DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0259 PM CDT THU APR 09 2015 VALID 092000Z - 101200Z ...THERE IS AN ENH RISK OF SVR TSTMS FROM THE ARKLATEX NORTHEAST INTO THE SRN GREAT LAKES/LOWER OH VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH AREA FROM E TX INTO THE UPPER OH VALLEY...WV AND WRN PA... ...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE ABOVE AREAS FROM S CENTRAL TX TO THE CENTRAL APPALACHIANS... ...SUMMARY... SEVERE THUNDERSTORMS ARE LIKELY TODAY INTO TONIGHT OVER A BROAD SWATH FROM PARTS OF TEXAS NORTHEASTWARD THROUGH THE LOWER AND MID-MISSISSIPPI VALLEYS INTO THE OHIO VALLEY AND SOUTHERN GREAT LAKES. THESE WILL PRODUCE DAMAGING WIND...HAIL...AND A FEW TORNADOES...ONE OR TWO OF WHICH COULD BE STRONG. ...MID-MS VLY TO SRN GRT LKS...AND LWR OH VLY TO E TX/LWR MS VLY... NO CHANGES ARE NEEDED WITH THIS OUTLOOK ISSUANCE FOR THE SLIGHT AND ENH AREAS...AS PREVIOUS FORECAST DISCUSSION REMAINS ON TRACK FOR THIS AFTERNOON INTO TONIGHT. THE GENERAL TSTM AREA AND MARGINAL SEVERE RISK AREA HAVE BEEN TRIMMED EWD SOME ACROSS WRN MO AND NERN-SRN OK...GIVEN THE ADVANCEMENT OF THE COLD FRONT. ...UPR OH VLY/CNTRL APPALACHIANS... THE ERN PART OF THE SLIGHT RISK AREA HAS BEEN EXPANDED EWD TO INCLUDE MORE OF WV AND INTO WRN PA...WHERE HAIL AND DAMAGING WIND THREATS ARE EXPECTED THIS AFTERNOON AND EVENING. OBJECTIVE ANALYSES INDICATED MUCH OF THE ENVIRONMENT ACROSS SRN OH INTO WV AND PARTS OF WRN PA HAS CONTINUED TO DESTABILIZE THIS AFTERNOON. THIS COMBINED WITH AN INCREASE IN EFFECTIVE BULK SHEAR WILL CONTINUE TO SUPPORT A THREAT FOR STRONG TO SEVERE STORMS. ...SC... GIVEN RECENT CONVECTIVE/TSTM DEVELOPMENT ALONG THE SEA BREEZE...THE GENERAL TSTM AREA HAS BEEN EXPANDED EWD SOME TO ACCOUNT FOR ANY ADDITIONAL TSTMS. ..PETERS.. 04/09/2015 .PREV DISCUSSION... /ISSUED 1130 AM CDT THU APR 09 2015/ ...SYNOPTIC SETUP... PROGRESSIVE...MULTI-STREAM FLOW WILL PREVAIL OVER THE CNTRL AND ERN U.S. THIS PERIOD...DOWNSTREAM FROM WRN STATES SPLIT. STRONG SHORTWAVE TROUGH NOW EXITING THE CNTRL HIGH PLNS SHOULD ACCELERATE ENE INTO ERN IA THIS EVE...BEFORE FURTHER ACCELERATING AND TURNING NE TO NEAR SSM EARLY FRI AS NRN BRANCH IMPULSE AMPLIFIES SE INTO MN. AT THE SAME TIME...WEAKER LEAD DISTURBANCE NOW CROSSING THE OZARKS SHOULD MOVE NE INTO THE MID-OH VLY BY THIS EVE...AND INTO NY/PA EARLY FRI...AS DEEP SWLY FLOW STRENGTHENS ACROSS THE E-CNTRL AND ERN U.S. AT THE SFC...NW MO LOW EXPECTED TO DEEPEN NEWD INTO SRN WI BY THIS EVE...AND UNDERGO FURTHER DEEPENING AS IT REACHES THE SSM AREA EARLY FRI. COLD FRONT TRAILING SSW FROM THE LOW SHOULD STRENGTHEN AND ACCELERATE E ACROSS THE MID-MISSISSIPPI VALLEY AND OZARKS BY LATE TODAY...AND INTO THE UPR OH...TN...AND LWR MS VLYS EARLY FRI...WHILE MORE DIFFUSE WARM FRONT ADVANCES N INTO LWR MI. IN SUMMARY...THE OVERALL SET-UP SUPPORTS A BROAD AREA WITH AN APPRECIABLE RISK FOR SVR WEATHER LATER TODAY THROUGH EARLY FRI...BUT WITH MITIGATING FACTORS THAT LIKELY WILL KEEP THE CORRIDORS OF GREATEST