Spring (April to June) and autumn (September to November) are the best times to visit Baltimore. The weather is mild, the waterfront is pleasant without being oppressively hot, and the outdoor markets and festivals are in full swing. May and September in particular have the combination of comfortable temperatures and full seasonal activity.
Summer is hot and humid — July and August can be brutal — but the Inner Harbor and Fells Point come fully alive, and the Blue Crabs season peaks from June through September, which is a good reason to endure the heat. The Preakness Stakes, the second leg of thoroughbred racing's Triple Crown, runs at Pimlico in May and draws large crowds to the city.
Winter is cold and occasionally snowy, but the cultural institutions are as good as ever. The city is genuinely festive in December — the Miracle on 34th Street display in Hampden runs from Thanksgiving through New Year's, and the Inner Harbor has its own holiday decorations.