Shillong is pleasant year-round but has two clear seasons.
October to April is the dry, cool half of the year — daytime temperatures of 15–22°C, cold nights, sunny days, and the best time for the falls overlooks and viewpoints. Clear winter mornings (December–February) give the best chance of seeing the Bangladesh plains from Shillong Peak. Pine forests turn colour in October.
May to September is the southwest monsoon, when nearby Cherrapunji and Mawsynram compete for the wettest place on earth. Shillong itself is drier than the southern hills but still soaked: count on rain every day. This is the only time to see the waterfalls in full spate and the cleanest time of year for the living root bridges, but landslides close roads regularly.
The Shillong Autumn Festival (October) and the Wangala Garo harvest festival (November, in nearby Tura and the surrounding villages) are both worth timing a trip around. The Cherry Blossom Festival at Polo Grounds in mid-November is a recent addition that has taken off — the Japanese cherries planted in 2017 now bloom impressively.