Even though Uttarakhand is a place that is generally visited throughout the year, the best time to visit Uttarakhand is during the summers while some places are better off during the winter season. The summers in Uttarakhand, at certain places, can get pretty hot.
However, the day might be hot but the nights are cool. Hence, it is advisable for the tourists visiting in summers to wear loose cotton clothes. Also, if you visit places like Rishikesh and Haridwar during summers, remember to drink lots of fluids like water, fruit juice, etc. to prevent dehydration.
The winters in Uttarakhand can be quite chilly. October to March are generally the winter months. Winters in Uttarakhand are very cold and snowfall is a regular phenomenon in many of the upper areas of the place. The days are very pleasant with the nights very cold. It is advisable to take heavy woolen clothes if you are visiting Uttarakhand during the winters.