SPC AC 160538

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1238 AM CDT Tue Apr 16 2024

   Valid 161200Z - 171200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE MIDWEST...

   ...SUMMARY...
   Scattered severe thunderstorms are likely today, centered mostly
   over the midwestern states of northern Missouri/Iowa/northwestern
   Illinois. Hail, wind, and tornadoes are expected in this corridor.
   More isolated activity could develop as far south as the Ozarks of
   northern Arkansas.

   ...Midwest...

   Upper low is currently located over southeast CO, and will soon
   begin ejecting northeast in line with latest model guidance into the
   central Plains. By 18z this feature should advance into eastern NE
   as 90kt 500mb speed max translates through the base of the trough,
   across northern OK, into northwestern MO. In response to this
   dynamic system, strong LLJ will focus across the eastern Plains
   early then shift into the mid/upper MS Valley by 18z.

   Low-level warm advection is expected to prove instrumental in
   early-day convection, in association with the LLJ. This activity
   should be ongoing at the start of the period, focused over the
   mid-MO Valley. Subsequent movement/development is expected
   downstream across IA/southern MN as the warm conveyor shifts east.
   While strong shear will support this convection, the primary concern
   will be with secondary development in association with a pronounced
   mid-level dry slot. Latest model guidance suggests surface-3km lapse
   rates will steepen to near 9 C/km across southeast NE/northeast KS
   by 18z. Leading edge of this steeper lapse-rate plume will advance
   across western IA, immediately ahead of the surface low. As a
   result, boundary-layer heating will contribute to substantial
   buoyancy and some areas may experience MLCAPE near 2000 J/kg. 
   Surface-based parcels are forecast to be uninhibited by 17-18z
   across western IA. Current thinking is scattered convection should
   develop within this zone of destabilization then spread northeast.
   Surface warm front is expected to serve as a northern limit to
   surface-based convection, along with any appreciable tornado risk.
   Large hail can be expected with supercells, and favorable shear will
   support the potential for tornadoes, a few potentially strong. This
   activity will spread across IA/extreme northern MO into northwestern
   IL during the evening.

   Farther south into the Ozarks, severe threat is much more
   conditional. Forecast soundings exhibit poor lapse rates and at
   least weak inhibition through much of the period. It's not real
   clear how robust updrafts will be, despite the strong shear, given
   the marginal lapse-rate environment. Will maintain SLGT Risk into
   this portion of the lower MS Valley but convection may struggle much
   of the period.

   ..Darrow/Lyons.. 04/16/2024

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