The Climate -- Northern Thailand has three distinct seasons. The hot season (Mar-May) is dry, with temperatures up to 97°F (36°C). At this time of year, there is little difference between the north and other regions. 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, mud and leeches should be taken into consideration. The cool season (Nov-Feb) is brisk and invigorating, with daytime temperatures as low as 50°F (10°C) in Chiang Mai town, and 41°F (5°C) in the hills. Bring a sweater and some warm socks, and a jacket if you plan to head for the hills. November to February is the best time for trekking, with December and January drawing a peak of visitors. In October and November, after the rains, the forests are lush, rivers swell, and waterfalls are more splendid than usual.
Festivals -- Northern Thailand celebrates many 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.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.