Berlin tends to be gray and cold; it can be warm and beautiful in summer but there's no guarantee, so it's best to always pack a jacket.
The best time to visit is from May to early September, though late July and early August can get hot—in which case, everyone heads to one of the city’s many lakes.
In summer, daylight lingers well past 9 pm in this northern city, giving plenty of time for happy denizens to picnic in parks, swim in lakes, and cycle about town. Many open-air events are staged in summer, when the exceedingly green city is at its most beautiful.
October and November can be overcast and rainy, though the city occasionally sees crisp blue autumn skies.
If you want to get a real feel for Berlin, come during the long winter months, when a host of indoor cultural events combat perpetually gray skies and you can experience the prized feeling Gemütlichkeit (coziness), but bring a heavy winter coat to combat the sleet, icy rain, strong winds, and freezing temperatures.