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2017-11-05 EVENT: IL/IN/OH/MI

Jesse Risley

Staff member
Sunday's forthcoming system is certainly one to keep an eye on for the Central Lowlands region. As of 0z/03 and 6z/03, there is some disparity between the major American guidance, as well as the ECMWF, especially regarding timing and placement of key surface features, including the depth and placement of the surface cyclone and wind profiles in the lower kilometers.

It does appear that a fairly potent, albeit latitudinous mid-level stream will overspread the eastern parts of the Corn Belt by early Sunday. The main area of lowest H5 pressure and its immediately associated basal jet core, however, is poised to remain up near the international border. An associated area of surface low pressure should gyrate towards the southern Great Lakes, bringing an associated warm front proximal to I-80 and/or US 24 by early evening Sunday. A strong cold is poised to approach from the west, and the potency of the mid-autumnal system looks to pull ample moisture northward into parts of IL, IN, western OH, and perhaps even extreme southern MI. Of note is the more favorable wind profiles on the recent NAM runs, although the low pressure system still appears fairly elongated and not as deep as a previous run of the ECMWF was indicating. GFS is trying to depict further northeastern placement of the low, as well as winds more parallel to the frontal forcing. Nevertheless, hodograph curvature near the warm frontal boundary is noteworthy, in an otherwise amply sheared environment. Wind profiles aloft will favor rather respectable storm motions; instability profiles, assuming ample solar insolation materializes, are yielding MLCAPE values AOA 1000 J/KG in the areas of more favorable SRH, along with favorable mid (AOA 7C) and low-level lapse rates. However, recent NAM runs have indicated a more ambient portion of CAPE on rawinsonde plots to appear available at higher pressure levels, so actual vertical profiles of temperature and dewpoint could remain a critical play come Sunday. Recent NAM runs (06z/03) are also depicting what appears to be a secondary area of lower pressure in far eastern IL around 21z.

Biggest caveats for actual tornado potential appear to be wind profiles relative to the primary surface forcing, thus relative to storm mode itself, and the timing and placement of potential maintenance of discrete storms. It definitely bears watching since shear and instability parameters are locally promising, as CINH looks to perhaps prohibit early contamination of the warm sector, other factors notwithstanding. The most recent guidance might suggest that tornadic potential would be maximized in a corridor from far eastern IL into NW and WC IN during the early evening hours on Sunday, especially INVO the warm front and perhaps a meso low, should it come to fruition. Shear profiles further east would indicate the continued threat of QLCS-type tornadic activity, along with damaging straight-line winds and likely some severe hail reports too.