Category: Flooding

Updated 06.18.21 @ 5:37p

Type: Severe weather event

What: Severe weather event and flash flood threat

When: This afternoon through tonight

Severe Risks: Damaging wind, large hail, embedded tornado potential, flash flooding

Summary: A complex of thunderstorms to our north this morning will diminish. As a result, the cloud canopy engulfing much of the region this morning will give way to mostly sunny skies late morning and into the afternoon. Intense heat is expected this afternoon, courtesy of a southerly flow ahead of an approaching warm front and upper air disturbance. Highs will reach the lower to middle 90s this afternoon and heat indices will climb to between 100° and 105°. This heat, combined with a multitude of other ingredients: dew points into the 70s, convective available potential energy (CAPE) in excess of 4000 j/kg (suggestive of extreme instability), and steep low level lapse rates (rate of temperature change with height) all will play into what looks like a significant setup for a severe weather outbreak later this afternoon and tonight.

Initially, individual cells are likely to erupt (targeting mid to late afternoon) along an OFB (outflow boundary) across n-central Indiana. Damaging wind and large hail are the biggest concerns with these cells, but a tornado threat is also on the table in this highly unstable environment. Eventually the scattered, intense cells should congeal into more of a widespread storm complex by evening and impact most of central and southern parts of the state. Precipitable water values will be in excess of 2” and promote a flash flood risk, especially if thunderstorms back-build and train over the same communities. Should this be the case, localized rainfall amounts of 3”-4” will be a good bet. As we progress into the overnight hours, the storm complex and associated flood risk will shift downstate.

Confidence: HighN