Indianapolis rainfall data, 1996 to 2025

Prepared by the Celtic Rainwater Wiki editorial team · Created 9 November 2026 · Last checked 9 November 2026

Summary: NOAA records for Indianapolis International Airport average 43.61 inches of precipitation a year over 1996 to 2025, peaking in May and June at about 4.8 inches a month, with about 10.7 days a year of an inch or more. A 2,000-square-foot roof sheds about 54,338 gallons in an average year^[1][2].

What does the data show?

Over the 30 years from 1996 to 2025, the NOAA weather station at Indianapolis International Airport recorded an average of 43.61 inches of precipitation a year^[1]. The wettest year was 1996 (56.85 in) and the driest was 1999 (32.40 in). The wettest months on average were May (4.80 in) and June (4.81 in), followed by July and April; the driest was February (2.58 in). The station averaged 10.7 days a year with an inch or more of precipitation, and the largest single-day total in the period was 7.20 inches, in Sep 2003.

For a house, the useful translation is volume. One inch of rain on one square foot of roof is about 0.623 gallons^[2]. On a 2,000-square-foot roof, the average Indianapolis year is roughly 54,338 gallons, and a single 1-inch day is about 1,250 gallons, all of which the gutters and downspouts have to move.

Month by month

The spring and early summer peak lines up with the season of thunderstorms in central Indiana, when rain falls hard and fast. That is when undersized gutters overflow and buried downspout lines back up, even if they cope with a steady autumn rain. See sizing gutters for heavy rain.

Year by year

Comparing the two halves of the record, 1996 to 2010 averaged 43.73 inches a year and 2011 to 2025 averaged 43.49 inches; days with an inch or more averaged 10.5 and 10.9 a year. Thirty years at one station is too short and too noisy to call a trend, and this page does not claim one.

How was the dataset built?

Daily precipitation values (PRCP) for station USW00093819 were downloaded from NOAA’s Global Historical Climatology Network daily (GHCNd) data service^[1][3]. Values carrying a quality-control flag were dropped. Daily totals were summed by month, and for each month the file records the number of days with data, the total in inches, the count of days with at least 0.5 and at least 1 inch, and the wettest day. Snowfall is included as its melted water equivalent, as GHCNd reports it. The cleaned monthly file is published here as indianapolis-monthly-precipitation-1996-2025.csv under CC BY 4.0. Roof volumes use 0.623 gallons per square foot per inch and ignore losses from evaporation and splash.

What are the limits?

Daily totals say nothing about intensity within a day. A 2-inch day could be a gentle all-day rain or a 30-minute downpour, and gutters care about the second. For design intensities, engineers use NOAA’s precipitation frequency estimates (Atlas 14) rather than daily station records. The airport sits on the southwest side of the city; totals at any one house can differ, especially in summer storms. And the data is about rain, not about any company: it does not show anything about Celtic Rainwater Systems’ work.

See also

• Sizing gutters for heavy rain
• Location and hours
• Company history
• Service area
• Gutter installation

Common questions

References

1. ^ ^{a b c} Global Historical Climatology Network daily (GHCNd), station USW00093819, Indianapolis International Airport. NOAA National Centers for Environmental Information. Accessed 9 November 2026.
2. ^ ^{a b} Rain and Precipitation (How much water falls during a storm?). U.S. Geological Survey Water Science School. Accessed 9 November 2026.
3. ^ Global Historical Climatology Network daily (GHCNd) documentation. NOAA National Centers for Environmental Information. Accessed 9 November 2026.