SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT SAT APR 28 2012 VALID 282000Z - 291200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER AREAS FROM ERN MO THROUGH SRN IL/IND AND KY... ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF OK AND NWRN TX... ...ERN MO TO LOWER OH VALLEY... EARLY AFTERNOON SURFACE ANALYSES SHOWED AN ELONGATED AREA OF LOW PRESSURE LOCATED FROM NEAR STL TO SOUTH CENTRAL IL...WITH A WARM FRONT EXTENDING SEWD THROUGH SWRN IND TO NRN KY. A MODERATELY-STRONGLY UNSTABLE AIR MASS RESIDES ACROSS THE WARM SECTOR SWWD INTO SRN MO. THIS INSTABILITY COMBINED WITH STRONG EFFECTIVE BULK SHEAR REMAINS SUPPORTIVE FOR ORGANIZED SEVERE STORMS. GIVEN TRENDS IN REGIONAL RADAR IMAGERY...THE SLIGHT RISK AND ATTENDANT 15 PERCENT SVR HAIL AND DAMAGING WIND PROBABILITIES HAVE BEEN EXPANDED A LITTLE NWD TO INCLUDE MORE OF EAST CENTRAL MO /N OF STL/ TO ACCOUNT FOR ONGOING TSTMS /SVR THREAT/ ACROSS THIS AREA. MEANWHILE...THE NWD MOVEMENT OF THE WARM FRONT...AND SOME DRYING OVER FAR WRN KY HAS LIMITED THE THREAT FOR SEVERE...AND THUS THE PORTION OF THE SLIGHT RISK AREA HAS BEEN SHIFTED A LITTLE NWD. THE 5 PERCENT TORNADO PROBABILITY WAS NARROWED SOME ALONG THE WARM FRONT AND INVOF OF THE SURFACE LOWS WHERE LOW LEVEL SHEAR SHOULD BE MAXIMIZED. AND...GIVEN THE STRENGTH OF THE INSTABILITY/SHEAR PARAMETER SPACE COMBINED WITH STEEP LAPSE RATES...THERE EXISTS A SIGNIFICANT HAIL THREAT FROM PARTS OF ERN MO INTO SRN IL/SWRN IND AND NWRN KY. ..PETERS.. 04/28/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT SAT APR 28 2012/ ...MO TO OH VALLEY... SURFACE ANALYSIS REVEALS QUASI-STATIONARY FRONT EXTENDING ESE FROM A WEAK SURFACE LOW OVER NERN MO INTO SRN IL/IND AND THEN ACROSS NRN KY. A WARM AND MOIST AIRMASS EXISTS NEAR THE SURFACE LOW AND ALONG/SOUTH OF THE FRONTAL ZONE BENEATH STEEP MID LEVEL LAPSE RATE PLUME SAMPLED WELL BY THE 12Z SGF RAOB. EXPECT THE AIRMASS NEAR THE LOW AND FRONT WILL BECOME INCREASINGLY UNSTABLE THROUGH THE AFTERNOON WITH SBCAPE FORECAST TO RISE TO AT LEAST 2000 J/KG FROM SRN MO TO NRN KY. WEAK TO MODEST LARGE SCALE ASCENT IN SUPPORT OF TSTM DEVELOPMENT AND SUSTENANCE NEAR THE LOW AND FRONT SHOULD BE PROVIDED BY A LOW AMPLITUDE SHORT WAVE TROUGH CURRENTLY TRACKING EAST FROM KS PER WATER VAPOR IMAGERY AND SHORT-TERM MODEL DATA. FORCING WITH THIS IMPULSE IS EXPECTED TO DRIVE INITIAL DEEP CONVECTIVE DEVELOPMENT ALONG AND NORTH OF THE SURFACE FRONT...PERHAPS FROM N OF STL ACROSS SCNTRL IL OVER THE NEXT FEW HOURS. DESPITE