ZCZC SPCSWOMCD ALL ACUS11 KWNS 101524 SPC MCD 101524 IAZ000-MNZ000-NEZ000-SDZ000-101800- MESOSCALE DISCUSSION 0584 NWS STORM PREDICTION CENTER NORMAN OK 1024 AM CDT SUN MAY 10 2015 AREAS AFFECTED...PORTIONS OF ERN NEB...WRN IA...SERN SD...FAR SWRN MN CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY VALID 101524Z - 101800Z PROBABILITY OF WATCH ISSUANCE...80 PERCENT SUMMARY...THE RISK FOR SEVERE THUNDERSTORMS WILL BE INCREASING INTO THE LATE MORNING/AFTERNOON HOURS...AND THIS INCLUDES THE RISK FOR TORNADOES. THE ISSUANCE OF A TORNADO WATCH IS LIKELY DURING THE NEXT COUPLE OF HOURS. DISCUSSION...THUNDERSTORM DEVELOPMENT IS UNDERWAY IN SERN SD AT THE LEADING EDGE OF STRONGER DCVA PRECEDING A COMPACT MID-LEVEL VORT MAX THAT WATER VAPOR LOOPS DEPICT AS ADVANCING NNEWD ACROSS THE CNTRL/NRN PLAINS. A RELATED SFC CYCLONE IS ANALYZED N OF ONL...WHICH WILL CONTINUE TO DEVELOP NNEWD INTO A ZONE OF MODEST PRESSURE FALLS. A SFC TROUGH EXTENDS S OF THE CYCLONE CENTER...WITH A WARM FRONT ARCING EWD/SEWD FROM THE CYCLONE INTO CNTRL/SRN IA. WITHIN THIS REGIME OF STRONG/COMPACT DEEP ASCENT...THE WARM FRONT WILL ADVANCE NWD WHILE THE TROUGH SHIFTS EWD/NEWD...YIELDING A SECTOR OF UPPER 50S/LOWER 60S DEWPOINTS TRACKING NEWD/NEWD ACROSS THE DISCUSSION AREA THROUGH THE AFTERNOON. THINNING CLOUDS ASSOCIATED WITH A MID-LEVEL DRY SLOT ARE ENCOURAGING DIABATIC SFC-LAYER HEATING ACROSS THIS AREA...YIELDING MARGINAL INSTABILITY. DEEP SHEAR WILL BE SUFFICIENT FOR SUPERCELL STORMS...WITH AN INCREASE IN THE COVERAGE AND INTENSITY OF THIS ACTIVITY EXPECTED INTO THE AFTERNOON. WITH OAX AND FSD VWPS SAMPLING 35 KT SLYS IN THE 2-3-KM LAYER AGL...LOW-LEVEL SHEAR WILL BE SUFFICIENT FOR TORNADOES -- ESPECIALLY NEAR THE WARM FRONT WHERE BACKED/ESELY SFC WINDS INCREASE STREAMWISE VORTICITY AND NEAR THE SFC CYCLONE CENTER WHERE BACKGROUND VERTICAL VORTICITY IS STRONGEST. THE OVERALL SVR-TSTM/TORNADO RISK MAY BE RELATIVELY MORE CONFINED IN THE SHORT-TERM...AND THEN INCREASE INTO THE AFTERNOON AS MODEST DIURNAL HEATING CONTINUES. ..COHEN/CORFIDI.. 05/10/2015 ...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT... ATTN...WFO...MPX...DMX...FSD...OAX... LAT...LON 44079715 43709489 42919438 41659469 41019594 41219694 42299777 43429866 44079715 NNNN