GDD base 50 accumulated since April 1 = 89
http://agebb.missouri.edu/weather/reports/gddTable.asp
Phenology stages according to the Modified E-L system
http://door.uwex.edu/files/2010/10/ModifiedEichhornLorennzsystem.pdf
Most grapes were at the wooly bud stage. The cultivars furthest along included Delaware, Valvin Muscat and Concord since they were showing some green/pink. You could see some points of leaves on Delaware, but not to the point of bud burst.
Tonight the predicted low is 26 degrees F. At full swell a temperature of 26 F is may result in 50% kill. Thankfully, most are not at full swell, so we will keep our fingers crossed. Estimate is from Michigan State “How Cold Can Grapes Go?” http://grapes.msu.edu/weather_climate/how_cold_can_grapes_go