Decatur, IL Climate: Temperature & Rain by Month
Annual temperature and rainfall from NOAA NCEI's 1991–2020 normals →; comfort score computed by PlainClimate
30-year climate normals (1991-2020) from Decatur's primary NOAA station, DECATUR AP.
The climate verdict for Decatur
Decatur, Illinois has a mixed annual climate rather than one dominant extreme. Its NOAA normal shows an annual average of 53°F. Its climate comfort score of 68/100 (good) lands mid-pack nationally, exceeding 56% of station-mapped location scores.
- 53°F
- average temperature, NOAA 1991-2020 normal
- 68/100
- comfort score, above 56% of station-mapped location scores
- 36.4"
- precipitation, annual total
- 189 days
- frost-free days per growing season
Decatur: NOAA 1991-2020 normals describe a typical year, not a forecast. Method: /methodology.
Normals record plate
Sheet USW00003887 · Decatur, IL 53°F mean · 36.4" precip
TEMP-COOL · RANK-MID · PHOTO-FINISH · PRCP-MID · SWING-WIDE · COMF-MID · LOAD-HEAT · STN-1 · BOOK-FULL
- TEMP-COOL 53°F
- RANK-MID #3,705
- PHOTO-FINISH ≈ Salt Lake City…
- PRCP-MID 36.4"
- SWING-WIDE 48°F
- COMF-MID 68/100
- LOAD-HEAT 5,393 HDD
- STN-1 USW00003887
- BOOK-FULL 6/6 fields
Nearest mean-temperature peer: Salt Lake City E Bench, UT (+ 0 °F mean)
Instrument codes from this station's NOAA 1991–2020 normals, mean temperature, corpus warmth rank, photo-finish peer station, precipitation band, seasonal swing, comfort composite, degree-day load, and field book, not a livability rating.
Mean-temperature neighbourhood
Nationwide NOAA normal poles and nearest peers, not a reprint of every IL station list.
- Decatur (this station) 53°F
- Cold Wfo Pueblo, CO 53°F
- Hot Indianapolis Nw…, IN 53°F
- Near Salt Lake City…, UT 53°F
- Near Bowling Green, MO 53°F
Climate Living Index · Decatur
Decatur: 62/100 · grade C
Decatur publishes 5 of 6 Living Index dimensions (NOAA annual/seasonal normals · NOAA daily multivariate normals · NOAA hourly normals); 1 missing weight rescale to 100.
PlainClimate-derived for Decatur, not an official NOAA rating. Rankings still use Comfort Score 68/100 (separate formula). Breakpoints and limits.
| Dimension | Station value | Score |
|---|---|---|
| Precipitation balance | 36.4 in · 1.4 from 35 in | 93/100 · A |
| Normal heat + freeze calendar | 114 calendar days | 68/100 · C |
| Frost-free season | 189 days/year | 56/100 · C |
| Annual temperature balance | 53.1°F · 14.4° from 67.5°F | 53/100 · D |
| Summer moisture balance | 64.2°F mean dew point | 39/100 · F |
Decatur · 2026-08-04 · NOAA NCEI Climate Normals · method · Comfort Score method.
Decatur is a continental Köppen climate: Dfa
Coldest-month mean 27.4°F and warmest-month mean 75.7°F place this station in continental, no dry season, hot summer climates (Dfa). Class Dfa is the Peel et al. (2007) label for this station's monthly mean temperature and precipitation normals: continental, specifically continental, no dry season, hot summer.
- Köppen code
- Dfa
- Group
- Continental
- Warmest month
- 75.7°F
- Coldest month
- 27.4°F
Source: official public datasets monthly normals (1991–2020) at the city’s primary station. This is a station classification, not a mapped regional consensus.
National standing · heating-led station
Where Decatur sits across the climate record
Three NOAA fields for Decatur's primary station, temperature, precipitation, and seasonal swing, are ranked against every station-mapped normal that carries the same field.
- Annual temperature
- 54th percentile warmth
- Mid-pack annual mean versus 6,861 station normals.
- Annual precipitation
- 50th percentile wetness
- Neither arid nor torrential versus 6,352 station totals.
- Seasonal temperature swing
- Wider than 75%
- Warmest-to-coldest month gap for Decatur is large versus 6,861 complete station-years.
How Decatur compares across U.S. station-mapped locations
Decatur's comfort score vs. all station-mapped locations
PlainClimate composite comfort index (1–100), NOAA 1991–2020 normals
68 Top 44% score exceeds 56% of 6,189 station-mapped location scores
- 0–10: 0 station-mapped locations (0%). Below this entry.
