Mae Sariang has three seasons typical of northwestern Thailand, though the surrounding mountains moderate the extremes somewhat.
Cool season (November to February) is the best time to visit. Temperatures are comfortable — rarely above 30°C and cooler at night, especially in the hills — the sky is clear, and the roads are dry. This is trekking season and when the hill-country villages are easiest to reach.
Hot season (March to May) is hazy from agricultural burning across the border and in the valley. Temperatures climb to 35–38°C in April. The mountains still catch cool breezes, but it is not comfortable for walking. The Songkran water festival in mid-April brings the town to life briefly.
Wet season (June to October) sees the Yuam River rise and the surrounding forest turn an intense green. Rain usually falls in the afternoon and evenings rather than all day. Mountain roads can become impassable after heavy rain and some villages are cut off. River levels on the Salawin make boat trips more dramatic but check with locals on conditions before heading to Ban Mae Sam Laep.