.Short Term...(Today through Monday) Issued at 237 AM EDT Sun Aug 1 2021 
Today...  A deep upper level trough will begin its descent into the Ohio
Valley today, progressing within the NW flow and strong vorticity maximum.
This will push cooler mid to upper level air over central Indiana and
should lead to sub-seasonal temperatures over the next few days. At the
surface, a weak boundary will traverse downstream of the upper wave,
passing through central Indiana between 15Z and 20Z. This cool air mass
should decrease the near PBL temperatures, but with partly cloudy
conditions and a relatively dry surface layer, near dry adiabatic lapse
rates within the PBL this afternoon should allow temperatures to approach
80.  The cool air mass within the trough and high surface layer lapse rates
will create a brief window of weak instability (500-1000 J/kg) this
afternoon. As the aforementioned boundary passes through central Indiana,
concentrated lift along the boundary could initiate a few isolated showers
and even an occasional thunderstorm late this morning into the afternoon.
Best chances will be in NE central Indiana where a closer proximation to
the upper level jet should provide slightly better dynamics for updraft
development. By this evening, any showers should be east of central
Indiana.  A secondary concern today is on the renewed potential for
smoke/haze with model guidance suggesting there should be fairly
significant smoke concentrations aloft. The high lapse rates in the lowest
3km, could allow for some better mixing this afternoon, allowing some of
the smoke layer to breach the boundary layer. Current expectation are for
limited impacts, but slightly lower visibilities are possible at times. By
late this evening, the concentrated smoke layer should be far enough
downstream to reduce any impacts.   Tonight and Tomorrow...  The increased
CAA in the lower levels will help create another area of pressure
depression aloft, of which is expected to detach from the upper level flow,
positioning a cut off low over the Ohio Valley. This isnt expected to be
established quite yet by the end of tomorrow, but will still create a
cooler environment than usual for early August. With cyclonic flow aloft,
scattered cloud cover is likely, but with dew points in the low 50s, no
showers are expected to develop. Expect highs to be in the upper 70s on
Monday. 

NWS IND Office Area Forecast Discussion