VIX futures contango from the front month to the next month usually narrows to under 10% while the market is fiddling around before the market drops big. VIX contango right now is at around 13%.
The instances of the contango narrowing and market dropping big would be July 2011, August 2015, and December 2016. It even narrowed before the November elections which resulted in the crazy futures drop on election night.
At VIXcentral.com, one can view contango since 2011.