Janesville, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Janesville, a city in Bremer County, Iowa.
Overnight
48°F
Chance Rain Showers
A chance of rain showers. Cloudy. Low around 48, with temperatures rising to around 51 overnight. West wind around 10 mph. Chance of precipitation is 30%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast for Janesville
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Overnight | 48°F | Chance Rain Showers | 10 mph W | 32% |
| Wednesday | 52°F | Chance Rain Showers | 12 to 17 mph WSW | 39% |
| Wednesday Night | 44°F | Chance Rain Showers | 16 mph W | 52% |
| Thursday | 52°F | Chance Rain Showers | 15 mph NW | 43% |
| Thursday Night | 37°F | Mostly Cloudy | 8 to 13 mph N | 11% |
| Friday | 48°F | Mostly Sunny | 5 to 9 mph N | 3% |
| Friday Night | 28°F | Partly Cloudy | 0 to 3 mph N | 0% |
| Saturday | 50°F | Mostly Sunny | 0 to 6 mph W | 0% |
| Saturday Night | 35°F | Mostly Clear | 5 mph W | 2% |
| Sunday | 56°F | Sunny | 5 to 8 mph W | 3% |
| Sunday Night | 36°F | Clear | 5 mph SW | 0% |
| Monday | 62°F | Sunny | 5 to 12 mph SW | 0% |
| Monday Night | 40°F | Mostly Clear | 3 to 7 mph W | 0% |
| Tuesday | 60°F | Mostly Sunny | 5 mph NW | 0% |
Forecast source: National Weather Service (api.weather.gov) for Janesville (42.646, -92.462). Updated through the day.
Growing snapshot for Janesville
Last spring frost
Apr 27
First fall frost
Oct 10
Growing season
165 days
Hardiness zone
5a
More local growing data for Janesville: nearby ZIP 50647 weather · frost dates · planting calendar · Iowa frost dates
Nearby towns & communities
Climate data from the nearest NOAA station, Waterloo Muni Ap, Ia (8.3 mi from Janesville). Frost dates are 1991–2020 averages, not a forecast. Page updated Nov 4, 2026.