Actually, I think this is the fourth time the roof has malfunctioned due to snow accumulation
In addition to the 1981 incident, another mega-snowstorm in Dec-1982 caused the roof to collapse. And then, the next spring (1983) snow caused another cave in that postponed an April Twins' game. Those two incidents lead to a redesign of the roof and new process for clearing snow, one that worked very well until this past weekend.
The real issue over the weekend was the wind. The high winds forced clean-up crews off the roof, which allowed the snow to accumulate. If not for the winds, the crews might have been able to use high-pressure hot water hoses to clean the roof, which is what they normally do to avoid the snow accumulation.