Copenhagen is in the oceanic climate zone, bordering on a humid continental climate (Köppen: Cfb). As the city is in the path of Atlantic low-pressure systems, Copenhagen experiences unstable and changing weather patterns in all four seasons, as well as temperatures about 5 degrees higher than average for its latitude worldwide. (about 55 Degrees North). The main reason for this warmth is the Atlantic Gulf Stream, which pushes warm water from around the Sargasso towards the northwest, and the low-pressure systems follow with the oceanic stream.

Precipitation is moderate throughout the year, with a small peak during June to August. Snowfall occurs mainly from late December until early March, but snow cover seldom lasts for long. Rain during January and February is as common as snow, and the average temperatures for these two winter months is almost exactly on the freezing point.

During winter, the weather is dependent on which latitude the Atlantic low pressure centre takes. With a stable high pressure system around the Alps, the low pressure from the southwest makes way to southern Scandinavia and northern Germany. Temperatures then usually get above freezing, day and night. When a stable high pressure system sits in Denmark itself, or towards the northeast, such as Finland or Russia, the mild Atlantic winds from the southwest can be blocked. With this follows the northern or northeastern polar air, and the temperature drops rather fast to below freezing (rarely below ?5 °C (23 °F) during the day and ?12 °C (10 °F) during the night). If the European continent experiences cold due to the eastern Russian winds, which rarely occurs, it can "freeze from the south"[citation needed]. This was a phenomenon that took several centuries to understand.

Spring is comparable to continental Europe, but delayed about a week because of the cold surrounding water. On the other hand, in late autumn Copenhagen is kept milder due to the same factor, but reversed. In late November and December, water temperatures are generally higher than the air with wind-chill conditions. In the period from mid-October to February, one or two storms (or even hurricanes) occur. Storms in the summertime are very rare.

Summer is, like the other seasons, a mixture of southwestern mild, windy and rainy low pressure systems, and periods of stable high pressures. In summer, high pressure systems usually bring sunny and fairly warm weather. But these warm periods, which can occur anytime from late April until mid September, usually last no longer than ten days.