Sullivan, Wisconsin climate: Normal weather by month, frost dates and records
Sullivan's normal year runs from 11°F January nights to 82°F July afternoons, with 37.5 inches of precipitation and 51 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.1°C, January lows of −11°C, July highs of 28°C, 953 mm of precipitation a year.
- NOAA stationSullivan (3 mi SE)
- Station IDUSC00478316
- Location42.97°N 88.55°W
- Elevation933 ft (284 m)
- From the center4 miles
- Population653
On October 23, the normal high in Sullivan is 57°F and the normal low 37°F, and the chance of measurable rain or snow is 35%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Sullivan.
- Jan 27° 11°
- Feb 31° 14°
- Mar 43° 24°
- Apr 56° 35°
- May 69° 46°
- Jun 78° 56°
- Jul 82° 60°
- Aug 80° 59°
- Sep 73° 51°
- Oct 60° 40°
- Nov 45° 28°
- Dec 33° 17°
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 Sullivan each month?
July is the warmest month, with normal highs of 82°F; January the coldest, with normal lows of 11°F. The most precipitation falls in June (4.90 in), the least in January (1.68 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 27°F | 11°F | 19.1°F | 1.68 | 13.2 | 11 | <1 | 30 | 9 h 20 min |
| February | 31°F | 14°F | 22.6°F | 1.78 | 11.7 | 10 | <1 | 26 | 10 h 30 min |
| March | 43°F | 24°F | 33.5°F | 2.13 | 6.3 | 10 | <1 | 25 | 11 h 50 min |
| April | 56°F | 35°F | 45.6°F | 3.85 | 2.4 | 13 | <1 | 11 | 13 h 20 min |
| May | 69°F | 46°F | 57.3°F | 4.25 | 0.0 | 14 | 1 | 1 | 14 h 40 min |
| June | 78°F | 56°F | 67.2°F | 4.90 | 0.0 | 13 | 3 | <1 | 15 h 20 min |
| July | 82°F | 60°F | 71.1°F | 4.11 | 0.0 | 10 | 4 | <1 | 15 h |
| August | 80°F | 59°F | 69.4°F | 3.97 | 0.0 | 11 | 3 | <1 | 14 h |
| September | 73°F | 51°F | 62.0°F | 3.47 | 0.0 | 9 | 1 | <1 | 12 h 30 min |
| October | 60°F | 40°F | 49.8°F | 2.95 | 0.4 | 11 | <1 | 7 | 11 h 10 min |
| November | 45°F | 28°F | 36.5°F | 2.35 | 3.2 | 10 | <1 | 20 | 9 h 50 min |
| December | 33°F | 17°F | 24.9°F | 2.08 | 13.5 | 11 | <1 | 28 | 9 h |
| Year (annual) | 57°F | 37°F | 46.6°F | 37.52 | 50.7 | 132 | 11 | 148 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −3°C | −11°C | −7.2°C | 43 mm | 34 cm |
| February | −1°C | −10°C | −5.2°C | 45 mm | 30 cm |
| March | 6°C | −5°C | 0.8°C | 54 mm | 16 cm |
| April | 14°C | 2°C | 7.6°C | 98 mm | 6 cm |
| May | 20°C | 8°C | 14.1°C | 108 mm | 0 cm |
| June | 26°C | 13°C | 19.6°C | 124 mm | 0 cm |
| July | 28°C | 16°C | 21.7°C | 104 mm | 0 cm |
| August | 27°C | 15°C | 20.8°C | 101 mm | 0 cm |
| September | 23°C | 10°C | 16.7°C | 88 mm | 0 cm |
| October | 16°C | 4°C | 9.9°C | 75 mm | 1 cm |
| November | 7°C | −2°C | 2.5°C | 60 mm | 8 cm |
| December | 0°C | −8°C | −3.9°C | 53 mm | 34 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00478316; 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 Sullivan?
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 (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 USC00478316.
When is the last frost in Sullivan?
In Sullivan, the last spring frost (32°F) comes after May 3 in half of years and after May 21 in one year in ten; the first autumn frost comes before October 9 in half of years and before September 25 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
- May 31 year in 10 after May 21; 9 in 10 after April 18
- First autumn frost, half of years before
- October 91 year in 10 before September 25; 9 in 10 before October 25
NOAA puts the median frost-free season at 157 days, and the season without a hard freeze (28°F) at 181 days.
A hard freeze (28°F) comes after April 22 in half of springs and before October 22 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Sullivan in zone 5b in ZIP code 53178, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Sullivan's NOAA station is in zone 5b: the coldest night of a typical year reaches −15°F (26 complete years).
