DeKalb, Illinois climate: Normal weather by month, frost dates and records
DeKalb's normal year runs from 13°F January nights to 83°F July afternoons, with 37.3 inches of precipitation and 33 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.2°C, January lows of −10°C, July highs of 28°C, 946 mm of precipitation a year.
- NOAA stationDe Kalb
- Station IDUSC00112223
- Location41.93°N 88.78°W
- Elevation873 ft (266 m)
- Population40,491
On October 14, the normal high in DeKalb is 63°F and the normal low 42°F, and the chance of measurable rain or snow is 32%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for DeKalb.
- Jan 28° 13°
- Feb 33° 17°
- Mar 45° 27°
- Apr 59° 37°
- May 70° 49°
- Jun 80° 60°
- Jul 83° 63°
- Aug 81° 61°
- Sep 75° 53°
- Oct 62° 41°
- Nov 46° 30°
- Dec 34° 19°
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 DeKalb each month?
July is the warmest month, with normal highs of 83°F; January the coldest, with normal lows of 13°F. The most precipitation falls in May (4.79 in), the least in January (1.69 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 28°F | 13°F | 20.6°F | 1.69 | 10.2 | 10 | <1 | 30 | 9 h 30 min |
| February | 33°F | 17°F | 24.5°F | 1.71 | 8.7 | 8 | <1 | 26 | 10 h 30 min |
| March | 45°F | 27°F | 35.9°F | 2.24 | 4.4 | 10 | <1 | 23 | 11 h 50 min |
| April | 59°F | 37°F | 48.0°F | 3.56 | 1.3 | 12 | <1 | 8 | 13 h 20 min |
| May | 70°F | 49°F | 59.7°F | 4.79 | 0.0 | 13 | 1 | 1 | 14 h 30 min |
| June | 80°F | 60°F | 69.7°F | 4.57 | 0.0 | 11 | 4 | <1 | 15 h 10 min |
| July | 83°F | 63°F | 73.2°F | 4.00 | 0.0 | 10 | 4 | <1 | 15 h |
| August | 81°F | 61°F | 71.3°F | 4.06 | 0.0 | 9 | 3 | <1 | 14 h |
| September | 75°F | 53°F | 64.0°F | 3.32 | 0.0 | 9 | 2 | <1 | 12 h 30 min |
| October | 62°F | 41°F | 51.5°F | 2.96 | 0.1 | 10 | <1 | 6 | 11 h 10 min |
| November | 46°F | 30°F | 37.9°F | 2.31 | 1.8 | 9 | <1 | 19 | 9 h 50 min |
| December | 34°F | 19°F | 26.3°F | 2.04 | 6.6 | 10 | <1 | 28 | 9 h 10 min |
| Year (annual) | 58°F | 39°F | 48.6°F | 37.25 | 33.1 | 121 | 13 | 141 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −2°C | −10°C | −6.3°C | 43 mm | 26 cm |
| February | 0°C | −9°C | −4.2°C | 43 mm | 22 cm |
| March | 7°C | −3°C | 2.2°C | 57 mm | 11 cm |
| April | 15°C | 3°C | 8.9°C | 90 mm | 3 cm |
| May | 21°C | 10°C | 15.4°C | 122 mm | 0 cm |
| June | 27°C | 15°C | 20.9°C | 116 mm | 0 cm |
| July | 28°C | 17°C | 22.9°C | 102 mm | 0 cm |
| August | 27°C | 16°C | 21.8°C | 103 mm | 0 cm |
| September | 24°C | 12°C | 17.8°C | 84 mm | 0 cm |
| October | 17°C | 5°C | 10.8°C | 75 mm | 0 cm |
| November | 8°C | −1°C | 3.3°C | 59 mm | 5 cm |
| December | 1°C | −7°C | −3.2°C | 52 mm | 17 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00112223; 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 DeKalb?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, August has the fewest days with rain (9).
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 USC00112223.
When is the last frost in DeKalb?
In DeKalb, the last spring frost (32°F) comes after April 24 in half of years and after May 10 in one year in ten; the first autumn frost comes before October 18 in half of years and before October 4 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 241 year in 10 after May 10; 9 in 10 after April 9
- First autumn frost, half of years before
- October 181 year in 10 before October 4; 9 in 10 before October 31
NOAA puts the median frost-free season at 177 days, and the season without a hard freeze (28°F) at 198 days.
A hard freeze (28°F) comes after April 13 in half of springs and before October 28 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts DeKalb in zone 5b in ZIP code 60115. By the map's own method, the average of each year's coldest night over 1991-2020, DeKalb's NOAA station is in zone 5b: the coldest night of a typical year reaches −12°F (27 complete years).
