MESOSCALE DISCUSSION 0726 NWS STORM PREDICTION CENTER NORMAN OK 1226 PM CDT MON MAY 20 2013 AREAS AFFECTED...MUCH OF OK INTO NWRN TX AND SERN KS CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY VALID 201726Z - 201930Z PROBABILITY OF WATCH ISSUANCE...95 PERCENT SUMMARY...SEVERE STORMS ARE LIKELY TO FORM THIS AFTERNOON WITH A FEW SIGNIFICANT TORNADOES...EXTREMELY LARGE HAIL...AND DAMAGING WINDS ALL POSSIBLE. TWO WATCHES WILL BE NEEDED SOON FROM KS INTO N TX. DISCUSSION...SURFACE MAP SHOWS A QUASI-STATIONARY BOUNDARY FROM SERN KS INTO NRN OK AND BENDING SWWD W OF THE I-44 CORRIDOR. FARTHER SW...A WEAK AREA OF LOW PRESSURE WAS NOTED OVER NWRN TX...ON THE NOSE OF A LOW LEVEL LAPSE RATE PLUME WITH DRYLINE EXTENDING SW ACROSS W TX. VISIBLE IMAGERY SHOWS DEEPENING CU ALONG THE BOUNDARY FROM NRN OK INTO SERN KS WHERE A DEEP MOIST LAYER EXISTS. GIVEN A GRADUAL INCREASE IN THETA-E AND BREAKS IN THE CLOUDS...THIS AREA COULD BE WHERE INITIAL DEVELOPMENT OCCURS. LONG HODOGRAPHS AND STEEP MIDLEVEL LAPSE RATES WILL FAVOR VERY LARGE HAIL...AND LOW LEVEL VEERING WIND PROFILES WILL BE SUFFICIENT FOR TORNADOES GIVEN AFOREMENTIONED THERMODYNAMIC FACTORS. TO THE S...AN EXTREMELY VOLATILE AIR MASS EXISTS WITH AN INCREASING CU FIELD FROM NWRN TX INTO SWRN OK WHERE STRONG HEATING PERSISTS. WIND FIELDS ALOFT ARE MORE THAN FAVORABLE FOR SUPERCELLS...WITH VERY LARGE HAIL LIKELY. ALTHOUGH SHEAR IN THE LOWEST 1-2 KM IS NOT PARTICULARLY STRONG...VERY LARGE VERTICAL ACCELERATIONS...AS WELL AS HODOGRAPH AUGMENTATION NEAR THE SFC FRONT WILL AID IN TORNADO POTENTIAL. HP SUPERCELLS ARE EXPECTED WITH STRONG MESOCYCLONES AND POSSIBLE RAIN-WRAPPED TORNADOES. ACTIVITY MAY EVENTUALLY MERGE INTO ONE OR MORE BOWS...AND RAPIDLY EXPAND NEWD ACROSS ERN OK LATER THIS EVENING PER MULTIPLE CONVECTION ALLOWING MODELS. ..JEWELL/KERR.. 05/20/2013