MESOSCALE DISCUSSION 0040

NWS STORM PREDICTION CENTER NORMAN OK

0955 AM CST THU JAN 21 2010

AREAS AFFECTED...NERN AR...WRN TN...NRN MS...NWRN AL

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY VALID 211555Z - 211700Z

WELL DEFINED UPPER VORT IS JUXTAPOSED WITH SFC LOW OVER NCNTRL AR...JUST NORTH OF LIT. THIS FEATURE IS SHIFTING EAST AT ROUGHLY 25KT WITH A WELL PRONOUNCED DRY SLOT SPREADING AHEAD OF WIND SHIFT ACROSS ERN AR/WRN MS INTO WRN TN. ALTHOUGH SFC TEMPERATURES ARE NOT THAT WARM...SFC-3KM LAPSE RATES HAVE STEEPENED SIGNIFICANTLY...AOA 7 C/KM...JUST AHEAD OF SFC LOW WHICH APPEARS TO BE ENHANCING LOW-TOPPED CONVECTION ALONG ADVANCING BOUNDARY. SHEAR PROFILES STRONGLY SUPPORT ROTATING UPDRAFTS AND IT IS BECOMING INCREASINGLY LIKELY THAT SUPERCELLS WILL EVOLVE WITH TIME. HAIL SHOULD CERTAINLY ACCOMPANY THE STRONGER STORMS AND GIVEN THE MOIST BOUNDARY LAYER...AND EXPECTED LOW LCL/CLOUD BASES...A FEW TORNADOES MAY ALSO DEVELOP WITH STRONGER STORMS. TORNADO WATCH WILL LIKELY BE REQUIRED OVER THIS REGION BY 18Z. ..DARROW.. 01/21/2010

...