SPC AC 180549

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1249 AM CDT Sun Sep 18 2022

   Valid 181200Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID MISSISSIPPI VALLEY...

   ...SUMMARY...
   Scattered severe thunderstorms should develop across the Mid
   Mississippi Valley late Sunday afternoon. Hail, wind, and some
   threat for a few tornadoes will spread toward central Illinois
   during the evening hours.

   ...Mid Mississippi Valley...

   Late-evening model guidance suggests upper ridge will build across
   the southern Plains and strengthen during the day1 period. This
   feature will force a notable short-wave trough currently located
   over WY to top the ridge over eastern SD/NE around 18z before it
   turns southeast and digs toward the OH Valley by 19/12z. As a
   result, broad height rises will be noted across much of the
   western/central US during the first half of the period.

   Early this morning, thunderstorm clusters continue across southern
   IA with more isolated activity into eastern KS. This activity is
   likely being sustained by a focused LLJ that should move little over
   the next 36hr, aside from veering toward central IL Sunday evening.
   Remnants of this convection are expected to be ongoing at the
   beginning of the period from southeast IA into central IL. Latest
   guidance suggests weakening is likely after sunrise, though it may
   not completely dissipate as it propagates southeast. While
   marginally severe hail/wind could occur with this early-period
   convection, the primary concern for more significant severe will
   occur later in the afternoon/evening as influence of the
   aforementioned short wave approaches.

   Strong boundary-layer heating is forecast once again across KS where
   surface temperatures may approach 100F in the central part of the
   state. Readings into the low-mid 90s are possible across northwest
   MO. If this occurs convective temperatures may be breached around
   22z. There is some concern that isolated convection could develop
   along the boundary shortly after peak heating but large-scale
   forcing will not be particularly focused before sunset. However, as
   the short wave digs southeast, scattered convection will likely
   develop near the boundary over central IA. Forecast soundings favor
   supercells, which should mature and dig east-southeast toward a very
   unstable air mass with MUCAPE in excess of 4000 J/kg. Very steep
   lapse rates and favorably forced/sheared environment suggest very
   large hail with the stronger storms. Additionally, while these
   updrafts may be slightly elevated, low-level shear appears favorable
   for some risk of tornadoes. Latest HREF guidance supports this
   scenario with a cluster of supercells evolving over IA and growing
   upscale as they spread toward central IL during the late evening.
   Damaging winds may also occur, especially if storm mergers and
   bow-type features evolve.

   ..Darrow/Squitieri.. 09/18/2022

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z