Back in November, when the Met Office was still doing its "mild winter" schtick, Corbyn said it would be the coldest for 100 years. Indeed, it was back in May that he first predicted a snowy December, and he put his own money on a white Christmas about a month before the Met Office made any such forecast. He said that the Met Office would be wrong about last year's mythical "barbecue summer", and he was vindicated. He was closer to the truth about last winter, too.
Fallacy: anecdote