 In winter, overnight temperatures in the wine growing regions of Eastern Washington can drop to as low as .The sudden drop to these sub-zero temperatures can make the water in a vine's wood canopy quickly freeze which can cause the vine to literally burst open.The severity of these conditions can wreak havoc on a year's harvest, as was the case in the Walla Walla AVA with the big winter freezes of 1996 and 2003.