Clematis Blooming One Month Early

For the last three and a half years I have kept track of the blooming period of several different plants, including a quartet of Clematis montana var. rubens 'Freda' planted along a chain link fence. I mark the bloom time from the day the first bud fully opens to the day the last petal falls from the last flower. In 2013 the plants bloomed for 40 days starting on April 21. The next year blooming also lasted for 40 days, but started almost two weeks earlier on April 9. This year the plants are in full bloom already, with the first bloom open on March 25, nearly a month early compared to the beginning of my record keeping. This winter was exceptionally warm, which might account be the cause. It will be interesting to keep tabs for years to come.