SPC MESOSCALE DISCUSSION 2229 FOR ABOVE 7000FT IN THE NRN/CENTRAL
SIERRA NEVADA MTNS OF CA
CONCERNING...HEAVY SNOW...

VALID 121613Z - 122100Z

SNOWFALL RATES OF 2 INCHES/HOUR ARE EXPECTED IN THE NRN AND CENTRAL
SIERRA NEVADA MTNS...WITH SNOW BEGINNING AROUND 12/19Z AND
INTENSIFYING THIS AFTERNOON AS N-S PRECIPITATION BAND TRANSLATES
SLOWLY EWD INTO THE MOUNTAINS. 

AT 12/16Z...FULL AMPLITUDE UPPER TROUGH ALONG 128W IS ASSOCIATED
WITH A STRONG UPPER-LEVEL JET ALONG ITS SRN PERIPHERY AND APPARENT
UPPER DIVERGENCE AND EXPANDING/COOLING CLOUD TOPS NEAR THE CENTRAL
CA COASTLINE PER WV AND IR IMAGERY. THE FRONTAL PRECIPITATION BAND
MOVING EWD THROUGH THE SACRAMENTO VALLEY IS ASSOCIATED WITH HOURLY
RAINFALL RATES OF 0.15-0.20 INCHES...AND RATES AS HIGH AS 0.59IN IN
THE PAST HOUR AT SFO. INTENSIFYING LARGE-SCALE UVV FIELD WILL BE
FURTHER ENHANCED BY FAVORABLE OROGRAPHIC LIFT AS PRECIPITATION BAND
INTERCEPTS THE SIERRA NEVADA MTNS...LIKELY PRODUCING SNOWFALL RATES
OF 2 INCHES/HOUR ONCE FRONTAL BAND REACHES THE DISCUSSION AREA THIS
AFTERNOON. ISOLATED LIGHTNING STRIKES ARE ALSO POSSIBLE WITH
EMBEDDED CONVECTIVE SNOWS. 

SNOW LEVELS ARE EXPECTED TO REMAIN HIGH WITH THIS SYSTEM. BASED ON
MODEL FORECAST SOUNDINGS...SNOW LEVELS ARE EXPECTED TO BE NEAR
8000FT INITIALLY...AND DROP TO AROUND 7000 FT DURING THE LATE
AFTERNOON HOURS.  

..BANACOS.. 11/12/01