While artificial intelligence has ushered in a new era of more accurate weather forecasting, A.I. models may still struggle to predict freak storms. This week a historic blizzard blanketed the Northeast in snow, dumping more than 2 feet on parts of New York and Massachusetts, and a conventional weather model outperformed A.I. models in accurately predicting the storm.The blizzard was a nor’easter, a winter cyclone known to spin up quickly when cold air over land collides with warm ocean currents brought northward by the Gulf Stream.