Udon Thani has the three classic Isan seasons: hot (March to May, with temperatures regularly above 35 C), wet (June to October, when afternoon thunderstorms are common but rarely all-day), and cool (November to February, when daytime temperatures of 25–30 C and cool evenings make this the comfortable time to visit).
The cool season is also when the Red Lotus Sea is in bloom — December to February is the only time to see it. The Buddhist festival of Asalha Puja in July and the Songkran new year in mid-April are the city's biggest popular events. Pick December for the best combination of weather, lotus flowers, and clear roads.