The SPC is forecasting ...severe thunderstorms expected over a broad swath of the southern and central plains today through tonight.... Please read the latest public statement about this event.
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SPC AC 260600 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0100 AM CDT SUN APR 26 2009 VALID 261200Z - 271200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PART OF SWRN KS...WRN OK...ERN OK/TX PANHANDLES TO WRN PART OF N TX... ...THERE IS A SLGT RISK OF SVR TSTMS EXTENDING FROM THE SRN/CENTRAL PLAINS TO UPPER MS VALLEY... ...SYNOPSIS... A LEAD SHORT WAVE TROUGH/ACCOMPANYING 70 KT SWLY MID LEVEL JET WILL TRACK NEWD FROM THE CENTRAL ROCKIES/HIGH PLAINS TO THE NRN PLAINS/ UPPER MS VALLEY THIS FORECAST PERIOD. MEANWHILE...A SECOND SHORT WAVE TROUGH AND SPEED MAX...CURRENTLY MOVING EWD THROUGH BASE OF WRN U.S. TROUGH OVER NRN BAJA/LOWER CO RIVER VALLEY WILL PROGRESS EWD TODAY REACHING THE SRN HIGH PLAINS/W TX BY THIS AFTERNOON. THIS IMPULSE WILL THEN TRACK ENEWD ACROSS THE SRN PLAINS SUNDAY NIGHT. IN THE LOW LEVELS AT 12Z...A SURFACE BOUNDARY IS EXPECTED TO EXTEND WSWWD FROM THE ST LAWRENCE RIVER VALLEY/LOWER GREAT LAKES THROUGH SRN LOWER MI TO SRN IA...AND THEN SWWD THROUGH KS TO AN AREA OF LOW PRESSURE OVER THE WRN OK PANHANDLE. ERN EXTENT OF THIS BOUNDARY WILL ADVANCE SEWD THROUGH NY/NEW ENGLAND TODAY...THE REST OF THE BOUNDARY RETREATS NWD AS A WARM FRONT REACHING CENTRAL/NRN LOWER MI WWD TO CENTRAL WI/SRN MN BY LATE AFTERNOON. THE TRAILING PORTION OF THE FRONT WILL EXTEND SWWD FROM NWRN IA TO CENTRAL KS BY AFTERNOON. A SURFACE LOW ATTENDANT TO THE LEAD SHORT WAVE TROUGH IS EXPECTED TO TRACK NEWD ACROSS ERN NEB/WRN IA THIS AFTERNOON...REACHING SERN MN BY EVENING. MEANWHILE...A DRY LINE WILL INITIALLY EXTEND SSWWD THROUGH W TX TO FAR SERN NM/SW TX...AND IS EXPECTED TO MIX EWD REACHING THE ERN OK/TX PANHANDLES AND W TX BY MID-LATE AFTERNOON. ...SRN PLAINS INTO SRN KS... A 60-70 SWLY MID LEVEL JET IS EXPECTED TO EXTEND FROM THE WRN PORTION OF THE SRN PLAINS TO ERN DAKOTAS BY THIS AFTERNOON...ALONG ERN PERIPHERIES OF RESPECTIVE SHORT WAVE TROUGHS AFFECTING THESE AREAS TODAY. POTENTIAL EXISTS TODAY FOR SUPERCELLS TO DEVELOP ALONG THE DRY LINE/SURFACE FRONT INTERSECTION IN SWRN KS/ERN OK PANHANDLE AND SWD ALONG THE DRY LINE TO PART OF WEST CENTRAL TX. MODERATE INSTABILITY COMBINED WITH STRONG EFFECTIVE BULK SHEAR /40-50 KT/ SUGGESTS LIKELIHOOD FOR SUPERCELLS. SECOND BRANCH OF SLY LLJ IS EXPECTED TO DEVELOP/STRENGTHEN ACROSS WRN N TX/WRN OK INTO SRN KS BY LATE AFTERNOON RESULTING IN INCREASED LOW LEVEL HODOGRAPH CURVATURE/ATTENDANT TORNADO THREAT. MODELS DIFFER WITH THE TIMING OF TSTM INITIATION FROM THE TRIPLE POINT SWD...BUT THERE IS SOME INDICATION THAT ACTIVITY MAY DEVELOP AS EARLY AS LATE MORNING OR EARLY AFTERNOON. STRONG SURFACE HEATING SHOULD OCCUR ALONG NRN EXTENT OF DRY LINE...WHILE MORE FILTERED SUNSHINE MAY OCCUR SWD ACROSS MUCH OF WRN/CENTRAL TX INTO SRN OK DUE TO MID/HIGH LEVEL CLOUDS SPREADING ACROSS THIS REGION CURRENTLY AND DURING THE MORNING. STEEP LAPSE