Climate Insights for Grinnell

The climate in Grinnell is temperate. The average annual temperature is 11°C and approximately 1050mm of precipitation falls per year. Grinnell receives a notable amount of rainfall throughout the year, including during its driest month. Grinnell is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: July, June, August. The coldest months are January, February, December, when temperatures can drop to -8°C. Snowfall occurs from January to December, with around 85cm accumulating over the season.

Grinnell has a wide annual temperature range, spanning 38°C from the coldest to warmest months. The warmest month is July, when average highs reach 30°C and the mean temperature sits around 24°C. The coldest month is January, when overnight lows fall to -8°C and the daily average is -5°C. On average, daily temperatures fluctuate by about 10°C between overnight lows and afternoon highs. The sharpest temperature change occurs between September and October, with a 9°C shift in average temperatures.

Grinnell is a moderately rainy area, receiving approximately 1050mm of precipitation annually, which averages out to around 87mm per month. The wettest month is May, averaging 152mm of rainfall. September and June also tend to see above-average precipitation. The driest month is December, with just 43mm. That's 110mm less than May, the wettest month. Precipitation varies noticeably between seasons, with the first half (January to June) of the year generally seeing more rainfall. Snowfall is a regular feature from January to December, with around 85cm accumulating over the season. January typically sees the most snow at around 24cm.

Grinnell is relatively calm, with an average annual wind speed of 4km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is April, averaging 5km/h, though still comfortable for most outdoor activities. The calmest conditions occur in August, with average winds dropping to 3km/h, making it an ideal period for wind-sensitive activities. There is moderate seasonal variation in wind speed, with a 2km/h gap between the calmest and windiest months.

It is currently spring in Grinnell, which began on March 20, 2026. Grinnell is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in July at around 30°C, while the coldest stretch bottoms out in January near -8°C. Summer is next, beginning on June 21, 2026 — 7 days from now.

The best time to visit Grinnell is during July and August, when the weather is most comfortable for travellers. During these months, average temperatures hover around 24°C with modest rainfall averaging 75mm per month. By contrast, January can be quite cold with temperatures dropping to -8°C. Despite being the best months overall, some rain is still likely — pack a waterproof layer and plan a mix of indoor and outdoor activities.

The table below shows monthly climate averages for Grinnell based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Snow is measured in centimetres (cm) and reflects average monthly snowfall accumulation. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.