The Climate -- Northern Thailand has three distinct seasons. The hot season (Mar-May) is dry, with temperatures up to 97°F (36°C). Many Thais vacation in this region to get away from scorching temperatures elsewhere. The rainy season (June-Oct) is cooler, with the heaviest daily rainfall in September (predictably heavy daily afternoon downpours). While trekking and outdoor activities are still possible, rainy and mud should be taken into consideration. The cool season (Nov-Feb) is brisk, with daytime temperatures as low as 59°F (21°C) in Chiang Mai town, and 41°F (5°C) in the hills. Bring a sweater and some warm socks. November to May is the best time for trekking, with February, March, and April (when southern Thailand gets extremely hot) usually the most crowded months. In October and November, after the rainfall, the forests are lush, rivers swell, and waterfalls are more splendid than usual.
Festivals -- Northern Thailand celebrates many unique festivals -- even the nationwide ones -- in different ways than the rest of the country. Many Thais travel to participate in these festivals and advance booking in hotels is a must.
