Janesville’s winters are milder than most of the U.S.; July afternoons average 91°
A typical July afternoon reaches 91°, a January night drops to 23°.
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 California 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 143 frost-free days a year
In half of years the last 32° night comes by May 16 and the first by October 8. Frost and day counts come from NOAA’s station at Susanville 2sw, CA, 12 miles from the town’s center, at about the same height.
The 2023 USDA map puts Janesville’s center in zone 7a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 2°. 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 13 inches of rain a year
December is the wettest month and August the driest.
Rain + melted snow by month
Inches of water
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 Susanville 2sw, CA.
Living with Janesville’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
143 frost-free days in zone 7a. The last frost comes by May 16 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 8.
Months with highs of 62–84° and lows of 40° or more: June and September. 7.8 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Janesville from natural hazards, wildfire is the largest share (60%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Janesville and similar climates
TownRatings has no climate map of the towns around Janesville yet.
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Janesville averaged 1.3° warmer than the 1900s. The biggest change is in January (+2.6°).
A smaller shift than in 54% 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 California’s.
Janesville weather by month
Highs, lows and precipitation from NOAA’s grid at Janesville’s center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 44° | 23° | 2.0" | 24° – 41° |
| February | 49° | 26° | 1.8" | 30° – 44° |
| March | 56° | 29° | 1.5" | 36° – 49° |
| April | 62° | 33° | 0.9" | 42° – 52° |
| May | 72° | 40° | 0.9" | 48° – 64° |
| June | 82° | 46° | 0.6" | 58° – 70° |
| July | 91° | 52° | 0.2" | 65° – 75° |
| August | 89° | 49° | 0.2" | 66° – 73° |
| September | 82° | 43° | 0.2" | 58° – 66° |
| October | 69° | 35° | 0.8" | 46° – 57° |
| November | 53° | 27° | 1.0" | 31° – 46° |
| December | 43° | 22° | 2.3" | 26° – 37° |
| Year | 66° | 35° | 12.5" |
How much a month can swing
A normal is an average. January swings the most: from 1991 to 2020 its average ranged from 24° to 41°. August 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.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Susanville 2sw, CA, 12 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 Janesville’s climate
What is the weather like in Janesville?
A typical July afternoon reaches 91°, a January night drops to 23°. Milder January nights than 55% of U.S. towns; hotter July afternoons than 81% of U.S. towns.
How cold does it get in Janesville in winter?
December nights average 22°. About 149 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 26°.
How hot does it get in Janesville?
July, with a typical high of 91° and a low of 52°. About 31 days a year reach 90° (Susanville 2sw, CA).
When is the first and last frost in Janesville?
In half of years the last spring frost (32°) comes by May 16 and the first fall frost by October 8, about 143 frost-free days, at Susanville 2sw, CA.
What growing zone is Janesville in?
Zone 7a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 2°.
What is the best time of year to visit Janesville?
By one simple rule (highs of 62–84° and lows of 40° or more), June 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 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 54% 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.