Johnston, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Johnston, a city in Polk County, Iowa.
Tonight
69°F
Chance Showers And Thunderstorms
A chance of showers and thunderstorms before 1am, then patchy fog and a chance of showers and thunderstorms. Mostly cloudy, with a low around 69. Southeast wind 7 to 10 mph, with gusts as high as 18 mph. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.
7-day forecast for Johnston
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 69°F | Chance Showers And Thunderstorms | 7 to 10 mph SE | 53% |
| Saturday | 81°F | Chance Showers And Thunderstorms | 8 mph WSW | 42% |
| Saturday Night | 63°F | Chance Showers And Thunderstorms | 8 mph NNW | 36% |
| Sunday | 67°F | Showers And Thunderstorms Likely | 12 mph NNE | 56% |
| Sunday Night | 57°F | Showers And Thunderstorms Likely | 10 mph ENE | 56% |
| Monday | 61°F | Rain Showers Likely | 12 mph ENE | 63% |
| Monday Night | 53°F | Rain Showers Likely | 6 to 9 mph NE | 59% |
| Tuesday | 60°F | Slight Chance Rain Showers then Mostly Cloudy | 8 mph NE | 15% |
| Tuesday Night | 49°F | Partly Cloudy | 2 to 6 mph ENE | 2% |
| Wednesday | 65°F | Mostly Sunny | 5 mph E | 2% |
| Wednesday Night | 53°F | Partly Cloudy | 3 mph ESE | 5% |
| Thursday | 67°F | Slight Chance Rain Showers | 3 mph SE | 18% |
| Thursday Night | 56°F | Mostly Cloudy then Slight Chance Rain Showers | 2 mph ESE | 15% |
| Friday | 68°F | Slight Chance Rain Showers | 1 to 5 mph E | 15% |
Forecast source: National Weather Service (api.weather.gov) for Johnston (41.692, -93.724). Updated through the day.
Growing snapshot for Johnston
Last spring frost
Apr 19
First fall frost
Oct 18
Growing season
179 days
Hardiness zone
5b
More local growing data for Johnston: nearby ZIP 50131 weather · frost dates · planting calendar · Iowa frost dates
Nearby towns & communities
Alleman
Altoona
Ankeny
Bondurant
Clive
Des Moines
Elkhart
Granger
Grimes
Maxwell
Mitchellville
Pleasant Hill
Polk City
Runnells
Saylorville
Sheldahl
Slater
Urbandale
West Des Moines
Windsor Heights
Climate data from the nearest NOAA station, Des Moines Wsfo-Johnston, Ia (2.8 mi from Johnston). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.