Most of the upper reaches of Himachal Pradesh, including tourist destinations Shimla, Kufri and Manali, witnessed sub-zero temperatures on Thursday, a day after widespread snowfall across the state.Meanwhile, over 900 snowbound roads in the state, including five national highways and one state highway, remain blocked till the afternoon.Train service between Shimla and Kalka was normal. Six up and down trains ran between Shimla and Kalka on both Wednesday and Thursday as usual, bringing relief to tourists.