Frost dates for every NOAA station in Wisconsin · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00478316; 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 Sullivan?
In a normal year in Sullivan, 11 days a year reach 90°F, 148 nights fall to 32°F or colder and 132 days bring measurable precipitation.
- Days at 90°F or more
- 11a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 148a normal year
- Days that stay below freezing
- 61high of 32°F or less
- Days with 0.01 inch of precipitation
- 132a normal year
- Days with 1 inch of snow or more
- 15a normal year
The highest temperature in this station's record (since 1995) is 106°F, on July 13, 1995; the lowest is −30°F, on January 31, 2019.
The wettest calendar year on that record is 2008, with 50.58 in; the snowiest season is 2007–08, with 106.2 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00478316; records: ACIS (NOAA Regional Climate Centers), station USC00478316. Records use complete months only; a month missing more than three days is left out.
How sunny is Sullivan?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Sullivan, 3.9 kWh per square metre a day. July is the sunniest month (80%) and December the cloudiest (61%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 63% | 1.7 |
| February | 67% | 2.6 |
| March | 67% | 3.6 |
| April | 69% | 4.7 |
| May | 70% | 5.5 |
| June | 76% | 6.1 |
| July | 80% | 6.3 |
| August | 79% | 5.4 |
| September | 78% | 4.3 |
| October | 69% | 2.8 |
| November | 66% | 1.9 |
| December | 61% | 1.4 |
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 Sullivan need?
A normal year in Sullivan brings 7,267 heating degree days, 35% more than the median U.S. place (5,373), and 590 cooling degree days, 35% 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 2,600 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,423 | 0 |
| February | 1,188 | 0 |
| March | 975 | 0 |
| April | 586 | 2 |
| May | 273 | 33 |
| June | 60 | 126 |
| July | 13 | 202 |
| August | 21 | 159 |
| September | 149 | 60 |
| October | 481 | 8 |
| November | 857 | 0 |
| December | 1,241 | 0 |
| Year (annual) | 7,267 | 590 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00478316. 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 Sullivan been warmer than normal lately?
2025 averaged 47.0°F, 0.4°F above the 1991-2020 normal of 46.6°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 48.6°F | +2.0°F | 22.07 | 36.8 |
| 2022 | 46.1°F | −0.5°F | 35.90 | 39.8 |
| 2023 | 49.0°F | +2.4°F | 32.49 | 46.7 |
| 2024 | 50.0°F | +3.4°F | 41.41 | 47.2 |
| 2025 | 47.0°F | +0.4°F | 38.00 | 40.9 |
Source: observed years: ACIS, station USC00478316. A year counts only with all twelve months complete.
How does Sullivan's climate compare?
Sullivan is warmer than 123 of the other 164 places with their own NOAA record in Wisconsin, and wetter than 135. Across the 7,247 U.S. stations with normals, its annual mean of 46.6°F is warmer than 26%.
In the Köppen classification computed from these normals, Sullivan is Dfb: continental, no dry season, warm 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 Sullivan 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.
- Dousman, WI2,551 people · 5 mi NE
- North Prairie, WI2,214 people · 8 mi E
- Eagle, WI2,131 people · 7 mi SE
- Palmyra, WI1,719 people · 6 mi S
- Rome, WI609 people · 5 mi W
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 Sullivan's climate
What is the coldest month in Sullivan?
January, with a normal high of 27°F and a normal low of 11°F. The warmest is July (82°F by day, 60°F at night).
Does it snow in Sullivan?
Yes: 51 inches in a normal year, falling on 36 days with 0.1 inch or more, the most in December (13.5 inches).
What is the rainiest month in Sullivan?
June, with 4.90 in of precipitation in a normal year; the driest is January with 1.68 in.
What plant hardiness zone is Sullivan in?
The USDA's 2023 map puts Sullivan in zone 5b in ZIP code 53178, the nearest ZIP area. By the same method at Sullivan's NOAA station, the coldest night of a typical year reaches −15°F (26 years, 1991-2020): zone 5b.
How late can frost come in Sullivan?
In half of years the last 32°F night comes after May 3; in one year in ten it comes after May 21. Waiting until May 21 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Wisconsin climateThe statewide normals and every place in the state
- Oconomowoc, WI9 miles from this station, 47.2°F a year
- Whitewater, WI12 miles from this station, 47.0°F a year
- Jefferson, WI13 miles from this station, 47.2°F a year
- Waukesha, WI16 miles from this station, 46.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made