SPC AC 151727

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 PM CDT Mon Apr 15 2024

   Valid 161200Z - 171200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST
   IOWA...NORTHERN MISSOURI...AND WEST-CENTRAL ILLINOIS...

   ...SUMMARY...
   Scattered severe thunderstorms are likely from Tuesday morning into
   the evening across a portion of the central states from the Corn
   Belt to the Ozark Plateau. The most concentrated area of significant
   severe hail and tornado potential is forecast over southern Iowa
   into northern Missouri and west-central Illinois. A more isolated
   severe threat is anticipated across portions of the Mid-Atlantic
   states.

   ...Synopsis...
   A robust upper-level low is evident in mid-morning water-vapor
   imagery over the Four Corners region. At the surface, pressure falls
   are ongoing as a lee cyclone begins to consolidate across the High
   Plains. Over the next 24-48 hours, this surface low is forecast to
   migrate east towards the MS River Valley, likely reaching northern
   IA by late afternoon/early evening as it begins to occlude.
   Thunderstorms will be focused within a preceding warm advection
   plume, along a leading outflow boundary associated with
   early-morning convection, and along a trailing cold front. The most
   intense convection is expected in the vicinity of the surface low
   along the northern fringe of the warm sector where strong synoptic
   ascent will overspread a buoyant air mass with favorable low-level
   wind shear; however, several mesoscale details that will likely
   determine the overall magnitude of the severe event will be
   dependent on the intensity/coverage of early-morning convection,
   which introduces uncertainty into the forecast. 

   ...Corn Belt/Lower MO and Mid-MS Valleys...
   Latest guidance continues to show reasonably good agreement in the
   potential for ongoing showers and thunderstorms across eastern NE/KS
   at 12 UTC Tuesday morning. This activity should intensify through
   the morning across northern MO/central IA amid diurnal heating of a
   moist, and weakly capped warm sector. While somewhat modest
   mid-level lapse rates (6-7 C/km) will limit MLCAPE to around 1000
   J/kg, strong veering flow in the lowest 2 km and 60-70 knot flow
   aloft may support early supercell development with an attendant
   tornado/wind threat. Low-level helicity will likely be maximized
   along the surface warm/occluding front across portions of western IL
   into IA, and recent CAMs continue to show a strong UH signal across
   this region. 

   However, this potential will likely be modulated by two factors. The
   first is the degree of cloud cover/stratiform precipitation on the
   northern fringe of the warm sector - especially across MO/IA/IL,
   which may limit the degree of low-level destabilization. The second
   is storm coverage, which remains very uncertain given high spread in
   recent CAMs' depiction of convective evolution over the next 24
   hours. Greater thunderstorm coverage than currently anticipated at
   12 UTC may complicate convective mode later in the day, and the
   strong synoptic ascent in the vicinity of the surface low, coupled
   with weak capping, may favor higher convective coverage. If this
   occurs, northerly storm motions along the primary boundary may favor
   storm interactions/consolidation into one or more clusters/lines
   that may favor a severe wind risk over tornado/hail. Regardless, the
   overall synoptic regime and forecast environment support maintaining
   the current risk probabilities. The strong effective bulk shear
   values (60-70 knots) and effective SRH near 250 m2/s2 suggest that
   significant hail and/or significant tornadoes are possible if a
   predominantly discrete mode can be realized. Some solutions hint at
   re-development late afternoon along the cold front across northern
   MO/southern IA, but confidence in this scenario is low given the
   high dependence on rapid destabilization after preceding convection.


   ...OH Valley into the Mid-Atlantic...
   Isolated to scattered thunderstorms are expected to develop by late
   morning within a warm advection regime over the OH River Valley.
   While buoyancy will be somewhat meager (500-1000 J/kg MLCAPE),
   elongated deep-layer hodographs may support storm longevity as they
   meander southeast into the Appalachians/Mid-Atlantic region. Surface
   temperatures warming into the low to mid 80s will steepen low-level
   lapse rates to near 8 C/km, which may support a few damaging gusts
   with the stronger cells.

   ..Moore.. 04/15/2024

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