Winter Storm and Avalanche in California, December 21 to 24, 2012

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE RENO NV
340 AM PST FRI DEC 21 2012

.SHORT TERM...
CURRENT RADAR AND SATELLITE IMAGERY SHOWS A SWATH OF PRECIPITATION
MAKING ITS WAY THROUGH NORTHERN CALIFORNIA. SNOW HAS COMMENCED
ACROSS PORTIONS OF LASSEN COUNTY THIS MORNING WITH THE BOGARD REST
AREA WEB CAM SHOWING A FEW INCHES OF SNOW COVERING THE ROADWAY.
THIS MOISTURE WILL CONTINUE TO WORK ITS WAY SOUTH THROUGH THE TAHOE
BASIN THIS MORNING. WINTER STORM WARNINGS START THIS MORNING
ACROSS THE TAHOE BASIN AND INTO LASSEN COUNTY. MONO COUNTY WILL
BEGIN LATER THIS AFTERNOON. MAIN UPDATES TO THE FORECAST THIS
MORNING WERE TO DELAY THE ONSET OF THE WINTER STORM WARNING ACROSS
THE TAHOE BASIN AND ALSO TO ISSUE A WINTER STORM WATCH ACROSS THE
SURPRISE VALLEY AND NORTHERN WASHOE COUNTY ON SATURDAY.

CURRENT RADAR TRENDS AND LATEST MODEL GUIDANCE INDICATE A BIT OF
SLOW DOWN OF THE FIRST BAND OF PRECIPITATION AND HAVE DELAYED THE
START OF THE WINTER STORM WARNING ACROSS THE TAHOE BASIN TO 10 AM
THIS MORNING. THOUGH THIS FIRST WAVE WILL BE THE LEAST POTENT,
TRAVEL IMPACTS AND CHAIN RESTRICTIONS ARE LIKELY ACROSS SIERRA
PASSES TODAY. MAIN PUSH OF MOISTURE ACROSS THE TAHOE BASIN WILL
BEGIN BY EARLY AFTERNOON WHERE 6 TO 10 INCHES OF SNOW ACCUMULATION
IS POSSIBLE WEST OF HIGHWAY 89 AND 3 TO 6 INCHES POSSIBLE EAST OF
HWY 89 THROUGH TONIGHT. THE NEXT SURGE OF MOISTURE WILL BE RIGHT ON
THE HEELS OF THE FIRST AND WILL HELP PUSH PRECIPITATION ACROSS MONO
COUNTY BY LATE AFTERNOON INTO EARLY EVENING.

THE NEXT SUCCESSION OF WAVES WILL PROVIDE THE HEAVIEST SNOWFALL
FOR THE SIERRA ON SATURDAY AND SUNDAY WITH A GOOD POTENTIAL FOR
SPILLOVER INTO WESTERN NEVADA BY SATURDAY. STILL ON TRACK TO SEE
SEVERAL FEET OF SNOW IN THE SIERRA WITH UP TO 5 FEET OF
ACCUMULATION ALONG THE CREST. MAIN FORECAST PROBLEM WITH THE
SYSTEM ON SATURDAY LIES WITH THE POTENTIAL VALLEY SNOWFALL
ACCUMULATION ALONG THE SIERRA FRONT. WE DO HAVE A GOOD SET UP FOR
SPILLOVER, BUT THE POINT OF CONTENTION WILL BE WITH SNOWLEVELS.
CURRENT FORECAST HOVERS THEM RIGHT AROUND THE VALLEY FLOOR AHEAD
OF THE COLD FRONT WHERE THEY WILL THEN CRASH BEHIND ITS PASSAGE.
FOOTHILL AREAS SHOULD DO WELL WITH AREAS ABOVE 5000 FEET SEEING UP
TO A FOOT. WILL CONTINUE THE WATCH AS THERE REMAINS SOME
UNCERTAINTY WITH FRONT TIMING AND SNOWLEVELS AT THE VALLEY
FLOORS. OTHERWISE, ACCUMULATIONS OF 2 TO 6 INCHES STILL A
POSSIBILITY AT THE VALLEY FLOOR BY SATURDAY AFTERNOON. NORTHERN
WASHOE COUNTY AND THE SURPRISE VALLEY WERE ALSO ADDED TO THE WATCH
SATURDAY BUT THE WATCH HAS BEEN SHORTENED TO COVER ONLY THE FIRST
ROUND OF SNOWFALL THROUGH SATURDAY NIGHT. THE THIRD IMPULSE OF
MOISTURE WILL PUSH INTO THE SIERRA SUNDAY MORNING AND WILL ALSO
PROVIDE ANOTHER SHOT OF VALLEY SNOW BY SUNDAY AFTERNOON. FUENTES

.LONG TERM...MONDAY THROUGH THURSDAY...
COLD AND GENERALLY QUIET MONDAY THROUGH CHRISTMAS DAY BEFORE THE
NEXT SYSTEM BRINGS ANOTHER CHANCE OF SNOW FOR WED-THU. ON MONDAY,
THIS WEEKENDS SYSTEM WILL BE EXITING TO THE EAST WITH THE ECMWF
FASTEST TO DRY THINGS OUT. MAINTAINED A LOW CHANCE OF SHOWERS
ALTHOUGH MOST OF THEM WILL BE WINDING DOWN BY AFTERNOON. CLEARING
SKIES WILL RESULT IN A VERY COLD NIGHT GOING INTO CHRISTMAS MORNING
WITH SHORTWAVE RIDGE AND VALLEY INVERSIONS TO PRECLUDE ANY
SIGNIFICANT WARMING. MOS GUIDANCE IS TOO HIGH AND IF THERE IS SNOW
COVER, THE FORECAST MAY STILL BE TOO WARM.

