Decatur, Tennessee climate: Normal weather by month, frost dates and records
Decatur's normal year runs from 28°F January nights to 89°F July afternoons, with 57.6 inches of precipitation and 3 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 14.7°C, January lows of −2°C, July highs of 32°C, 1,463 mm of precipitation a year.
- NOAA stationDecatur (7 mi NE)
- Station IDUSC00402388
- Location35.64°N 84.67°W
- Elevation750 ft (229 m)
- Population1,652
On October 23, the normal high in Decatur is 70°F and the normal low 42°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Decatur.
- Jan 48° 28°
- Feb 53° 30°
- Mar 62° 36°
- Apr 71° 44°
- May 79° 54°
- Jun 86° 63°
- Jul 89° 67°
- Aug 89° 66°
- Sep 84° 59°
- Oct 73° 46°
- Nov 61° 35°
- Dec 51° 30°
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 89°F; January the coldest, with normal lows of 28°F. The most precipitation falls in December (5.72 in), the least in October (3.24 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 48°F | 28°F | 37.9°F | 5.62 | 0.9 | 11 | <1 | 22 | 10 h |
| February | 53°F | 30°F | 41.4°F | 5.24 | 1.7 | 11 | <1 | 19 | 10 h 50 min |
| March | 62°F | 36°F | 48.7°F | 5.32 | 0.1 | 11 | <1 | 14 | 11 h 50 min |
| April | 71°F | 44°F | 57.5°F | 5.42 | 0.0 | 11 | <1 | 4 | 13 h |
| May | 79°F | 54°F | 66.4°F | 4.60 | 0.0 | 12 | 1 | <1 | 14 h |
| June | 86°F | 63°F | 74.3°F | 4.79 | 0.0 | 11 | 8 | <1 | 14 h 30 min |
| July | 89°F | 67°F | 78.0°F | 5.36 | 0.0 | 13 | 15 | <1 | 14 h 20 min |
| August | 89°F | 66°F | 77.2°F | 3.28 | 0.0 | 10 | 14 | <1 | 13 h 30 min |
| September | 84°F | 59°F | 71.3°F | 4.35 | 0.0 | 7 | 8 | <1 | 12 h 30 min |
| October | 73°F | 46°F | 59.2°F | 3.24 | 0.0 | 8 | 1 | 4 | 11 h 20 min |
| November | 61°F | 35°F | 47.6°F | 4.65 | 0.0 | 9 | <1 | 16 | 10 h 20 min |
| December | 51°F | 30°F | 40.7°F | 5.72 | 0.6 | 11 | <1 | 20 | 9 h 50 min |
| Year (annual) | 70°F | 46°F | 58.4°F | 57.59 | 3.3 | 123 | 46 | 99 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 9°C | −2°C | 3.3°C | 143 mm | 2 cm |
| February | 11°C | −1°C | 5.2°C | 133 mm | 4 cm |
| March | 16°C | 2°C | 9.3°C | 135 mm | 0 cm |
| April | 22°C | 7°C | 14.2°C | 138 mm | 0 cm |
| May | 26°C | 12°C | 19.1°C | 117 mm | 0 cm |
| June | 30°C | 17°C | 23.5°C | 122 mm | 0 cm |
| July | 32°C | 19°C | 25.6°C | 136 mm | 0 cm |
| August | 32°C | 19°C | 25.1°C | 83 mm | 0 cm |
| September | 29°C | 15°C | 21.8°C | 110 mm | 0 cm |
| October | 23°C | 8°C | 15.1°C | 82 mm | 0 cm |
| November | 16°C | 1°C | 8.7°C | 118 mm | 0 cm |
| December | 11°C | −1°C | 4.8°C | 145 mm | 2 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00402388; 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 April, May, September and October. Of those, September has the fewest days with rain (7).
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 USC00402388.
When is the last frost in Decatur?
In Decatur, the last spring frost (32°F) comes after April 10 in half of years and after April 28 in one year in ten; the first autumn frost comes before October 27 in half of years and before October 14 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 101 year in 10 after April 28; 9 in 10 after March 24
- First autumn frost, half of years before
- October 271 year in 10 before October 14; 9 in 10 before November 9
NOAA puts the median frost-free season at 199 days, and the season without a hard freeze (28°F) at 220 days.
