Heidelberg enjoys an oceanic climate with relatively mild weather all year round.
Summer (June – August): The summer temperatures can be quite unpredictable with highs ranging from 20 to 30 degree Celsius. July and August are both hottest and wettest months of the year. This is the peak season for tourists in Heidelberg.
Winter (December – February): The temperatures in winter can be about 3-5°C on an average. This is basically off-season in Heidelberg.
Spring (March – May): Spring is often pleasant with blue skies and enjoyable weather and the temperature is around 11°C.
Autumn (September – November): The weather in autumn is similar to that of spring seasons and average high ranges between 8-14°C.
Heidelberg is a great place to be on your trip planner all year round, but the best time to visit is during the summer months, especially May through August when the town is bustling with events and a lot of other things to do.