Decatur weather in May: Decatur, Illinois: normal highs, lows, rain and records for May
Decatur in May has a normal high of 74°F and a normal low of 53°F, a daily mean of 64°F, rising from 69°F on the 1st to 79°F by the 31st. Measurable precipitation falls on 13 days in a normal May, 4.38 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 24°C and low of 12°C, 111 mm of precipitation in May.
- NOAA stationDecatur Airport
- Station IDUSW00003887
- Location39.83°N 88.87°W
- Elevation675 ft (206 m)
- From the center4 miles
- Population68,763
- Jan 35° 20°
- Feb 40° 23°
- Mar 52° 32°
- Apr 64° 42°
- May 74° 53°
- Jun 83° 62°
- Jul 86° 66°
- Aug 84° 63°
- Sep 79° 55°
- Oct 66° 44°
- Nov 51° 34°
- Dec 40° 25°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Decatur in May?
The normal high is 74°F and the normal low 53°F, for a daily mean of 63.9°F. May is 10.8°F warmer than April and 8.8°F cooler than June. May is the 5th warmest month of the year in Decatur and the wettest. Across the month the normal high rises 10°F, from 69°F on May 1 to 79°F on May 31. From one year to the next May's mean temperature typically moves about 3.0°F either way (NOAA's standard deviation), so roughly two Mays in three average between 61°F and 67°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 42%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| May 1 | 69°F | 48°F | 41% | 27% |
| May 8 | 72°F | 51°F | 42% | 28% |
| May 15 | 74°F | 53°F | 42% | 27% |
| May 22 | 76°F | 56°F | 41% | 25% |
| May 31 | 79°F | 58°F | 41% | 24% |
Every day of May: normal high, low and chance of precipitation (warmest afternoon May 31, coldest night May 1)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| May 1 | 69°F | 48°F | 41% | 27% | 13 h 50 min |
| May 2 | 70°F | 48°F | 41% | 28% | 13 h 50 min |
| May 3 | 70°F | 49°F | 41% | 28% | 14 h |
| May 4 | 70°F | 49°F | 41% | 28% | 14 h |
| May 5 | 71°F | 50°F | 42% | 28% | 14 h |
| May 6 | 71°F | 50°F | 42% | 28% | 14 h |
| May 7 | 71°F | 50°F | 42% | 28% | 14 h |
| May 8 | 72°F | 51°F | 42% | 28% | 14 h 10 min |
| May 9 | 72°F | 51°F | 42% | 28% | 14 h 10 min |
| May 10 | 72°F | 51°F | 42% | 28% | 14 h 10 min |
| May 11 | 73°F | 52°F | 42% | 28% | 14 h 10 min |
| May 12 | 73°F | 52°F | 42% | 27% | 14 h 10 min |
| May 13 | 74°F | 52°F | 42% | 27% | 14 h 20 min |
| May 14 | 74°F | 53°F | 42% | 27% | 14 h 20 min |
| May 15 | 74°F | 53°F | 42% | 27% | 14 h 20 min |
| May 16 | 74°F | 54°F | 42% | 27% | 14 h 20 min |
| May 17 | 75°F | 54°F | 42% | 26% | 14 h 20 min |
| May 18 | 75°F | 54°F | 42% | 26% | 14 h 30 min |
| May 19 | 75°F | 55°F | 42% | 26% | 14 h 30 min |
| May 20 | 76°F | 55°F | 41% | 26% | 14 h 30 min |
| May 21 | 76°F | 55°F | 41% | 25% | 14 h 30 min |
| May 22 | 76°F | 56°F | 41% | 25% | 14 h 30 min |
| May 23 | 77°F | 56°F | 41% | 25% | 14 h 30 min |
| May 24 | 77°F | 56°F | 41% | 25% | 14 h 40 min |
| May 25 | 77°F | 57°F | 41% | 24% | 14 h 40 min |
| May 26 | 78°F | 57°F | 41% | 24% | 14 h 40 min |
| May 27 | 78°F | 57°F | 41% | 24% | 14 h 40 min |
| May 28 | 78°F | 58°F | 41% | 24% | 14 h 40 min |
| May 29 | 79°F | 58°F | 41% | 24% | 14 h 40 min |
| May 30 | 79°F | 58°F | 41% | 24% | 14 h 40 min |
| May 31 | 79°F | 58°F | 41% | 24% | 14 h 50 min |
- Normal high
- 74°FMay average
- Normal low
- 53°FMay average
- Precipitation
- 4.38 inmonth total
- Days with precipitation
- 130.01 inch or more
- Days at 90°F or more
- 1
- Daylight
- 13 h 50 min to 14 h 50 minMay 1 to May 31
- Days at 70°F or more
- 22
- Days at 80°F or more
- 12
- Sunshine
- 73%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00003887; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Decatur in May?
On a given May day the chance of 0.01 inch or more is 41% on average, highest around May 11 (42%). In all, 4.38 in falls on 13 days of a normal May, 1 of them with an inch or more.
In a normal May in Decatur, 1 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00003887.
How humid and windy is Decatur in May?
At 3 p.m. the normal temperature is 77°F with 51% relative humidity and a dew point of 58°F; at 6 a.m. it is 62°F with 83% humidity. The wind averages 9.2 mph, most often from the southwest in the afternoon.
| Time | Temperature | Dew point | Humidity | Wind | Clear or few clouds |
|---|---|---|---|---|---|
| 6 a.m. | 62°F | 57°F | 83% | 7.2 mph | 60% |
| 9 a.m. | 71°F | 58°F | 65% | 10.5 mph | 62% |
| noon | 76°F | 59°F | 55% | 11.3 mph | 52% |
| 3 p.m. | 77°F | 58°F | 51% | 11.5 mph | 54% |
| 6 p.m. | 74°F | 58°F | 56% | 10.6 mph | 59% |
| 9 p.m. | 67°F | 58°F | 72% | 7.7 mph | 68% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00003887. Hourly normals exist only for NOAA's first-order stations; a dash where NOAA publishes no value for that hour (the sky at some hours).
What are the records for May in Decatur?
The warmest May temperature on this station's record (since 2000) is 97°F, on May 28, 2018; the coldest is 29°F, on May 3, 2005. The wettest May brought 9.32 in (2002).
The May mean against the 1991-2020 normal of 63.9°F: 2021 61.6°F (−2.3), 2022 66.0°F (+2.1), 2023 65.3°F (+1.4), 2024 67.8°F (+3.9), 2025 64.0°F (+0.1), 2026 61.7°F (−2.2). 4 of 6 ran warmer than normal.
| May | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 61.6°F | −2.3°F | 5.37 in |
| 2022 | 66.0°F | +2.1°F | 3.52 in |
| 2023 | 65.3°F | +1.4°F | 1.81 in |
| 2024 | 67.8°F | +3.9°F | 4.82 in |
| 2025 | 64.0°F | +0.1°F | 3.44 in |
| 2026 | 61.7°F | −2.2°F | 3.10 in |
Source: records: ACIS, station USW00003887; recent months: ACIS, station USW00003887. Records and recent months use complete months only.
How does May in Decatur compare across Illinois?
Across the 144 places PlainClimate covers in Illinois, May normal highs run from 67°F in Waukegan to 79°F in Belleville; Decatur's is 74°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.