New AFD issued by LOT:
".MESOSCALE...
Issued at 325 PM CDT Thu May 15 2025
Watching a couple of areas where convection could initiate and
affect northern Illinois.
First, an area of enhanced cumulus along a pre-frontal
convergence axis from Jo Daviess County south to near KPIA then
KSPI. Starting to see some convection develop over southwest WI
within this axis, but thus far cumulus isn't terribly impressive
over Illinois. A bit of a complicated environment over our area
with an axis where low level moisture has mixed out over about the
western half of our CWA, resulting in stronger capping and a
dearth in cumulus. This more capped, better mixed out air mass
will probably spread into eastern portions of the CWA over the
next couple of hours. A second area we're watching is along the
dryline over eastern IA, where we're starting to see some more
robust cumulus development west of the Quad Cities. As large scale
ascent increases, should see convective initiation with either or
both of these features between 21-23z.
Supercells are likely to be the storm mode when convection
develops, with large to very large hail (2-3" in diameter) and
locally damaging winds the primary threat. Given the higher LCLs
and more mixed out dewpoints, the tornado threat looks to be quite
low in Illinois for the next couple/few hours. Early this
evening, toward 23-00z, should begin to see low level jet
developing resulting in increasingly strong low level shear. By
this point, storms should be moving into our eastern CWA, where
there could be a window of opportunity for a somewhat greater
tornado threat, in particular northwest Indiana and portions of
IL closer to the IN border."