MESOSCALE DISCUSSION 2311
   NWS STORM PREDICTION CENTER NORMAN OK
   1241 AM CST WED DEC 27 2006
   
   AREAS AFFECTED...SIERRA MOUNTAINS OF CA
   
   CONCERNING...HEAVY SNOW 
   
   VALID 270641Z - 271115Z
   
   SNOW LEVELS WILL STEADILY LOWER OVERNIGHT IN THE SIERRA
   MOUNTAINS...WITH SNOW RATES IN EXCESS OF 2-3 IN/HR POSSIBLE THROUGH
   THE OVERNIGHT...ESPECIALLY ACROSS THE NORTHERN/CENTRAL SIERRAS ABOVE
   6000 FT.
   
   WATER VAPOR/INFRARED SATELLITE IMAGERY FEATURES COLD UPPER LOW
   MOVING EASTWARD ALONG THE NORTHERN CA/ORE COAST...WITH COLD/OCCLUDED
   FRONT MOVING ONSHORE THE PAST FEW HOURS. WITH THE ARRIVAL OF COLDER
   AIR ALOFT...SNOW LEVELS WILL STEADILY LOWER OVERNIGHT ACROSS THE
   SIERRAS WITH HEAVY SNOW BECOMING MORE COMMON. MESONET RAWS/SNOTEL
   OBSERVATIONS SUGGEST SNOW LEVELS ARE ALREADY AS LOW AS 4500-5000 FT
   IN THE WEST SLOPES OF THE NORTHERN SIERRAS...WITH HIGHER SNOW LEVELS
   IN THE CENTRAL SIERRAS AND LAKE TAHOE VICINITY...WHERE SNOW LEVELS
   ARE AROUND 6500-7000 FT PER MESONET OBS AND RECENT ACARS SOUNDING
   DATA. RUC SOUNDINGS SUGGEST A LOWERING OF SNOW LEVELS BY 1000-2000
   FT ACROSS THE NORTHERN/CENTRAL SIERRAS BY AROUND 15Z WEDNESDAY
   MORNING.
   
   ASIDE FROM PRONOUNCED OROGRAPHIC LIFT VIA STRONG SOUTHWESTERLY
   LOW/MID LEVEL FLOW INTO THE WESTERN SLOPES OF THE
   SIERRAS...STEEPENING MID LEVEL LAPSE RATES WILL RESULT IN AN
   INCREASED CONVECTIVE COMPONENT OF THE SNOWFALL...FURTHER ENHANCING
   SNOW RATES OVERNIGHT. ISOLATED CLOUD-GROUND LIGHTNING STRIKES HAVE
   ALREADY BEEN OBSERVED ALONG THE CA/ORE COAST THIS EVENING.
   
   ..GUYER.. 12/27/2006
   
   
   ...NOTICE...
   SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
   SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
   TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
   FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.
   
   ATTN...WFO...REV...HNX...STO...
   
   40212153 40152092 39112005 38351937 37921931 37771966
   38022000 38602039