Janesville, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Janesville, a city in Bremer County, Iowa.
This Afternoon
74°F
Showers And Thunderstorms Likely
Showers and thunderstorms likely. Mostly cloudy. High near 74, with temperatures falling to around 72 in the afternoon. East northeast wind around 7 mph. Chance of precipitation is 60%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast for Janesville
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 74°F | Showers And Thunderstorms Likely | 7 mph ENE | 59% |
| Tonight | 59°F | Chance Showers And Thunderstorms | 7 to 13 mph NNE | 41% |
| Sunday | 66°F | Chance Rain Showers then Chance Drizzle | 16 mph NE | 33% |
| Sunday Night | 52°F | Slight Chance Drizzle then Chance Rain Showers | 15 mph ENE | 44% |
| Monday | 60°F | Rain Showers Likely | 15 mph NE | 65% |
| Monday Night | 48°F | Rain Showers Likely | 9 to 13 mph NE | 65% |
| Tuesday | 60°F | Chance Rain Showers then Partly Sunny | 12 mph ENE | 28% |
| Tuesday Night | 46°F | Partly Cloudy | 5 to 8 mph NE | 2% |
| Wednesday | 64°F | Mostly Sunny | 7 mph ENE | 1% |
| Wednesday Night | 50°F | Partly Cloudy | 2 to 6 mph E | 4% |
| Thursday | 66°F | Slight Chance Rain Showers | 5 mph ESE | 15% |
| Thursday Night | 54°F | Slight Chance Rain Showers | 3 mph ESE | 22% |
| Friday | 70°F | Slight Chance Rain Showers then Partly Sunny | 2 to 6 mph E | 15% |
| Friday Night | 55°F | Mostly Cloudy | 5 mph ESE | 8% |
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 Sep 20, 2026.