Portsmouth, IA Weather & Growing Conditions
This Afternoon
78°F
Slight Chance Showers And Thunderstorms
A slight chance of rain showers before 1pm, then a slight chance of showers and thunderstorms. Mostly cloudy. High near 78, with temperatures falling to around 75 in the afternoon. North northwest wind around 8 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 | 78°F | Slight Chance Showers And Thunderstorms | 8 mph NNW | 22% |
| Tonight | 59°F | Slight Chance Showers And Thunderstorms | 9 mph N | 19% |
| Sunday | 63°F | Chance Rain Showers | 12 mph NE | 48% |
| Sunday Night | 54°F | Rain Showers Likely | 7 to 10 mph NE | 67% |
| Monday | 59°F | Rain Showers | 10 mph NE | 79% |
| Monday Night | 50°F | Rain Showers Likely then Mostly Cloudy | 5 to 9 mph NE | 56% |
| 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 | 64°F | Chance Showers And Thunderstorms | 5 to 8 mph SSE | 33% |
| Thursday Night | 55°F | Slight Chance Rain Showers | 2 to 6 mph SE | 19% |
| Friday | 66°F | Slight Chance Rain Showers | 2 to 6 mph ESE | 20% |
| Friday Night | 56°F | Chance Rain Showers | 6 mph ESE | 27% |
Forecast source: National Weather Service (api.weather.gov). Updated through the day.
Growing snapshot for Portsmouth, IA
Last spring frost
Apr 27
First fall frost
Oct 9
Growing season
165 days
Hardiness zone
5b
Explore more for Portsmouth, IA: full frost dates · planting calendar · Iowa frost dates
Climate data from the nearest NOAA station, Harlan, Ia (9.8 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.