SPC AC 161242

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0742 AM CDT Tue Apr 16 2024

   Valid 161300Z - 171200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   IOWA...NORTHERN MISSOURI...AND NORTHWESTERN ILLINOIS...

   ...SUMMARY...
   Scattered severe thunderstorms appear likely today, centered mostly
   over northern Missouri, Iowa, and northwestern Illinois. Large hail,
   damaging winds, and tornadoes should occur in this corridor. More
   isolated activity could develop as far south as the Ozarks of
   northern Arkansas.

   ...Synopsis...
   An upper trough/low over the central Plains this morning will
   continue to eject east-northeastward across the mid MO Valley and
   Upper Midwest through tonight. A 70-90 kt mid-level jet will
   overspread parts of the Midwest through the day, contributing to
   substantial deep-layer shear and thunderstorm organization. At the
   surface, a 990 mb low over central NE will likewise develop
   east-northeastward through the day in tandem with the upper wave. A
   warm front should lift northward across parts of the Midwest, with
   generally low to mid 60s surface dewpoints present across the warm
   sector as far south as the Ozarks. A composite Pacific cold
   front/dryline will move quickly eastward from the southern/central
   Plains into the mid Ms Valley by this evening. This boundary should
   stall across the southern Plains, and may begin to lift northward
   late tonight.

   ...Midwest/Mid Mississippi Valley...
   A large area of showers and thunderstorms is ongoing this morning
   from parts of eastern KS/NE/SD into IA. Much of this activity across
   the central Plains is being driven by large-scale ascent associated
   with the ejecting upper trough/low, along with strong warm/moist
   advection with a 40-50 kt southerly low-level jet. As this
   convection continues to spread eastward this morning in tandem with
   the migrating low-level jet axis, it will probably become more
   elevated, especially as it moves into northern MO and IA and a less
   unstable airmass to the north of the warm front. Still, an isolated
   severe threat may persist in the short term with these
   thunderstorms. The effect of this early-day convection on robust
   destabilization in its wake along/ahead of the cold front remains a
   concern and potentially limiting factor for additional severe
   thunderstorm development this afternoon. Even so, most guidance,
   including multiple recent runs of the RAP, shows a narrow corridor
   of weak to moderate instability developing along/south of the warm
   front in IA, and ahead of the cold front sweeping eastward across
   MO/IA. This re-destabilization should be aided by a pocket of steep
   mid-level lapse rates and cold temperatures aloft on the southeast
   side of the upper trough/low.

   Assuming that low to mid 60s surface dewpoints and modest daytime
   heating can aid in this instability actually materializing, then a
   risk for supercells should exist over parts of IA, northern MO, and
   northwestern IL. Both low-level and deep-layer shear appear strong
   enough for supercells. Steep lapse rates will aid in hail
   production, with some chance for 2+ inch diameter stones with the
   more robust cores. Tornadoes will also be a concern, as the enhanced
   boundary-layer flow and enlarged/curved hodographs associated with a
   the low-level jet will aid in updraft rotation. The best tornado
   potential will probably be focused along/near the warm front in IA,
   where the greatest low-level shear is forecast. Here, a strong
   tornado appears possible. Isolated to scattered damaging winds may
   also occur.

   Farther south into the Ozarks and Mid-South, the potential for
   severe thunderstorms appears more conditional. Various NAM/RAP
   forecast soundings exhibit generally poor lapse rates, with at least
   weak inhibition through much of the period. Given these regions
   displacement from the upper trough/low to the north, it remains
   unclear how robust updrafts will be in a more marginal low/mid-level
   lapse rate environment. Still, have maintained the Slight Risk into
   parts of the lower MS Valley, but convection may struggle to
   intensify this afternoon/evening.

   ..Gleason/Grams.. 04/16/2024

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