Plano's climate follows the Dallas pattern: hot and humid summers (June–August), short mild winters, and pleasant springs and autumns. The best times to visit are April through May and October through November, when temperatures are comfortable for walking the historic district.
The Plano Balloon Festival in September at Oak Point Park is worth timing a trip around if you're in the area — it's a genuinely cheerful event with dozens of balloons launching at dawn. The historic downtown has outdoor events and farmers markets in spring and autumn.