Temperatures combined with very high levels of humidity to produce a heat index in the lower 100s Tuesday afternoon. Shelbyville peaked at 102°, while Indianapolis reached 97° just after 4 p.m. The official high of 91° marked the fifth 90°-day of 2021 in Indianapolis, all coming in the month of June. This is the most 90°-days in a June in three years.
The highly humid air that is unstable brought to life afternoon storms while aided by the peak heating of the afternoon. A very heavy storm over Frankfort around 5 p.m. Tuesday was scanned to over 50,000 feet, produced blinding rainfall, frequent lightning strikes and gusty winds.
The slow-moving storm would eventually weaken, providing a mini cold front or gust of cool air that would spur on new storms early Tuesday evening. This outflow of cool air will likely induce additional storms for a few hours after sunset before diminishing.
Temperatures can certainly cool with a thunderstorm this time of the year, bringing temporary relief. At 6 p.m., the cooler temperatures reached Zionsville while many locations were still well in the 90s.
RAIN COVERAGE TO RISE
A pesky front will finally be on the move but only slowly drifting south on Wednesday. Showers and thunderstorms are to increase in coverage Wednesday, nearing 60% of the area by early afternoon. The slow-moving front along with highly humid air will offer some locally heavy rainfall at times.
The threat for rain showers and storms is to linger well into Thursday as the front gains momentum and becomes a southbound moving cold front. A real break is coming as the front heads south Thursday night with a huge drop in humidity coming behind the front starting late Thursday evening.