RISK SOMEWHAT FRAGMENTED AND MULTI-MODAL. ...MID-MS VLY TO SRN GRT LKS THIS AFTN THROUGH EARLY TNGT... SEVERAL FACTORS MAY COMBINE TO YIELD A MESOSCALE CORRIDOR OF SOMEWHAT ENHANCED SVR THREAT...INCLUDING THE POTENTIAL FOR A COUPLE STRONG TORNADOES...OVER THE ERN IA/NE MO/NRN IL/SRN WI AREA LATER TODAY INTO EARLY TNGT. PERSISTENT HEIGHT FALLS ACROSS REGION...LARGELY DUE TO AMPLIFICATION OF UPSTREAM...LARGER-SCALE TROUGH...WILL OFFSET SINKING/DESCENT OCCURRING IN WAKE OF LEAD UPR IMPULSE AND EMBEDDED MCV NOW CROSSING THE OZARKS. AT THE SAME TIME...SATELLITE SUGGESTS LIKELIHOOD FOR AT LEAST MODEST SFC HEATING AHEAD OF COLD FRONT AND DEEPENING SFC LOW APPROACHING FROM NW MO. WITH 700 MB SWLY WINDS INCREASING TO AOA 60 KTS ATOP 40+ KT SSW FLOW AT 850 MB...HODOGRAPHS WILL BE FAVORABLE FOR SUSTAINED SUPERCELLS WITH LARGE HAIL. THE DIRECTIONAL COMPONENT TO LOW-LVL SHEAR LIKELY WILL NOT BE GREAT. BUT COMBINATION OF STRENGTHENING FLOW AND EXPECTED BACKING OF NEAR-SFC WINDS/ENHANCED SRH IMMEDIATELY AHEAD OF SFC LOW SUGGEST THAT A CORRIDOR OF HEIGHTENED TORNADO POTENTIAL COULD EVOLVE LATER THIS AFTN...BEFORE THE STORMS MERGE INTO BROKEN LINES/SMALL CLUSTERS EARLY TNGT. ALTHOUGH CLOUDS AND SHOWERS MAY DELAY NWD ADVANCE OF WARM FRONT ACROSS IL/IND...STRENGTHENING SFC PRESSURE FALLS/TRACK OF SFC LOW FURTHER INDICATE THAT THE SVR THREAT COULD EXTEND NWD INTO SRN WI AND SW LWR MI...WITH DMGG WINDS BECOMING THE DOMINANT THREAT OVER TIME. ...LWR OH VLY SW INTO E TX/LWR MS VLY LATE TODAY THROUGH EARLY FRI... SFC HEATING AND UPLIFT ALONG COLD FRONT AND PRE-FRONTAL CONFLUENCE AXES EXPECTED TO INITIATE TSTMS LATER TODAY THROUGH TNGT AS EML CAP IS BROKEN. ALTHOUGH WIND FIELDS WILL BE WEAKER RELATIVE TO POINTS N...AMPLE /40+ KT/ WSWLY DEEP SHEAR WILL EXIST FOR SUSTAINED STORMS/SUPERCELLS...ESPECIALLY OVER THE LWR OH AND TN VLYS. GIVEN FAIRLY RICH MOISTURE AVAILABILITY /PW AOA 1.50 INCHES/...IN THEIR EARLY STAGES THESE STORMS COULD YIELD LARGE HAIL AND A FEW TORNADOES. WITH TIME...DEGREE OF LOW-LVL FORCING SHOULD RESULT INTO AMALGAMATION OF CONVECTION INTO AN EXTENSIVE...BROKEN SQLN. EMBEDDED LEWPS AND BOWING STRUCTURES LIKELY WILL BE ACCOMPANIED BY A SLOWLY DIMINISHING RISK FOR DMGG WIND INTO EARLY FRI. ...UPR OH LY/CNTRL APPALACHIANS THIS AFTN/EVE... A CONDITIONAL RISK WILL EXIST FOR LOOSELY-ORGANIZED CLUSTERS OF MAINLY MULTICELL STORMS WITH HAIL AND LOCALLY DMGG WIND THIS AFTN OVER PARTS OF OH...KY AND WRN SLOPES OF THE CNTRL APPALACHIANS...WHERE SFC HEATING WILL FURTHER DESTABILIZE REGION OF MODEST LOW-LVL MOISTURE AND MID-LVL INSTABILITY. SOME OF THIS ACTIVITY COULD ARISE FROM EXISTING AREAS OF ELEVATED CONVECTION NOW OVER PARTS OF THE REGION...WITH OTHER STORMS INITIATED BY DIFFERENTIAL HEATING ALONG RESIDUAL SFC BOUNDARIES. MOST OF THE STORMS SHOULD WEAKEN WITH NIGHTFALL...ALTHOUGH PARTS OF THE OH VLY COULD EXPERIENCE A SECOND ROUND OF STORMS LATE TNGT AS MID MS VLY COLD FRONT APPROACHES REGION.
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