SNOW SHOWERS FOR
AREAS WEST OF THE CASCADES WITH SCATTERED ACTIVITY STILL POSSIBLE
NEAR THE SISKIYOUS AND FROM THE CASCADES EAST. THEN SHOWERS DIMINISH
DURING THE DAY SATURDAY.

THIS UPPER TROUGH SHIFTS EAST SATURDAY NIGHT WITH COLD NORTHERLY
FLOW OVER THE REGION. THIS PATTERN WILL BRING VERY COLD ARCTIC AIR
INTO THE AREA SATURDAY NIGHT THROUGH EARLY MONDAY. MODEL GUIDANCE
IS SHOWING EXTREMELY COLD TEMPERATURES SUNDAY MORNING AND MONDAY
MORNING. ON MONDAY THE 00Z NAM SHOWS A WEAK DISTURBANCE MOVING
SOUTH DOWN THE COAST BUT THE OTHER MODELS ARE MUCH WEAKER WITH
THIS FEATURE. SO HAVE ONLY INTRODUCED SLIGHT CHANCE FOR
PRECIPITATION TO THE COAST AD WEST SIDE AREAS. IF THE NAM
VERIFIES, THEN CLOUD COVER SUNDAY NIGHT INTO MONDAY MORNING MAY
MODERATE THE VERY COLD TEMPERATURES SLIGHTLY, ESPECIALLY FOR WEST
SIDE LOCATIONS.

&&

.AVIATION...BASED ON THE 06/06Z TAF CYCLE.

CONDITIONS REMAIN VFR EARLY THIS MORNING, EXCEPT FOR LOCAL MVFR IN
THE COOS AND DOUGLAS COUNTY. MID AND HIGH LEVEL CLOUDS ARE INCREASING
AHEAD OF A COLD FRONT. DUE TO THIS FRONT, IFR CIGS/VSBYS IN
RAIN/SNOW/FOG WILL DEVELOP NEAR THE COAST BETWEEN 12Z-15Z THEN
SPREAD INLAND TO THE CASCADES DURING THE AFTERNOON TODAY WITH THE
HIGHER TERRAIN BECOMING OBSCURED. AREAS OF IFR CIGS/VSBYS IN SNOW
WILL DEVELOP EAST OF THE CASCADES FRIDAY AFTERNOON AND EVENING
WHILE THE IFR DUE TO SNOW LINGERS WEST OF THE CASCADES. SNOW
SHOWERS ARE EXPECTED TO DECREASE IN NUMBER LATE TONIGHT INTO
SATURDAY MORNING BUT THIS LINGERING ACTIVITY WILL PRODUCE VARIABLE
CONDITIONS WITH CIGS AND VSBYS FREQUENTLY IFR. THIS WILL ALSO KEEP
THE HIGHER TERRAIN FREQUENTLY OBSCURED.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 10 AM PST
     SATURDAY FOR ORZ029>031.
     WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 4 AM PST
     SATURDAY FOR ORZ029>031.
     WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR
     ORZ021-022.
     WINTER STORM WARNING FROM 7 AM THIS MORNING TO 4 AM PST SATURDAY
     FOR ORZ024-026.
     WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR ORZ023.
     WINTER STORM WARNING FROM 7 AM THIS MORNING TO 4 AM PST SATURDAY
     FOR ORZ025.
     WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 4 AM PST
     SATURDAY FOR ORZ027-028.
     WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR
     ORZ021>023.

CA...WINTER STORM WARNING FROM 7 AM THIS MORNING TO 4 AM PST SATURDAY
     FOR CAZ080-081.
     WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 4 AM PST
     SATURDAY FOR CAZ082-083.
     WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 10 AM PST
     SATURDAY FOR CAZ084-085.
     WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 4 AM PST
     SATURDAY FOR CAZ083>085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM THIS AFTERNOON
     TO 4 AM PST SATURDAY FOR PZZ350-356.
     SMALL CRAFT ADVISORY FOR WINDS FROM 4 PM THIS AFTERNOON TO 4 PM
     PST SATURDAY FOR PZZ370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM THIS AFTERNOON
     TO 10 PM PST SATURDAY FOR PZZ370.
     SMALL CRAFT ADVISORY FOR WINDS FROM 4 PM THIS AFTERNOON TO 10 PM
     PST SATURDAY FOR PZZ376.
     HAZARDOUS SEAS WATCH FROM THIS EVENING THROUGH SATURDAY MORNING
     FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM THIS AFTERNOON
     TO 10 PM PST THIS EVENING FOR PZZ376.

CC