What Are the Odds

What are the odds that 5 - 500 year events will occur in 15 years?  Or, more likely what are the odds that 6 -  500 year events will occur in 16 years?

These extreme heat events are all connected to a slower jet stream that locks weather systems into place... The loss of sea ice in the Arctic is amplifying warming in the northernmost regions of our planet, and that is disrupting the natural jet stream patterns, said Dim Coumou of Vrije Universiteit Amsterdam and PIK. Jet stream winds are driven by the temperature difference between the icy air of the Arctic and hot air from the tropics. A rapidly warming Arctic—this past winter it saw its lowest ever ice cover—reduces that temperature difference and slows the jet stream.