Dense to very dense fog conditions will continue during night and morning hours over Himachal Pradesh, Punjab, Haryana, Chandigarh and UP on December 31 and January 1, said IMD. Dense fog conditions would be prevalent over Sub-Himalayan West Bengal, Bihar, Assam, Meghalaya, Nagaland, Mizoram, Tripura and Odisha till January 1. Isolated moderate rainfall likely over Punjab on December 31-January 1.