The plain of La Mancha bakes in summer (35°C and up through July and August) and freezes in winter (down to –5°C is not unusual in January and February). Spring and autumn are the obvious sweet spots — clear, dry, warm days and crisp nights.
If you can plan a trip around it, time the visit for the Feria de Albacete (7–17 September), one of the great Spanish provincial fairs: bullfights, processions, all-night dancing in the circular fairground, and the entire city in a holiday mood. Hotels book up months ahead.