Weather in Indianapolis in August

A good month. August is a solid month to be in Indianapolis. Highs average 28.4 °C, lows 17.5 °C, and rain falls on 12 days — nothing in the month is working against you.

August ranks 5 of 12 in Indianapolis: past the worst of the year but short of September, which is the month to book if the dates are open.

Rain on 12 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for 28.4 °C days and 17.5 °C nights; the spread matters more here than any single number.

What the averages hide

Averages flatten a month, and this one hides a few things: 9 days top 30 °C — hot spells arrive, but they break. Across the twenty years measured, the hottest August day reached 37.1 °C and the coldest night fell to 8.4 °C, and the wettest single day dropped 62 mm — roughly 65% of the month's rain in one day.

August is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest August on record still delivered 155 mm against 40 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 95 mm average is a reasonable planning figure, not a promise.

Wind is light at 7.2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 75%, high enough to notice on the warm days without dominating them.

How August sits in the year

Temperatures hold steady either side: 28.4 °C in July, 28.4 here, 25.8 in September. Nothing about the timing within the month matters much.

Daylight in August

13.8 hours of daylight, losing 1.1 hours across the month. That is between Indianapolis's extremes of 15 and 9.4 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 35.6 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

August in Indianapolis versus nearby

If Indianapolis is one option among several, the nearby comparison is worth making. Louisville is the weaker option in August — 2.1 °C warmer, the same number of rain days. Fort Wayne is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: August works, with September the better month by 13 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in Indianapolis

See all twelve months in Indianapolis, or where else to go in August.