486  
ACUS01 KWNS 281631  
SWODY1  
SPC AC 281630  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1130 AM CDT MON JUL 28 2025  
 
VALID 281630Z - 291200Z  
 
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON  
INTO TONIGHT FROM EASTERN SOUTH DAKOTA ACROSS SOUTHERN MINNESOTA AND  
NORTHERN IOWA...  
   
..SUMMARY  
 
SEVERE STORM CLUSTERS ARE EXPECTED TO FORM THIS AFTERNOON IN SOUTH  
DAKOTA AND THEN SPREAD SOUTHEASTWARD INTO MINNESOTA AND IOWA THROUGH  
TONIGHT. SWATHS OF DAMAGING WINDS, POTENTIALLY 75-90 MPH, A FEW  
TORNADOES AND ISOLATED LARGE HAIL WILL ALL BE POSSIBLE.  
   
..DAKOTAS TO MN/IA THROUGH TONIGHT  
 
AROUND THE NORTHERN PERIPHERY OF A MIDLEVEL HIGH COVERING THE  
SOUTHERN PLAINS AND SOUTHEAST, A SERIES OF EMBEDDED SPEED MAXIMA  
WILL PROGRESS FROM MT ACROSS THE DAKOTAS TO MN THROUGH EARLY  
TUESDAY. ELEVATED CONVECTION IS ONGOING IN ASSOCIATION WITH TWO  
SUCH SPEED MAXIMA - ONE OVER ND AND ANOTHER MOVING EASTWARD OVER  
EASTERN MT. AT THE SURFACE, A LEE CYCLONE IS PRESENT NEAR THE SD/NE  
BORDER, AND A BAROCLINIC ZONE ARCS INTO NORTHEAST SD AND THEN  
SOUTHEASTWARD ACROSS SOUTHWEST MN INTO NORTHERN IA. A PRIOR OUTFLOW  
BOUNDARY (FROM DISSIPATED OVERNIGHT CONVECTION) WILL BECOME MORE  
DIFFUSE WITH TIME AS A RESULT OF STRONG SURFACE HEATING ACROSS  
IA/NE/SD WITHIN THE OLD COLD POOL.  
 
THE ELEVATED CONVECTION ACROSS SOUTHERN ND, AND MOVING FROM MT INTO  
SOUTHWEST ND, COULD PERSIST IN THE POST-FRONTAL ENVIRONMENT WITH  
WEAK WARM ADVECTION ATOP THE FRONTAL SURFACE. STEEP MIDLEVEL LAPSE  
RATES AND 40-50 KT MIDLEVEL FLOW SUGGESTS A CONTINUED THREAT FOR  
OCCASIONAL SEVERE OUTFLOW GUSTS AND ISOLATED LARGE HAIL. THE MORE  
SUBSTANTIAL SEVERE-STORM THREAT IS EXPECTED TO EVOLVE FARTHER  
SOUTHEAST BY MID-LATE AFTERNOON ALONG THE BAROCLINIC ZONE IN SD, TO  
THE NORTHEAST OF THE LEE CYCLONE. STRONG SURFACE HEATING, CONTINUED  
MOISTURE ADVECTION AND EVAPOTRANSPIRATION WILL LEAD TO THE  
DEVELOPMENT OF STRONG-EXTREME BUOYANCY (3000-4500+ J/KG MLCAPE)  
BENEATH AN ELEVATED MIXED LAYER WITH 8.5-9 C/KM MIDLEVEL LAPSE  
RATES. STORMS THAT FORM IN SD ARE THEN EXPECTED TO CONGEAL INTO A  
CLUSTER OR TWO THAT WILL SUBSEQUENTLY SPREAD EAST-SOUTHEASTWARD  
ALONG THE MORE NORTHWEST-SOUTHEAST ORIENTED BAROCLINIC ZONE NOW  
NOTED IN VISIBLE IMAGERY AND SURFACE OBSERVATIONS FROM SOUTHWEST MN  
INTO NORTHERN IA. THE THERMODYNAMIC ENVIRONMENT WILL FAVOR BOTH  
INTENSE UPDRAFTS AND DOWNDRAFTS, WHILE DEEP-LAYER VERTICAL SHEAR  
WILL BE SUFFICIENT FOR AN ORGANIZED/BOWING MCS. THUS, THERE WILL BE  
THE POTENTIAL FOR SWATHS OF SIGNIFICANT-SEVERE OUTFLOW (75-90 MPH),  
AS WELL AS ISOLATED LARGE HAIL AND A FEW TORNADOES (EITHER WITH  
INITIALLY DISCRETE SUPERCELLS OR WITH EMBEDDED CIRCULATIONS WITH  
BOWING SEGMENTS).  
   
..CENTRAL MT THIS AFTERNOON THROUGH EARLY TONIGHT  
 
AN EMBEDDED SPEED MAX WILL CREST THE RIDGE AND MOVE FROM ID TO  
SOUTHWEST MT THIS AFTERNOON/EVENING. RESIDUAL BOUNDARY-LAYER  
DEWPOINTS IN THE MID-UPPER 50S IN THE POST-FRONTAL ENVIRONMENT,  
ALONG WITH SURFACE HEATING AND THE NORTH EDGE OF THE STEEPER  
MIDLEVEL LAPSE RATES WILL FAVOR SCATTERED THUNDERSTORM DEVELOPMENT  
BY EARLY-MID AFTERNOON (NEAR AND JUST NORTHEAST OF THE HIGHER  
TERRAIN SOUTHWEST INTO CENTRAL MT). MLCAPE OF 1500-2000 J/KG,  
EFFECTIVE BULK SHEAR IN EXCESS OF 40 KT AND SEASONABLY COOL MIDLEVEL  
TEMPERATURES SUGGEST THE POTENTIAL FOR INITIAL SUPERCELLS WITH LARGE  
HAIL (1-2.5 INCHES IN DIAMETER), AND ALSO THE POTENTIAL FOR UPSCALE  
GROWTH INTO A CLUSTER WITH THE ATTENDANT THREAT FOR WIND DAMAGE.  
 
..THOMPSON/THORNTON.. 07/28/2025  
 
 
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