Portsmouth, IA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Portsmouth, a city in Shelby County, Iowa.
Overnight
40°F
Slight Chance Rain Showers
A slight chance of rain showers before 5am. Cloudy. Low around 40, with temperatures rising to around 43 overnight. Northwest wind around 16 mph, with gusts as high as 24 mph. Chance of precipitation is 20%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast for Portsmouth
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Overnight | 40°F | Slight Chance Rain Showers | 16 mph NW | 17% |
| Wednesday | 49°F | Chance Rain Showers | 16 mph WNW | 36% |
| Wednesday Night | 38°F | Cloudy then Slight Chance Rain Showers | 13 mph WNW | 21% |
| Thursday | 50°F | Slight Chance Rain Showers then Mostly Cloudy | 9 to 13 mph NW | 20% |
| Thursday Night | 35°F | Mostly Cloudy | 3 to 8 mph N | 0% |
| Friday | 50°F | Mostly Sunny | 3 mph N | 2% |
| Friday Night | 30°F | Partly Cloudy | 1 mph SE | 0% |
| Saturday | 53°F | Mostly Sunny | 1 to 6 mph SSW | 0% |
| Saturday Night | 34°F | Mostly Clear | 2 mph WSW | 0% |
| Sunday | 58°F | Sunny | 2 to 6 mph WSW | 0% |
| Sunday Night | 37°F | Clear | 2 to 6 mph SSW | 0% |
| Monday | 63°F | Sunny | 6 to 9 mph SW | 0% |
| Monday Night | 39°F | Mostly Clear | 1 to 5 mph WNW | 0% |
| Tuesday | 63°F | Mostly Sunny | 1 to 5 mph NNW | 0% |
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 Nov 4, 2026.