In general, the best time to visit is May-September, when the day temperatures are in the 70s-90s F/23-35 C, and nights are in the 50s-70s F/10-23 C. Spring and early fall, however, are unpredictable: Snow flurries and temperatures in the mid 20s F/-5 C are possible in May and September. Be sure to take waterproof shoes for spring or fall visits - there's a lot of mud.