- 10–20: 0 station-mapped locations (0%). Below this entry.
- 20–30: 96 station-mapped locations (2%). Below this entry.
- 30–40: 280 station-mapped locations (5%). Below this entry.
- 40–50: 1,113 station-mapped locations (18%). Below this entry.
- 50–60: 1,329 station-mapped locations (21%). Below this entry.
- 60–70: 1,236 station-mapped locations (20%). This entry sits in this band.
- 70–80: 650 station-mapped locations (11%). Above this entry.
- 80–90: 921 station-mapped locations (15%). Above this entry.
- 90–100: 564 station-mapped locations (9%). Above this entry.
Source NOAA U.S. Climate Normals, PlainClimate comfort index · 1991–2020
Monthly Temperatures
Average daily high and low temperatures by month
| Month | Avg High | Avg Low | Mean | Precip | Freeze Days | 90°F+ Days |
|---|---|---|---|---|---|---|
| January | 35°F (2°C) | 20°F (-7°C) | 27°F (-3°C) | 2.0" | 26.5 | 0.0 |
| February | 40°F (4°C) | 23°F (-5°C) | 32°F (0°C) | 1.8" | 23.9 | 0.0 |
| March | 52°F (11°C) | 32°F (0°C) | 42°F (6°C) | 2.5" | 17.0 | 0.0 |
| April | 64°F (18°C) | 42°F (6°C) | 53°F (12°C) | 3.7" | 4.6 | 0.0 |
| May | 74°F (24°C) | 53°F (12°C) | 64°F (18°C) | 4.4" | 0.2 | 0.8 |
| June | 83°F (28°C) | 62°F (17°C) | 73°F (23°C) | 4.4" | 0.0 | 6.3 |
| July | 86°F (30°C) | 66°F (19°C) | 76°F (24°C) | 3.3" | 0.0 | 9.0 |
| August | 84°F (29°C) | 63°F (17°C) | 74°F (23°C) | 3.0" | 0.0 | 6.6 |
| September | 79°F (26°C) | 55°F (13°C) | 67°F (19°C) | 3.0" | 0.0 | 3.9 |
| October | 66°F (19°C) | 44°F (7°C) | 55°F (13°C) | 3.2" | 3.0 | 0.4 |
| November | 51°F (11°C) | 34°F (1°C) | 43°F (6°C) | 3.0" | 13.9 | 0.0 |
| December | 40°F (4°C) | 25°F (-4°C) | 32°F (0°C) | 2.1" | 23.6 | 0.0 |
The year, day by day
Summer here tops out rather than builds: the warmest normal high is 86°F around July 8, short of 90°F on every date, while 114 dates carry a normal low at or below freezing, the coldest 20°F near January 19.
The freezing stretch
The normal low stays at or below 32°F into March 14, then returns to freezing around November 22, covering 114 dates in all.
Derived from the normal daily minimum. This is a different measure from the 50%-probability frost dates shown elsewhere on this page, which come from NOAA’s frost product.
Where the wet dates fall
The likeliest wet date is May 11, when 42% of years recorded at least a hundredth of an inch. The driest is January 24 at 25%. Summed across the calendar, that is about 118 wet dates a year.
The widest day
September 21 carries the biggest normal gap between afternoon and dawn, 24°F between the normal high and the normal low.
Look up any date
Any date's 1991–2020 normal for Decatur.
Monthly Precipitation
Average monthly rainfall
7.7 days with precipitation
7.4 days with precipitation
10.5 days with precipitation
11.3 days with precipitation
13.2 days with precipitation
11.1 days with precipitation
10.0 days with precipitation
9.2 days with precipitation
8.9 days with precipitation
10.2 days with precipitation
9.3 days with precipitation
8.9 days with precipitation
Decatur spreads its precipitation across the year
Neither half of the year dominates here: June through August take 30% of the annual total and December through February 16%, with neither reaching the 35% that would mark a distinct wet season. Decatur has no dry season to plan around, though it does carry a wide 48.3°F gap between its warmest and coldest month.
The gap between the wettest and driest month still matters: May averages 4.4" and February 1.8". The three wettest months together take 34% of the year, against the 25% a perfectly flat distribution would give them.
Shares are computed from this station's own 1991-2020 monthly precipitation normals. "Spread across the year" means neither the June-August nor the December-February share reaches 35%; it describes an average year, not the variability of any single one.
