The panel wrote that Hydro followed standard emergency management practices and generally did well. But it noted some communication and damage assessment problems. The report will be considered by the city's executive committee on July 2.
The panel interviewed 80 stakeholders for the report, including city workers and residents.
Its most damning feedback was that "customers could not obtain timely and accurate information about their outage status" during the storm.
"About 400,000 Toronto Hydro customers lost power at one point during the December ice storm, affecting more than one million City residents," said David McFadden, the chair of the independent review panel. "Our review indicates that Toronto Hydro's response followed standard emergency management practices, however, we identified several areas in need of improvement to bring Toronto Hydro's performance in line with industry norms and leading practices."
The report said the scope and magnitude of the storm was "unprecedented." Fallen trees and tree limbs took down power lines, blocking roadways, disrupting city services and causing a city-wide power outage.
According to the report, approximately 86 per cent of all customers affected by power outages were restored within 72 hours, and all remaining Hydro customers got power back within 11 days of the storm.
Toronto Hydro convened the independent review panel in January to look at the utility's performance during the storm and to confirm practices that worked well and identify areas in need of improvement.
Of the 25 recommendations made in the report, many revolved around emergency preparedness and communication both between Hydro and its customers and with the city.