Portsmouth, IA Weather & Growing Conditions
Overnight
40°F
Cloudy
Cloudy. Low around 40, with temperatures rising to around 44 overnight. Northwest wind around 16 mph, with gusts as high as 24 mph. New rainfall amounts less than a tenth of an inch possible.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Overnight | 40°F | Cloudy | 16 mph NW | 8% |
| Wednesday | 49°F | Mostly Cloudy | 16 mph WNW | 14% |
| Wednesday Night | 38°F | Cloudy then Slight Chance Light Rain | 13 mph WNW | 22% |
| Thursday | 50°F | Slight Chance Light Rain then Mostly Cloudy | 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 | 59°F | Sunny | 2 to 6 mph WSW | 0% |
| Sunday Night | 37°F | Clear | 6 mph SSW | 0% |
| Monday | 64°F | Sunny | 6 to 10 mph SW | 0% |
| Monday Night | 40°F | Mostly Clear | 5 mph WNW | 0% |
| Tuesday | 63°F | Mostly Sunny | 5 mph NNW | 0% |
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 Nov 4, 2026.