Tanana River at Nenana goes out

The ice broke on the Tanana River at Nenana Monday evening, tipping the tripod on the Nenana Ice Classic at 839pm ADT. This is the fourth earliest break-up of the ice on the Tanana since the Nenana Ice Classic started in 1917. Here is a plot of break-up dates since 1917. The black lines represent simple linear regression. From 1917 through 1976 there is no trend at all. Since 1977 (corresponding to the shift of the phase of the PDO from negative to positive), the trend is not (yet) statistically significant, due to the comparative small sample size since then. However, for the entire 96 years of record, the trend toward earlier break-up dates, by more than a week is significant.