SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0303 PM CDT SUN MAY 06 2012 VALID 062000Z - 071200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID TO UPPER MS VALLEY...OZARKS...CNTRL PLAINS AND SRN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GULF COAST STATES... SEVERAL CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST CHANGE IS TO REMOVE THE SLIGHT RISK AREA FROM SRN WI AND CNTRL IA WHERE A COLD FRONT IS STABILIZING THE AIRMASS FROM NORTHWEST TO SOUTHEAST. THE SECOND CHANGE IS TO MAKE THE 30 PERCENT WIND DAMAGE PROBABILITY SMALLER AND CO-LOCATED WITH THE 5 PERCENT TORNADO PROBABILITY OVER NCNTRL IL JUST AHEAD OF A CLUSTER OF SEVERE STORMS. ANOTHER CHANGE IS TO REMOVE THE SLIGHT RISK AREA FROM NE MS...CNTRL AL AND SCNTRL GA WHERE ANALYSIS SHOWS WEAKER INSTABILITY THAN IN AREAS TO THE SOUTH AND WEST. ANOTHER CHANGE IS TO MOVE THE WRN EDGE OF THE SLIGHT OVER CNTRL OK TO AREAS EAST OF I-35 DUE TO A DRY SLOT THAT IS APPROACHING CNTRL OK FROM THE WEST. THE FINAL CHANGE IS TO ADD A NARROW 5 PERCENT WIND AND HAIL PROBABILITY OVER NW OK TO COINCIDE WITH A NARROW AXIS OF MODERATE INSTABILITY. ..BROYLES.. 05/06/2012 .PREV DISCUSSION... /ISSUED 1119 AM CDT SUN MAY 06 2012/ ...SYNOPSIS... UPPER LOW ALONG THE MT/SASKATCHEWAN BORDER WILL PROGRESS EWD INTO SRN MANITOBA WITH A TRAILING POSITIVE-TILT TROUGH EXTENDING SWWD INTO THE LOWER CO VALLEY. ELSEWHERE...WEAK MIDLEVEL IMPULSES WILL CREST RIDGE AXIS OVER THE UPPER GREAT LAKES AND MIDWEST WHILE A WEAK PERTURBATION MOVES FROM THE CNTRL/SRN HIGH PLAINS ACROSS KS/OK TODAY. AT THE SURFACE...COLD FRONT FROM THE UPPER MS VALLEY THROUGH MID MO VALLEY INTO WRN TX WILL ADVANCE SWD/SEWD WHILE A WARM FRONT LIFTS NWD ACROSS PORTIONS OF THE OH VALLEY. MEANWHILE...A DRYLINE WILL DEVELOP TODAY FROM THE INTERSECTION OF THE COLD FRONT SWD INTO THE EDWARDS PLATEAU OF TX. ...UPPER MIDWEST INTO OZARKS THIS AFTERNOON/EVENING... 12Z WARM SECTOR SOUNDINGS SHOWED A VERY MOIST BOUNDARY LAYER BENEATH STEEP MIDLEVEL LAPSE RATES WITH MUCAPE VALUES ALREADY ON THE ORDER OF 3500-5000 J/KG. THE STRONGEST HEIGHT FALLS ASSOCIATED WITH THE UPPER LOW MENTIONED ABOVE WILL REMAIN ACROSS POST-FRONTAL AIR MASS. HOWEVER...INFLUENCE OF WEAKER MIDLEVEL PERTURBATIONS EMBEDDED WITHIN SWLY FLOW REGIME AND UPLIFT ALONG SYNOPTIC FRONTS AND EXISTING OUTFLOW BOUNDARIES WILL BE SUFFICIENT TO FOSTER AN INCREASE IN TSTM ACTIVITY TODAY. VERTICAL SHEAR WILL REMAIN MARGINALLY SUPPORTIVE OF STORM ORGANIZATION. BUT...THE DEGREE OF INSTABILITY MAY COMPENSATE WITH THE POTENTIAL FOR LARGE HAIL...DAMAGING WINDS...AND PERHAPS A BRIEF TORNADO. ...CNTRL/SRN PLAINS THIS AFTERNOON/EVENING... AS MENTIONED ABOVE...A WEAK MIDLEVEL IMPULSE WILL PROGRESS ACROSS THE REGION TODAY...PROVIDING A FAVORABLE BACKGROUND ENVIRONMENT FOR STORM FORMATION ALONG THE COLD FRONT AND PERHAPS DRYLINE. HERE TOO...A MOIST BOUNDARY LAYER WILL COINCIDE WITH AN EML/STEEP MIDLEVEL LAPSE RATES TO YIELD AFTERNOON MLCAPE VALUES OF 2500-3500+ K/JG. STRONGER CAPPING ACROSS THE SRN PLAINS MAY TEND TO LIMIT STORM COVERAGE WITH SWD EXTENT ALONG THE COLD FRONT...WHILE GENERALLY WEAK VERTICAL SHEAR WILL MODULATE THE DEGREE OF STORM ORGANIZATION. NONETHELESS...THE PRESENCE OF THE STEEP LAPSE RATES AND MODERATE-STRONG INSTABILITY SUGGEST THE POTENTIAL FOR VIGOROUS UP/DOWNDRAFTS WITH AN ASSOCIATED RISK FOR DAMAGING WINDS AND HAIL. ...CNTRL/ERN GULF STATES THIS AFTERNOON/EVENING... TSTMS HAVE ALREADY FORMED THIS MORNING ACROSS PORTIONS OF AL/GA...APPARENTLY IN ASSOCIATION WITH A COLD POOL WHICH HAS SURGED SWD OUT OF THE TN VALLEY. 12Z BMX SOUNDING REVEALED SEASONABLY COOL MIDLEVEL TEMPERATURES /I.E. AROUND -15 C AT 500 MB/ ATOP A MOIST BOUNDARY LAYER WITH MUCAPE ESTIMATED TO BE AROUND 3000 J/KG. PRE-EXISTING CONVECTIVE OUTFLOW BOUNDARIES WILL LIKELY SERVE AS THE FOCUS FOR RENEWED TSTM DEVELOPMENT TODAY WITHIN THE MOIST...MODERATE-STRONGLY UNSTABLE ENVIRONMENT. VERTICAL SHEAR WILL REMAIN WEAK...BUT THE PRESENCE OF THE STEEP LAPSE RATES AND DEGREE OF INSTABILITY WILL PROMOTE ORGANIZED MULTICELL CLUSTERS CAPABLE OF DAMAGING WINDS AND SEVERE HAIL.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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