SPC not making many changes to the Day 1 forecast except extending the 10% tornado risk and CIG 2 north. There maybe more small changes but it’s too late to dig into it. A great read below.
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Wed Jun 17 2026
Valid 171200Z - 181200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER ILLINOIS
AND INDIANA...
...SUMMARY...
An outbreak of severe thunderstorms is expected today, with primary
threat centered over Illinois and Indiana. Several intense
tornadoes, swaths of damaging gusts over 75 mph and damaging
wind-driven hail will all be possible.
...IL...IN...MO...OH...
An intense mid and upper level jet will nose southeastward across
the Midwest today, with a prominent leading disturbance moving out
of IA and into IL through midday. Severe storms are likely to be
associated with this early wave as a southwesterly low-level jet
increases to 60 kt and rapidly bring instability into the area. This
initial activity will bring damaging winds to eastern IA and
northern/central IL. This system is expected to weaken later in the
afternoon, but some remnants will move across IN.
Ahead of this early activity, a warm front will push north across IN
and OH. New severe storm development, perhaps transitioning out of
the remnant activity and/or forming near the warm front, is possible
across northern IN into northwest OH. Shear profiles will be
excessive, with tornado risk only conditional on minimal instability
being present. The result may be a isolated tornadic supercells.
To the west, the air mass across northern MO, IL, and into central
IN will easily recover and rapidly destabilize due to strong
southwest winds. A 60+ kt low-level jet is forecast, with notably
strong winds around 700 mb as well (surface to 3 km shear values may
exceed 60 kt). A plume of 65-70 F dewpoints will likely extend from
central MO into IL and western IN in the 21-00Z time frame,
contributing to 2000-3000 J/kg MLCAPE.
A broken line of supercells is likely to develop and mature roughly
from northern IN into central IL and MO around 21Z and spreading
east/southeast through early evening. Given the clearly
supercellular shear profiles, linear storm mode is unlikely for most
of the event. Long-tracked supercells producing tornadoes and
damaging hail are likely.
Finally, the warm frontal position will need to be monitored near
the IN/MI border. Even if instability is elevated into MI, extreme
shear and lift may still yield damaging winds and even a tornado
risk. As such, probabilities have been increased into far southern
Lower MI.
...Upper TX Coast into the northern Gulf Coast...
The NHC forecast shows Potential TC One moving into southwest LA by
00Z. Wind fields associated with this system will strengthen out of
the south ahead of it, resulting in areas of strong low-level shear
from TX into southern LA, and possibly into MS. Mid to upper 70 F
dewpoints will contribute to modest CAPE values, supporting embedded
stronger cells with tornado potential.
..Jewell/Weinman.. 06/17/2026
