Photo: I, the copyright holder of this work, hereby publish it under the following license: · CC BY-SA 3.0Winter nights in Sullivan are colder than in 91% of U.S. towns
The warmest part of a July day comes in at 82° on average. Seasons differ by 70°, from the coldest nights to the warmest afternoons. Its July afternoons stay fresher than in 77% of U.S. towns. The frost-free window for a garden runs roughly May 3 to October 9.
A year in Sullivan at a glance
Each month’s typical high and low, and what it brings.
What stands out about Sullivan’s climate
Compared with towns across the U.S., with Sullivan’s place in Wisconsin beside it.
What a year in Sullivan feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 157 frost-free days a year
In half of years the last 32° night comes by May 3 and the first by October 9. Frost and day counts come from NOAA’s station at Sullivan 3se, WI, 3 miles from the town’s center, at about the same height.
The 2023 USDA map puts Sullivan’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −14°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 51 inches of snow a winter
Snow, measured at Sullivan 3se, WI, falls mostly in January and December. Precipitation (rain plus melted snow) adds up to 36 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 132 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Sullivan
92% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Sullivan 3se, WI.
Living with Sullivan’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
157 frost-free days in zone 5b. The last frost comes by May 3 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 9.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 4.3 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Sullivan from natural hazards, river flooding is the largest share (54%); heat waves, cold waves, winter storms and ice storms together are 16%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Sullivan and its neighbors
Every town next door is within a degree of Sullivan in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Sullivan’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Sullivan, WI | 12° | 82° | 36" | 51" |
| Bath, NY | 15° | 82° | 35" | 48" |
| Big Rapids, MI | 14° | 82° | 36" | 61" |
| Colchester, VT | 10° | 81° | 38" | 50" |
| Mason City, IA | 8° | 82° | 36" | 44" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Sullivan averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.8°).
A smaller shift than in 63% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Sullivan compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Sullivan’s place among Wisconsin’s.
Sullivan weather by month
Highs, lows and precipitation from NOAA’s grid at Sullivan’s center; snow, wet days and snow on the ground from Sullivan 3se, WI. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 28° | 12° | 1.6" | 13.2" | 11 | 23 | 10° – 32° |
| February | 32° | 16° | 1.5" | 11.7" | 10 | 21 | 11° – 35° |
| March | 44° | 25° | 2.0" | 6.3" | 10 | 9 | 27° – 50° |
| April | 57° | 35° | 3.6" | 2.4" | 13 | 1 | 37° – 52° |
| May | 69° | 47° | 4.1" | 0.0" | 14 | 0 | 52° – 64° |
| June | 79° | 56° | 4.9" | 0.0" | 13 | 0 | 64° – 72° |
| July | 82° | 61° | 4.0" | 0.0" | 10 | 0 | 66° – 79° |
| August | 81° | 59° | 3.9" | 0.0" | 11 | 0 | 64° – 76° |
| September | 73° | 51° | 3.4" | 0.0" | 9 | 0 | 56° – 67° |
| October | 61° | 40° | 2.8" | 0.4" | 11 | 0 | 46° – 57° |
| November | 46° | 29° | 2.2" | 3.2" | 10 | 3 | 28° – 47° |
| December | 33° | 18° | 1.8" | 13.5" | 11 | 16 | 13° – 37° |
| Year | 57° | 37° | 36.0" | 50.7" | 132 | 72 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 11° to 35°. June is the most reliable, staying within 8°.
Where Sullivan’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Sullivan’s center.
- Snow: Sullivan 3se, WI.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Sullivan 3se, WI, 3 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Sullivan’s climate
What is the weather like in Sullivan?
A typical July afternoon reaches 82°, a January night drops to 12°, and about 51 inches of snow falls in a normal winter. Colder January nights than 91% of U.S. towns; cooler July afternoons than 77% of U.S. towns.
How cold does it get in Sullivan in winter?
January nights average 12°. About 148 nights a year reach 32° or below and 17 reach 0° or below. In the coldest January of the last 30 years the month averaged 10°.
How much snow does Sullivan get?
About 51 inches in a normal winter at Sullivan 3se, WI, most of it in January and December, with snow on the ground about 72 days a year.
How hot does it get in Sullivan?
July, with a typical high of 82° and a low of 61°. About 11 days a year reach 90° (Sullivan 3se, WI).
When is the first and last frost in Sullivan?
In half of years the last spring frost (32°) comes by May 3 and the first fall frost by October 9, about 157 frost-free days, at Sullivan 3se, WI.
What growing zone is Sullivan in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −14°.
What is the best time of year to visit Sullivan?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Sullivan getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 63% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Sullivan.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.