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Mesoscale Discussion 2066

December 6, 2013

Mesoscale Discussion 2066

mcd2066

MESOSCALE DISCUSSION 2066
NWS STORM PREDICTION CENTER NORMAN OK
1131 AM CST FRI DEC 06 2013

AREAS AFFECTED…NWRN MS…AR…SRN MO…EXTREME NWRN MS…WRN TN…WRN AND CNTRL KY…SRN IL…SRN IND…AND SWRN THROUGH CNTRL OH

CONCERNING…WINTER MIXED PRECIPITATION

VALID 061731Z – 062130Z

SUMMARY…A WINTRY MIX OF PRECIPITATION WILL CONTINUE TO AFFECT A LARGE SWATH OF THE ERN U.S. FROM THE LOWER MS VALLEY INTO PARTS OF THE TN AND OH VALLEYS. MOSTLY SNOW IS EXPECTED FROM NRN AR…SRN MO…SRN IL…SRN IND…EXTREME WRN KY THROUGH SWRN AND CNTRL OH WITH RATES FROM 0.5 TO LOCALLY UP TO 1 INCH AN HOUR. A RELATIVELY NARROW ZONE OF FREEZING RAIN…POSSIBLY MIXED WITH SLEET SHOULD PERSIST NEXT SEVERAL HOURS FROM SERN AR…WRN TN…EXTREME NWRN MS…CNTRL KY AND NCNTRL KY INTO EXTREME SRN OH. FREEZING RAIN RATES SHOULD RANGE FROM A FEW HUNDREDS OF AN INCH PER HOUR TO OCCASIONALLY WELL IN EXCESS OF 0.1 INCH PER HOUR.

DISCUSSION…AS OF MID-DAY AN EXPANSIVE AREA OF MIXED PRECIPITATION EXTENDS FROM NERN TX THROUGH THE LOWER-MID MS VALLEY INTO THE TN AND OH VALLEYS. THIS WINTRY MIX WAS DEVELOPING WITHIN ZONE OF ISENTROPIC ASCENT ALONG A SW-NE ORIENTED BAROCLINIC ZONE IN WAKE OF A SFC COLD FRONT THAT EXTENDS FROM SERN LA NEWD THROUGH THE SRN APPALACHIANS AND INTO CNTRL/ERN VA. A LARGE AREA OF ARCTIC HIGH PRESSURE IS BUILDING SEWD…AND THE COLD AIR HAS BECOME DEEP ENOUGH TO SUPPORT ALL SNOW NORTH OF A LINE FROM CNTRL AR NEWD THROUGH EXTREME WRN KY AND SRN OH WITH A RELATIVELY NARROW ZONE OF FREEZING RAIN AND SLEET SOUTH OF THIS LINE. THE NEAR SFC SUBFREEZING AIR IS MORE SHALLOW ACROSS THE LOWER MS VALLEY REGION…SUPPORTING A BROADER SWATH OF FREEZING RAIN COMPARED TO FARTHER NE ACROSS THE OH VALLEY.

FRONTOGENETIC FORCING FOR ASCENT AND PRECIPITATION RATES ARE CURRENTLY MAXIMIZED FROM AR THROUGH WRN TN…SRN MO…WRN KY AND SRN IL WHERE EXIT REGION OF UPPER JET EJECTING NEWD FROM THE SRN PLAINS IS COUPLED WITH ENTRANCE REGION OF A POLAR JET LOCATED FROM THE OH VALLEY INTO THE GREAT LAKES. THIS ZONE OF FORCING FOR ASCENT ALONG WITH HIGHER PRECIPITATION RATES WILL DEVELOP NEWD THROUGH THE TN AND OH VALLEYS THIS AFTERNOON. SOME CONVECTIVE ENHANCEMENT WILL REMAIN LIKELY IN FREEZING RAIN CORRIDOR FROM AR THROUGH WRN TN AND WRN KY WHERE THE WARM LAYER ALOFT IS MORE PRONOUNCED…RESULTING IN STEEPER MID LEVEL-LAPSE RATES AND A CONDITIONALLY UNSTABLE LAYER BETWEEN 700-400 MB.

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