Jesse Risley
Staff member
Wednesday offers a marginal local setup for the Corn Belt region, namely far eastern MO, much of IL, and perhaps parts of W IN. A 500 mb impulse will nose into the Upper Mississippi Valley by late in the period. Overnight tonight an associated disturbance should create some convection that continues early into the 09/12z period, before moving out by late morning, which, if models are correct, allows ample clearing across the area through mid to late afternoon.
As associated area of low pressure should move into the Upper Mississippi Valley Wednesday afternoon, with an attendant cold front approaching the axis of greatest instability across the risk area. If the atmosphere destabilizes as forecast, MUCAPE value AOA 2500 J/KG should lie across parts of SE MO/IL/W IN, partly owed to a modest return of moisture overnight, with LI values AOB -7 across the region. Overall bulk shear profiles are rather anemic, precluding a more substantial severe risk (even the best skew-T profiles on the NAM across EC IL barely approach classic supercell threshold), though a broken line of mostly multi-cell to possible transient supercell structures should evolve by 20z-21z proximal to the Illinois River, as more convection ignites along the area of greatest forcing and propagates east through early evening.
Though possibly a nice gentleman's chasing opportunity, this one has the possibility of producing one or two diamonds in the rough, depending on the evolution and extent of the progged overnight convection. Though surface flow is otherwise modest and directional shear is mostly unfavorable for tornadic activity, historically speaking, remnant, localized boundaries from overnight or early morning convection co-located with ample instability may be enough to enhance low-level rotation and get a few of these storms to produce brief, low-end tornadoes. Given the overall synoptic setup, the usual threats of marginally severe hail and some damaging wind reports would be the primary threats.
As associated area of low pressure should move into the Upper Mississippi Valley Wednesday afternoon, with an attendant cold front approaching the axis of greatest instability across the risk area. If the atmosphere destabilizes as forecast, MUCAPE value AOA 2500 J/KG should lie across parts of SE MO/IL/W IN, partly owed to a modest return of moisture overnight, with LI values AOB -7 across the region. Overall bulk shear profiles are rather anemic, precluding a more substantial severe risk (even the best skew-T profiles on the NAM across EC IL barely approach classic supercell threshold), though a broken line of mostly multi-cell to possible transient supercell structures should evolve by 20z-21z proximal to the Illinois River, as more convection ignites along the area of greatest forcing and propagates east through early evening.
Though possibly a nice gentleman's chasing opportunity, this one has the possibility of producing one or two diamonds in the rough, depending on the evolution and extent of the progged overnight convection. Though surface flow is otherwise modest and directional shear is mostly unfavorable for tornadic activity, historically speaking, remnant, localized boundaries from overnight or early morning convection co-located with ample instability may be enough to enhance low-level rotation and get a few of these storms to produce brief, low-end tornadoes. Given the overall synoptic setup, the usual threats of marginally severe hail and some damaging wind reports would be the primary threats.