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00112223; 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 DeKalb?
In a normal year in DeKalb, 13 days a year reach 90°F, 141 nights fall to 32°F or colder and 121 days bring measurable precipitation.
- Days at 90°F or more
- 13a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 141a normal year
- Days that stay below freezing
- 56high of 32°F or less
- Days with 0.01 inch of precipitation
- 121a normal year
- Days with 1 inch of snow or more
- 11a normal year
The highest temperature in this station's record (since 1966) is 103°F, on August 17, 1988; the lowest is −27°F, on January 20, 1985.
The wettest calendar year on that record is 2008, with 46.46 in; the snowiest season is 1978–79, with 80.3 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00112223; records: ACIS (NOAA Regional Climate Centers), station USC00112223. Records use complete months only; a month missing more than three days is left out.
How sunny is DeKalb?
Over a year 73% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around DeKalb, 3.9 kWh per square metre a day. July is the sunniest month (81%) and January the cloudiest (61%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 61% | 1.7 |
| February | 65% | 2.6 |
| March | 67% | 3.6 |
| April | 70% | 4.8 |
| May | 71% | 5.5 |
| June | 77% | 6.1 |
| July | 81% | 6.2 |
| August | 80% | 5.4 |
| September | 80% | 4.5 |
| October | 71% | 3.0 |
| November | 67% | 2.0 |
| December | 61% | 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 DeKalb need?
A normal year in DeKalb brings 6,745 heating degree days, 26% more than the median U.S. place (5,373), and 790 cooling degree days, 13% 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 2,987 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,376 | 0 |
| February | 1,133 | 0 |
| March | 903 | 1 |
| April | 515 | 4 |
| May | 215 | 51 |
| June | 34 | 175 |
| July | 5 | 259 |
| August | 12 | 206 |
| September | 114 | 85 |
| October | 428 | 9 |
| November | 812 | 0 |
| December | 1,198 | 0 |
| Year (annual) | 6,745 | 790 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00112223. 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 DeKalb been warmer than normal lately?
2025 averaged 49.7°F, 1.1°F above the 1991-2020 normal of 48.6°F. 3 of the 3 complete years since 2023 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2023 | 50.6°F | +2.0°F | 29.98 | 18.8 |
| 2024 | 52.0°F | +3.4°F | 32.82 | 23.3 |
| 2025 | 49.7°F | +1.1°F | 28.48 | 28.5 |
Over 43 complete years from 1967 to 2025, the station's annual mean temperature rose at a fitted 4.9°F per century (+0.27°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00112223; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does DeKalb's climate compare?
DeKalb is warmer than 14 of the other 143 places with their own NOAA record in Illinois, and wetter than 18. Across the 7,247 U.S. stations with normals, its annual mean of 48.6°F is warmer than 34%.
In the Köppen classification computed from these normals, DeKalb 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 DeKalb share this climate record?
9 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.
- Sycamore, IL18,968 people · 7 mi NE
- Genoa, IL5,514 people · 12 mi N
- Cortland, IL4,592 people · 4 mi E
- Kirkland, IL1,621 people · 11 mi N
- Maple Park, IL1,482 people · 9 mi E
- Malta, IL1,137 people · 5 mi W
- Kingston, IL1,095 people · 12 mi N
- Burlington, IL526 people · 13 mi NE
- Virgil, IL284 people · 13 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 DeKalb's climate
What is the coldest month in DeKalb?
January, with a normal high of 28°F and a normal low of 13°F. The warmest is July (83°F by day, 63°F at night).
Does it snow in DeKalb?
Yes: 33 inches in a normal year, falling on 24 days with 0.1 inch or more, the most in January (10.2 inches).
What is the rainiest month in DeKalb?
May, with 4.79 in of precipitation in a normal year; the driest is January with 1.69 in.
What plant hardiness zone is DeKalb in?
The USDA's 2023 map puts DeKalb in zone 5b in ZIP code 60115. By the same method at DeKalb's NOAA station, the coldest night of a typical year reaches −12°F (27 years, 1991-2020): zone 5b.
How late can frost come in DeKalb?
In half of years the last 32°F night comes after April 24; in one year in ten it comes after May 10. Waiting until May 10 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Shabbona, IL7 miles from this station, 47.8°F a year
- Rochelle, IL16 miles from this station, 47.9°F a year
- Chicago Aurora Municipal Airport, IL19 miles from this station, 49.4°F a year
- Paw Paw, IL21 miles from this station, 47.8°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made