Carlisle is a four-season destination in the Cumberland Valley, though spring and autumn are the most rewarding times to visit. Summers are warm and humid, winters cold but manageable.
Spring (April–May) brings mild temperatures, blooming dogwoods, and the best conditions for walking the LeTort Spring Run trail and the outdoor exhibits at the Army Heritage and Education Center. Dickinson College is lively during the academic year, and spring weekends often see local events in the historic district.
Autumn (September–October) is perhaps the best time overall — foliage colours are excellent in the Cumberland Valley, temperatures are pleasant for outdoor exploring, and the Carlisle Car Fairs (held in spring and autumn) draw large crowds of automotive enthusiasts. If a car show is your reason for coming, book accommodation well in advance.
Summer (June–August) is warm and can be muggy, but the outdoor military trail is still well worth the walk, and the Saturday farmers' market in the central square runs through the season. Indoor sites like the USAHEC museum and the Trout Gallery at Dickinson provide relief from the heat.
Winter (November–March) is quiet. Most outdoor sites are still accessible, but the atmosphere is less inviting. The Army Heritage Trail is open year-round. It is a good time to focus on indoor history and to take day trips to Gettysburg or Harrisburg without the summer crowds.