...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN MT/NERN WY EWD ACROSS SD/NEB...IA...SRN MN...SRN WI...NRN IL AND IND... ...SYNOPSIS... A SHORTWAVE TROUGH WILL MOVE RAPIDLY NEWD FROM THE GREAT BASIN INTO THE NRN HIGH PLAINS BY 00Z WITH A LOW PRESSURE TROUGH EXTENDING FROM ERN WY INTO SWRN NEB/NWRN KS. COOL AIR ALOFT WILL OVERSPREAD A VERY UNSTABLE AIR MASS FOR SCATTERED SEVERE THUNDERSTORMS FROM SERN MT INTO THE BLACK HILLS DURING THE AFTERNOON. FORCING WITH THIS TROUGH SHOULD RESULT IN A CONTINUED SEVERE THREAT EWD OVERNIGHT...SUPPORTED BY A 50 KT SWLY LOW LEVEL JET. TO THE E...AN UPPER TROUGH WILL DEPART THE ERN SEABOARD BY MIDDAY...BUT A LOW PRESSURE TROUGH AND RESIDUAL MOISTURE AND INSTABILITY WILL EXTEND SWWD FROM SC INTO AL WITH ISOLATED SEVERE STORMS POSSIBLE. ...SERN MT...NERN WY...WRN SD...NWRN NEB... STRONG HEATING WILL OCCUR AND WILL STEEPEN DEEP LAYER LAPSE RATE PROFILES ALONG AND W OF THE SURFACE TROUGH FROM SERN MT INTO SD/NEB. MEANWHILE...ELY LOW LEVEL FLOW WILL MAINTAIN AN AXIS OF MID 60S F DEWPOINTS ACROSS SRN SD AND NRN NEB...WITH UPSLOPE FLOW ACROSS THE BLACK HILLS AND INTO SERN MT. WITH COOLING ALOFT...STRONG INSTABILITY WILL RESULT. DEEP LAYER SHEAR WILL BE EXTREMELY FAVORABLE FOR LARGE HAIL...AND EVENTUALLY DAMAGING WINDS WITH A FORWARD PROPAGATING MCS. SIGNIFICANT HAIL IS LIKELY WITH SUPERCELLS ACROSS MUCH OF SWRN SD AND NWRN NEB. ...SRN SD/NRN NEB INTO SRN MN/NRN IA... ACTIVITY ACROSS WRN SD/NEB WILL EVENTUALLY MERGE INTO AN MCS DURING THE EVENING...AND IS EXPECTED TO TRAVEL EWD ACROSS SRN SD/NRN NEB INTO SRN MN/NRN IA OVERNIGHT WITH DAMAGING WIND AND HAIL THREAT. FORCING FOR THE MCS WILL HAVE TO OVERCOME CAPPING OVERNIGHT. AS A RESULT...IT COULD END UP BEING A RELATIVELY SMALL MCS/BOWING SYSTEM...BUT STILL SEVERE. ...CNTRL GA...AL...SC... MODERATE INSTABILITY WILL REMAIN IN PLACE TODAY WITH STRONG HEATING. BY MID/LATE AFTERNOON...A WEAK LOW PRESSURE TROUGH IS EXPECTED TO SET UP ACROSS SC SWWD INTO GA AND AL. WITHIN THIS TROUGH WILL BE WEAK WIND CONVERGENCE...BUT DRY AIR ALOFT AND A SUBSIDENCE INVERSION IS ALSO FORECAST TO BE IN PLACE. THE END RESULT SHOULD BE ISOLATED THUNDERSTORMS...AND THE STRONGEST STORMS WILL HAVE LARGE HAIL AND LOCALLY STRONG WIND GUSTS. WITH NLY FLOW ALOFT...AND WLY SFC/850 MB FLOW...A FEW CELLS WILL MOVE IN A SWLY DIRECTION...AND MAY BE LONG LIVED. THESE CELLS WOULD HAVE THE GREATEST HAIL THREAT. ...ERN IA...NRN IL...IND... A WEAK DISTURBANCE NOW OVER THE NRN PLAINS IS FORECAST TO ROUND THE RIDGE AND MOVE INTO ERN IA/NRN IL BY LATE AFTERNOON. MIDLEVEL LAPSE RATES WILL BE VERY STEEP IN A CORRIDOR FROM IA INTO IND...AND SURFACE BASED PARCELS WILL BE CAPPED FOR MUCH OF THE PERIOD. HOWEVER...FORECAST SOUNDINGS SUGGEST LIFT WITH THIS FEATURE AND SOME MOISTENING ALOFT MAY BE ENOUGH TO INITIATE THUNDERSTORMS CAPABLE OF LARGE HAIL. THESE STORMS WOULD THEN MOVE SEWD ACROSS IL AND INTO IND. WITH AMPLE DEEP LAYER SHEAR AND STEEP LAPSE RATES ALOFT...SOME OF THE HAIL COULD APPROACH 2.00 INCH DIAMETER.
Posted on: Tue, 11 Jun 2013 12:08:29 +0000
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