Uttarakhand authorities on Saturday issued an alert about heavy rains in the next 72 hours.The annual 'Chaar Dhaam Yatra' has also been halted at some places due to landslides and rains.The Kali and Gore rivers are already in spate, officials said. Regional Met director Vikram Singh said there is a possibility of very heavy rainfall in most parts of the state on Saturday, Sunday and Monday.The Regional Met Office has has alerted district officials and the State Disaster Response Force (SDRF) about cloudbursts at some places.Trekking has been postponed and an advisory sounded for tourists not to venture to higher altitudes in the next three days.The week-long rain spell has affected traffic on 112 roads, officials said.