Rochester has four genuine seasons, though "genuine" in this context includes winters that can be severe. The city sits in the snow belt south of Lake Ontario, and lake-effect snowstorms from November through March can dump a foot of snow in a day. Locals are stoic and well-equipped; visitors should be aware that winter travel can be disrupted, though the city remains fully functional.
May is the finest month to visit. The Lilac Festival in Highland Park runs for about ten days in mid-May, when over 1,200 lilac varieties bloom simultaneously and the park fills with music, food vendors, and a genuinely festive atmosphere. The festival is free and draws up to half a million visitors — book accommodation early if you're timing a trip around it.
June through September is pleasant: warm but rarely oppressive, with outdoor farmers' markets in full swing and the Genesee trails accessible for hiking and cycling. September brings the Clothesline Festival at the Memorial Art Gallery, one of the region's largest outdoor art fairs.
October is beautiful for fall foliage — the gorge trail below High Falls is spectacular under autumn colour — though temperatures drop quickly toward the end of the month. November through March is winter, with the understanding that winter here means business. If you come in February, dress accordingly and lean into the fact that indoor Rochester — the George Eastman Museum, the Strong, the market — is genuinely excellent.