Portsmouth, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Portsmouth, a city in Shelby County, Iowa.
Overnight
66°F
Slight Chance Showers And Thunderstorms
A slight chance of showers and thunderstorms. Mostly cloudy. Low around 66, with temperatures rising to around 68 overnight. South wind around 3 mph. Chance of precipitation is 20%.
7-day forecast for Portsmouth
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Overnight | 66°F | Slight Chance Showers And Thunderstorms | 3 mph S | 18% |
| Tuesday | 77°F | Slight Chance Showers And Thunderstorms then Chance Showers And Thunderstorms | 3 to 12 mph N | 45% |
| Tuesday Night | 59°F | Chance Showers And Thunderstorms then Patchy Smoke | 3 to 12 mph NE | 85% |
| Wednesday | 72°F | Patchy Smoke | 7 mph ENE | 48% |
| Wednesday Night | 54°F | Mostly Clear | 1 to 6 mph ESE | 3% |
| Thursday | 80°F | Sunny | 0 to 6 mph SE | 1% |
| Thursday Night | 61°F | Mostly Clear | 5 mph SSE | 3% |
| Friday | 84°F | Sunny | 5 to 10 mph S | 3% |
| Friday Night | 67°F | Mostly Clear | 7 mph S | 8% |
| Saturday | 89°F | Sunny | 3 to 14 mph S | 3% |
| Saturday Night | 71°F | Mostly Clear | 14 mph S | 11% |
| Sunday | 90°F | Mostly Sunny | 9 to 14 mph SSE | 10% |
| Sunday Night | 70°F | Chance Showers And Thunderstorms | 14 mph SSE | 26% |
| Monday | 90°F | Slight Chance Showers And Thunderstorms then Mostly Sunny | 15 mph S | 23% |
Forecast source: National Weather Service (api.weather.gov) for Portsmouth (41.650, -95.519). Updated through the day.
Growing snapshot for Portsmouth
Last spring frost
Apr 27
First fall frost
Oct 9
Growing season
165 days
Hardiness zone
5b
More local growing data for Portsmouth: nearby ZIP 51565 weather · frost dates · planting calendar · Iowa frost dates
Nearby towns & communities
Climate data from the nearest NOAA station, Harlan, Ia (9.8 mi from Portsmouth). Frost dates are 1991–2020 averages, not a forecast. Page updated Aug 4, 2026.