MODELS ARE IN GENERAL AGREEMENT WITH NEXT SYSTEM ALTHOUGH THEY ARE
SHOWING MORE OF A SPLIT AS SYSTEM MOVES INLAND FROM THE PACIFIC.
THIS WOULD FAVOR THE SOUTHERN SIERRA AND WESTERN NV FROM HIGHWAY 50
SOUTHWARD. THERE ARE SOME SLIGHT TIMING ISSUES BUT MOST POINT TO WED
NIGHT AS THE WETTEST PERIOD. SO BUMPED POPS UP CONSIDERABLY FOR WED
NIGHT WITH THE UNDERSTANDING THIS WETTEST PERIOD COULD CHANGE AS
MUCH AS 12 HOURS IN EITHER DIRECTION. HAVE MAINTAINED A CHANCE ON
BOTH SIDES, WEDNESDAY AND THURSDAY DAYTIME PERIODS. BASED ON CURRENT
PROJECTED TRACK, UP TO A FOOT OF NEW SNOW IS POSSIBLE IN THE TAHOE
BASIN WITH 1 TO 2 FEET FURTHER SOUTH IN THE SIERRA OF MONO COUNTY.
IF MODELS TREND MORE SPLIT, THEN THESE AMOUNTS WOULD BE LESS.
CONFIDENCE IS INCREASING IN THIS MORE SOUTHERN PATTERN AS MODELS
SHOW EVEN MORE SPLIT BEYOND THIS FORECAST. THUS CONFIDENCE IN EXACT
SNOW AMOUNTS REMAINS BELOW AVERAGE. SYSTEM IS COLD AND SNOW LEVELS
WILL BE AT MOST VALLEY FLOORS. SO SOME ACCUMULATING SNOW IS POSSIBLE
IN WESTERN NV VALLEYS AS WELL. HOHMANN
&&

.AVIATION...
FIRST ROUND OF PRECIPITATION WILL MOVE SLOWLY INTO THE TAHOE BASIN
LATER THIS MORNING INTO THIS AFTERNOON WITH DETERIORATING CONDITIONS
AT KTVL/KTRK. SNOW WILL REDUCE CIGS/VSBY TO NEAR LANDING MINIMUMS
AFTER 21Z AND CONTINUE OVERNIGHT BEFORE FALLING BELOW ALL LANDING
MINIMUMS IN MORE PERSISTENT HEAVY SNOW SATURDAY. FURTHER SOUTH ALONG
THE EASTERN MONO COUNTY SIERRA INCLUDING KMMH, CONDITIONS ARE NOT
EXPECTED TO DETERIORATE UNTIL LATE TONIGHT INTO SATURDAY. SCATTERED
SNOW SHOWERS WILL DOMINATE THE HIGHWAY 395 CORRIDOR TONIGHT BEFORE
BECOMING MORE WIDESPREAD ON SATURDAY WHEN WIDESPREAD SNOW AND
TERRAIN OBSCUREMENT IS LIKELY TO IMPACT AVIATION. SIGNIFICANT SNOW
ACCUMULATION IS LIKELY AT ALL SIERRA RUNWAYS BY LATE SATURDAY.

FOR WESTERN NV, ISOLATED TO SCATTERED SHOWERS WILL DEVELOP THIS
AFTERNOON AND BECOME MORE NUMEROUS TONIGHT. SNOW LEVELS WILL BE NEAR
OR JUST ABOVE VALLEY FLOORS WITH LITTLE ACCUMULATING SNOW THROUGH
TONIGHT. SNOW IS EXPECTED TO BE MORE WIDESPREAD ON SATURDAY WITH
CIGS/VSBY FALLING BLO 020/1SM AT TIMES AFTER 18Z. WHILE THE BEST
CHANCE OF ACCUMULATING SNOWFALL WILL BE ABOVE 5000 FEET, HEAVIER
SNOW BANDS WILL BE CAPABLE OF PUTTING DOWN 1 OR 2 INCHES OF SNOW ON
AREA RUNWAYS BELOW 5000 FEET SATURDAY AFTERNOON INTO EARLY EVENING.

WINDS WILL REMAIN GUSTY WITH SFC WIND GUSTS 25-35KT AT TIMES OUTSIDE
OF SNOW AREAS AND NEAR 85KT ON RIDGES THROUGH SATURDAY. HOHMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY
     EVENING NVZ005.

     LAKE WIND ADVISORY UNTIL 10 AM PST THIS MORNING FOR LAKE
     TAHOE IN NVZ002.

     WINTER STORM WARNING FROM 10 AM THIS MORNING TO 4 AM PST MONDAY
     NVZ002.

     WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY
     EVENING NVZ003.

CA...WINTER STORM WARNING UNTIL 10 PM PST SUNDAY CAZ071.

     WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY
     EVENING CAZ070.

     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 4 AM PST MONDAY
     CAZ073.

     LAKE WIND ADVISORY UNTIL 10 AM PST THIS MORNING FOR LAKE
     TAHOE IN CAZ072.

     WINTER STORM WARNING FROM 10 AM THIS MORNING TO 4 AM PST MONDAY
     CAZ072.

&&

FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/RENO (ALL LOWER CASE)