THIS ACTIVITY LIKELY BEING ROOTED WELL ABOVE A STABLE BOUNDARY LAYER...MAGNITUDE OF BOTH SHEAR AND ELEVATED INSTABILITY WILL RESULT IN SOME THREAT FOR HAIL. THERE IS SOMEWHAT GREATER UNCERTAINTY REGARDING THE DEVELOPMENT OF TRUE SURFACE-BASED CONVECTION ALONG AND SOUTH OF THE FRONT THROUGH THE AFTERNOON. WITH LATEST VISIBLE IMAGERY DEPICTING GOOD POTENTIAL FOR STRONG INSOLATION FROM SERN MO TO NRN KY...EXPECT THAT INHIBITION IN THIS CORRIDOR SHOULD CONTINUE TO WEAKEN. LIFT ACROSS THIS CORRIDOR IS NOT AS PRONOUNCED AS NORTH OF THE SURFACE FRONT. HOWEVER...IT SEEMS REASONABLE TO EXPECT MORE ROBUST TSTM DEVELOPMENT NEAR THE LOW ON THE MO/IL BORDER...AND PERHAPS ALONG LOCALLY REINFORCED FRONT/OUTFLOW BOUNDARIES EAST TO NRN KY IN THE 20-00 UTC TIME FRAME. ANY STORMS DEVELOPING IN THIS REGIME ARE LIKELY TO ACQUIRE SUPERCELL STRUCTURE AND POSE A RISK OF LARGE HAIL AND WIND. TORNADO POTENTIAL WILL BE LOCALLY ENHANCED NEAR THE LOW AND IMMEDIATELY ON THE FRONT WHERE MESO/STORM-SCALE INFLUENCES MAY BOOST LOW LEVEL SRH AND STORM INFLOW. STORMS MAY MERGE AND GROW SOMEWHAT UPSCALE THROUGH THE EVENING WITH LOCAL WIND DAMAGE POTENTIAL POSSIBLY SPREADING ESEWD ACROSS THE OH RIVER FROM IND/SWRN OH INTO NRN KY BEFORE BOUNDARY LAYER STABILIZATION SETS IN AND LIMITS PROSPECTS FOR STRONGER WINDS REACHING THE SURFACE. ...TX/OK TONIGHT... VERY UNSTABLE CONDITIONS EXPECTED TO EVOLVE ALONG THE STALLED SEGMENT OF THE DEEPER FRONTAL ZONE FROM SWRN MO ACROSS CNTRL/ERN OK AND INTO TX. LARGER SCALE FORCING FOR ASCENT ACROSS THIS ZONE IS MORE NON-DESCRIPT/AMBIGUOUS THROUGH THE DAY WHEN COMPARED TO AREAS NORTH AND EAST. HOWEVER...WATER VAPOR IMAGERY AND MODEL DATA SUGGEST A SHORT WAVE TROUGH...CURRENTLY ROUNDING THE BASE OF THE LARGER SCALE TROUGH OVER THE LOWER CO RIVER VALLEY AND GREAT BASIN...WILL BEGIN TO HAVE SOME INFLUENCE OVER THE SRN PLAINS BY EVENING. IN CONCERT WITH DIURNAL STRENGTHENING OF THE LOW LEVEL JET...EXPECT PROSPECTS FOR TSTM DEVELOPMENT TO INCREASE ALONG AND NORTH OF THE FRONT...FROM TX TO OK...DURING THE EVENING HOURS. LATEST MODEL GUIDANCE CONTINUES TO SUPPORT THE EVOLUTION OF ONE OR MORE CONVECTIVE SYSTEMS EXPANDING NWD/NEWD ACROSS THE SRN PLAINS DURING THE NIGHT. MAGNITUDE OF EFFECTIVE SHEAR AND AMBIENT INSTABILITY SHOULD RESULT IN AN INCREASING RISK OF LARGE HAIL AND POSSIBLY FAST MOVING CONVECTIVE ELEMENTS CAPABLE OF DAMAGING WINDS INTO EARLY SUNDAY.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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