https://www.nps.gov/yose/planyourvisit/tiogaopen.htm
A regression shows there is - no surprise here - a strong correlation between the amount of snow on April 1 and the opening date (r2 = 0.75) and the regression line allows me to predict an opening date of June 14 for 2017. You can see though that there is a lot of variation, with very similar snowpacks producing dates from May 24 (137%), to July 1 (156%). Here's the data (not sure why Excel converted the real dates to a 5-digit number