RATES ACROSS THIS AREA WITH STRONG EFFECTIVE BULK SHEAR WILL ALSO BE CONDUCIVE TO LARGE HAIL...SOME VERY LARGE ACROSS THE MODERATE RISK AREA. ACTIVITY SHOULD SPREAD EWD ACROSS SRN KS/OK AND N TX AS NRN BAJA TROUGH MOVES ACROSS THE SRN PLAINS SUNDAY NIGHT. AIR MASS IS SHOULD REMAIN MODERATELY UNSTABLE INTO SUNDAY EVENING/NIGHT SUPPORTING A CONTINUED SEVERE WEATHER THREAT AFTER DARK ACROSS THE SRN PLAINS. ...CENTRAL/ERN KS TO UPPER MS VALLEY/GREAT LAKES... STORMS DEVELOPING NORTH OF RETREATING WARM FRONT EARLY IN PERIOD MAY POSE A THREAT FOR HAIL. A STRONG SSWLY LOW LEVEL JET /50-60 KT/ WILL BE MAINTAINED AND SHIFT NNEWD THROUGH THE LOWER MO TO UPPER MS VALLEYS AS LEAD SHORT WAVE TROUGH EJECTS NEWD TOWARD NRN PLAINS. GIVEN STRENGTH OF LOW LEVEL WINDS...RELATIVELY NARROW CORRIDOR OF MOISTURE IS EXPECTED TO ADVECT QUICKLY NNEWD WITH PRE-FRONTAL WARM SECTOR WITH SURFACE DEWPOINTS IN THE LOWER 60S REACHING SERN MN/ CENTRAL WI BY MID-LATE AFTERNOON. EXTENT OF DESTABILIZATION ALONG MOIST AXIS REMAINS UNCERTAIN DUE TO POTENTIAL FOR WIDESPREAD CLOUDS AND MODEST MID-LEVEL LAPSE RATES. HOWEVER...SOME BOUNDARY LAYER WARMING IS POSSIBLE IN WAKE OF MORNING CONVECTION WITH MLCAPE FROM 500 TO 1000 J/KG POSSIBLE. STORMS SHOULD INTENSIFY ALONG AND POSSIBLY AHEAD OF SEWD ADVANCING FRONT FROM KS NEWD THROUGH IA... SERN MN AND WI THEN SUBSEQUENTLY DEVELOP SEWD. STRONG WIND PROFILES ATTENDING THE EJECTING IMPULSE AND ATTENDANT LOW LEVEL JET WILL RESULT IN LARGE HODOGRAPHS /0-1 KM SRH 200-300 M2/S2/ AND SUFFICIENT BULK SHEAR FOR ORGANIZED STORMS INCLUDING LINES WITH EMBEDDED BOWING SEGMENTS AND SUPERCELLS. THREAT WILL EXIST FOR MAINLY DAMAGING WIND WITH THIS ACTIVITY. HOWEVER... ISOLATED TORNADOES AND HAIL WILL ALSO BE POSSIBLE...BUT EXTENT OF THESE THREATS WILL DEPEND ON AVAILABLE INSTABILITY AND MODE. MODELS SUGGEST ACTIVITY SHOULD EVOLVE INTO A LINEAR MCS SUNDAY EVENING/NIGHT...WITH THE COMPLEX ADVANCING ESEWD ACROSS IA...NRN MO AND ERN KS. DAMAGING WINDS WILL BE THE PRIMARY THREAT WITH THIS LINEAR MCS AS WELL. FARTHER NE...INSTABILITY IS EXPECTED TO BE WEAK WITH NEWD EXTENT INTO THE GREAT LAKES TODAY. HOWEVER...TSTMS SHOULD DEVELOP AND/OR SPREAD NNEWD INTO THE UPPER GREAT LAKES REGION AND PARTS OF LOWER MI WITHIN STRONG LOW LEVEL WAA REGIME ALONG NOSE OF STRONG LLJ TRANSLATING NEWD INTO THIS AREA. EFFECTIVE BULK SHEAR SHOULD BE SUFFICIENT FOR A FEW ORGANIZED SEVERE STORMS. ...PARTS OF SRN/SERN NY...FAR NERN PA...WRN MA/CT... SURFACE DEWPOINTS IN THE MID-UPPER 60S ARE EXPECTED TO SPREAD EWD ACROSS THE PRE-FRONTAL WARM SECTOR ACROSS SRN NY INTO SRN NEW ENGLAND. MODEST LAPSE RATES AROUND 6.5 C/KM ARE EXPECTED TO LIMIT DESTABILIZATION ACROSS THIS REGION TODAY. HOWEVER...MODELS SUGGEST A POTENTIAL FOR A FEW TSTMS THIS AFTERNOON/EARLY EVENING...WITH ACTIVITY SPREADING EWD GIVEN 30-40 WLY MID LEVEL FLOW. STEEP LOW LEVEL LAPSE RATES/WELL MIXED BOUNDARY LAYER SUGGESTS A FEW STRONGER WIND GUSTS WILL BE POSSIBLE. WEAK INSTABILITY SHOULD TEND TO LIMIT THE THREAT FOR HAIL. ..PETERS/GARNER.. 04/26/2009 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z