[MCD] SWOMCD

Sun Dec 10 03:26:33 UTC 2006

ACUS11 KWNS 100327
SWOMCD
SPC MCD 100327 
CAZ000-100930-

MESOSCALE DISCUSSION 2274
NWS STORM PREDICTION CENTER NORMAN OK
0927 PM CST SAT DEC 09 2006

AREAS AFFECTED...WRN SLOPES OF CENTRAL AND SRN SIERRA NEVADA MTNS
ABOVE 6000 FT

CONCERNING...HEAVY SNOW 

VALID 100327Z - 100930Z

HEAVY SNOW WITH ACCUMULATION RATES UP TO 3 IN/HR FOR A SEVERAL HR
PERIOD WILL OVERSPREAD THE CENTRAL/SRN SIERRA NEVADA MTNS OF CA
BEGINNING BETWEEN 04-06Z. SNOW LEVELS WILL INITIALLY START AROUND
6500 FT BEFORE FALLING TO AROUND 5000 FT WITH A COLD FRONTAL
PASSAGE.

MOD/HVY RAINFALL RATES HAVE BEEN OBSERVED AT SEVERAL SITES IN THE
SFO/MRY BAY AREAS AND CENTRAL COAST REGION SINCE 01Z...ASSOCIATED
WITH A STRONG UPPER TROUGH MOVING INTO THE CA COAST. THIS
PRECIPITATION WAS BEING SUPPORTED BY STRONG VERTICAL MOTION
ASSOCIATED WITH DIFFLUENT UPPER LEVEL FLOW AND A STRONG VORTICITY
CENTER MOVING INTO THE CENTRAL CA COAST. ADDITIONAL STRONG MESOSCALE
VERTICAL MOTION WAS OCCURRING ALONG/AHEAD OF A SFC-850 MB FRONTAL
ZONE WHICH RECENTLY PASSED THROUGH KSFO. THE 00Z OAK SOUNDING AND
RECENT BLU SFC OBS INDICATED SNOWFALL LEVELS SHOULD START OUT
BETWEEN 6000-6500 FT. HIGH PWAT VALUES AHEAD OF THE FRONT ALONG WITH
MDT /30 KT/ SSWLY LOW LEVEL FLOW WILL SUPPORT ENHANCED SNOWFALL
RATES ON THE WRN UPSLOPE REGION OF THE CENTRAL/SRN SIERRA NEVADA.
GIVEN THE RECENT PRECIP RATES/TRENDS AROUND 0.25-0.30 IN/HR AT
SNS...MRY AND PRB...2-3 IN/HR SNOWFALL RATES WILL BE POSSIBLE FOR A
SEVERAL HR PERIOD PRIOR TO FRONTAL PASSAGE OVER THE WRN SLOPES OF
THE CENTRAL/SRN SIERRA. CURRENT EXTRAPOLATION OF THE FRONTAL
MOVEMENT /EWD AROUND 30 KTS/ TAKE THE FRONT THROUGH THE SIERRA
BETWEEN 06-09Z. AFTER THE FRONTAL PASSAGE...SNOW LEVELS WILL FALL TO
AROUND 5000 FT...AND FORCING WILL BE PRIMARILY DRIVEN BY MDT UPSLOPE
FLOW...WITH RATES DECREASING TO LESS THAN 2 INCH/HR BY 09Z.

..CROSBIE.. 12/10/2006

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

...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...VEF...REV...HNX...STO...

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