Comparison with criteria used by Prowse et al. (2002) found that a minimum of 25 MDD over a 7-day period was a poor predictor of mid-winter break-up events, with only six of 52 events preceded by MDD of this magnitude (Table 2). A total of 32 events were preceded by the thresholds given by Carr & Vuyovich (2014): a minimum of eight MDD or 2.8 mm of rain over a 5-day period. The classification of mid-winter break-up events by biomes reveals the regional variability in hydro-climatic triggers. In particular, the threshold of eight MDD or 2.8 mm of rainfall is a good predictor of mid-winter break-up events in Temperate Grasslands, but a poor predictor of mid-winter break-up events in Boreal Forests. Examination of mean and maximum temperatures preceding mid-winter break-up events revealed that above-freezing temperatures and/or rain on snow over as little as 3 days is sufficient to generate a mid-winter break-up in all hydro-climatic regions.