Sunday, February 14, 2010

Heavy Snow - Mesoscale Discussion by SPC




   MESOSCALE DISCUSSION 0129
NWS STORM PREDICTION CENTER NORMAN OK
0942 PM CST SUN FEB 14 2010

AREAS AFFECTED...FOR PARTS OF NRN AL...SRN MIDDLE AND SERN TN...AND
FAR NWRN GA

CONCERNING...HEAVY SNOW

VALID 150342Z - 150845Z

SNOWFALL RATES APPROACHING AND/OR LOCALLY REACHING 1 INCH/HOUR
SHOULD DEVELOP OVER NRN AL/SRN MIDDLE TN BY 06Z...AND THEN REACH
SERN TN/NWRN GA BETWEEN 08-09Z. SOME SLEET MAY MIX WITH RAIN OR
SNOW...PRIOR TO THE COLD FRONT PASSAGE...AS ELEVATED CONVECTION
SPREADS ENEWD FROM MS. GIVEN THE RELATIVELY NARROW BAND OF
PRECIPITATION ALONG AND IN THE WAKE OF THE COLD FRONT MOVING E
THROUGH THE TN VALLEY/CENTRAL GULF COAST STATES OVERNIGHT...ANY ONE
LOCATION ACROSS THE DISCUSSION AREA COULD HAVE A 1-3 HOUR PERIOD OF
THE FORECAST SNOWFALL RATES.

AT 0330Z...REGIONAL RADAR IMAGERY SHOWED A NARROW BAND OF ELEVATED
CONVECTION IN THE VICINITY OF A COLD FRONT...WITH THESE SHOWERS
EXTENDING SWWD FROM ERN MS TO SRN LA. THIS BAND WILL CONTINUE TO
SPREAD EWD WITH THE FRONT...WHILE ALSO DEVELOPING NEWD INTO NRN AL
LATE THIS EVENING. EARLY EVENING SURFACE OBSERVATIONS ACROSS PARTS
OF ERN AR/WRN TN AND MS INDICATED MOST LOCATIONS HAD LOW
VISIBILITIES /GREATER PRECIPITATION RATES/ FOR 1-2 HOURS EITHER
ASSOCIATED WITH THE SHOWERS OR POST-FRONTAL STRATIFORM
PRECIPITATION. INCREASING FORCING FOR ASCENT IS EXPECTED DOWNSTREAM
OF A DEEPENING...COMPACT CLOSED LOW APPROACHING THE LOWER OH/TN
VALLEYS TONIGHT/EARLY MONDAY MORNING. THIS ASCENT COMBINED WITH LOW
LEVEL MOISTURE/WARM AIR ADVECTION ALONG A STRENGTHENING SWLY LLJ
INTO THE SRN APPALACHIANS SUGGESTS THAT 1 INCH/HOUR RATES WILL BE
POSSIBLE. THE INCREASING UPWARD VERTICAL ASCENT WITH THE
APPROACHING LOW AND STRONG LOW LEVEL COLD ADVECTION IN THE WAKE OF
THE COLD FRONT SHOULD SUFFICIENTLY COOL THE COLUMN...CHANGING
PRECIPITATION TO ALL SNOW.


..PETERS.. 02/15/2010

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