For years there have been warnings of a coming recession. Why? The yield curve — the difference between yields of two different Treasury instruments had steadfastly been inverted. According to long-standing theory, that meant a recession within the next two years.

But it hasn't happened. And now the yield curve is headed back to "normal" waters. Has one of the country's favorite economic obsession signals passed its sell-by date?

A yield curve inversion is when the yield on the shorter-term instrument is higher than that of the longer-term one. Economists and traders typically look at the difference between the two-year yield and the 10-year, but there are other comparisons. The Federal Reserve Bank of New York often compares the 10-year and the 3-month.