Summer — June through August — is the prime season, when Presque Isle's beaches are in full swing, the brig Niagara is likely in port, and the waterfront is active. July is warm (average highs around 27°C/80°F) with low humidity by Great Lakes standards.
Spring and early autumn are pleasant for visiting without crowds. The birding at Presque Isle is exceptional during the spring migration (April–May) and autumn migration (September–October), when large numbers of warblers and raptors pass through.
Winter is harsh by most standards — Erie is one of the snowiest cities in the United States, receiving more lake-effect snow than almost anywhere else in the country. The snow can be extraordinary in quantity: a single storm in 2017 dropped over 60 inches on parts of the city. If you visit in winter, come prepared. The lake and the grey sky are atmospheric in their own way.