January 2004 was a time of great economic growth in the US. As you can see in the chart, there is a slight concave curve and a positive slope.

In August of 2006, the yield curves had inverted, showing a convex shape. The economy had not been impacted yet; however, The Great Recession was less than 18 months away.

Source: https://fred.stlouisfed.org/graph/?g=nf0p

This graph shows the 2 year and 3 month yield curve spread over time. The shaded areas are US recessions.