Official statement from the NWS

SYNOPSIS...
Issued at 330 PM EST Tue Feb 28 2017

Severe storms expected to develop and move through central
Indiana later tonight and during the overnight, with potential for
tornadoes, large hail and damaging winds. The threat will continue
into Wednesday morning until a cold front moves through to bring
it to an end. Small chances for rain or snow will be off and on
Wednesday night through Friday night for parts of the area, but a
warmup will come for the weekend. More rain chances arrive to end
the weekend and start the work week.

&&

.NEAR TERM /Tonight/...

Issued at 330 PM EST Tue Feb 28 2017

Forecast focus is on severe weather expected tonight-both the
threats and the timing. Incredible dynamics are coming into place
over the area with a strong upper jet and low level jet forecast
to come into phase tonight over the Ohio Valley. While instability
could be a somewhat limiting factor given the timing during the
night and no sunshine today, moisture return has been ample on
southerly flow and dewpoints in the 60s are already making their
way into central Indiana. The vertical shear profiles are
extremely favorable for rotating storms, and LCLs and LFCs are
sufficiently low to not impede tornado development.

Best estimate on timing of severe potential for the area at this
point is starting around 9pm in the western counties, 10-11
central and midnight or so east. Initially more discrete cells
are anticipated that could possibly morph into a line as they
move across the area, but some models are also indicating they may
keep their more discrete nature. There is also potential after
this first batch of storms that another may come behind them in
the form of a squall line ahead of the cold front.

Given the shear profiles, the tornado threat will continue through
the overnight hours, along with potential for very large hail and
damaging winds.

Also of note...southern counties received a couple of rounds of
showers and thunderstorms already today, with around an inch of
rain or more in some locations. With another couple of rounds
moving through tonight and ample moisture, see potential for
flash flooding and have issued a flash flood watch for that area.