964  
ACUS01 KWNS 210530  
SWODY1  
SPC AC 210528  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1228 AM CDT SAT JUN 21 2025  
 
VALID 211200Z - 221200Z  
 
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF  
THE GREAT LAKES REGION...  
   
..SUMMARY
 
 
THUNDERSTORMS ASSOCIATED WITH MARGINALLY SEVERE WIND GUSTS AND HAIL  
WILL BE POSSIBLE TODAY FROM THE NORTHERN PLAINS INTO THE UPPER  
MISSISSIPPI VALLEY AND GREAT LAKES.  
   
..GREAT LAKES
 
 
A MID-LEVEL RIDGE WILL MOVE QUICKLY EASTWARD INTO THE NORTHEAST  
TODAY, AS TRAILING SHORTWAVE TROUGH MOVES THROUGH THE GREAT LAKES.  
AN MCS WITH SOME SEVERE POTENTIAL WILL LIKELY BE ONGOING AT THE  
START OF THE PERIOD IN THE VICINITY OF LAKE SUPERIOR.  
WARM-ADVECTION-RELATED CONVECTION IS EXPECTED TO DEVELOP ALONG THE  
SOUTHERN EDGE OF THE DECAYING MCS FROM THE UPPER PENINSULA OF  
MICHIGAN EASTWARD INTO NORTHERN SECTIONS OF THE LOWER PENINSULA OF  
MICHIGAN. AS LOW-LEVEL LAPSE RATES STEEPEN DURING THE MORNING,  
ISOLATED DAMAGING WIND GUSTS WILL BE POSSIBLE WITH SHORT LINE  
SEGMENTS. DURING THE AFTERNOON, THE BRUNT OF THE CONVECTION IS  
FORECAST TO MOVE ACROSS SOUTHWESTERN ONTARIO. THE SOUTHERN EDGE OF  
THIS CLUSTER MAY MOVE BACK INTO THE LOWER 48, AFFECTING PARTS OF NEW  
YORK DURING THE LATE AFTERNOON. IN CENTRAL NEW YORK, MODERATE  
INSTABILITY IS FORECAST ALONG WITH NORTHWEST MID-LEVEL FLOW AROUND  
50 KNOTS. THIS SHOULD BE ENOUGH FOR AN ISOLATED WIND-DAMAGE THREAT  
WITH THE FASTER-MOVING SHORT LINE SEGMENTS. HAIL WILL ALSO BE  
POSSIBLE WITH THE STRONGER CORES.  
 
FURTHER SOUTH INTO PARTS OF NORTHERN PENNSYLVANIA, MODERATE  
INSTABILITY IS FORECAST TO DEVELOP BY AFTERNOON. DUE TO A LACK OF  
LARGE-SCALE ASCENT, CONVECTIVE COVERAGE IS EXPECTED TO BE VERY  
ISOLATED. ANY CELL THAT CAN INITIATE IN THE HIGHER TERRAIN COULD  
HAVE POTENTIAL FOR MARGINALLY SEVERE WIND GUSTS.  
   
..NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY
 
 
ANTICYCLONIC SOUTHWESTERLY MID-LEVEL FLOW WILL BE IN PLACE TODAY  
ACROSS MUCH OF THE NORTH-CENTRAL U.S. AT THE SURFACE, A POST-FRONTAL  
AIRMASS WILL BE IN PLACE OVER MUCH OF THE NORTHERN PLAINS. BEHIND  
THE FRONT, A MOIST AIRMASS WILL REMAIN OVER PARTS OF THE DAKOTAS,  
WHERE SURFACE HEATING SHOULD YIELD MODERATE INSTABILITY BY  
AFTERNOON. ALTHOUGH LARGE-SCALE ASCENT WILL REMAIN WEAK ACROSS MOST  
OF THE REGION, POCKETS OF LOW-LEVEL CONVERGENCE ARE FORECAST TO  
DEVELOP WITHIN THIS AIRMASS. THIS SHOULD BE ENOUGH FOR ISOLATED  
CONVECTIVE INITIATION DURING THE MID TO LATE AFTERNOON. MARGINALLY  
SEVERE WIND GUSTS AND HAIL WILL BE THE PRIMARY THREATS.  
 
FURTHER WEST INTO THE NORTHERN HIGH PLAINS, SCATTERED THUNDERSTORMS  
ARE EXPECTED TO DEVELOP DURING THE OVERNIGHT PERIOD, AHEAD OF A  
MID-LEVEL TROUGH IN THE NORTHWESTERN U.S. ALTHOUGH A RELATIVELY DRY  
AIRMASS WILL BE IN PLACE, LOW TO MID-LEVEL LAPSE RATES WILL BE  
STEEP, AND COULD BE ENOUGH FOR A MARGINAL WIND-DAMAGE THREAT.  
 
..BROYLES/MOORE.. 06/21/2025  
 

 
 
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