SPC AC 150559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Mon Apr 15 2024

   Valid 161200Z - 171200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN PARTS OF
   SOUTHERN IA...NORTHERN MO...AND WEST-CENTRAL IL...

   ...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.

   ...Synopsis...
   A seasonably deep surface cyclone should be located over central NE
   at 12Z Tuesday. This cyclone should gradually progress eastward and
   slowly weaken in IA Tuesday night. An initially intense mid-level
   jetlet (in excess of 80 kts) should become centered from the Ozark
   Plateau into the Mid-MS Valley by afternoon, before pronounced
   dampening occurs as it shifts east across the Mid-South to Lower OH
   Valleys. The initially north/south-oriented dryline/Pacific cold
   front to the south of the surface cyclone will progress into the
   Mid-MS Valley by 12Z Wednesday, with its trailing portion stalling
   by late afternoon before reaching the Ark-La-Tex.

   ...Corn Belt/Lower MO and Mid-MS Valleys...
   A broad spectrum of potential outcomes is evident ranging from
   mainly a large hail and few tornadoes day to a more substantial
   tornadic threat. The degree of tornado threat will be dependent on
   multiple uncertainties becoming more resolved, with the hail
   forecast the more confident of the three hazards. 

   Within the left-exit region of the aforementioned mid-level jet, a
   synoptically favorable corridor for mid-afternoon to early evening
   supercells is evident. Evening guidance varies in the degree of
   warm-conveyor convection that should be ongoing and how it evolves
   through midday, with the 00Z HRRR notably more aggressive. This
   early-day activity will have impacts on the degree of boundary-layer
   destabilization ahead of the dryline/cold front. At the other end of
   the spectrum, the 00Z NAM and NAM-NEST suggest a more substantial
   gap will occur between the warm conveyor activity and afternoon
   redevelopment along the dryline/front. Other guidance is somewhere
   in between these two scenarios, and even the HRRR does indicate
   isolated redevelopment occurring by late afternoon.

   Confidence is high that pronounced boundary-layer heating will occur
   behind the surface front and a plume of steep mid-level lapse rates
   attendant to the shortwave trough will overspread the northwest
   portion of the surface warm/moist sector during the afternoon.
   Backed low-level flow and veering of the wind profile with height
   should support supercells capable of producing significant severe
   hail and tornadoes. The NAM has been consistently farther west with
   the placement of the front by late afternoon with most guidance
   mixing the boundary more aggressively east in IA/MO. 

   ...Mid-South...
   NCEP guidance is highly insistent that convective coverage should be
   isolated at best and is substantially less than indicated by the
   ECMWF. This appears to be related to a lack of more pronounced
   boundary-layer heating, but also due to fairly warm and very dry
   mid-level profiles to the south side of the intense but eventually
   weakening mid-level jet. With the surface front stalling or even
   advancing back west late, large-scale ascent appears to be weak
   outside of low-level warm theta-e advection. As such, have begun
   reducing probabilities from south to north. Still, the deep-layer
   shear profile and rich boundary-layer moisture will conditionally
   support supercell potential during the period.

   ..Grams.. 04/15/2024

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