Wednesday, January 13, 2010

MESO: Mesoscale Discussion 0005

ACUS11 KWNS 130817
SWOMCD
SPC MCD 130817
CAZ000-NVZ000-131215-

MESOSCALE DISCUSSION 0005
NWS STORM PREDICTION CENTER NORMAN OK
0217 AM CST WED JAN 13 2010

AREAS AFFECTED...SIERRA NEVADA RANGE

CONCERNING...HEAVY SNOW

VALID 130817Z - 131215Z

HEAVY SNOW WITH RATES OF 2 INCHES/HOUR WILL CONTINUE THROUGH
12Z...MAINLY ABOVE 5000 FEET MSL. SNOW RATES SHOULD THEN BEGIN TO
DIMINISH BETWEEN 12-15Z.

EARLY MORNING SATELLITE AND RADAR IMAGERY SHOW THE NEXT SIGNIFICANT
SHORT WAVE TROUGH CURRENTLY APPROACHING THE NRN/CNTRL CA COAST. AN
ASSOCIATED BAND OF CONVECTIVE PRECIPITATION WAS OBSERVED
PROGRESSIVELY OVERSPREADING THE COASTAL RANGES AND SACRAMENTO VALLEY
AS OF 08Z. ISOLATED LIGHTNING ACTIVITY HAS BEEN ASSOCIATED WITH
THIS ACTIVITY...LIKELY SIGNALING THE ARRIVAL OF STEEPER MIDLEVEL
LAPSE RATES.

CURRENT MESONET OBSERVATIONS INDICATE THAT SURFACE FREEZING
TEMPERATURES ARE PRESENT GENERALLY ABOVE 8000 FEET.
HOWEVER...DYNAMIC COOLING ASSOCIATED WITH THE SHORT WAVE TROUGH
/I.E. 12-HR HEIGHT FALLS OF 60-90 M/ COUPLED WITH EVAPORATIONAL
COOLING SHOULD SUPPORT SNOW LEVELS LOWERING TO 5000-5500 FEET. THE
INFLUX OF AN INCREASINGLY MOIST AIR MASS OFF THE PACIFIC /PW VALUES
APPROACHING AN INCH/ COUPLED WITH THE DEEP-LAYER FORCING FOR ASCENT
/BOTH DYNAMICAL AND OROGRAPHIC/ AND THE STEEPENING LAPSE RATES WILL
ALL PROMOTE HEAVY SNOW WITH HOURLY RATES OF 2 INCHES LIKELY.

SNOW RATES SHOULD BEGIN TO DIMINISH BETWEEN 12-15Z AS THE STRONGER
LARGE-SCALE FORCING FOR ASCENT BEGINS TO SHIFT E OF THE REGION.

..MEAD.. 01/13/2010

...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...MFR...STO...

LAT...LON 36341860 37722032 39662137 40672206 41382165 41362116
39352019 37851898 36521802 36061817 36341860

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