Johnston, IA Weather & Growing Conditions
Today
83°F
Mostly Cloudy then Chance Showers And Thunderstorms
A chance of showers and thunderstorms after 1pm. Mostly cloudy. High near 83, with temperatures falling to around 80 in the afternoon. West northwest wind 3 to 9 mph. Chance of precipitation is 30%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 83°F | Mostly Cloudy then Chance Showers And Thunderstorms | 3 to 9 mph WNW | 32% |
| Tonight | 63°F | Showers And Thunderstorms | 6 to 9 mph NNE | 90% |
| Wednesday | 73°F | Showers And Thunderstorms Likely | 7 mph NE | 61% |
| Wednesday Night | 57°F | Chance Rain Showers | 1 to 5 mph NE | 26% |
| Thursday | 80°F | Sunny | 3 mph ENE | 3% |
| Thursday Night | 62°F | Mostly Clear | 3 mph SE | 3% |
| Friday | 85°F | Sunny | 2 to 7 mph S | 5% |
| Friday Night | 67°F | Mostly Clear | 6 mph SSE | 12% |
| Saturday | 89°F | Sunny | 2 to 9 mph S | 11% |
| Saturday Night | 72°F | Mostly Clear | 10 mph SSW | 11% |
| Sunday | 89°F | Mostly Sunny | 7 to 10 mph S | 11% |
| Sunday Night | 71°F | Slight Chance Showers And Thunderstorms | 9 mph SSE | 27% |
| Monday | 89°F | Chance Showers And Thunderstorms then Mostly Sunny | 8 to 13 mph S | 27% |
| Monday Night | 72°F | Slight Chance Showers And Thunderstorms | 8 to 13 mph ESE | 24% |
Forecast source: National Weather Service (api.weather.gov). Updated through the day.
Growing snapshot for Johnston, IA
Last spring frost
Apr 19
First fall frost
Oct 18
Growing season
179 days
Hardiness zone
5b
Explore more for Johnston, IA: full frost dates · planting calendar · Iowa frost dates
Climate data from the nearest NOAA station, Des Moines Wsfo-Johnston, Ia (2.8 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Aug 4, 2026.