The SPC is forecasting ...widespread severe thunderstorms are expected over parts of the upper mississippi valley later today and tonight.... Please read the latest public statement about this event.
| Categorical Graphic |
|---|
|
| Probabilistic Tornado Graphic |
 |
 |
| Probabilistic Damaging Wind Graphic |
 |
 |
| Probabilistic Large Hail Graphic |
 |
 |
SPC AC 131231 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0731 AM CDT MON AUG 13 2007 VALID 131300Z - 141200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS OF CENTRAL/SRN MN...NERN IA...WRN WI... ...THERE IS A SLGT RISK OF SVR TSTMS FROM PART OF THE NRN PLAINS TOWARDS THE WESTERN GREAT LAKES... ...NRN PLAINS ACROSS THE UPPER MS RIVER VALLEY... STRONG SHORTWAVE TROUGH WILL CONTINUE ATOP LARGE ANTICYCLONE ACROSS THE NRN PLAINS TODAY...AND THEN DIVE ESEWD INTO THE GREAT LAKES TONIGHT. THIS WILL BRING SIGNIFICANT CHANGES TO THE LOW LEVELS ACROSS THE ERN DAKOTAS/MN AS STRONG WARM FRONT DEVELOPS AND PUSHES NNEWD THROUGH THE DAY. AREA IS CURRENTLY UNDER THE INFLUENCE OF RATHER COOL/STABLE AIR ASSOCIATED WITH NRN GREAT LAKES SURFACE HIGH. IN ADDITION...RICHER MOISTURE /70+ F SURFACE DEW POINTS/ IS CURRENTLY SUPPRESSED WELL SOUTH OF AN OUTFLOW BOUNDARY FROM SUNDAY NIGHT/S BOW ECHO MCS WHICH EXTENDS FROM THE MID MS RIVER VALLEY INTO SERN NEB AT 12Z. HOWEVER...MODELS ARE CONSISTENT IN SHIFTING SURFACE WARM FRONT STEADILY ENEWD ACROSS THE DAKOTAS AND EXTEND NEARLY NNW-SSE FROM NWRN MN INTO SERN MN/ERN IA BY LATE TODAY. THIS SUPPORTS INFLUX OF 70+ SURFACE DEW POINTS INTO ERN SD/SRN MN DURING THE AFTERNOON. CAPPING WILL REMAIN QUITE STRONG...ESPECIALLY NORTH AND EAST OF THE WARM FRONT...SUPPRESSING MOIST CONVECTION FOR MUCH OF THE DAY. ALTHOUGH...INCREASED CONVERGENCE AND DEEP ASCENT ASSOCIATED WITH APPROACHING MID LEVEL TROUGH ARE EXPECTED TO INITIATE STORMS INTO FAR NWRN MN AND POSSIBLY ERN ND BETWEEN 21-00Z. MLCAPE IN EXCESS OF 2000 J/KG AND EFFECTIVE SHEAR GREATER THAN 40 KT SUGGESTS THIS DEVELOPMENT WILL LIKELY OCCUR AS SUPERCELLS. MODELS ARE VERY CONSISTENT IN WIDESPREAD DEVELOPMENT SSEWD ACROSS MUCH OF MN INTO WRN WI DURING THE EARLY TO MID EVENING AS CAP WEAKENS AND DEEP ASCENT INCREASES AHEAD OF MID LEVEL TROUGH AND STRENGTHENING LOW LEVEL JET/WAA. THIS ACTIVITY WILL DEVELOP WITHIN VERY STRONG DEEP LAYER SHEAR AND STEEP MID LEVEL LAPSE RATES...BOTH OF WHICH WILL BE MORE THAN ADEQUATE FOR LONG-LIVED SUPERCELLS. HOWEVER...OVERALL EVOLUTION INTO ANOTHER LARGE BOW ECHO SYSTEM /POTENTIAL DERECHO MCS/ IS EXPECTED LATER THIS EVENING AS STORMS BECOME DOMINATED BY COMMON OUTFLOW AND RACE SSEWD AFTER DARK. ALTHOUGH WIND DAMAGE MAY BECOME PRIMARY SEVERE TYPE...MUCH OF THIS IS DEPENDANT ON OVERALL STORM MODE. FORECAST SOUNDINGS SUGGEST VERY LARGE HAIL AND TORNADOES WILL BE ADDITIONAL HAZARDS WITH ANY SUSTAINED SUPERCELLS...AS LOW LEVEL SHEAR IS FORECAST TO BE QUITE STRONG WITH 0-1 KM SRH IN EXCESS OF 250 M2/S2 AS LLJ INCREASES THIS EVENING. ..EVANS/CROSBIE.. 08/13/2007 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z