A hard freeze (28°F) comes after March 30 in half of springs and before November 5 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Decatur in zone 7b in ZIP code 37322, 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 7b: the coldest night of a typical year reaches 8°F (23 complete years).
Frost dates for every NOAA station in Tennessee · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00402388; 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, 46 days a year reach 90°F (1 of them 100°F or more), 99 nights fall to 32°F or colder and 123 days bring measurable precipitation.
- Days at 90°F or more
- 46a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 99a normal year
- Days that stay below freezing
- 4high of 32°F or less
- Days with 0.01 inch of precipitation
- 123a normal year
- Days with 1 inch of snow or more
- 1a normal year
The highest temperature in this station's record (since 1997) is 107°F, on July 1, 2012; the lowest is −9°F, on January 17, 2024.
The wettest calendar year on that record is 2015, with 74.33 in; the snowiest season is 2023–24, with 7.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00402388; records: ACIS (NOAA Regional Climate Centers), station USC00402388. Records use complete months only; a month missing more than three days is left out.
How sunny is Decatur?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Decatur, 4.3 kWh per square metre a day. August is the sunniest month (79%) and February the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 67% | 2.4 |
| February | 63% | 2.9 |
| March | 68% | 4.0 |
| April | 75% | 5.3 |
| May | 76% | 5.9 |
| June | 79% | 6.3 |
| July | 78% | 6.0 |
| August | 79% | 5.5 |
| September | 79% | 4.8 |
| October | 76% | 3.8 |
| November | 75% | 2.8 |
| December | 65% | 2.1 |
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 3,840 heating degree days, 29% fewer than the median U.S. place (5,373), and 1,450 cooling degree days, 60% more than the median (908). Five months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 4,386 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 840 | 0 |
| February | 660 | 0 |
| March | 508 | 2 |
| April | 248 | 21 |
| May | 70 | 114 |
| June | 3 | 282 |
| July | 0 | 405 |
| August | 0 | 378 |
| September | 21 | 210 |
| October | 216 | 36 |
| November | 523 | 1 |
| December | 752 | 0 |
| Year (annual) | 3,840 | 1,450 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00402388. 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 58.9°F, 0.5°F above the 1991-2020 normal of 58.4°F. 4 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 59.0°F | +0.6°F | 55.03 | 0.0 |
| 2022 | 58.5°F | +0.1°F | 58.23 | 6.7 |
| 2023 | 59.3°F | +0.9°F | 59.64 | 0.0 |
| 2025 | 58.9°F | +0.5°F | 50.93 | 6.0 |
Source: observed years: ACIS, station USC00402388. A year counts only with all twelve months complete.
How does Decatur's climate compare?
Decatur is warmer than 56 of the other 115 places with their own NOAA record in Tennessee, and wetter than 74. Across the 7,247 U.S. stations with normals, its annual mean of 58.4°F is warmer than 70%.
In the Köppen classification computed from these normals, Decatur is Cfa: temperate, 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?
Sweetwater has no NOAA station with 1991-2020 normals of its 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.
- Sweetwater, TN6,676 people · 11 mi E
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 48°F and a normal low of 28°F. The warmest is July (89°F by day, 67°F at night).
Does it snow in Decatur?
Yes: 3 inches in a normal year, falling on 3 days with 0.1 inch or more, the most in February (1.7 inches).
What is the rainiest month in Decatur?
December, with 5.72 in of precipitation in a normal year; the driest is October with 3.24 in.
What plant hardiness zone is Decatur in?
The USDA's 2023 map puts Decatur in zone 7b in ZIP code 37322, the nearest ZIP area. By the same method at Decatur's NOAA station, the coldest night of a typical year reaches 8°F (23 years, 1991-2020): zone 7b.
How late can frost come in Decatur?
In half of years the last 32°F night comes after April 10; in one year in ten it comes after April 28. Waiting until April 28 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Tennessee climateThe statewide normals and every place in the state
- Spring City, TN11 miles from this station, 57.3°F a year
- Rockwood, TN14 miles from this station, 57.5°F a year
- Athens, TN15 miles from this station, 58.8°F a year
- Kingston, TN17 miles from this station, 58.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made