Predicting the onset of budbreak, bloom, and other phenological stages, is a very active topic of research. Recently, new results regarding the effect of winter temperature at hastening the onset of budbreak have been reported.
Zapata et al (2015) have shown that base temperature (ie. the minimal temperature above which vine “wakes up” and starts a new cycle) is varietal specific. It appears that a Chardonnay “wakes up” when temperature is at or above 8ºC while a Cabernet Sauvignon will start to “wake up” for base temperature at or above 13ºC. These findings gives a better insight to explain why we observe up to one month of difference in budbreak date according to varietal.