Heavy Snow in California, December 29 to 30, 2001

WESTERN NEVADA AND EASTERN CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
305 AM PST SAT DEC 29 2001

...CORRECTED VALID TIME OF WARNING IN ZONE 73 AT BOTTOM...

DEEP MOISTURE AND A NEARLY ISOTHERMAL LAYER BETWEEN 800 AND 600 MB
PRODUCED WET SNOWFLAKES OVER RENO AROUND MIDNIGHT EVEN THOUGH
MOUNTAIN TOP TEMPS WOULD HAVE GENERALLY BEEN TOO WARM TO SUPPORT
SNOW AT THE LOWER ELEVATIONS. THIS LARGE AREA OF PRECIP HAS MOVED
NORTHEAST WHILE ANOTHER LARGE AREA OF MOISTURE IS MOVING ACROSS THE
TAHOE AND MONO ZONES AND SPILLING INTO THE CARSON VALLEY AND
SOUTHERN LYON COUNTY. SNOW ACCUMULATIONS IN THE SIERRA AROUND TAHOE
HAVE NOT BEEN TOO IMPRESSIVE BUT A FEW HOURS OF HEAVY SNOW ARE
LIKELY AT THE HIGHER ELEVATIONS THROUGH MID MORNING. FOR
COORDINATION AND EXPECTED SHORTER TERM SNOW INTENSITIES...THE
WARNING WILL BE MAINTAINED FOR TAHOE BUT MAY END LATER THIS MORNING.
THE MOISTURE ASSOCIATED WITH THE NEXT SHORTWAVE OFF THE SOUTHERN CA
COAST WILL BE MOST WIDESPREAD AND LAST THE LONGEST OVER MONO
COUNTY...POSSIBLY THROUGH THIS EVENING. FARTHER NORTH...THE HEAVIER
PRECIP IS LIKELY OVER IN LASSEN COUNTY AND THE WARNING WILL BE
DOWNGRADED TO A SNOW ADVISORY ABOVE 6000 FEET WITH ANOTHER PROBABLE
EARLY EXPIRATION DURING THE MORNING. THE DECREASING PRECIP TRENDS OF
THE AVN MODEL FROM WEST TO EAST IS PREFERRED FOR TODAY DUE TO THE
FAST MOVEMENT OF THE SHORTWAVES.

STRONG PACIFIC JET WILL CONTINUE TO SEND FAST MOVING SHORTWAVES
LADEN WITH MOISTURE ACROSS OUR REGION THROUGH THE UPCOMING WEEK. DUE
TO THE STRENGTH OF THIS JET...ATTEMPTS BY THE ETA AND AVN MODELS TO
SLOW DOWN THE PACE OF THE NEXT SYSTEM AND FORCE SHORTWAVE RIDGING IS
LIKELY OVERDONE...SO THE FASTER PACE OF THE ECMWF/UKMET/NOGAPS/
CANADIAN IS PREFERRED. SOME LOW CHANCE POPS WILL BE INTRODUCED IN
LASSEN AND TAHOE FOR LATE SUNDAY AFTERNOON WITH LIKELY POPS IN ALL
ZONES EXCEPT FOR 50 PERCENT CHANCE IN ZONES 1/4 FOR SUNDAY NIGHT.
LIKELY POPS WILL BE CARRIED OVER INTO MONDAY WITH THE PRECIP
TAPERING OFF FROM WEST TO EAST. ANOTHER WINTER STORM WATCH MAY BE
NEEDED IN THE MOUNTAIN AREAS FOR THIS SYSTEM BUT TO AVOID CONFUSION
WITH THE CURRENT WARNINGS AND ADVISORIES...A WATCH WILL NOT BE
POSTED WITH THIS PACKAGE. WIDESPREAD CLOUD COVER AND PERIODS OF
PRECIP WILL REDUCE DIURNAL RANGES THROUGH MONDAY.

EXTENDED DISCUSSION...L/WS CONTINUED TO BE ANCHORED OVER THE EAST
COAST AND EASTERN PACIFIC. AS A RESULT WEST COAST UNDER THE
INFLUENCE OF S/W EJECTING EAST AND MOVING ONSHORE. THIS L/W PATTERN
IS ALSO KEEPING MOST OF THE COLD AIR OFFSHORE. THE S/WS THAT MOVE
INLAND DO HAVE SOME AMPLITUDE AND ALSO GOOD DYNAMICS AND HAVE
TYPICALLY PRODUCED MODERATE AMOUNTS OF PRECIP. TIMING OF THE S/WS
HAS BEEN A BIT OF A PROBLEM BUT NOT MORE THAN 12 HOURS OFF. THE NEW
MRF CONTINUES THIS TREND AND CURRENTLY HAS WX SYSTEMS MOVING LATE
WED AND THU. WILL GO WITH THIS TIMING ON THIS SET OF FCSTS. MJD/JF

.REV...SNOW ADVISORY ZONE 71 ABOVE 6000 FEET TODAY.
       WINTER STORM WARNING ZONE 72/2 ABOVE 7000 FEET TODAY.
       WINTER STORM WARNING ZONE 73 ABOVE 8000 FEET TODAY.