Decatur, Indiana climate: Normal weather by month, frost dates and records
Decatur's normal year runs from 18°F January nights to 84°F July afternoons, with 40.6 inches of precipitation and 28 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.4°C, January lows of −8°C, July highs of 29°C, 1,032 mm of precipitation a year.
- NOAA stationDecatur (1 mi N)
- Station IDUSC00122096
- Location40.85°N 84.93°W
- Elevation785 ft (239 m)
- From the center1 miles
- Population10,072
On October 23, the normal high in Decatur is 61°F and the normal low 40°F, and the chance of measurable rain or snow is 33%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Decatur.
- Jan 33° 18°
- Feb 36° 20°
- Mar 48° 29°
- Apr 61° 39°
- May 72° 50°
- Jun 81° 60°
- Jul 84° 63°
- Aug 82° 61°
- Sep 77° 53°
- Oct 64° 42°
- Nov 50° 33°
- Dec 38° 24°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Decatur each month?
July is the warmest month, with normal highs of 84°F; January the coldest, with normal lows of 18°F. The most precipitation falls in May (4.75 in), the least in February (2.07 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 33°F | 18°F | 25.7°F | 2.51 | 9.2 | 11 | <1 | 27 | 9 h 30 min |
| February | 36°F | 20°F | 28.2°F | 2.07 | 7.5 | 9 | <1 | 25 | 10 h 40 min |
| March | 48°F | 29°F | 38.0°F | 2.75 | 4.2 | 11 | <1 | 22 | 11 h 50 min |
| April | 61°F | 39°F | 49.8°F | 4.08 | 0.5 | 13 | <1 | 8 | 13 h 20 min |
| May | 72°F | 50°F | 61.0°F | 4.75 | 0.0 | 13 | 1 | <1 | 14 h 30 min |
| June | 81°F | 60°F | 70.5°F | 4.58 | 0.0 | 12 | 4 | <1 | 15 h 10 min |
| July | 84°F | 63°F | 73.2°F | 4.26 | 0.0 | 10 | 6 | <1 | 14 h 50 min |
| August | 82°F | 61°F | 71.3°F | 4.04 | 0.0 | 9 | 4 | <1 | 13 h 50 min |
| September | 77°F | 53°F | 64.7°F | 3.04 | 0.0 | 8 | 2 | <1 | 12 h 30 min |
| October | 64°F | 42°F | 53.1°F | 2.91 | 0.0 | 10 | <1 | 4 | 11 h 10 min |
| November | 50°F | 33°F | 41.2°F | 3.04 | 1.2 | 10 | <1 | 16 | 10 h |
| December | 38°F | 24°F | 31.1°F | 2.59 | 5.5 | 11 | <1 | 25 | 9 h 20 min |
| Year (annual) | 60°F | 41°F | 50.7°F | 40.62 | 28.1 | 127 | 18 | 127 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 1°C | −8°C | −3.5°C | 64 mm | 23 cm |
| February | 2°C | −6°C | −2.1°C | 53 mm | 19 cm |
| March | 9°C | −2°C | 3.3°C | 70 mm | 11 cm |
| April | 16°C | 4°C | 9.9°C | 104 mm | 1 cm |
| May | 22°C | 10°C | 16.1°C | 121 mm | 0 cm |
| June | 27°C | 16°C | 21.4°C | 116 mm | 0 cm |
| July | 29°C | 17°C | 22.9°C | 108 mm | 0 cm |
| August | 28°C | 16°C | 21.8°C | 103 mm | 0 cm |
| September | 25°C | 12°C | 18.2°C | 77 mm | 0 cm |
| October | 18°C | 6°C | 11.7°C | 74 mm | 0 cm |
| November | 10°C | 0°C | 5.1°C | 77 mm | 3 cm |
| December | 3°C | −4°C | −0.5°C | 66 mm | 14 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00122096; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Decatur?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, September has the fewest days with rain (8).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00122096.
When is the last frost in Decatur?
In Decatur, the last spring frost (32°F) comes after April 23 in half of years and after May 8 in one year in ten; the first autumn frost comes before October 19 in half of years and before October 5 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 231 year in 10 after May 8; 9 in 10 after April 7
- First autumn frost, half of years before
- October 191 year in 10 before October 5; 9 in 10 before November 1
NOAA puts the median frost-free season at 178 days, and the season without a hard freeze (28°F) at 201 days.
