It's been a cold April. We got down to 20 F last weekend. Luckily, I haven't seen any bud swell yet, so I don't expect any damage from the cold temperatures. I'm certain I faired better than the folks down south (Missouri, Tennessee, Arkansas) ... they reached record lows in the mid 20's to upper teens last weekend. Many of their vines already had significant growth. Much of this year's crop was lost due to the freeze.
This cold may actually help delay bud burst in my vineyard and therefore reduce the risk of loss because of a late frost. Forecasts for the next week are cold with only a slight moderation .... highs most days in the 40's F, a few 30's F, with lows in the 20's F.
We might get smacked with a big snow tonight and tomorrow(6" or more!!!) Things are still pretty dormant.
Found a good link that gives cold hardiness at different bud stages:
Refers to Concord, but should give me a ballpark idea anyway.