How Decatur's precipitation splits across the calendar
About 118 days a year record measurable precipitation here, carrying 36.4" between them, or roughly 0.31 inches on a typical wet day. That sits in the middle band: neither the many-light-days pattern of the Pacific Northwest and the Great Lakes, nor the few-heavy-events pattern of the Gulf and the desert Southwest.
A wet day is one recording at least 0.01 inches. These are 1991-2020 normals: they describe an average year and say nothing about the heaviest single storm on record.
Frost Dates & Growing Season
First Fall Freeze
October 22
50% probability date
Last Spring Freeze
April 16
50% probability date
Growing Season
189 days
Heating & Cooling Degree Days
Annual totals indicate energy demand for heating and cooling
Heating Degree Days
5,393
Higher = more heating needed
Cooling Degree Days
1,105
Higher = more cooling needed
Warmest Month
July
Coldest Month
January
Humidity & Wind
Monthly averages from hourly observations
| Month | Humidity | Wind (mph) | Clear Sky % | Overcast % |
|---|---|---|---|---|
| January | 76% | 11.2 | 43% | 37% |
| February | 72% | 11.7 | 40% | 39% |
| March | 67% | 11.8 | 45% | 30% |
| April | 67% | 11.0 | 45% | 27% |
| May | 68% | 9.2 | 48% | 21% |
| June | 71% | 7.7 | 54% | 11% |
| July | 73% | 6.5 | 56% | 9% |
| August | 73% | 6.9 | 59% | 12% |
| September | 68% | 8.3 | 62% | 15% |
| October | 70% | 10.4 | 49% | 31% |
| November | 75% | 10.9 | 45% | 38% |
| December | 78% | 11.1 | 42% | 43% |
Nationwide similar cities
Other rankable U.S. places outside IL closest to Decatur on two NOAA annual-normal axes (mean temperature and annual precipitation). Chip rows use distinct link sets.
Closest by average temperature
Nearest out-of-state peers by annual mean temperature (53°F here).
- Allentown, PA 53°F · 0.0°F off
- Dallas, OR 53°F · 0.0°F off
- Downieville, CA 53°F · 0.0°F off
- Lamar, CO 53°F · 0.0°F off
Closest by annual precipitation
Nearest out-of-state peers by annual precipitation (36.4" here), excluding temperature-peer places.
- Dalton, WI 36.4" · 0.0" off
- Shenandoah, IA 36.4" · 0.0" off
- Eaton Rapids, MI 36.3" · 0.0" off
- Manistee, MI 36.3" · 0.0" off
Data-derived climate profile
How Decatur's climate pattern fits together
heating led · moderate · mid swing
Decatur's energy balance leans toward cold weather: 5,393 annual heating degree days against 1,105 for cooling. Its 48.3°F seasonal range still makes the monthly rows more useful than the annual average alone.
Decatur's frost-free season lasts about 189 days, a middle-length window whose endpoints matter more than the annual average. It describes freeze probability, not year-specific planting conditions.
July and January mark the typical warm and cold ends of the calendar in Decatur's middle-range seasonal profile. The measured spread is 48.3°F. The annual average is 53°F. Neither the annual mean nor one extreme month represents the full calendar on its own.
Decatur's 36.4 inches of annual precipitation falls in PlainClimate's middle band, so “wet” or “dry” is not the leading description. Snowfall is not added to the interpretation because its annual value is missing. Temperature balance and the calendar distribution carry more information than the annual moisture label alone.
These labels group NOAA 1991-2020 normals from Decatur's primary station, so the winter figures are a thirty-year average and not a floor: a single hard season can run well below them. Treat each band as a descriptive range for Decatur, not an official NOAA class or a year-ahead forecast.
Questions about Decatur's climate
How much rain does Decatur get? ▼
How cold does Decatur get in winter? ▼
How much energy does heating and cooling require in Decatur? ▼
Data Sources
Data source: NOAA U.S. Climate Normals v1.0.1 (1991-2020). All figures on this page are from Decatur's primary station: DECATUR AP (USW00003887). For informational purposes only.
Place identity: U.S. Census Bureau 2024 Gazetteer places. The 2024 Census Gazetteer identifies the exact name-and-state match as an incorporated place (GEOID 1718823). Match rule for Decatur: exact normalized name + state only, no fuzzy expansion, so nearby differently spelled facilities stay unmatched.
On this page every temperature, precipitation, and derived score for Decatur comes from its primary NOAA station record. No figure on this page is typed in by an editor - each value is rendered from NOAA 1991-2020 U.S. Climate Normals. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 1991–2020 normals.