A hard freeze (28°F) comes after April 11 in half of springs and before October 31 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Decatur in zone 6a in ZIP code 46733, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Decatur's NOAA station is in zone 6a: the coldest night of a typical year reaches −7°F (15 complete years).
Frost dates for every NOAA station in Indiana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00122096; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Decatur?
In a normal year in Decatur, 18 days a year reach 90°F, 127 nights fall to 32°F or colder and 127 days bring measurable precipitation.
- Days at 90°F or more
- 18a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 127a normal year
- Days that stay below freezing
- 41high of 32°F or less
- Days with 0.01 inch of precipitation
- 127a normal year
- Days with 1 inch of snow or more
- 11a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00122096.
How sunny is Decatur?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Decatur, 3.9 kWh per square metre a day. August is the sunniest month (81%) and December the cloudiest (57%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 58% | 1.7 |
| February | 63% | 2.6 |
| March | 65% | 3.6 |
| April | 69% | 4.8 |
| May | 72% | 5.5 |
| June | 77% | 6.2 |
| July | 80% | 6.2 |
| August | 81% | 5.6 |
| September | 78% | 4.5 |
| October | 70% | 3.0 |
| November | 67% | 2.1 |
| December | 57% | 1.5 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Decatur need?
A normal year in Decatur brings 6,010 heating degree days, 12% more than the median U.S. place (5,373), and 818 cooling degree days, 10% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,135 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,218 | 0 |
| February | 1,030 | 0 |
| March | 839 | 2 |
| April | 462 | 6 |
| May | 180 | 56 |
| June | 21 | 185 |
| July | 5 | 260 |
| August | 10 | 205 |
| September | 98 | 89 |
| October | 384 | 13 |
| November | 713 | 1 |
| December | 1,049 | 0 |
| Year (annual) | 6,010 | 818 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00122096. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Decatur been warmer than normal lately?
2025 averaged 50.8°F, 0.1°F above the 1991-2020 normal of 50.7°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 52.0°F | +1.3°F | 41.31 | 23.8 |
| 2022 | 50.4°F | −0.3°F | 36.00 | 20.6 |
| 2023 | 52.5°F | +1.8°F | 38.90 | 9.0 |
| 2024 | 53.4°F | +2.7°F | 37.69 | 7.0 |
| 2025 | 50.8°F | +0.1°F | 30.43 | 26.5 |
Source: observed years: ACIS, station USC00122096. A year counts only with all twelve months complete.
How does Decatur's climate compare?
Decatur is warmer than 33 of the other 98 places with their own NOAA record in Indiana, and wetter than 27. Across the 7,247 U.S. stations with normals, its annual mean of 50.7°F is warmer than 44%.
In the Köppen classification computed from these normals, Decatur is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Decatur share this climate record?
5 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Convoy, OH1,002 people · 13 mi E
- Hoagland, IN886 people · 8 mi NW
- Wren, OH151 people · 9 mi E
- Preble, IN117 people · 4 mi W
- Maples, IN101 people · 11 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Decatur's climate
What is the coldest month in Decatur?
January, with a normal high of 33°F and a normal low of 18°F. The warmest is July (84°F by day, 63°F at night).
Does it snow in Decatur?
Yes: 28 inches in a normal year, falling on 19 days with 0.1 inch or more, the most in January (9.2 inches).
What is the rainiest month in Decatur?
May, with 4.75 in of precipitation in a normal year; the driest is February with 2.07 in.
What plant hardiness zone is Decatur in?
The USDA's 2023 map puts Decatur in zone 6a in ZIP code 46733, the nearest ZIP area. By the same method at Decatur's NOAA station, the coldest night of a typical year reaches −7°F (15 years, 1991-2020): zone 6a.
How late can frost come in Decatur?
In half of years the last 32°F night comes after April 23; in one year in ten it comes after May 8. Waiting until May 8 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Indiana climateThe statewide normals and every place in the state
- Bluffton, IN12 miles from this station, 50.1°F a year
- Berne, IN12 miles from this station, 50.8°F a year
- Fort Wayne, IN17 miles from this station, 50.9°F a year
- Van Wert, OH18 miles from this station, 51.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made