SPC AC 170600 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0100 AM CDT WED APR 17 2013 VALID 171200Z - 181200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NORTH TX AND OK TO EASTERN KS/SOUTHWEST MO... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS TO THE LOWER MO VALLEY/MIDWEST... ...SYNOPSIS... A PROMINENT/NEUTRAL TO SLIGHT POSITIVE-TILT UPPER TROUGH OVER THE WESTERN CONUS WILL CONTINUE EASTWARD TODAY FROM THE GREAT BASIN/ ROCKIES TO THE HIGH PLAINS...WITH PHASED POLAR/SUBTROPICAL JETS INCREASINGLY INFLUENCING THE CENTRAL/SOUTHERN PLAINS INTO THIS AFTERNOON/TONIGHT. SURFACE CYCLOGENESIS IS EXPECTED ACROSS THE SOUTHERN HIGH PLAINS...WITH AN EASTWARD MIXING DRYLINE ACROSS NORTHWEST/WEST-CENTRAL TX. NORTHEASTWARD FROM THE SURFACE LOW...A SURFACE FRONTAL ZONE WILL ONLY MOVE SLOWLY ACROSS OK/NORTHWEST TX THROUGH THE AFTERNOON...WITH A MUCH MORE AGGRESSIVE NORTHWARD PUSH AS A WARM FRONT ACROSS THE LOWER MO VALLEY/MIDWEST THROUGH TONIGHT IN RESPONSE TO LATE PERIOD SURFACE CYCLOGENESIS. ...SOUTHERN PLAINS TO LOWER MO VALLEY/MIDWEST... WELL-ABOVE TYPICAL GUIDANCE SPREAD CONTINUES INTO THE DAY 1 PERIOD...ACCENTUATED BY A MUCH MORE NORTHWARD AND SEEMINGLY LESS LIKELY SOLUTION OF THE 00Z GFS AS COMPARED TO THE 00Z NAM/12Z ECMWF. AMONG OTHER UNCERTAINTIES...THIS IS A FACTOR FOR ONLY MODEST CONFIDENCE IN SPECIFIC DETAILS LATER TODAY. EVEN SO...POTENTIALLY WIDESPREAD/MULTI-FACETED SEVERE WEATHER IS LIKELY ESPECIALLY INTO THIS AFTERNOON/EVENING. INITIALLY...ELEVATED STRONG/POTENTIALLY SEVERE TSTMS CAPABLE OF HAIL WILL LIKELY BE ONGOING THIS MORNING ACROSS PORTIONS OF THE LOWER/MIDDLE MO VALLEY AND ADJACENT MIDWEST. THIS WILL BE IN ASSOCIATION WITH A STRONG LOW LEVEL JET/WARM ADVECTION REGIME. FARTHER SOUTH...A MORE WIDESPREAD/SURFACE BASED TSTM THREAT WILL LIKELY EVOLVE AS EARLY AS THIS AFTERNOON...BUT ESPECIALLY INTO THIS EVENING/TONIGHT ACROSS THE SOUTHERN PLAINS TO THE LOWER MO VALLEY IN GENERAL VICINITY OF AFOREMENTIONED FRONTAL ZONE. WHILE NOT NECESSARILY LIKELY...THERE MAY BE SOME POSSIBILITY THAT TSTMS DEVELOP RELATIVELY EARLY IN THE AFTERNOON ACROSS PORTIONS OF NORTH TX INTO EASTERN OK AND PERHAPS EVEN THE OZARKS...AND POTENTIALLY BECOME SURFACE BASED WITHIN AN INCREASINGLY MOIST/UNINHIBITED BOUNDARY LAYER. SHOULD THIS OCCUR...DISCRETE SUPERCELLS CAPABLE OF LARGE HAIL/TORNADOES WOULD BE POSSIBLE. SURFACE BASED DEVELOPMENT DOES SEEM MORE PROBABLE NEAR THE TRIPLE POINT VICINITY OF DRYLINE/COMPOSITE FRONT...UNDER THE INFLUENCE OF A BIT STRONGER HEATING/MASS CONVERGENCE. THIS WOULD BE ACROSS PARTS OF NORTH-CENTRAL/NORTHWEST TX INTO SOUTHWEST/SOUTH-CENTRAL OK. ESPECIALLY GIVEN AN INTENSIFYING LOW LEVEL JET TOWARD/AFTER DARK...POTENTIAL WOULD EXIST FOR LARGE HAIL AND PERHAPS A FEW STRONG TORNADOES ACROSS THIS REGION. OTHERWISE...STORMS ARE EXPECTED TO INCREASE AFTER DARK IN VICINITY OF THE SOUTH-SOUTHWEST TO NORTH-NORTHEAST ORIENTED FRONTAL ZONE ACROSS OK INTO THE LOWER MO VALLEY AND EVENTUALLY MIDDLE MS VALLEY MIDWEST. SOME POTENTIAL FOR SURFACE BASED TSTMS/SUPERCELLS AND ASSOCIATED DAMAGING WIND/TORNADO POTENTIAL WILL EXIST MAINLY THROUGH THE EVENING IMMEDIATELY NEAR THE FRONT...BUT THERE WILL LIKELY BE A TENDENCY FOR UPDRAFTS TO BE UNDERCUT BY THE NOCTURNALLY SOUTH/SOUTHEASTWARD-ACCELERATING COLD FRONT. AS SUCH...LARGE HAIL MAY BECOME THE MOST PROBABLE/MORE WIDESPREAD CONCERN ACROSS THE REGION. ...TN VALLEY TO CENTRAL/SOUTHERN APPALACHIANS... AT LEAST ISOLATED TO WIDELY SCATTERED TSTMS ARE EXPECTED TO DIURNALLY INCREASE THIS AFTERNOON ACROSS THE REGION. WHILE FORCING ON THE LARGE SCALE WILL BE MODEST AND MID-LEVEL LAPSE RATES/VERTICAL SHEAR WILL BE WEAK...STEEPENING LOW LEVEL LAPSE RATES DURING THE AFTERNOON MAY CONTRIBUTE TO SOME POTENTIAL FOR EPISODIC BOUTS OF LOCALLY DAMAGING WINDS/HAIL. ..GUYER/MOSIER.. 04/17/2013 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z