Photo: Bobak Ha'Eri · CC BY 3.0Janesville sits near the bottom of U.S. towns for winter warmth
On a normal July day the thermometer tops out near 82°. Summers stay cool: July afternoons here are cooler than in 82% of U.S. towns. Compared with 1901–2000, the average now sits 0.9° higher. Seedlings are safe outdoors from about May 2, with the first autumn frost due around October 4.
A year in Janesville at a glance
Each month’s typical high and low, and what it brings.
What stands out about Janesville’s climate
Compared with towns across the U.S., with Janesville’s place in Minnesota beside it.
What a year in Janesville feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 155 frost-free days a year
In half of years the last 32° night comes by May 2 and the first by October 4. Frost and day counts come from NOAA’s station at Waseca S Rsch & Outreach Ctr, MN, 10 miles from the town’s center, 110 ft higher.
The 2023 USDA map puts Janesville’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −20°. 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 52 inches of snow a winter
Snow, measured at Waseca S Rsch & Outreach Ctr, MN, falls mostly in February and December. Precipitation (rain plus melted snow) adds up to 34 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 124 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Janesville
93% 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 Waseca S Rsch & Outreach Ctr, MN.
Living with Janesville’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
155 frost-free days in zone 5a. The last frost comes by May 2 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 4.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 0.5 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Janesville from natural hazards, river flooding is the largest share (36%); heat waves, cold waves, winter storms and ice storms together are 23%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Janesville and its neighbors
Every town next door is within a degree of Janesville in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Janesville’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 |
|---|---|---|---|---|
| Janesville, MN | 6° | 82° | 34" | 52" |
| Saratoga, WI | 7° | 82° | 34" | 48" |
| Plattsburgh, NY | 9° | 81° | 35" | 50" |
| Colchester, VT | 10° | 81° | 38" | 50" |
| Hanover, NH | 9° | 82° | 39" | 61" |
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 Janesville averaged 0.9° warmer than the 1900s. The biggest change is in December (+2.9°).
A smaller shift than in 86% 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 Janesville compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Janesville’s place among Minnesota’s.
Janesville weather by month
Highs, lows and precipitation from NOAA’s grid at Janesville’s center; snow, wet days and snow on the ground from Waseca S Rsch & Outreach Ctr, MN. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 23° | 6° | 0.9" | 10.7" | 9 | 26 | 4° – 27° |
| February | 28° | 10° | 0.9" | 10.8" | 8 | 22 | 7° – 31° |
| March | 41° | 23° | 1.7" | 9.0" | 10 | 13 | 24° – 48° |
| April | 56° | 35° | 3.3" | 3.0" | 12 | 2 | 34° – 54° |
| May | 69° | 47° | 4.4" | 0.4" | 14 | 0 | 52° – 65° |
| June | 79° | 58° | 5.1" | 0.0" | 13 | 0 | 64° – 73° |
| July | 82° | 62° | 4.6" | 0.0" | 11 | 0 | 65° – 77° |
| August | 79° | 59° | 4.5" | 0.0" | 11 | 0 | 64° – 73° |
| September | 73° | 51° | 3.6" | 0.0" | 10 | 0 | 55° – 67° |
| October | 59° | 37° | 2.5" | 0.7" | 10 | 0 | 42° – 53° |
| November | 42° | 25° | 1.6" | 5.8" | 8 | 6 | 23° – 46° |
| December | 28° | 13° | 1.2" | 11.9" | 9 | 21 | 6° – 29° |
| Year | 55° | 35° | 34.1" | 52.3" | 124 | 90 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 7° to 31°. June is the most reliable, staying within 8°.
Where Janesville’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 Janesville’s center.
- Snow: Waseca S Rsch & Outreach Ctr, MN.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Waseca S Rsch & Outreach Ctr, MN, 10 miles from the town’s center, 110 ft higher; 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 Janesville’s climate
What is the weather like in Janesville?
A typical July afternoon reaches 82°, a January night drops to 6°, and about 52 inches of snow falls in a normal winter. Colder January nights than 97% of U.S. towns; cooler July afternoons than 82% of U.S. towns.
How cold does it get in Janesville in winter?
January nights average 6°. About 162 nights a year reach 32° or below and 31 reach 0° or below. In the coldest January of the last 30 years the month averaged 4°.
How much snow does Janesville get?
About 52 inches in a normal winter at Waseca S Rsch & Outreach Ctr, MN, most of it in February and December, with snow on the ground about 90 days a year.
How hot does it get in Janesville?
July, with a typical high of 82° and a low of 62°. About 10 days a year reach 90° (Waseca S Rsch & Outreach Ctr, MN).
When is the first and last frost in Janesville?
In half of years the last spring frost (32°) comes by May 2 and the first fall frost by October 4, about 155 frost-free days, at Waseca S Rsch & Outreach Ctr, MN.
What growing zone is Janesville in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −20°.
What is the best time of year to visit Janesville?
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 Janesville getting warmer?
Yes: 1991–2020 averaged 0.9° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 86% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Janesville.
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.