In terms of precipitation, rainfall in Dortmund ranges from 2.1 - 3.7 inches per month. June is typically the wettest month, when rainfall can reach 3.7 in. February is typically the driest time to visit Dortmund when rainfall is around 2.1 in.
If weather is an important factor for your trip to Dortmund, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 64.4 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 35.6 F).