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   ACUS01 KWNS 281641   
   SWODY1   
   SPC AC 281640   
      
   Day 1 Convective Outlook   
   NWS Storm Prediction Center Norman OK   
   1040 AM CST Sun Dec 28 2025   
      
   Valid 281630Z - 291200Z   
      
   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF   
   EASTERN ILLINOIS INTO INDIANA AND WESTERN KENTUCKY...   
      
   ...SUMMARY...   
   Scattered severe thunderstorms are possible over parts of the   
   Midwest and lower Ohio Valley this afternoon through the evening.   
   Severe/damaging wind gusts and a couple of tornadoes are the primary   
   threats.   
      
   ...Mid Mississippi Valley into the Midwest/Ohio Valley...   
   An upper trough/low over the northern Plains this morning will   
   further intensify today as it develops towards the Upper   
   Midwest/Great Lakes through the period. Pronounced large-scale   
   ascent associated with a strengthening mid/upper jet (100-120 kt at   
   500 mb) over the mid MS Valley into IL/IN will encourage rapid   
   deepening of a surface low as it develops from central/northern IL   
   into Lower MI by this evening. A rather moist low-level airmass with   
   generally upper 50s to low 60s surface dewpoints will continue to   
   spread northward across the mid MS Valley into parts of the   
   Midwest/OH Valley and southern Great Lakes regions in tandem with a   
   northward-shifting surface warm front. A cold front is also expected   
   to sweep east-southeastward across these regions this   
   afternoon/evening as the surface low tracks northeastward. This cold   
   front should serve as a focus for strong to severe convection later   
   today.   
      
   The 12Z ILX sounding showed a moist but saturated profile through   
   much of the troposphere, with strong west-southwesterly   
   mid/upper-level winds already present over the warm sector. Current   
   expectations are for ongoing, mostly elevated convection across   
   central IL to pose a threat for isolated hail and strong to locally   
   severe gusts given the strength of the mid-level flow. This activity   
   may linger along/just north the warm front through the afternoon as   
   it spreads quickly east-northeastward into IN. Additional   
   thunderstorms are expected to form along/near the cold front across   
   IL and vicinity by 20-22Z as modest/filtered daytime heating occurs,   
   with come cloud breaks already noted in visible satellite imagery   
   across east-central MO/south-central IL. It does appear that surface   
   temperatures are warming faster/more than forecast by some guidance   
   across the warm sector in IL, with 16Z observations at some stations   
   already reaching into the upper 60s/low 70s.   
      
   The more aggressive 12Z guidance and recent RAP runs suggest that   
   around 500-1000 J/kg of MLCAPE may ultimately develop in a narrow   
   corridor across eastern IL and western IN/KY ahead of the front,   
   even though modest lapse rates aloft will likely inhibit more robust   
   destabilization. This weak instability should be sufficient to   
   support organized updrafts, as both low-level and deep-layer shear   
   will be quite strong owing to the strengthening wind profiles across   
   the warm sector this afternoon/evening with the approaching   
   mid/upper-jet. There is still some uncertainty regarding the   
   potential for pre-frontal convection. But, any low-topped supercells   
   that can form and be sustained should pose a threat for a couple of   
   tornadoes with upwards of 200-250 m2/s2 of effective SRH present.   
   Eventual development of a thin/forced line of convection along the   
   cold front appears likely, with a threat for scattered   
   severe/damaging winds and perhaps a couple of embedded tornadoes. At   
   least an isolated severe threat may persist this evening/tonight   
   across the OH Valley and parts of western PA, where low-level flow   
   is forecast to remain quite strong even with minimal instability.   
      
   ..Gleason/Wendt.. 12/28/2025   
      
   $$   
      
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