Portsmouth, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Portsmouth, a city in Shelby County, Iowa.
This Afternoon
77°F
Slight Chance Showers And Thunderstorms
A slight chance of showers and thunderstorms. Mostly cloudy. High near 77, with temperatures falling to around 72 in the afternoon. North northwest wind around 8 mph. Chance of precipitation is 20%.
7-day forecast for Portsmouth
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 77°F | Slight Chance Showers And Thunderstorms | 8 mph NNW | 18% |
| Tonight | 59°F | Slight Chance Showers And Thunderstorms | 9 mph N | 18% |
| Sunday | 63°F | Chance Rain Showers | 12 mph NNE | 49% |
| Sunday Night | 54°F | Rain Showers Likely | 7 to 10 mph NE | 68% |
| Monday | 57°F | Rain Showers | 10 mph NE | 79% |
| Monday Night | 50°F | Rain Showers Likely then Mostly Cloudy | 5 to 9 mph NE | 57% |
| Tuesday | 60°F | Partly Sunny | 5 to 8 mph NE | 2% |
| Tuesday Night | 46°F | Partly Cloudy | 5 mph E | 0% |
| Wednesday | 63°F | Mostly Sunny | 2 to 6 mph ESE | 2% |
| Wednesday Night | 51°F | Mostly Cloudy then Slight Chance Showers And Thunderstorms | 5 mph SE | 21% |
| Thursday | 66°F | Chance Showers And Thunderstorms | 5 to 8 mph SSE | 33% |
| Thursday Night | 56°F | Slight Chance Rain Showers | 5 mph SE | 23% |
| Friday | 68°F | Slight Chance Rain Showers | 2 to 7 mph ESE | 21% |
| Friday Night | 58°F | Chance Rain Showers | 6 mph ESE | 27% |
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 Sep 20, 2026.