Snowstorms in October are not unusual, yet there are also many sunny and pleasant autumn days during the month. From October to May temperatures fall below freezing nearly every night. The park typically experiences its coldest and snowiest periods from December through February. Spring storms in March and April can still produce heavy snowfall that may impact travel in the region. In summer the days tend to be pleasant, with daytime highs in June typically in the high 60s to low 70s (F), high 70s to low 80s in July and August, while September is similar to June. The rainy season occurs in July and August with frequent, usually brief, afternoon thunderstorms which produce heavy rain and frequent lightning. If visiting during these months remember that lightning kills and 'when thunder roars go indoors!'