Summerland Research and Development Centre
Cold Hardiness - Assessing Bud Damage
Winter temperatures in the hills surrounding Kelowna and areas to the north dipped below -27 °C over the holidays. 
Average bud hardiness (LTE50 – the ambient temperature at which 50% bud kill can occur) for Vitis vinifera at that time ranged between -23 °C to  -25 °C.  Widespread winter bud and vine damage is unfortunately to be expected. 
Below is a brief prepared by Carl Bogdanoff outlining ‘How to assess winter bud damage’.  It also provides some tips on pruning in response to winter damage.