NWS STORM PREDICTION CENTER NORMAN OK 0137 AM CDT SAT JUL 20 2013 VALID 211200Z - 221200Z ...NO SVR TSTM AREAS FORECAST... CORRECTED FOR WORDING ...SYNOPSIS... A WEAK UPPER TROUGH WILL MOVE EWD ACROSS THE UPPER MS VALLEY DURING THE DAY...AND INTO THE GREAT LAKES OVERNIGHT. ALONG AND W OF THIS TROUGH AXIS...RELATIVELY COOL TEMPERATURES ALOFT WILL RESULT IN A LARGE AREA OF STEEP LAPSE RATES ACROSS THE CNTRL AND NRN PLAINS...CONDITIONALLY FAVORING LARGE HAIL IN MANY AREAS. SLY SURFACE FLOW ACROSS THE PLAINS WILL MAINTAIN MOISTURE AND INSTABILITY FOR STORMS...WITH SEVERAL POCKETS OF RAIN AND STORMS THROUGHOUT THE PERIOD. BEHIND THE INITIAL WEAK TROUGH...A MORE POTENT BUT LOW AMPLITUDE SHORTWAVE WILL MOVE SEWD ACROSS THE DAKOTAS AND MN LATE SUNDAY WHICH WILL WORK WITH A WEAK SURFACE LOW TO FORCE AT LEAST ISOLATED STRONG TO SEVERE STORMS. ...NEB...KS...IA...MO...WRN IL... A SWLY FEED OF HIGHER THETA-E AIR WILL EXIST SUNDAY MORNING FROM KS INTO ERN NEB...IA...AND SRN MN WITH A 20-25 KT LOW LEVEL JET ASSOCIATED WITH THE WEAK UPPER TROUGH. ONGOING SHOWERS AND STORMS ARE DEPICTED BY SEVERAL MODELS...MAINLY FROM NERN KS INTO NWRN MO. PRECISE LOCATION OF EARLY CONVECTION MAY DEPEND ON EVOLUTION OF ANY OVERNIGHT CLUSTERS THAT FORM SAT NIGHT. THE EARLY ACTIVITY COULD POSE A MARGINAL HAIL THREAT. LATER IN THE DAY...STRONG HEATING WILL OCCUR ACROSS THE PLAINS...WITH A RELATIVE COOL POCKET CENTERED OVER THE LOWER MO RIVER VALLEY DUE TO EARLY CONVECTION. SEVERAL AREAS OF NEW STORMS WILL BE POSSIBLE...INCLUDING WRN NEB WITH A WIND AND HAIL THREAT PROPAGATING SWD INTO WRN KS...AND ERN NEB/IA/SRN MN DUE TO WEAK WARM ADVECTION AND BENEATH STEEP LAPSE RATES ALOFT. AT THIS TIME...IT IS DIFFICULT TO CONFIDENTLY DEPICT ANY SLIGHT RISK AREAS. ...ND INTO NWRN MN... AREAS OF THUNDERSTORMS MAY BE ONGOING ALONG AND N OF THE CANADIAN BORDER EARLY SUNDAY ASSOCIATED WITH THE LEFT EXIT REGION OF THE UPPER JET. STRONG HEATING WILL TAKE PLACE FROM MT INTO THE WRN DAKOTAS NEAR THE SURFACE LOW...WHERE CONVERGENCE WILL LEAD TO ISOLATED THUNDERSTORMS. ACTIVITY SHOULD PERSIST AS THE ENTIRE SYSTEM MIGRATES EWD INTO ERN ND AND NWRN MN...WITH LARGE HAIL AND DAMAGING WINDS POSSIBLE. CAPPING WILL INCREASE OVERNIGHT FROM THE SW...WHICH COULD LIMIT STORM COVERAGE. THUS...WILL DEFER ANY POSSIBLE UPGRADE TO SLIGHT RISK TO LATER OUTLOOKS. ...ERN VA...MD...DE... A WEAK LOW PRESSURE TROUGH IS FORECAST TO DEEPEN OVER MD DURING THE DAY WHERE STRONG HEATING WILL TAKE PLACE. AN UNSTABLE ENVIRONMENT WILL FORM BY AFTERNOON WITH AMPLE LOW LEVEL MOISTURE FOR STORMS. ALTHOUGH FLOW ALOFT WILL BE WEAK...A FEW STRONG TO SEVERE MULTICELLS WILL BE POSSIBLE CAPABLE OF BOTH LOCALLY DAMAGING WIND GUSTS AND MARGINALLY SEVERE HAIL BEFORE DWINDLING BY EARLY EVENING.
Posted on: Sat, 20 Jul 2013 11:54:25 +0000
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