SPC AC 190555

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1255 AM CDT Wed Mar 19 2025

   Valid 191200Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL
   ILLINOIS INTO FAR WESTERN INDIANA...

   ...SUMMARY...
   Scattered severe thunderstorms are possible on Wednesday across
   parts of central Illinois to western Indiana from mid-afternoon to
   early evening. Several tornadoes, large hail, and damaging wind
   gusts will be possible.

   ...Synopsis...
   A strong mid-level low will move from northeast Kansas this morning
   to Lower Michigan by 12Z Thursday. A strong mid-level jet streak
   along the southeastern periphery of this area of low pressure will
   translate from northeast Oklahoma to central Illinois. Meanwhile a
   surface low within the left exit region of this upper-level jet will
   move from northeast Kansas to north-central Illinois. 

   ...Central Illinois into north-central Illinois and western
   Indiana...
   A rapidly changing environment is forecast across Illinois today.
   Extensive cloudcover is expected across the state for much of the
   day as low-level moisture streams north within a narrow corridor
   ahead of the cold front. However, by mid to late afternoon, some
   clearing is expected which may allow for some brief heating and
   destabilization across central Illinois. In fact, the HRRR shows
   what appears to be a dryline by mid afternoon. Mid-level
   temperatures will be very cold (-22C at 500mb and -4C at 700mb)
   which will allow for rapid destabilization with only slight heating.
   Once destabilization begins ahead of the cold front/dry line, expect
   thunderstorm development. The wind profile across central and
   northern Illinois will support supercells, but the intensity of
   these supercells will be modulated by the instability. 250-500 J/kg
   MLCAPE will likely be sufficient for supercells capable of all
   severe weather hazards. However, if greater destabilization occurs,
   such as shown by the 00Z HRRR/ 03Z RAP, an even more volatile
   environment would be present. 56-57F dewpoints would support 1000+
   J/kg MLCAPE which is very significant in the low-topped environment
   with an EL below 30kft. HRRR/RAP soundings show STP values around
   2-3 with very favorable low-level hodograph shapes. Therefore, in
   the higher instability scenario, multiple tornadic supercells would
   be possible with the potential for strong (EF2+) tornadoes. While
   uncertainties remain regarding dewpoints and the amount of
   clearing/heating along/ahead of the front, an enhanced risk upgrade
   seems prudent given the expectation for several supercells capable
   of all hazards and the conditional potential for a more volatile
   environment.

   ...Southern Indiana southward to MS/AL...
   Additional thunderstorms are expected to develop along the cold
   front across Indiana at the nose of the mid-level jet streak during
   the evening as rapid ascent and mid-level cooling erodes inhibition.
   Forecast sounding show an environment favorable for supercells
   capable of all severe weather hazards to persist across Indiana
   before eventually outrunning the instability somewhere near the Ohio
   border. Mid-level cooling will not be as great farther south across
   KY/TN and into MS/AL. However, greater low-level moisture (upper 50s
   to low 60s dewpoints) should compensate with a few scattered
   supercells possible with a primary threat of large hail and damaging
   wind gusts during the evening.

   ..Bentley.. 03/19/2025

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