SPC AC 281633 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK ISSUED BY AFWA OFFUTT AIR FORCE BASE BELLEVUE NE 1133 AM CDT WED MAR 28 2007 VALID 281630Z - 291200Z ...THERE IS A MDT RISK OF SVR TSTMS FROM SW NEB TO NW TX... ...THERE IS A SLGT RISK OF SVR TSTMS FROM SRN SD TO SW TX... ...THERE IS A SLGT RISK OF SVR TSTMS FROM SRN VA TO NC/NRN SC... ...WIDESPREAD SEVERE THUNDERSTORMS INCLUDING DAMAGING WINDS...VERY LARGE HAIL AND POSSIBLY STRONG TORNADOES WILL DEVELOP OVER THE WESTERN HALF OF THE CENTRAL AND SOUTHERN PLAINS LATER TODAY AND TONIGHT... ...CENTRAL/SRN PLAINS... STRONG UPPER LOW WILL SHIFT INTO THE CENTRAL ROCKIES AND THEN BECOME STATIONARY OVERNIGHT. AS THIS OCCURS...SURFACE DRY LINE WILL BECOME WELL ESTABLISHED OVER THE HIGH PLAINS AND LIKELY EXTEND FROM A LOW OVER FAR NERN CO SWD JUST EAST OF THE KS/CO BORDER INTO THE CENTRAL TX PANHANDLE AND FAR SWRN TX BY EARLY THIS EVENING. WIDESPREAD THUNDERSTORM DEVELOPMENT JUST EAST OF THE DRY LINE IS EXPECTED AFTER 20Z AS THE CAP WEAKENS...WITH SUPERCELLS AND SEVERE WEATHER LIKELY. MLCAPE WILL RANGE FROM 1000-2000 J/KG ACROSS THE AREA...WHILE LOW LEVEL AND DEEP LAYER SHEAR WILL BE STRONG ALONG THE DRY LINE DESPITE STRONGEST MID LEVEL JET EXTENDING NNEWD BEHIND THE DRY LINE OVER ERN CO. NORTHEAST OF THE LOW INTO NEBRASKA AND NORTHERN KANSAS...LOW CLOUDS ARE LIMITING SURFACE HEATING SO THAT STRONG CAPPING MAY PREVENT THUNDERSTORMS FROM FORMING THERE UNTIL LATER THIS EVENING. HOW LONG ACTIVITY REMAINS IN THE FORM OF DISCRETE SUPERCELLS REMAINS HARD TO SAY...AS ACTIVITY WILL LIKELY EVOLVE INTO LINEAR STRUCTURES AS IT MOVES ENEWD THROUGH THE EVENING. HOWEVER...VERY STEEP LAPSE RATES AND STRONG SHEAR WILL ENHANCE THE POTENTIAL FOR SIGNIFICANT/DAMAGING HAIL AND STRONG TORNADOES INTO THE EARLY-MID EVENING WITH ANY DISCRETE STORMS. WIND DAMAGE THREAT SHOULD ALSO INCREASE AS LINEAR ORGANIZATION BECOMES MORE PREDOMINANT THIS EVENING...BUT THIS WILL BE TEMPERED BY SLOW FORWARD MOTION OF THE CONVECTION DUE TO LINE PARALLEL FLOW. LACK OF EWD PROGRESSION WITH OVERALL SYSTEM AND NARROW INSTABILITY AXIS SUGGESTS STORMS SHOULD WEAKEN AS THEY MOVE ACROSS CENTRAL SD/NE/KS/OK LATER THIS EVENING. NAM AND GFS ARE ALSO INDICATING SECONDARY LOBE OF ENERGY ROTATING AROUND LARGE UPPER LOW AND INTO THE NERN NM/SERN CO LATE TONIGHT. THIS SHOULD SUPPORT DEVELOPMENT OF ANOTHER MCS...POSSIBLY SEVERE...OVER WRN TX INTO WRN OK/SWRN KS OVERNIGHT. ...WY/SD/NE... RUC FORECAST SOUNDINGS INDICATE AROUND 500-1000 J/KG OF SBCAPE ALONG WITH 150-250 J/KG EFFECTIVE HELICITY AND 60-80 KNOTS OF DEEP LAYER SHEAR EARLY THIS AFTERNOON. CURRENT INDICATIONS ARE THAT SURFACE TEMPERATURES ARE SEVERAL DEGREES WARMER THAN IN THE RUC WHICH WILL ADD TO THE INSTABILITY. STRONG VERTICAL MOTION WITH THE APPROACH OF THE TROUGH SHOULD CAUSE SURFACE BASED THUNDERSTORM INITIATION AROUND 18-19Z POSSIBLY LEADING TO LOW TOPPED SUPERCELLS WITH LARGE HAIL AND A FEW TORNADOES POSSIBLE. ...CENTRAL APPALACHIANS INTO NC... COLD FRONT NOW EXTENDING FROM SERN VA INTO CENTRAL KY WILL SAG SSWWD AS A BACK-DOOR FRONT INTO NC AND EXTEND ROUGHLY E-W FROM ERN NC INTO SWRN VA BY LATE THIS AFTERNOON. THIS WILL OCCUR UNDER EJECTING SHORTWAVE TROUGH AND ASSOCIATED 35-45 KT MID LEVEL JET NOW OVER KY/TN WHICH WILL MOVE EWD ACROSS THIS REGION TODAY. NAM-KF SOUNDINGS NEAR AND JUST NORTH OF THE FRONT INDICATE EFFECTIVE BULK SHEAR WILL SUPPORT SUPERCELLS AND ORGANIZED CLUSTERS AS AIR MASS BECOMES MARGINALLY TO MODERATELY UNSTABLE. LARGE HAIL AND DAMAGING DOWNBURST WINDS ARE THE MAIN SEVERE THREATS...BUT A TORNADO OR TWO IS POSSIBLE. ..AFWA.. 03/28/2007