231242

DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0742 AM CDT FRI MAY 23 2008

VALID 231300Z - 241200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT OVER PARTS OF SOUTHWEST NEB AND WESTERN KS...

...THERE IS A SLGT RISK OF SVR TSTMS FROM WESTERN OK INTO SOUTHWEST SD...

...A REGIONAL OUTBREAK OF SEVERE STORMS IS ANTICIPATED AGAIN THIS AFTERNOON AND EVENING OVER PARTS OF NEB/KS...

A LARGE UPPER LOW WILL REMAIN OVER THE WESTERN STATES THROUGH THE DAY1 FORECAST PERIOD. ONE STRONG SHORTWAVE TROUGH HAS ROTATED ACROSS THE PLAINS AND IS NOW LIFTING INTO THE DAKOTAS. ANOTHER STRONG TROUGH IS ROUNDING THE BASE OF THE TROUGH OVER NORTHERN MEXICO AND WILL EMERGE INTO THE CENTRAL/SOUTHERN HIGH PLAINS THIS EVENING. THIS WILL YIELD ANOTHER VERY FAVORABLE SCENARIO FOR SIGNIFICANT SEVERE THUNDERSTORMS OVER PARTS OF NEB/KS/CO WITH THE RISK OF STRONG TORNADOES...VERY LARGE HAIL...AND DAMAGING WINDS.

...KS/NEB THIS MORNING... SCATTERED THUNDERSTORMS HAVE BEEN OCCURRING OVERNIGHT OVER MUCH OF KS AND SOUTHERN NEB. THESE STORMS ARE IN REGION OF STRONG LOW LEVEL WARM ADVECTION ASSOCIATED WITH 50-60 KNOT WINDS AT 850MB. ACTIVITY WILL REMAIN CAPABLE OF HAIL AND LOCALLY DAMAGING WINDS THROUGH MID MORNING. AFTER THAT...WEAKENING LOW LEVEL WINDS AND GRADUAL COUPLING OF BOUNDARY LAYER WILL TEND TO DIMINISH ACTIVITY BY MID/LATE MORNING.

...WY/CO/NEB PANHANDLE... EASTERN UPSLOPE FLOW CONTINUES TO TRANSPORT MOISTURE WESTWARD INTO THE HIGH PLAINS OF NORTHEAST CO/SOUTHEAST WY AND THE NEB PANHANDLE. MODELS ARE IN GENERAL AGREEMENT THAT DEWPOINTS WILL REMAIN IN THE 40S TO LOWER 50S IN THIS AREA. HOWEVER...COLD TEMPERATURES ALOFT AND STEEP LAPSE RATES WILL HELP YIELD SUFFICIENT INSTABILITY FOR INTENSE STORMS DESPITE LIMITED MOISTURE. BACKED SURFACE WINDS AND SIGNIFICANT VEERING/INCREASING WINDS WITH HEIGHT WILL RESULT IN EFFECTIVE HELICITY VALUES OF 150-250 J/KG AND EFFECTIVE SHEAR VALUES OF 40-50 KNOTS. THIS WILL PROMOTE SUPERCELLS CAPABLE OF LARGE HAIL AND A FEW TORNADOES BY MID AFTERNOON.

...KS/NEB... MORNING CONVECTION OVER MUCH OF KS AND SOUTHERN NEB WILL LIKELY LEAVE RESIDUAL OUTFLOW BOUNDARIES OVER PRIMARY THREAT AREA...BUT MAY ALSO LEAVE CONSIDERABLE CLOUD COVER FOR MUCH OF THE DAY. MUCH OF MODEL GUIDANCE SUGGESTS CLOUDS WILL BE MAINTAINED THROUGH AT LEAST MID AFTERNOON ALONG AND NORTH OF I-70. NEVERTHELESS... SOUTHEASTERLY LOW LEVEL WINDS WILL DRAW RICH GULF MOISTURE INTO REGION WITH AFTERNOON MLCAPE VALUES OF 1000-1500 J/KG IN CLOUDY AREA...TO 2500-3000 J/KG OVER SOUTHERN KS. SHORTWAVE RIDGING AND CAPPING WILL ALSO EXIST THROUGH MUCH OF THE DAYLIGHT HOURS...BEFORE NEXT STRONG SHORTWAVE APPROACHES TOWARD 00Z. THIS WILL RESULT IN ISOLATED SUPERCELL THUNDERSTORMS DURING THE AFTERNOON ALONG THE DRYLINE...BECOMING MORE WIDESPREAD AFTER DARK OVER WEST CENTRAL KS AND TRACKING NORTH-NORTHEASTWARD TOWARD SOUTHERN NEB. FORECAST SOUNDINGS SHOW IMPRESSIVE LOW LEVEL AND DEEP LAYER VERTICAL SHEAR FAVORABLE FOR STRONG AND POTENTIALLY LONG-LIVED TORNADOES WELL INTO THE NIGHT. VERY LARGE HAIL WILL ALSO BE LIKELY IN STRONGER STORMS. IF BOUNDARY CURRENTLY ANALYZED ALONG THE I-70 CORRIDOR REMAINS INTACT THROUGH THE AFTERNOON...THIS MAY BE THE AREA OF GREATEST TORNADO THREAT. THE NEED FOR AN UPGRADE TO HIGH RISK IN PARTS OF THE REGION WILL BE RE-EVALUATED IN LATER UPDATES AS AFFECTS OF MORNING CONVECTION...LOCATION OF BOUNDARIES...AND TRENDS IN CAPPING INVERSION ARE MORE CONFIDENTLY ASCERTAINED.

...OK/TX... STRONG INSTABILITY WILL BE PRESENT ALONG SURFACE DRYLINE FROM WESTERN OK INTO WEST TX TODAY. WEAK LARGE SCALE FORCING IS EXPECTED TO KEEP CONVECTIVE ACTIVITY EXTREMELY ISOLATED ALONG THIS AXIS. HOWEVER...ANY STORMS THAT FORM WILL HAVE A THREAT OF LARGE HAIL...DAMAGING WINDS...AND POSSIBLY TORNADOES.

RETURN TO May 23, 2008 Chase Report