Johnston, IA Weather & Growing Conditions
This Afternoon
83°F
Slight Chance Showers And Thunderstorms
A slight chance of showers and thunderstorms. Mostly cloudy. High near 83, with temperatures falling to around 78 in the afternoon. West wind around 6 mph. Chance of precipitation is 20%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 83°F | Slight Chance Showers And Thunderstorms | 6 mph W | 22% |
| Tonight | 62°F | Chance Showers And Thunderstorms then Showers And Thunderstorms Likely | 6 to 9 mph N | 61% |
| Sunday | 65°F | Chance Rain Showers then Chance Drizzle | 12 mph NE | 39% |
| Sunday Night | 57°F | Rain Showers Likely | 12 mph NE | 64% |
| Monday | 59°F | Rain Showers | 10 mph NE | 83% |
| Monday Night | 53°F | Rain Showers Likely | 6 to 9 mph NE | 71% |
| Tuesday | 60°F | Slight Chance Rain Showers then Mostly Cloudy | 8 mph NE | 18% |
| Tuesday Night | 48°F | Partly Cloudy | 2 to 7 mph NE | 1% |
| Wednesday | 64°F | Mostly Sunny | 5 mph ENE | 0% |
| Wednesday Night | 53°F | Partly Cloudy | 3 mph ESE | 6% |
| Thursday | 67°F | Slight Chance Rain Showers | 1 to 5 mph SE | 22% |
| Thursday Night | 58°F | Slight Chance Rain Showers | 3 mph ESE | 21% |
| Friday | 69°F | Slight Chance Rain Showers | 5 mph ESE | 20% |
| Friday Night | 59°F | Mostly Cloudy | 3 mph ESE | 11% |
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 Sep 20, 2026.