Kazakhstan has a sharply continental climate: very cold winters and very hot summers, with spring and autumn being the sweet spots for most travelers.
Spring (April–May) is one of the best times to visit. Temperatures are mild, the steppe turns briefly and dramatically green, and wildflowers — including tulips in the south — carpet the hillsides. The Aksu-Zhabagly reserve is at its best in late April when the Greig tulips bloom. The weather can be variable, with some rain, but the landscape rewards it.
Summer (June–August) is peak season in the mountains. The Tien Shan hiking season runs from June to September, and the Kolsai Lakes and Charyn Canyon are most accessible. City temperatures in Almaty are warm and pleasant; on the steppe and in the desert regions they can exceed 40°C (104°F), which makes touring on foot exhausting. The Baikonur cosmodrome area in the southwest gets brutal summer heat.
Autumn (September–October) is arguably the best season overall. The summer heat has eased, the mountains are still open, and the Altai forests in the east turn gold. Rafting and kayaking are popular in September when glacial melt is still high. Almaty's outdoor restaurant terraces are still active well into October.
Winter (November–March) is cold in a serious way. Astana regularly sees temperatures below -30°C (-22°F), with biting steppe winds. Almaty is milder but still genuinely cold. That said, Shymbulak ski resort above Almaty is excellent and attracts skiers from November through March. If winter sports are the goal, this is the time.
Nauryz, the Kazakh New Year, falls on 22 March and is celebrated for three days. It's the most important cultural festival in the country — if you can time your visit around it, do.